176

Conclusions regarding transposition of “pm in the a,™t cultures.

The progeny tests described both in this section and in the last
section provide some information regarding stability of location of Spm.
It is clear from thaw that the time of occurrence of transposition of
Spm during development, and the frequency of this at any one time, is
controlled in some manner. Change in this undergone by an Spm element
appeured to be associated with transposition, its behavior in the former
location and in the new location often being deicdedly different. The
altered control of its behavior may be an expression of some modification
occurring to Spm during the transposition process, or it may reflect
participation in this of the particular-locus in the chromosome complement
at which Spm is inserted. Up to now, no evidence is available fwom
study of ‘pm favoring one or the other of these interpretations. As
mentioned earlier, evidence favoring the second interpretation was obtained
from study of transposition of Ds. Evidence of altered behavior of Spm,
following transposition of it, was given by several of the described tests.
+t was shown that following some transpositions, the relative frequency
of occurrence of subsequent trensposition of Spm, and the time of this
during development, could be strikingly different from that which it

expressed at its former location. Cases were cited in which it had been
L?7

relatively stable when present at one location but became quite unstable
after it had been inserted at a new location. Cases in which the
reverse of this occurred, also were cited.

It was shown that when Spm resided at a particulur site in
chromosome 6 in those plants in culture 6629A and in thier progeny which
gave approximately 35 percent recombinants with Y (table 29), it remained
relatively stable in this location, the frequency of appe.rance of progeny
plants in which Spm occuppied a new location being low. Nevertheless,
transposition of it from this location to a new location was observed
and several cases of this were subse uently analyzed (Progeny Tests

was

20 to 23, figure 2). Among them/one bazaar case involving the Behavior
of “pm in plant 6666C-7 and its progeny (Progeny Tests 14 to 16, figure 2).
In this plant, transposition of Spm occurred at a very high rate. From
the type of sterility that was expressed by each of the two testcross
ears obtained from this plant, it is suspected that insertion of Spm
at some locations in the chromosome complement may result in chunge in
gene action at the site of insertion, and this may cause either lethality

for the cell having it at one such site, or it may cause some modification

of gene action that alters the capacity of the cell to function normally.
178

In those cases where its insertion at a new location did not produce such
deleterious effects, viable kernels in which Spm occupied a new location
were produced. The location and behavior of Spm in the plants derived
from each could be analyzed. This was done for five kernels on one of
the ears of plant 6666C-7. In the plants derived from each of them
Spm occuppied a different location. One transposition had inserted Spm
close to Y in chromosome 6 and from this location few subsequent
transpositions occurred (Progeny Test 15, figure 2). In ontrast, an
insertion of it into chrommsome 9 resulted in a high frequency of
subsequent transpositiom, and these occurred both during early and late
development of those plants th:t had it at this location in their
zygote nuclei (Progeny Test 16, figure 2). In contrast to this, another
case of insertion of “pm into chromosome 9 was followed by subsequent
transpositions of it that were confined mainly to the early stages of
plant development (Progeny Tests 6 to 13, figure 2).

The mode of examining transposition of Spm did not allow detection
of those cases that placed it at a new location in the same chromosome in
which it had been residing when this new location was close to that which

it formerly occuppied. Therefore, accurate estimates of rates of

transposition of Spm could not be made. Estimates of this may be
179

formulated only from those detected cases th:t placed Spm in a new
location, either in another chromosome of the complement or at a location
in the same chromosome sufficiently distant from its former location to
markedly alter the frequency of appearance of recombinants with the
gene marker in the chromosome that wasused for determining its presence in
this chromosome. Even though it is realized that transposition of a
controlling element frequently places it at a new location that is not
far removed from its former location in the same chromosome,and that in
this study estimates of the frequency of occurrence of this could not be
made, it was apparent, nevertheless, that difference:s in rates and times
of occurrence of transposition of Spm could be expressed to a striking
degreeywhen measured only by those cases of it that were readily detectible.
The test methods used in this study allowed detection of the location
of Spm if it had been inserted into chromosomes 3, 5, 6, or 9, and v u

t
resided close enought to an allele of the markers Shy; Pr, Y, or Wx
to give evidence of linkage of it with any one of them. Cases of its
insertion at d#fferent locations in chro.:osomes 5, 6, and 9 were

discussed in this section along with the characteristic behavior of Spm

at each location in one of these chromosomes. It is probably only a
180

coincidence that the examined cases of insertion of Spm at diffe cnt
locations in chromosome 6 were followed by a considerable degree of
Stability of Spm at exch of these locations whereas, in contrast, the
examined cases of insertion of it in chromosome 9 were followed by high
rates of subsequent transposition. It was also noted that in
sequentia& transpositions of Spm no evidence of preferance of one location
over another was exhibited. In other words, if Spm were transposed
from a known location to a new location, subsequent transposition of it
did not tené to return it to the location it formerly occuppied.
Linkage of Spm with a given gene marker, carried either in
chromosome 5, 6, or 9, was examined in a number of plants. In some of
the tables in this section is entered the percent of the recombinant
Classes or the percent of one of them. It is obvious from those given
in the tables accompanying the descriptions of Progeny Tests 5, 6, 24,
and 26, that such percents do not serve as a measure of crossing over
between the site of insertion of pm in the chromosome and the locas of

the gene marker. “f the rate of late
18}

occurring transposition is high, then many individuals within the
recédmbinant class carry in them a newly transposed Spm element, as
discussed earlier \page ). Also, the closer is ‘pm to the marker, the
less reliance may be placed on the given percent of recombination in
estimating the location of Spm with reference to the marker. Only by
means of progeny tests can an accurate estimate of this be made,

In this study, a number of cases were mentioned in which plants
having two or more Spm elements appesred in the progeny of ones in wich
only one “pm was present. An explanation of the probable origin of cells
having two Spm elements in them from ones in which only one was present,
and the relation of this to cells having no Spm, was discussed e rlier
‘pageO00). It might be suspectcd that cells having more than 2 “pm
elements in them could arise from successive transpositions of Spm in
the progeny of cells in which two were present. This may be the sequence
of events that is responsible for the appearance of some cells having more
than 2 Spm elements in them but possibly this explanation may not apply
to all of them, Cases of similzr type were examined by Brink with the
controlling element Mp (= Ac) in which he could not relite all of this type
to sucdessive transpositions of Mp. For study of transposition, Ac is rund

more f.vorable than Spm because change in dose of it leads to recognizable
“A
182

change in phenotypéc expression, each dose being correlated with a

particular type of change in expression of the gene whose mutation

pattern it controls. The dose of Spm is difficult to determine on the
priudly pe

basis of pattern produced by ae, A change in this has not effect on

the pattern of mutation but it does have an effect on the frequency of

appearance of the pale pigmented areas, either in plant or kernel,

that arise from loss or inactivation of Spm. The higher the dose of Spm,

the less frequent will cells be formed in which Spm is either absent or

inactive.

From the discussions given in this and the previous section, it is
evident that the number of Spm elements that will appear in individuals
of the progeny of one having a known number of them will depend upon the
behavior of the particular Spm elements that are present in the parent.
Nevertheless, a summary of the relation between the number of “pm elements
in a palnt and that in its progeny may be of some interest and, therefore,
table 60 was prepared to illustrate this. In its preparation, the Spm
number in the part of the plant that produced the first ear on the
main stalk was used. Included in the table are the progeny tests that

were conduced during the summers of 1952 to 1955. In this table, no

consideration is given to the number of plants in which a newly transposed
183

Spm element was known to be present. The table merely gives the
number of Spm elements that were present in the part of the plant that
produced the first ear on the main stalk. Tables 61 and 62 illustrate
the agreement with and the differences in the number of “pm elements
that were present in different parts of the same plant. In these
tables, also, no consideration is given to known differences in location
of “pm in different parts of one plant. Only %pm number is considered.
In the studies so far reported, no case was detected of complete

stability of location of Spm, thatis, in which “%pm remained at one location.

 

lo¢atton inthe chro-osome-commlément and it is a-case—in-weich-the—

state of Spm different from that which was present. in.all.plants..so.far_

8
consitered. This-stete-of tpm,-symbolized Spm-w because of its weakened

capacity to suppress-gene-actionat a," -and-as™) ana to-induce-mtation

to or towards AL or Ay; will be considered in thé next part-of tiris

réport.

iN
\s

Wire

184
PART LV
Change in Mode of Action of Spm
See wes ntanwd ation tape sev.
On some of the ears produced by plants in culture 6629, grown in
the summer of 1953, a few kernels appeared that had only one or several

dots of Ay type pigment in a non-pigmented background instead of the many

spots of this pigment type that were exhibited by most of the variegated

C Aen putoe ~ }
kernels on the ears of these plants. Sernels of the former type were
“a
( act Waiky v4)

selected from 8 of the ears Each of the 37 plants derived from them
weatied AL beng votg acid fr by Anealig wm mon- prcurcull a indkerguuncl

was pale pigmentedy as if no Spm were present in any one of them. On the

testcross ears produced by the majority of these plants, only pale

pigmented kernels appeared. Un the ears of several of them, however,’
pheno
many kernels appeared showing the smame/type as that given by the kernel
C are pako }

from which the plant arose. One of them was plant 6683B~2, which was
A

am (state 5719A-1) Sh,/a, shy, Pr/Pr, y/y, Wx/wx in constitution.
toto
An ear of this plant had been used in a cross with a plant that was lly But

A
mn-1 pra s

homozygous for state 5719A-1 a : ‘
vé 1 » for Sho pr =e anc wx and it had

no Spm. This same tester plant had been used in making many crosses
pe et Murua ine€ =
during the summer of 1954 and it was known that the amt in it would
A

respond to Spm by giving the pattern of pigmentes shots whown in photo °

ube
On the ear produced by plant 6683B-2, there were both pale and variegated
A

kernels but in the variegated class, the number of pigmented spots .
185

C VLD og |

was very low, the majority of kernels having only 1 or 2 such spots.
Also, as stated above, plant 6683B-2 was pale pigmented instead of being
variegated, as would be expected if Spm were present. The kernels on the
testcross ear of plant 6683B-2 were of three types; 169 were uniformly
pale pigmented, 118 were colorless except for 1 or several dots of the

Ay type pigment, and 51 were totally colorless. If the last two classes
are combined, there is a 1 to 1 ratio of pale colored kernels to those
that are colorless, or nearly so. This ratio suggested that in this
plants some factor resembling Spm in its action was segregating. Jt
suppressed gene action at ant in the kernel but not in the plant, and

it was muck less effective in inducing mutation to or towards A, in the

UL

kernel. Some of the kernels that. had T or several small Ay dots ina

colorless background were sown in the summer of 1955 under culture

number 6888. Tests conducted with the plants derived from them indicated
that the factor responsible for the altered phenotysic expression of
amt had been carried in one of the chromosomes 5 of the parent plant,
6683B-2, ao resembled an Spm whose capacity for action had been much
weakened and for this reason it was given the symbol Spm-w. Study of
this Spm-w extended through 5 generations of plants and these included

»
a)

examination of the effects it produced on different states of eth amt
A o
185

Before these investigations are reported, several other cases will be
reviewed briefly in which a modified type of Spm action was detected in the
progeny of individual plants in which a fully active Spm was known to be
present.

As mentioned above, only a few of the plants derived from kernels
having the described modified type of variegation pattern that were grown
in the summer of 1954 gave evidence of the presence in them of Spm, either
by their appe rance or from the phenotypes of the kernels on thei» testcross
ears. At thet tine, the reason for this was not understood. Ttwas only
sometime later that it was learned thatone of the types of change in Spm,
responsible for the appesrance of some of the kernels with only a few A,
dots in them may be inactivation of Spm. In plants having a fully
active Spm, change from the active to the inactive phase may take place
in some cells, and when this is occurring in a kernel, the altered activity
may be noted by an altered pattern of v riegation within the aleurone
layer of the kernel. In plants derived rom such kernels, *pm may
remain in its inactive phase throught development of the plant. Lhe
nature of this type of change in Spm will be described .1 the scetion of
this report dealing with inactivation of Spm. Change of Spm from fully

active to partially active likewise occurs in some cells and the differences

in grage of this
186

may be distinguished. It is these anges in Spm that.t

      

 

Rn tld iced

  

ieee ety

section will consider.
Listimeti .
age
On, testcross ears produced by game-ef-the fully v rieg:ted plants
grown in the summer of 1954, hernels having the above mentioned types of
change in Spm were noted. Often, ony one to several kernels on an
ear exhibited an altered pattern of variegation. On a few ears, however,
a large number of them appeared, and this was true of the testcross ear

produced by plant 6665E-9 which was s M-1( state 5919A-1) Sh,/a, shy, Y/y

1
in constitution (see table 18 for origin of plant). Pollen from a plant

of the tester stock that was homozygous fora shy, pr, and y had been

1?
used in making the cross to plant 6665E-9, Among the 169 Sh, keinels
on the resulting ear, 1 was totally A, in phenotype, 38 were uniformly

vn dud bee wine mummy Ri apets wa cotirtear doch oud,
pale pigmenied, 84 were fully variegated, 40 were colotless except for one
or several Ay dots, and 7 were totally colorless. If the pale colored
class and the two latter classes are combined, the ratio of kermels types
on this ear suggested that a fully active Spm might be carried in the
Y bearins chromosome 6 of plant 6665E-9 because among the pale colored

kernels and those with the modified phenotype, 30 were Y and 56 were y,

and among the fully variegated class of kernels 45 were Y and 38 were y.

In the former group, about one half of the kernels exhibited the modified
187

oy’
oa

phenotype, being colorless or colorless with one or several AL dots.

ny. Cre ABS, “Res 4

This suggested that some tae tor Was present in plant 6665E-9 whese

é

presenee was responsible for modification of a expression, that it
. vhs é Haut c a af xd fut ett te Aas > tn Sees cee yy oS AL where we
Was segregatiie independently of Spm ‘but, could be recognized readily only
X A

2
when ‘pm was absent. It was decided, therefore, to examine plants

derived from some of the colorless kemels that had only a few A, dots

1

in them and these were grown in the summer of 1955 under culture number
cael toolh.| | aide hat wee to feel -
6886. & Spm-w was found to be present in , rom, and_again, it was loested

im—ehremeseme—5 ,

On the testcross ear produced by plant 6662E-16, that was ay sh, /

ay sh,, ¥/y in constituticn (see table 18 for origin of this plant),

some variegated kernels appeared that exhibited a much reduced number of
Mag Megas faye

< “k ey ” ot _
A dots in a colorless background in addition to fetty variegated kernels.

The pollen parent th .t was used in making the cross to plant 6662E-16

was homozygous for state 5718 am, for Sho, pr, y and wx and it had no
° m-1
Spm. The expected behavior in the presence of Spm’of the ay ~~ in this

tester plant had been fully attested as it had been used in making many
,?
testcrosses to plants having Spm in them. On the ear produced by plant

6662E-16 there were 76 pale colored kernels, 26 of which were ¥ and 50

were y. In addition, there were 299 variegated kernels, 117 of which
188

were Y and 112 were y. However, the pattern of variegation among them

was not the same. Some were fully variegated but others had a much
Nn wetecn
reduced number of AL spots. , Plants were grown from the fully variegated
_under culture number 6870 in the summer of 1955)

kernels on this ear/and’thoh tested for the presence or absence of “%pm-w

: boat
in them in addition to tre-futly=settve Spm’ From tests coméweted—wi-th

these—pients it was learned that anfullg-aetive Spm naa YOR call in

the Y bearing chromosome 6 in plant 6662E~ 16 but in addition, an Spm-w
od oud wit Linhtel yyich J. UT oppooud m s 4 Wud
also was present, i++—~was —presont—in—halt—ef—bie phants derived from
the: fully variegated kernels on the eir of plant 6662E-16.
/ The Spm-w in plant 6683B-2
Discussion of Spm-w will commence with the plants in culture 6888,
derived from kernels on the testcross e-r ofplant 6683B-2. As given

above, this plant was a7 (state 5919A-1) Sh,/a, sh, Pr/Pr, y/y, Wx/wx

in constitution and the pollen parent used in making the cross with this

7 a
at 4 ts!
plant had been homozygous for stxte 5719A-1 amt and for Sho, pr, %% and
C wee Vote 14)
wx and it had no Spm. As reported, half of the kernels on this ear were
N

uniformly pale pigmented and half were either colorless or had one to
several dots of Ay in xk a colorless bickground. Eight plants were

grown from the uniformly pale class of kernels on this ear. Each was

UAL,
uniform.y pale pigmented and am earyof e@ek plants wes used in a cross with

a plant that was homozygous for a sh,, and y and in which one febiy

Ll’ 2
189

Conbtechoel . te ala:

aetixe Spm’ was present. This was dome in examxmex or der
Pp

the, toposly & B ase pk A a,
ot the a7 in each plant wertd react mermmetiy to Spmé~

Ears were obtained from 7 of the 8 plants and the kernel types on these

ears are entered in table 63. Half of the aw carrying kernels on earh

ear were pale colored and half were variegated, giving the pattern of

CSpum-s) variegated
this expected when a fully active Spm element is present. Only two
i A .

kernels on these 7 ears had a reduced number of Ay dots in them. The

tok

kernel types on these ears contrasted greatly with the tyves appearing on
A
in culture 6888
the ears of plunts/th:t had been derived from colorless kernels in which

only 1 or several Ay dots were present when the same pollen parents were

5 het pha aa
used in making crosses to them. The kernel types on “nese eurs'’ are ae
te We eae Me 7 [re [! netted au Ue Coe wo Te Mae thy pity | te ay ULCN Ca Aa. weer Be Ht ery ~
given in table 64. Half of the a,” -1 carrying kernels on these earg

were fully variegated but among the remain:ng half, half of these, in
turn, were ¥muxix uniformly pale pigmented and half were either totally

colorless or were colorless with 1 or several Ay dots in them. Segrega-

ti:n of the alleles,wf Pr and pr, to the uniformly pale kernels and to

the colorless kernels with 1 or several A, dots left little doubt that

1

the factor responsible for the appe:rance of the colorless or nearly

dah il wich ait x
colorless kernels was carried-in--the Pr ehromosone in-these—plants,—and

“\

it.was-the-ehromoseme that had been received from the p-rent plant, 6683B-2
190

dey

we ne

The plants in culture 6888 teat gave on their ears the kernels types

(were pale pi gmented but _they#) " whoa ap ur?
entered in table 64/dtéd-xet—-devetoep: pigment Zs rapidly | asi the plants
heel way Borie % Pole pucendid ©

thit gave the kernel types entered in table 63. Phe—pigment—deverered
athe pice

mck-mere showly-in- them. +n some Stenses the intensity of Sats was

Tame dy fal. ed aebuad anvar

not uniform. Seekers appeared in which the intensity of this was much

at
’

reduced or occasianally incre sed.
In addition to the crosses entered in tables 63 and 64, an ear
was obtained from one plant in culture 6888 that had been derived from

with in ated ® dite Dy uscay parce feo ab aut wea byte

a weer colorless kernel

 
 
 

 

1 had intel wa,
for ay" (stute 5718), and for Sho» pr, y, and wx and # had no Spm.
“a

A

On this ear there were 468 kernels; 253 were uniformly pale colored of
which 70 were fr and 183 were pr, 143 were colorless with 1 or several
Ay dots and 112 of these were Pr ana 954 were pr, and in addition there
were 69 totally colorless kernels. Again, it was clear that the

Dh gaa wrt tank debor)
Wesdesed SpmYin tris: plant was carried in the chromosome 5 that had been

\

ao yori
neces From Plant, 0685B-2. Ten plants were grown from the uniformly
Pr Peary aoe

pale colored/kernels and ten other plants were grown from the colorless
J z

k:rnels with or several dots of AD that were Pr in phenotype, under

culture numbers 7264A and 7264B in the summer of 1956. All ten plants

derived from the uniformly pale colored kernels were themselves, uniformly
1921

pale pigmented. Those derived from the colorless kernels with few A

1

dots in them also were pale pigmented but

 

wo Abst
i Pfui oped very “slowly. Also,

 

WAS wk ban, ‘hu sey oo bt AA
intensity of this appeared within some of these plants,

 

OF ; —
wep Qi gae . : : Tr eu ae “
aor Yay Ag nevll ¥ te ede %. ua. fae

ob
ami=in distinct seeters within the plant. ALL plants in culture 7264
were crossed by plants thzt were homozygous for either state 5719A-1 a™°!

7, and for Shy, y, pr, and wx and that had no “pm in them

or state 5718 a

On ears produced by all plants in A of culture 7264, only uniformly pale

pigmentei\kernels appe:red. On all ears produced by vlants in B of this

culture, pale colored kernels, colorless kernels, and colorless kernels

with ore or several Ay dots appe.red. Linkage of the latter phenot wé

with Pr and the chon phenotyp with pr was clearly evident on all ears.

The phenotypes of kernels on eurs of 9 plants in culture 7264B are

entered in line 4 of table 65. 4n one plant, 7264B-6, Spm-w was

present and carried in the chromosome 5 with Pr but it was almost

completely inactive in many kernels on this ear. The kernel types on
Vor:

this esr a-e entered in the last line of table 65. The-kerneis placed

in the "inactive " > $iew class were lightly pigmented and the distribution

of this was uneven, giving a mottled appe:rance to the aleursne layer.

i ’ aan ¢ 3b me, Deyn “ys bey )
¥his is the typical appearance of the aleurone Layer (eimtise Spm =e
192

is very weakly active.

Continued examination of the Spm-w, originally present in plant
6683B-2, included tests of its presence or absence in plants having
a number of different constitutions. In order to facilitate presentation
of the evidence obtained from these tests, several chants were constructed,
figures 5 to 7. Figure 5 illustrates the origin of the plants in

Leer OW

culture 6688 Teraved trom kernel? on the ear of plant 6683B-2, and the
constitution of the pollen parent used in making a cross to each. From
the ear of plant 6888D-2 (see 2, under Progeny Grown in Summer of 1955)
kernels were selected and plants grown from then given culture number

Te Opera oy Due Newt ued Ue tod Crete uedth Bcan wer Zeieyicet adel, y

7264 (see 3, under Progeny Grown in Stmmer of 1956), Kernels were alsa §

~
selected from both the first and the second exr on the main stalk of SS
<
plant 6888C-3 (see under 1 of Progeny Grown in Summer of 1955) and the °
s
>
plants grown from the,were given culture numbers 7262 and 7263. The %
x
phenoty-es of the kernels selected from each of these two ears are xs
given in figure 5 under 1 and 2 of Progeny Grown in Summer of 1956. g

a)

All plants in cultures 7262 to 7264 were crossed by plants that were

owes

exthker homozygous for a 4 ; Stat amt and —_
Phat Dowco dow adaty S719 0-1 acm uty wrod fowl yt curarso (gud faa dourcsitin . &

Shy, pr, y and wx and they had no Spm in them. On the ears produced

 

by plants in culture 7262A and 7264A, no vuriegated kernels of any type
193

4
appeared. All were uniformly pale pigmented. Variegated kernels appeare

on the testcross euirs of all other plants in these three cultures.
Bach plant in cultures 7262C and D, in 7263C and D and in 7264B carried
Spm-w but not Spm-s and figure 6 was prepared to show the constitution of

maa”
these plants with resect to vwonukiexenxat the alleles of Pr, and—the

tien OPPO

location of Spm-w. The kernel tyves on the “ears of these plants are
A

entered in table 65 according to the constitution given in figure 6.

*“t may be seen that Spmw was carried in chromosome 5 in 22 of the 24 plants
A

that were Pr/pr but in two plants, no evidence was given of linkaxve of

it with this marker in chromosome 5.

The kernels that gaveyx rise to the plants having pms item
dod Sams uation -
t¢hese in B of culture 7262 and in A and B of culture 12637 | eouid_not

“
ae

pe Selected for the presence or absence of Spm—w in thom cox for the co
wn ceelrn nut wit be rod aby plants drat fun

number of location of the Spm-s elements. In this respect, they proved
A A
to be quite heterogenous. Altogether there were 11 different nora aby
constitution among the 21 tested plants) and these are given in figure 7.
In 12 plants, no Spm—w was present J» a+ was present in the remaining 9
J we
plants and carried in chromosone 5 in each. The male parent of these
A

plants had 1 Spm-s element in it, and it was located in one of its 2wo

y bearing chromosomes 6. Thirteen of the 21 plants in figure 7 were Y/y.
194

In 11 of them, one Spm-s was present and it was linked with qin 10 of
these 11 plants. Two °pm-s elements were present in one plant (7263A-3,
figure 7)one of which was carried in the y bearing chroriosome 6. In

the remaining plant that was Y/y (plant 7262B-2), three Spm-s elements
were present, one of which was carried in ik y bearing chromosome 6.

The types of kernels appearing on the ears of vlants entered in figure

7 under the heading "No Spm-w" are given in table 66. They reveal the
number of “pm-s elements present in each plant and the location of them
with respect to the alleles of Y. in those plants that had an Spm-s
element not linked with Y, no evidence was given of its linkage with

Ayyod

cays Cth Pe . ;

gae”, etther fr in chr mosome 5 or Wx in chromosome 9. Also, on these ears,
only one kernel was present that had a much reduced number of Ay spots in
its aleurone layer. The kernel types on the ears of plants entered in
1 and 2 under the heading "Spm-w present" in figure 7 awe shown in table
67, and those entered in 3 and 4 under this heading are given in table 68.
From the data g@t¥ven in each of these two tables, it is evident that opm—s
and Spm-w segregated independently of one another, and that in the
majority of the Y/y plants, “pm-s was carried in chromosome 6, and Spm-w
pried

we in the chromosome 5 originally derived from the grandparent plant,

6683B-2,. It also was clear that Spm-s is epistatic to Spm-w, all kernels
195

with Spm-s having many A, dots im-them regardless of whether or not Spm-w
is also present in them.

Response of state 5700A ae to Spm-w

Lhe following year, 1957, plants were grown from some of the kernels

having °pm-w but no Spm—s in order to introduce Spm-w into plants having

a state of aw other than 5718 or 5719A-1. With either of these two

st tes, tthe number of mutations to or twards Ay is very much reduced when

al w Oly

Spm-w is present, there being mumk only 1/Shalf "SF “dos: or none apper.
4
It was dewired, therefore, to determine to what degree Spm-w wo 1d reduce
mutation frequency with a state that gives a large number of mutant spots
a tale 5996-4
when Spm-s is present. For this test’, state 5700A w&r@ selected (see-photo.
A
907. State 5700A produced very many mutant areas both in plant and kernel
with Som-s and a number of mutations occur early in development of both

(aie pao oo)

plant and kernel.

To obtain plants having state 5700A and no Spm in them, pale colored
kernels were selected from the self-pollin=ted exr of plant 6702-2 which
was a7 (state 5700A ) Sh,/a, sho, Pr/pr and it had no Spm in it (see
table 18 and 23), and from the pale Sh, class of kernels on each of two

ears produced by the cross of plant 6702-2 to plants that were homozygous

for ay and shy and in which no Spm was present. The plants having Spm-w,
196

grown in the summer of 1957, were derived from Spm-w carrying kernels on
5 °
the ears of two plants, 7262C-2 and 7262D-4, entered in figure 6 and table 6f
Each was Br Spm-w/pr i amt (state 5719A-1) hp/a, sh2 in constitution,
and the ear of each was produced by a cross with a plant that was homozygous
for state 5719A-1 amt and for Sho, Y, pr, and wx and in which no Spm was
13KOA

present. Plants were grown from kernels on each e#r that had purphe
spots (Pr/pr) or red spots (pr/pr) in them. Tests were conducted with
each plant that was used in a cross with a plant carrying state 5700A
amt in order to determine its constitution. For this purpose, pollen
from plants homozygous for state 5719A-1 amt and for Sho, pr, y and wx
and in which no “pm was present was placed on the silks of these plants.
The kernel tyves on the resulting ears produced by 4 plants that were

7 and Sh, and were Pr Spm-w/pr + are

homozygovs for st°:te 5719A-1 a
given in txble 69. Spm-w was carried in the chromosome 5 with Pr in each
of these plants.

Examination of kernel types appearing on the ears produced by
intercrosses between plants carrying §Spm-w and those having state 5700A
indicated that state 5700A a a responded to Spm-w by producing many

1

fewer mutant spots than it does with Spm-s (see photos 00 and 00). Also,

the time of occurrence of mutation was much delayed. Most of the Ay
196a

spots in the kernels having state 5700A were small and this contrested with
the many spots of large size that appear when Spm-s is present. The
number of pigmented spots was much greater, however, than that which appeareé

in kernels having either state 5718 or state 5719A-1 when Spm-w is present.

m=l

For further study of the effect of Spm-w on state 57004 ay ;

kernels were selected from ears produced by plants that were homozygous for

state 5700A in which no “pm was present when crossed by plants that were

homozygous for st:te 5719A-1 and having Spm-w in them. All kernels on
an

these ears had state 5700A and state 57194-1 in them. It wes necessary

to grow plants from kernels having both states of ant in them and to

cross them by plants that were homozygous for ay and in which no Som was
present in order to compare the response of each state $6 the Spm—-w present
in the plant. Among the kernels on the resulting ears, half should carry
state 5719A-1 and the other half should carry st te 5700A. The response
of each state to Spm-w could then be campazred directly among the kernels

on an e@°2%.
197

Hor one of the tests conducted wake state 5700 amt to determine
oh aan
its response to Spm-w, plants were grown from kernels on an ear produced
by the cross of a plant that was Pr/pr and homozygous for state 5700A and
Sh, and in which no Spm was present, by one that was homozygous for state
5719A-1, sh, and pr and in which 1 ‘Spm-w was present. “alf of the
kernels on this ear were pale colored and the other half were v riegated.
The pattern of Ay spots among the variegated class of kernels resembled
that produced by state 5719A-1 when Spm-s is present (see photos )o

Br
Ten kernels were sown in the summer of 1958 from the pale,class of kernels

saga

under culture number 7530A and 16 kernels were sown from the variegated,Pr
, an

Glass under culture number 7530B. All plants arising from the pale kernel
were uniformly pigmented. Those arising from the variegated chass showed
small streaks of Ay pigment in a non-pigmented background during early
development and the pattern of streaks resembled that produced by state
OTLQA-1 in the presence of Spm-s. As the plants matured, pigment develop-
ed in the background. The patt-rn of small snots of AS in the kernels and
of small stre:ks in the plant most probably were produced by mutation
occurring to state 5700A, the contribution to thes of state 5719A-1 being

small. This wis made evident by the kernel tyves that appeared on the

testcross ears of these plants.
198
nab
yo
++ was necessary to te=rm th t the uniformly pigmented plants,
A
arising from the pale class of ke rnels on the ear jut described, had no
these
Spm in them and also to verify that exzk plants carried stxte 5719A-1 in
one chroosone 3 and state 5700A in the other chromosome 3, bot of which
would respord in the expected manner to the presence of Spm-s. therefore,

crosses were mde to plants in culture 7530A using for t is purpose pollen

from plants thit were homozygous for ay and sho, Some of the pollen

came from plants that had no Som in them whereas it was present in other

usw luda p lan wns Otto af-

plants. The types of kernels appearing on the ears of five plants in
A

70
culture 7530A, produced by these crosses, are shown in table 6%,

Chcan

It was ob¥teus from theae tests th t no Spm was present in these plants and

ww Wen

that the-twe states of ay 1 omesent in-eaeh would respond in the expected

peo Verte aD Ddrwede )

manner to pms. 4 The Sontrest—in—the pattern of variegation given by
wo “ aut , taken,

each st.te was so gesat'th:t no difficulties were experienced in separa: ing

Ade 5100R Kom Wore Lagu, ad aly : nant
tee kernels having ane or eR owl ofthese twe—~statem

Plants in B of culture that Were Vambeerted were crossed by plants

homozygous for ay and sh, and in which no Spm was present. seven test
cross ears were obtained from these plants and the tyves of kernels on
each ear are given in table 7p. All plants in culture 7530B were Pr/pr

in constitution. tt had been planned to cross these plants by ones that
199

were homozygous for ays shy, and pr but all plants of this constitution

died in early stages of development due to unusually unfavorable growing

podion wos cotlvelat pew :

conditions in the summer of 1958. Therefore, plants wongliced from a
A

thane
culture in which the alleles of Pr were segregating. Some plants were
nn “a
Pr/Pr, others Pr/pr and still others pr/pr. The constitution of any one
plant with regard to the alleles of Pr could not be known in advance of
ow To Wr play va tulip IS30R
test of each. bibse used in the crosses, all three constitutions were
represented. It was expected that the Spm-w would be carried in the pr
chromosome in theg plants in culture 7530B and that linkage of the
variegated class with pr would appear among the kernels on the testcross
ears they produced. Among the ears given in table 79, one pollen parent
was Pr/Pr, 4 were Pr/pr and 2 were pr/pre | It was evident th:it Spm-w was
carried in the pr chromosome in each of the plants, entered in table 7¢.
On the two ears produced by the cross with a plant that w:s homozygous for
recombinant
pr, the percent of/kernels mwxkk among the variegated class was 33.
Among the varieg:ted class of kernels on the ears entered in table 7f

Cpe

two classes could be distinguished readily. One had many dots of AD
and the other had only or several of them. In tHe total, therewcre

Tae | N
659 kernels th the former class—and 579 i the latter ote. In -ddition,

there were 90 colorless kernels. ‘+f the colorless kernels are added to
200

to those in the latter class, al: 1 segpesatien ratio appears. eens

we

wo-tyaeses-ef kernels having Spm-w in them. The latter class resembles

in phenot.pe that appearing with state 5719A-1 and Spm-w and the former

aa’ in the kernel
type the same as that/whath gave rise to bach plant, and these kernels

had both state 5700A and state 5719A~1 in them. Obviously, then, the

kernels that have many A, dots carry in them stzte 5700A and those with

1

oe AM -talhy,
or several AL dots or,ape colorless with no—4,—dets hive State 5719A-1

in then. In other words, halle of the kernels on these ears had no

Spm-w in thes and were uniformly pale colored and half carried Spm—w

4p

Half of these, in thrn, carried state 5700A and half carried stute 5719A-l.
A
AWA

It appeurs evident that “pm-w reduces mutation frequency in a proportional
A

manner, the number of mutant spots that are produced in its presence
being a fraction of that which appe rs wwhen “pm-s is present. This

relationship was also found to be true when “%pm-w was introduced into

wh very
lants carrying state 5996-4, which peeduces/many mutant spots with “pom-s

but far fewer of them with Spm-w. Before this is considered, another

test conducted with st=te 5700A and Spm-w will be discussed. a was

pag WY poaguat prot Aun, Spm aed aera Wael wy,

examined because ef change in action of “pm-w had oceurred| thet reduced

“A
nreddive UN ww

even further its capacity to induce mutation.
201

The ear of a plant homozygous for state 5719A-1 and Sh, that was
Pr +/pr Spm-w was used in a cross with a slant homozygous for st:te
5700A, Sho, and Pr in which no Spm was present. On thés ear there were
148 pale colored kernels and 140 colorless kernels whth spots of A

in
1

them. However, the number of Ay spots wasefar fewer than that appearing
au so

on ears of other plants produced by crosses conducted with theplant

carrying state 5700A. “nstead of several hundred A, dots, the number

among the varieg ted kernels on this ear ranged from as low as 15 to

as high as approximately 100 with the majority of kernels hiving about

30 to 50 of them. Some of the variegated kernels were selected from

this ear and grown in the summer of 1958 under culture number F829, the

ears of five of these plants were used in the cross with plants that were

honozygous for ay and in which no Spm was present. The kernel tynes on

these ears are shown in table 72 and the plxnts are arranged according to
on their ears

the proportion of kernels/that were colorless whth no AS spots in then.

This was done because there was a distinct correlation between the percent

of colorless kernels and these ears and the number of Ay dots that

were present in the kernels having state 5700A and Spm-w, the higher the

proportion of totally colorless kernels on the ear, the lower the averase

number of AD dots that appesured in the kernels having state 5700A.
202

However, on all e-rs, a few kernels appe:red with very many dots of Ay

in them or sectors appeared in some kernels in which the number of A,

dots was very much increased. +t appe red that the Spm—-w in the parent

plant that introduced it into the plants of cubture 7529 was less

ata m—1

effective in its capacity to induce mutat_on/eithtr with state 5700A or

arden quour§

with state 5719A-1, and also that, change in this was occurring in

individual cells leading to a much increased capacity of it to

induce mutation. Differences in mutation-inducing capacity of Spm as
Tentoeney’ cance

well as its inhibitery capacity gene action at a." hive been noted

in studies of other Spm-w isolates. Just as Spm-s may undergo change

to give Spm-w type action, so mawy Spm-w undergo change to or toward

Spm-s type action. . a

pyaddoen? S

Change in degree of action of Spm-w may be noted in the plant as

nN

ws

well as the kernel. In some plants, distinct sectors appear in which the
capacity of “pm-w to suppress gene action at amt was increased. The

anthocyanin pigment in these sectors was much lighter than in the rest of
the plant. Also, some sectors appe red in which no pigment could be
detected and within a few of them, small streaks of Ay type pigment

were present. From studies of the type described here and also from

to be
those that investigated inactivations of pm, there seems little doubt
203

that the capacity of Spm to induce mutation is directly correlated with

its capacity to inhibit gene expression at am. Spm—-w represents and

intermedi te state between a fully active Spm and one that is totally
inactive. *ts capacity to induce mutzotion is reduced along with its

cayadity to inhibit gene expression. It is possible that the apparent

a

m—1 m-1L

double mode of action of %pm--supression of gene action ata and An

1
and induction of mutation at both of these loci,--is the consequence of a
single initial reaction in the cell for which pm is responsible. -

Another factor enetering into consideration of “pm-w will be mentioned
here as it has significance in appreciating the relation of Spm-w to Spm-s.
A modifier was found to be present in a single kernel on an ear of a plant
carrying Spm-s. Its presence is made evident only when Spm also is
present. The origin and detailed mode of behavior of it will be

considered in the section of this report dealing with the Modifier. When

present with either -’pm-s or Spm-w, an approximate three-fold increase in

m=1
1 e

mutation frequency is produced with states 5718 and 5719A-1 of a
The importance of menti ning it here is to indicate that the mutation
increase it induces is the same with either “pms or Spm-w. Kernels
having in them an Spm with a low grade of action can nog be distinguished

from ones in which the Spm is fully active whenever the Modifier also is

present. However, if Spm is totally inactive, the Modifier has no effect
204

tall.
au 8 Response of state 5996-4 to Spm-w

Tests of the effect of “pm-w, derived initially from plant 6683B-2, on
state 5996—4 amt were conducted at the same tiuwe as those with stute
57004, just dese ibed. in tnepresence of Upm-s, svate 5996-4 gives an

exceedingly high number of small mutant spots in both plant and kernel.

the number of them may be so high that a kernel having this state and pm-s

often appears to be totally pigmented. Examination with magnification
alg pronuad ppcalod
reveals that this phenotype is produced by many mutant syvots very close
A
to one another. In some kernels that are purpbe, (Pr), the diffusion

rims about each muvant spot may run together and this may make it

frome then Bi amenaligy deere whee he

difficult tr impossible to know withcertainty if-the phenotype arose from

Of
veo &

a germinal mutation to Ay or was produced by many mutant ssots whose diffusi .
A

diffusion rims have run together, making the aleurone layer appear to be
" . Feom Pogu, Wr Uh A dest web ie Cole le iden.

totally Ay in phenotype. | In Kernels that are homozygous for pr,

however, the diffusion rims are much lighter in shade and in these
Cook B Ry nf Uae

kernels no such difficulties are experienced. The many dots, pl:ce very
A A 4

close to one another may be dttected. By-uwse-ef the pr vhenotyve, it

. 4
was learned that germinal mutation is infrequent with state 5996-4,

Because state 5996-4 produced many late occurring mutations with a

fully active Spm-s, it is a very sensitive indicator of any somatically
205

rn
occurring change in Spm- anéd—this—eppttes—hetketo-any state of Som—that
A
sometimes
may _be—present. Sectors/appear in kernels in which the action of Spm

is altered. If the “pm present is undergoing change in a number of cells

during development of the kernel, the pattern of mutant spots in the

kernel is quite irregular. If Spm undergoes few changes during development
the pattcrn is quite regular. Tilustrations of tris with Spm-s are
kyo

shown in photographs 0O and 00} A ais state very effectively shows) the
types of change occurring to Spm-w. Yom-w, initially obtained from plant
6683B-2, reduces the percent of mutations with state 5996-4 as it did
with state 5700A, and the mode of testing for this was the same as that
just described for state 5700A. In one test, pollen from a plant that
was am? (state 5996-4) Sh,/a, sh, was placed on the silks of a plant

homozygous for state 5919A-1, and Sh, and having one Som-w. On the
Vo 2k Lm peat yr tle fount « Qn oolettlin, WSO wb!
resulting ear there were 196 pale colored kernels, 86 k rnels with Be mete,
_ dndreotine ip purdug cD Qed pra WP rial
number—of A, dots*in them Ynateiviously had state 9996-4) in them, 98
4

kernels with 1 or several Ay dots cea 4 kernels that were totally colorless,
anditeillin ss th pOue wa thous % at ato 5719R4 al OS ut Spom-w-
<, The change in action occurring to Spm-w during the develonment of the

UA

kernels hav.ng it wes illustrated in a striking manner b¥ those that had
Shun w awed

, State 5996-4 in them. In the majority of kernels, sectors were present

d
in which many dots of A, wort CO or the $¥€tern of this was similar
to that given when Spm-s is present. (See photos 00). in the kernels

that had only state 5719A-tin them, more than the usual number of Ay dots
nN
up dageat
were—present. +t seemed clear that the Spm-w in thatributed by the female
mw trkion Cop aut

parent was undergoing rather frecuent change during development of the

A
~ ,
kernel and this occurred early enough in some cells)>that thir progeny

a
yoy? allind tp noon. eels pected:
could sew theschange reedeey by the pattern of AL dots in them
A A

« When the pollen from the plant carrying state 5996-4 was placed on the

of an ear QO \ynit Que UN
silks/of_another/Spm-w Carrying of similar constitution to that just
Ao ori ou

described, there were 167 uniformly pale pigmented kernels, 92 thathed

a urge .
anumber—-ef dots of AS ta—them, 39 that had only 1 or 2 AL dots and 62
that were totally colorless. it was obvious from the reduced number of

Ay dots and from the infrequent appearance of sectors in which many AS

dots appe red, that the Spm-w contributed by the female parent was

early
undergoing very few changes during/development of the kernel. Change in

Ande 3 ty fiat
Spm-w was occurring but in individual cells quite late in development.
A

(See Photos 00). The impression gainea from the study of state 5996-4
with m-1

and Spm-w is thet mutation to A, will occur ak any state of a) only

after some modification has occurred to “pm itslef during development and

that the number of mutant spots seen in a kernel with any one state

is a reflection of the time of occurrence of change in Spm and the

frecuency of this occurrence at any one time.