TW odes ou
coral v alyuelalin wy beef eu
Roleddiay b Cpl 206 4 @. ¢. wy, Mlayp
Pune) Aleedog wehioy Spy “el ey at g,usl gran, wyrAas
Stabe quay eltawnt Clan 2 + Un abatDy

shu Spun aka Tuan pone
vat Lang iapleSpa
Depfocono 3 Spm ug Aart + Ae oublun -

ayaa

Pao gluy & 11 0¢ - Ougu .4 T1097

1109 biped - Yabls |

1109B-2 Wn & 2ar >
Toho. 2- GH TIoVB-1 poy Saul
w Y para Tat Qunsie. Cubed
Typed TFs - Typhi 1, 23
Pinger tar + ¢ T1o?B- 1 TAleg
is ao Fy TOI 4 . ‘
Ae 3 pau thoue Yoke 7
Meu > On tw Spun plaid 1208 wd) M456
TaW- 142 09 Yho-s Wr Cox

kom Thysy ov hur 4 al iy Lb vyss - T0be, Ss, 9
. ete ew THE Tab 1011 12

ete | usel we Spun - Joli wen pas gea lla

Wn Oeb ue Spun - Yoltho +3, 1f
ni

—_——

iy

Pogo 41109 8-1 hin - T ake 1x Teeblbskb
wo=- 2 Table lb

* nS y
his] eo

PYGLICAL CHaANGS IN PHASE OF aAGTIVITY OF THE SUPPRESSOR-NUTATOR
CUNTROLLING Bub sNT IN MATZE.

lhe nature and mode of action of enntrolling elements in maize
“s
has been discussed in a number of publications by the author and by
others. Two or more elements may operate as a unit in the control
of action of a snecific gene, and each such set of interrelated
controlling elements forms a system. Eech system, in turn, operates
quite indenendently of all others. Systems of controlling elements in
maize were originally discovered because the individual members within
each transposed from one location to another in the chromosounie
compile ent without los:ng their identifying chamacteristics in the process.
By this means, it was possible to distinguish different svs:ems of
controlling elements and the manner by which each system operates in the
Li Reurad }
control of sene action. | Because of transposition of tee component
. Vo . . ; .

elements of a system, it was it+eewise vossible to examine the operation

of a particular system at a number of different gene loci and conversely,

to examine the operation of different systems at the s me gene locus.
p

‘

It should be emphasized, however, that although trensrosition of
controlling elements in maize made it vossible, origi ally, to recognize
their presence and their modes of operation, such trenscosition need not

charact»rize the beh-vior of all controlling elements, for it is know
th t a controlling element that hid previously undergone trunspositi.n
may becoue fixed in locstion in the chromosoiie comzle:ent.

Recent discovery of systems of "controlling elenents"] in bacteria

vonk oak

(Jacob, et al., 1960 a b) whose modes of action resemble those of sozie
systems alrendy examined in maize, eases the task of discussing controlling
elements in maize. the systems described by Jacob are composed of two
elements each. One of them,called the "operator", is located adj cent
to the "structural gene”. The latter, when activated, is responsible
for the amino acid sequence of a snecific protein whereas the former
serves to control the activation of the adj:cent "structural gene".
the second elenent of the system, termed the "regulator", may be located
close to the "structuraa gene” or it may be located elsewhere in the
bact:rial chrosjwosone,. It is responsible for the production of a
repressor substance, -= not a protein -- ,that appe .rs in the cytoolasm.
The "operator" elenent,responds to chan;es in degree of effective action
of the repressor subst:nce by co:.trolling the degree of activity of the
structural gene in accordance with such chan,es. Bach system is hig ly

specific, for each operztes quite independently of all others.

The resemblance of the "operator-regulator" systems in bact:ria to
the systems of controlling elements in maize appears to be more than
coincidental. The "Operator" in bacteria may be homologized with

the controlling element in a system in maize that is located adjacent to

/ gu
the "structural gene". The 1 aque. element in bacteria may be

homologized with the element of a system in maize th:it is independéntly

located in the chromosome comolement. As in the bacteria, the element
alt) ork wiles tLe *

at the locus of the structural gene resvonds to by inducing modification

of te action of the structural gene. In maize, the response of the

"operator" element to change in the effective action of the "

element may result in controlled types of mutation at the locus of the

a .

"structural gene", or in some cases it may respond merely by turning on

2. *

or turning off the action of the structure2l gene. That these two

apparently quite different types of effects ppnduced by the "op-rator"

w wanna o te Adeuteier "

are merely two aspects of the type of control of gene action by ast aungly

thoeiere

toperatore” will be made evident in this report. It is probable, that

A

the basic mechanism of action of controlling elements is alike in all

organisms,even though the responses of the structural sene to such

3
controls may appear to be quite diferse. It is expectcd that the nature

of this basic mechanism will be revealed in further studies of the bacteria’

systems as it is possible to examine this with a greater degree of

precision, both at the chemical and the genetic level, than ts usually
possible in many of the higher orgsnisms.

“t is the purpose of this rezort to consider a type of co: trol of

thot

gene action by a system in maize weese—mede—of -etion resembles tht of swe
3 ’ ¥
revorted oeees in bacteria. An oper tor controlling element is present

at the locus of the gene 45 ( associated with production of anthocyanin

pigment in plant and kernel) in the short arm of chromosone 5. the

roguliclr

independently located element of this system, comp rable to the "wepreseer

element, discussed above, has been designated Suppressor-—mut=tor and
symbolozed as Spm. this system was first discovered when the overator
was present at a gene locus associated with development of chlorovhyll and
tocus was then designated lu” for mutable luteus. Trinsposition of

the operator element to the locus of_A, occurred in a plant having lu”

hoe m-1

Following its i»sertion, the locus was designated a

9 as it was the
A ’

~

first case of mutability arising at the Ao locus in the VYold Spring “arbor

cultures. Subsequently, the operator element avpeard at the locus of

a kernel on the ear, of

Ay in the long arm of chromosome 3 in,a plant in aie an~ culture

and the modified locus was designated am, Recently, te operator

was inserted at the "x locus in the short arm of chromosome 9 and it

first appeared in a kernel on the ear of a plant carrying amt, his

case received the symbol wx 8 as it is the eighth case of i-stability
  

arising at the Wx locus t
a

oprins “grbor oulturedé It hos been nossible, then, to examine the
mede—eF operation of the “pm system at four different sene loci. It has
been determined that the operator element, adjacent to the structural gene,
controls the ty e of action of the gene that will be expressed in the

presence of Spm and also the tyne that will be expressed in its absence.

Basically, the mode of operation of this system is the same at all four
Qn Gen? EC ea abe)
gene loci (lu™, at, ay and wxt8 )
A

: The original isolate, in each

case, exhibited some degree of scene action in the absence of Spm and this

 

action remained the same in successive cell and plant generations as long

(any rte phere)
as Spm was absent. In the presence of Spm, however, gene action was
A
suppressed until a mutation-induci g event occurred. With each of the

original isolates, this ever} occurred in sore ce’ls, early in plant or
>
kernel deVelopment, and there were two main corse uences of it: oo
; . ‘ : OTA
diatiy atallo vn Ween pT ou ww tee} eet ha ey War werent ay 3
to a“gtaete allele of the gene concerned, or a modification, probibly
affecting the operator element at the locus, that is reflected in
subse iuent cell and plant generations by altered responses of the locus
voth in the presence and in the absence of Spm. In the past, the

latter modification hss been termed"cheange in st-te" of the locus. In
a)

the pr sence of Spm, the altered states are distinguished, one from the

vVO—_—
other, by difference in the time of occurrence of mutation-inducing

events during development of a tissue, by the frequency of their

occurrence at any ove time, and by differences i> tyvnes of stable alleles
that result from the mutation-irnducirg events. They are also distinguishe

one from the other, by the tyoe of gene action th=t occurs in the absence

of Spm,and among the many different states of ant and ast that have

been isolated, a wide range is exhibited in tyse and intensity of antho-

cyanin pigment in plant and kernel in the absence of Spm, from no

MBA MOU DY Oh parccetly

pigment with one state to, nean_normet—oer-enite normal Ay type pigment
lls amtioun 4 Weer ON Suey un ao, .

production with others. , All those states that respona to Spm by producing
stable mutations are grouped under the heading of the class I states.

In addition, a stite, designated class IT, has arisen on several independent —

occasions from the original state of ayn, This state has been of

considerable significance in the study of controlling elev ents in thit its .
behavior mimics that of some of the described gene control systems in

bacteria. In the absexce of Spm (or when it is present but in its

. ‘ . -1 .
inactive phase, see below) this state of 25" produces anthocyanin

wa Ciyyd Qu) wa bounty

pigment in vlant and kernel that ete that produced by the

A, locus before the opsrator element entered it. when Spm is present

a

and fully active, no anthocyanin is produced either in vlant or kernel.
However, in contrast to the class I states, no gene mut*=tions occur and
no evidence has been found of removal of the operator from the locus by
transposition, as occurs wtth the class I states. This statement is

based on an analysis of the class II state in hundreds of vlants and

ARs ,

through 7 successive plant senerations. the state appears to be quite

A

stable. The action of the Ay gene is "turned on" in the 2b6sence of Spm
wlio op ued fudle, Gah UP

and "turned off" in-++s5 presenté. It cannot be aruged successfully that

A 4

the "turning off" of gene action, that is, the absence of pigment in
andl owe
plant and kernel when Spm is present, occurs at the level of the gene and
° nevertheless
under the direct control of the operator. +t is clear, Kuweyer, th:t

the operator is necessary for thé observed effect as no "turning off" of

toe * wl Hi

gene action occurs in the presence of “pm when an—vwamodified Ay locus is

present. Whehhe normal A, locus is present, 27d also an active Spm element

2

the plants and kernels are fully pigmented.
The behavior of the Spm ele:ent likewise h:s been examined in detail.

ft undergoes mutation, transyosition, and cyckically occurring change in
(AE iboe. dy tee.
phase of activity, th=t is,—active to inactive end return to actives
’ A
asp “

“ome of the mutations result in a weakening of its canacity to induce

 

mutetion with the class I st tes without inducivg a correspondirg

weakening of its suppressive action.

 
Others result in a weakfning both of its cavacity to suppress _ene
action and its capacity to induce mutation with the cluss I stutes.
“ome of the mutants are highly stuble whereas others are quite unstobole,

Arun donde quart

- Sa s
we 2 return to full Spm expression occurring in some so z%tic cells in

beh ‘
dtfferent ports ef-e plant kernel. Illustrations of these mu mt

AL ~

tyres are shown in figure 2. ©“seteral different mete-ds have been used
to examine transposition of Spm and these are reviewed elsewh=re
(Me-lintock, 1956). It h»s been learéned th t different isolstes of Spm
undergo transposition at different times in plant develonment. Une
isolate, extensively examined through three successive plant csenerations,
uncersoes trensvosition early in plant development. Uther isolates,
on the other hand, may rarely undergo transpositi..:, either during sant
2 pao kighic ov no Ic

atox development. otill other isolates may undergo
transposition only late in plant development. It his been le:rned
thet 2 change from ea fu.ly active Spm to one that is weakly active, or the
reverse, arises as the corseiuence of a si-gle (mutstional) event affecting
Spm btself. lt is not yet known, however, whether a mutational event
is responsible for the expressed differences in time of occurrence of

te
transposition of Spm during vlant development and the freyuency of this
“an

at any one time.
LO

the third mentioned modification of »pm rel.tes to its alternating
cycles of activity within a plant and a description of this will be the
main subject of this report. or exauple, a fully active ~,m may he
introduced into a zygote. AS the plant develops from t’is zygote, the
activty of Spm may be turned off completely in some cells. No evicsence
will be given of its presence in the descendent cells until, in some of
them, Spm activity is turned on again. The presence of Som will then be
made evident in the descendents of these latter cells. The duration of
any one phase of activity of “pm, -- either active or inactive -- may be
long in some c:ses, or short in others. In some cases, the duratior of
one phase may extend over a number of plant generations where:s in others a,

AwLeeAnUnM Ae dururg The dbvedes mace 4 Cus Leadli eAbioot pout

rather frequenty, alterations in phase of activity may occur. qe
is present, and also an opm

part euler

with a long duration of its active phase, a very-—peeeter p=:tern of

a class I state of either ant or Ags

anthocyanin streaks in a non-pigmented background anpe rs in the plant,

Out Wine atroaly orirotome auuctallgy weoteaot ebbbonth ,
4 The particular onttern, in any onecane PGAa, MAUD the porticular

QD watn OH yw" Oratory

state th:t is present in the plant. If, however, the Spm element

“ih

is undergoing freq ent change in its phase of activity during the

Cawets, State, Leek Gud Toul oF be

development of the plant, the pattern of anthocyanin distribution in 2 they

-mciwoPlant may be exceedingly irregular. Pigment will anpear in those ares
a

noauluig qu ruubalioa - day vot ad
a, uf QA) A Qyw-i kinda ager ©
of the plant in which Spm is in its inactive vhase. Pigmented stresks in

ra

a non~pigmented backszround will asvear in those areas of the olant in

hoe

which Y*pm is in its active phase. However, the patterns of pigmented
A

stresks in-a_non—piemented backeround_in these tet+ter areas may be
difhowilt aroeo A

quite different witnin ene same vlant. this is because no mutational

events will occur at either amt or ayn until Spm enters its active

phase. If it enters this phase early in plant development, large
wit sowed Wy Class 1 aviles

pigmented areas may anpeor in a non-pigmented backsround. If, however,
A

it enters the active phase rather 1l=te in develonment, only small pirmented

My)
streaks will appear in a non-pigmented background. ‘ 1, the
class It state of att is present in a vlant, the distribution of nigmente

and nol-pigmented areas r-flect for each area, regirdless of its size, thes

3

a

ox
varticular phase of activity of “pm that is present in the cells of the ‘3
wy
5
area. In thw non-pigmented areas, Spm is in its active phase and in SS
S
the vigmented areis, Spm is in its inactive phase. Often, witnin a I

nonpigmented area, a number of Similiar sized, uni ormly distributed

streaks Conk Gunung a We Comeqguawert & Woes ff" Spun actus.

pigmented axExE appear, Agalk, within a large pigmented area, a number

muon pcuunitid euairn, ta” wld 0 ae

of similar“sizedg+ uniformly distributed, Bernpigcmented 4xXBxR may sopeary #

C t S
ws here ane ane Oak @Spa

; Puch patterns of pigment distribution reflect t 4 and a su ney of
dua

eocusrence any any one timerot a—channe in phsse 9f eetivity of 2p

“4 attey antly

 
Ll

from active to inactive in the former example tnd from inactive to active

in the latter exarple. “hus, the class II state of amt has been

particularl, useful in examining cyclically occurring chanzes in phase of

activity of Spm

anslg

the Som eherent | whose cyelicnlly occurring chanses in phase of
activity hove been examined in consideruble detail was the one that was

present in a plant of. the-ericirs} eulture having the class Il state of

_ VT wor 4oeleweel plant

25 : lis-beh-vior-hes-been-foltewed through 7 successive senernticns
Wb “pelavun We er aud) Origa
out ae -tensively (se only during the last 4 of these, cenerations. t
A

was loc ted in the siort arm of chromosome 9 and wes closely linked with

Voy four

Whe gene merker Wx. Re cases of enrly occurring transposition of tis Spm.
A

isolzte huy yet been detected,

 

number—of-ttents. However, it does transpose and the time of occurrence

of this anpe:rs to he confined to Late staves in s_ oronxhytic and saretonhyt
A

development. The frequency of transposition is not very “igh, ss will

A
Mode gous

be twediested Inter.

Nave auedte oT poveib b

Sefore considering the experiment2l resvlts that s

arbeat thy allmattig Ulugd ur pbarced et ud

 

phase—cycies of Yom, some men s ould be made of the earlier studiss of -
m-1 m-l . top. .
Bo and By and of the reasons for the divtfevences encountered in
control

eise of detection of the,syst-m associated with e:ch. study of awl
_ aw Vw elbiN§ Code
was undertiken before tht of a." 1 However, Be Gheer eyi-exced vaso

obtained of the node of operation of the system thet—was res onsible for

wan ovit atoelisd on The Levitg abushion

m-1

eontrol of gene action at Ae At In contr st, vrogress in this reecect
was relstively ranid in the study of amt, the reasong for this .
gonttol in the two cases Wap mek euubul -

TN eee

difference in ease of detection of the/system, beeawe-elear when it was

realized thet the Spm ele: ent in the original ant culture had a very

dural 4
Long active tenation phase wheres the “om ekement in the ant cultures
+ adhvwilsy
was undergbing frequent chsense in phase, during DbLint develonment.
. in the two cultures
vonfirmation of thee di“ferenceg in behyvior of the °pm elene.ts,was

This n—1

obtained through interchan-e of Spm element¢ bet»een the ay” “and 25

m=]

cultures, and also by isolation of Som derivatives within e-ch culture

whose behavior was modified, either towsré stability of es vhase of
. A

Oth
- rm “a -
activity or towirds frequently changes in och»se of activity.
A
e

eed
SXPLRIPENT L + p Nia? pend

2 asd f

“xperiments aimed at elucidating the veculiar behavior of Som
commenced in the summer of 1956, utilizi:.g for tris purpose both the
class I and cass II states of ayw fhis revort will coreentrute on
those studies that utilized the class II stute and for reasons outlined

UNL

above. In earlage studies of this ckese-—] state, it hedbeen log#grned

that an a parent, full Ay gene expression would appear in pbhant and kernel

in the absence of Spm, and thet gene action would he suppressed in its

presence. However, pigmented sreas did appe:r in plants and kernels having
: n= “1 : :
this stste of Bo 1 and Spm. It was also realized that, in general, the
areas

ymattern of such pigmented sxmks reflected the number of Spm elements that
were present: the more pm elements that were present, the fewer and
smaller were the pigmented areas. Removal of Spm from sowe cells duri og
development by the transposition mechanism might h»eve been invoked to
account for the apnpe-rance of the pigmen:ed areas. dowever, the pacterns .
of pigment distribution made it evident that removal of Svm by +rancsositic:
could not be responsible for many of the pigmented areas thot annezred.
this was because within a fully pismented area, smaller nonpigmented areas

often
were,present and within some of these litter, in turn, pigmented strenks

ow at d WY wos tn utube atts
avpe=red. fests thit hav mede it possible to understand titty phenomena

-
13

commenced in the summer of 1956 with orogeny of plants in ecclture
number 7109, to be described below.

the plants in culture number 7109 originated from viriegated kernels
(pigmented syots in a colorless background) on an esr of a plant that
had the following corstitution: ayw (elauss II st te) Bt/a,y bt in
chro:osomes 5, Wx +/wx Spm in chromosoies 9, and one additional Spm not
linked to m rkers in either of these chr -mosomes. fhe silks of this

ear head received pollen from a plant that was homozygous for a bt,

2?
and vx and heaé no pm, among the amo ca rying class of kernels on the
ear, there weve fully vignented kernels and viriegated kernels, tunt is,
tnose thst had ssots of anthocyanin piguent in 2 colorless background.
Yome of the v rivsated kernels showed only svecks of piz: ent and were

tho :.gnt to have received both of the ~pm elenents that were gresent in th
female parent, ane Oth-r hed a number of lerger spots of Digme:t and
the kernels showins, this pattern were thou,ht to have received only ore
of the two ~pm element th t were present in the female parcnt. Plants
were grown from the two classes of vurie,ated kurnels, 5 frou kernels

of the first tyve and 6 from kernels of the latter tye. a number

test crosses were co ducted with e ch pl nt.
vonfirnetion was obt-ined from these tests of the presence of two opm

wlenerts in the plants derived from the former mentivned t.-e or
variegited k-rnel and of the presence sf orie spm in euch of the six planis
derived from the lattcr tyce of verie..ted Kernel. this resort will
consiver mainiy the tests th t were co ducted in successive years with pres
progeny s.emming from three of these la.ter six pl.nts, thet is, those that.
arose from kerneis th.t snowed many pigmented spots in a colorless
background. the constitution of these three nlanvs proved tu be as

m-1

follows: two plants were Ao Bt/a, bt, ix +/wx opm (plants 7109B-1 and

B-2) and one »lant (71090-4) was a m-1 Btha, bt, wx/wx, and acd 1 %pm ,

2

not c.rried in the short arm of chro.oscue 9.

the aopesrance of the kernels on ears sroduced by the six Ilsant

in culture 7109 5 and © (that is, those that wexe-considersd to hat one
opm itmereh/ when crossed recicrocrtlly with plants homozygvus for a,, bt, ©
and «x and having no Spm, are entered in wable l. wa cle rly expressed

1: 1 ratio of fully pisme: ted k- r els to k-rnels thit showed pisnented

spots in a colorless background ayoczred on the exrs produced by all

til ers of these oclents except that of tiller-1l of pl:nt J-l. However, 2

pronounced de iation in f.ivor of the pij;mented class appesred a:onz the

xe nels on the ear produced by the main stalk of plants 71095-1 and

7109¥-3, and to a lesser extent on this ear produced by plants 7109v-1
15
and v-2, ‘tany of the kernels in the pigmented class were uniformly and
deeply pigmented but in so..e kez>nels placed in tunis class in the tuble, the
intensity of sigment over the aleuro:e layer wis not uniform. wigntly
pigmented areis or even sovue colorless ares were present but sharply
defined borders between arezs witn different -ignment intensities, or vet een
pigmented and nohpigmented arezs were not usual. This gave the kernels a
diffusly-mottled app.arance ‘see photo, figure ). at the tine of
obse vation of these kernels, no attempt was mice to place in a sevar:-te
class those kernels exhibiting different grades of this diffusely-mottled
pnenot.:pe as it was evident that this class graded int: the fully and
uniformly pigmented class. Ssubseyuent tests proved, however, tht all of
the plants derived from the diffusley=mottled kernels ec :rried an ~pm
elerent in them as did some of the plants derived from kernebs on t.:ese

ears that were uniforiiy and deeply pigmented.
goose

16
the esr of tiller-1l of plant 7109B-2 was self-pollin: ed. AMONS

the 367 Bt k=-nels on the resulting esr only 23 were corpletely colorless.

sixteen of tliese colorless kernels wee “x and 7 were wx. smons the
Bt oud) UML
remal- ing 344 kernels , 87 were uxkfermiy deeoly piemented of w'tch 84 were
A

Vx and 3 were wx. One Bt kernel exribited the diffuse-mottled phenotyre,

oly’, 256

and it was “x. All of the remai-ing,Et kernels were variesnted in that
pigmented soots appeared in a colorless backsround. These kernels weve
diviied, roughly, into three classes: those thit showed only 2 few specks
of pigment, of which 11 we e x and 20 were wx, thase that head 2 number of
lerger spots as well as sove specks of nigment, of wrich 105 were Wx and
42 were wx, and those thet exhibited some suite lerge pnivrent d aress as
, Be. . ?

well as a number of smaller vismented akbeas, of which64 were Jx and 14
were WXe Other crosses co duct d with olants 71095-1 and 7109R-2

tla
thet need not be outlined here, had indicated th t in both sleet one Som
was present and th:t it was located close to wx in chro:oso e 9. On the
self-pollinited ear of the tiller of nlant 7LO9B~2 the ratio of 84 ‘x : 3
wx acong the uniformly wxrx -igmented kcrnels and of 180 Vx to 76 wx among
the varieg»ted class xkmxEKKEKXWKXHXXKHEXHEXKXEXCNXOLXKIRMEKKERX SKOKE XX XENEX
WMAXXRRKERAXEKRREX wis in conformity with this vlacement of Som.

in the summer of 1957, pewa WO (Rawids vA

é—~ Plants w re grown,under culture number 7308, from the uniformly
“
17

varlezgated wa WS
pigmented Bt, wx ciass, from so e of the,kernels in the Bt, wx and St, wx -
i A

classes and from 5 kernels in the colorless, bt, wx class. gklants
derived “rou the latter class of kernels were exvected to be houozysous
for Bos bt, and wx, and to ca ry Spm at a known loc-tiun in chr some 9.
Unly two of the five plants survived. In both of them, a sizgle opm
elenent was present, and subseuent .ests indicated thst it wes loexated

close to wx in one offr@moso.ie 9. nese two plants, 7308D-1 and D-2, were

extensively used as pollen parents in crosses to vlants ec rrying not only

a
the class II st-te of a mt but also to yvlants carrying kkr class I
gan m= a . . ; . a
dtate of B5 1, the benavior in subsejuent generations oi vhe Spm elenent .

x

in esch of these two slants (see 0 and D of tuble 3) has contributed
much to an unders anding of cyclical changes in phase of activity of Spm, as
will be mide evicent later.

Becsuse hundreded of plants hive been tesvied to determine whether or
not Spm was present in them, and if so, the phzse of its activity in
diffe-ent parts of the same plant, it will not be feasible to give a
detailed sccount of the results obtained from each such test. Therefore,
exanjles will be chosen that will illustrate the neture of the tests that
were coiducted with these plants and the conclusions th:t may be drawn

from exch. Before doins so, the resder is advised to inspect table 2
18

which sunmm rizes the r-sults obt»ined from tests th:t were conducted
through successive generztions wit. the Spm element thut was present in
plant 71LO9B-1. This plant had one Som element closely linked with wx in
the short arm of chro..osome 9. The Som elenent das in its inactive phase
in the cells that g:ve rise tu the esr of the main stalk. Tmis was
indicsted by the uniform distribution of anthocyanin pigmentution in the
main stalk of this plant and also by the pnenot,;ves of the kernels on the
enr it oroduced (table 1). However, the phenotyves of a few of the
kernels on this esr indicuted that »om was present in the cells that
contributed to this ear and that it had entered its acti-e phase very

e rly in development of a few of them, or had entercd the uctive phase
later in development in sonie cells of otner kernels. In the cells that
gave rise to the esr on each of the three tillers of plant 7109B-1, opm
was in its 2ctive phase. This was made evident not only by the aope:rance
of these tillers, in that they exhibited streaks of anthocyanin pigment

in a nonpigmented background, but also by the ratio of kernel types on

the e:rs produced by exch (table 1). fhe pollen of the main stulk of
plant 71O9B-1 was also used in making cross:s and it was meade evident

from the types of kernels on the resulting ears thet some grains c. ried

Som in its active phase whereas soe others carried som in its inxictive

phase.
19

Table 2 includeg@ the tesults of tests o ly of tho:e proseny of
vlant 7109B-1 that curried Spm. A number of pro.eny olints thit did not
carry Spm was aiso tested anc the methods used to determine whether spm
is absent in a plant or is present in its inactive pnase will be
Considered shortly. In tzis table, the symbol "-" indicates that Spm
was inactive not only in the cells that g ve rise to the enr, but also in th
cells that gave rise to the aleurone layer in all k=rnels on the ear.
The symbol "va" (very delayed return to the active phase) indic tes that
Spm was inacti e in the ceils that gxve rise to the e r and also in
those thit gave rise to neirly all of the kermeis on the e»r3 a return
to the =ctive phase was seen only in so :e parts of a few kernels on these
ears. The symbol #d" (delayed return to the acti e phase) indiestes that
the opm eleient was inactive in the ce ls that g ve rise to the e.r, but
that it had changed tu the active pnase in a numver of kerneis on the
eur, being in its ac.ive purse in sone of them at the st rt of endosperm
develoouent. The symbol "+" ind cates that Spm was in its active
phase in the cells that g ve rise to the eur, turning to its ii-etive
puase in some cells curing endosperm development. The symbol (+ -)
inaicates that a part of the ear arose from cells in which ~pm was in its

active pnase whereas another purt arose from cells in which opm was in

its inictive phase, aars of this tye exhibited shsrvly defined sectors
With spm active in one sector and iiactive in the other. -

Table 2 reveals th.t the inactive phise of Spm, present in the main

stalk of  ,lant 7109B-1, remained in this phsse in the tested sarts of

plants over four successive plant generations, and exhibited the same

pattern of behavior in each gener tion. In plants h:viit,y this inactive
Spm, return of it to the active phase was very much delayed. In general,
visual evicence of this in the slant wis given oniy by tiilers. In sone

tillers, the chan,e of »pm from inactive to active was exhibited by the
presence of nonsigmented sectors in an otherwise pigmented tiller, and
within some of these latter sectors, in turn, small pigmented streuks were
present.

In this study of alternating changes in phase of activity of Spm, a
number of tests were cs.ducted to determine whether or not the presence of
an active “pm in the same nucleus with an inactive spm would effect a change

+

in the latt.r. avidence obtai:ed from tests of this tssce indicate that the
active Spm does not initiate change in phase of the in:ctive opm nor does it
appe r to alter the durati-n of an inactive phase. One sucn test,
conducted with the inactive opm originally present in the main stalk of

plant 7109B-1, is recorded in A of table 2 under culture number 7780a,

Year 1960. ‘The plants in this culture arose from au-1 carrying kernels
el

m1
2

on an er of plant 7599B-4 (see Year 1958, Table 2 a) that was a
(elass II) Bt/ a, bt, Wx +/wx Spm-inzctive in co.stitution when crossed by
a plant that was ho.ozygous for Bos bt, and wx, and that had an active Spm
liked with wx in ore chromosoize 9. The plants in culture 77804 grew

from kornels selected from tunis ear bevcuse euch had recenved the inective
Spm from the female parent (originally derived frou the main stalk of plant
7109B-1) and the active Spm elexent from the male parent (this opm
originally derived from tiller-l of plant 7109b-2). fhe plant in 3 of
culture 7780 were derived from kernels thot hed received the active opm
from the male parent but no Som from the female purent. AS the tible
lndicstes, the inactive »pm, originally present in the main stalk of 231 int
7LO9B-1, a penred in the progney plants of culture 77804 and exnibited
quite the same behavior with respect to phase as it exhibited in the
ancestor plants in which it was the only Spm element that wes present.

The same Spm element that was in an inactive phase in the main stalk
of plant 71095-1 was in an active phase in the cells that Save rise to the
exr of e:ch of the tillers of this plant (table 1). The activity phases
of tais opm in cells giving rise to ears in successive generati.vns of

plants are recorded in 3 of tuble 2, In the t-ble, the letter T (trans-

positi-n) before the plant number i dientes that tie plent carried this
22

Spm at a new location in the chroi.osorie co. plevient. The olents in B of
culture 7306 (1te.r 1957) were derived from the very few kernels on the ear
of tiller-1 that we e suspected to have received more than one Som element
from the 7109B-1 parent plant, the additional Som h-ving arisen throuzh

the transpositi n mechanism. the plants in culture 7560 (te r 1958)

were derived “rom the recombis.sant class of kernels on the second ear of the
main stalk of plant 7306a-1. as indicsted in a previous public» tin
(hieVlintoeck, 1956) the shenotynic recumbinant class may be a concos.t of
individuals some of which recresent the true crossover class and otner of
which carry a tronssosed Spm eleument, and do not represent the true crossove
class. “t will be nosed thet the bensvior of Spm derived from tiller-1

of slant 7109B-1, whether in its original loc:tion or transzosed, with
reg-rd to phase of activity in the ce ls that g¢ ve rise to the tested ears
in B of tzble 2, is suite different from that of the s.ne Yom element in an
inactive ohase, derived from the main stalk of plant 7109b-1 and registered
in a of this table. Vhange from the active to the in:ctive phase occurred
in some ceils ecrly in plant development, but in many other parts of the
plant, such chenge was delayed, occurring i some ceils only ls.e in lant

development.
25

Similar tyoes of test as those outlined above, we-e co duct d with
thespn carrying progeny of tiller-2 of plant 71095-1. opm was in its
active phase in the ce ls that gave rise to the e.r of this tiller.

Its beh:vior in succé@ssive gener:ztions is recorded in VU of table 2.

In general, its beh=vior was similar to that in tiller-l. Unly two
comments regarding this need be made here. “irstly, it may be -ointed

out that tests of %pm locxztion in eight plants derived from the
recombinant class, entered in cultures 7561, and 7562, Year 1958, did not
reveal a case of trinsposition among them. the second comment is
directed to the first enr of the main stalk of »lant 7561-4. ‘The
constitution of tiis plant was aot (class iI) Bt/a, bt, wx Spm/wx +.

fhe silks of the first ear of the main stulk of this plant received pollen
from a slant hoviozygous for Bos bt, and wx, and in which no oom was
present. the resulting ear was sectorial. Som was in its active phase
in all parts of this ear except for a sector in the middle of the ear in

-1

es . 7 . , m ; ; 7
wnich no evidence of Spm was ,iven oy any of the Ao Rarrying, Kernels

a. : . m— 7 :
within it. nernels with <« 1 that were also Bt and wx and having an

2
2
active Spm in them, derived ‘rom that p rt of thee r in w:ich Spm was

active, were sown in 1960 under culture number 77774 and 3%. Mylly

jen: (qg m-L 5 5
pigmented \3, ) carrying kernels that were Bt and «x were sown under
24

C and D of culture 7777. all of the slants in culture 7777 cavried oom
in the sx chromosoiie co-tributed by the female pa ent. However, it was
totally inactive in all of tne cells that con ributed to evch of the tested
ears of lants in © and 2 of culture 7777 and remaind in the in ctive
phase during develooment of all but a very few kernels on these eurs.
in the le ves o* these slants, several small sectors were present in which
~pm od chuinged from its inictive to itw active phase in the ceil thzt
eu.ve rise to eich such sector. In most of the slan:s, the e small sectors
appe:red only in tillers or in oarts of the sus ort roots,of the main
stilk. ft was obvious, ho ever, that the durstion of this purticular
inactl.e pnase was long. In contr st to tnis the sane spm ele ent in the
plants of a and B of culture 7777 wes undergoing frejuent change in phase
of its activity.

as ment.sned enrlier, the pollen talizen from the t»ssel oroduced by
the main stalk of slant 71095-1 contrined soue grains in wuich °pm was in
its inictive phise and others in which it w-s in its active phase. It is
presumed that the tassel was sectorial with regard to shase of activity of
“pm. Tests of the hase of activity of Yom in srogeny wroduced by use of

tais sodlen is given in » of table 2.
25

In order to obtain evidence of Spm activity in cells that g ve rise
to the ears summ rized in table 2, it was necess ry in making the cross to
each e:ir to use sollen from a slant huving a particul-r combi. sation of
mairkers. vith regard to such marker, tne te: .ed plants were of two main
types: those that were homozygo.s for Bo and bt \and also for sone other
m.rxers that need not be considered at tis tie), and those that c rried

m-L (+

in their chro 2s0 e5 a slass I stnte of As sree different class I

; a m=1L ;
st tes selected for this oursose), or 2 class II sta e of a> » and also

bt. *hese aut ca rying tester -vlants weve homozygous for wx and they had
no »pm. the tester plancs, homozygous for Ao and bt, wereof three main
typea: homozygous for x and having no Spm (tyve-1), ho:ozyso s for wx and
having no Spm (type-2), and homozygous for wx and carrying one or more

Spm ele..ents e:ch in its active phase \type-3). most of the latter

plants curried one Spm, linked with wx in oe chrovcsoie 9. “ome had

two Som elements loc ted close to wx in each chro oso.e 9 (design: ted
Spm/Spm in the tables) or two Spm, one loc:ted close to wx in one

chromosome 9 and the other locented elsewhere in the chromosone co... lemnent
(design ted %pm + Spm in the tables), the latter h ving been trans>osed

from a Lloc:ztion close to wx to a new location. Hach tyoe of tester clant

served a purvose in examining spm beh vior.