The development of the maize seed is dependent on the orderly unfolding of events in which each component of the developing caryopsis has a particular role to play. The ultimate control of these events must depend upon numerous genes, which if altered will interfere with normal development. Many mutants of this type have been described, ranging from those which produce relatively slight alteration in the caryopsis to those which prevent practically all development. Among those producing relatively slight changes are mutants which give rise to premature germination. The seeds of these mutants develop normally until late in ontogeny. During the early dough stage the plumule begins to elongate, and the seeds germinate while still attached to the ear. Such mutants have been called viviparous

Robertson, Donald S.

English

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GENETICS: D. S. ROBERTSON
be possible, by studying strains from asci with both normal and defective
spores, to show that the cross of pyr-3a to pyr-3b yields strains which are
not phenotypically wild but from which both parent mutants can be re-
covered. If so, investigation in this manner of other pyr mutants which
are phenotypically similar to pyr-3a and -3d may prove to be of interest
in showing how many types there are with respect to the ability to produce,
in intercrosses, strains of this kind which are phenotypically wild.
* This work was supported in part by funds from the Rockefeller Foundation and by
funds from the Atomic Energy Commission administered through contract with the
Office of Naval Research, U. S. Navy, Contract N6-onr 244, Task Order V.
' Horowitz, N. H., Bonner, D. M., and Houlahan, M. B., J. Biol. Chem., 159, 145
(1945).
2 Mitchell, H. K., and Houlahan, M. B., Fed. Proc., 6, 506 (1947).
3 Mitchell, M. B., and Mitchell, H. K., PROC. NATL. ACAD. Sci., 38, 205 (1952).
4 McClintock, B., Am. J. Bot., 32, 671 (1945).
6 Houlahan, M. B., Beadle, G. W., and Calhoun, H. G., Genetics, 34, 493 (1949).
6 Kolmark, G., and Westergaard, M., Hereditas, 25,490 (1949).
7 Srb, A. M., and Horowitz, N. H., J. Biol. Chem., 154, 129 (1944).
8 Singleton, J. R., unpublished Ph D. Dissertation, California Institute of Technology
(1948).
9 Westergaard, M., and Mitchell, H. K., Am. J. Bot., 34, 573 (1947).
10 Dodge, B. O., J. Agr. Res., 35, 289 (1927).
11 Lawrence, W. J. C., J. Genetics, 24, 257 (1931).
THE GENOTYPE OF THE ENDOSPERM AND EMBRYO AS IT
INFLUENCES VIVIPAR Y IN MAIZE
By DONALD S. ROBERTSONt
CALIFORNIA INSTITUTE OF TECHNOLOGY* AND THE BIBLE INSTITUTE OF Los ANGELES
Communicated by G. W. Beadle, May 13, 1952
The development of the maize seed is dependent on the orderly unfolding
of events in which each component of the developing caryopsis has a par-
ticular role to play. The ultimate control of these events must depend
upon numerous genes, which if altered will interfere with normal develop-
ment. Many mutants of this type have been described, ranging from those
which produce relatively slight alteration in the caryopsis to those which
prevent practically all development. Among those producing relatively
slight changes are mutants which give rise to premature germination.
The seeds of these mutants develop normally until late in ontogeny.
During the early dough stage the plumule begins to elongate, and the seeds
germinate while still attached to the ear. Such mutants have been called
viviparous.
PROC. N. A. S.580
VGENEI1CS: D. S. ROBERTSON
The viviparous gene may induce changes in one or more of the various
tissues of the developing caryopsis. Since viviparous seeds segregate on
the ear, any changes induced in maternal tissue cannot determine whether
a seed will be viviparous. Changes responsible for vivipary must be
produced in tissues resulting from the union of male and female gametes-
the embryo and/or the endosperm. There are three possible ways that
the viviparous gene can promote premature germination: (1) by inducing
in the embryo changes which allow it to germinate under conditions nor-
mally not conducive to germination; (2) by inducing in the endosperm
changes which alter the normal germination inhibiting mechanism; and
(3) by inducing changes in both the endosperm and embryo which interact
to overcome the normal germination inhibition. In order to determine
which of these three possibilities actually is operative within the mutant
seed, it is first necessary to isolate the effect produced by the viviparous
genotype of the endosperm from that of the emnbryo.
Seeds resulting from hetero-fertilization frequently have embryos and en-
dosperms of different genetic constitution. Such seeds are produced when
the egg and polar nuclei of the egg sac fuse with sperm nuclei of different
* TABLE I
GENOTYPE OF THE GENOTYPE OF THE
ENDOSPERM EMBRYO
Class A Vp Vp vp vp Vp
Class B v1p Vp VP Vp Vp
pollen grains. Sprague' observed a few such seeds on an ear segregating
for one of the viviparous mutants. He found that only the seeds with
genetically viviparous embryos germinated. This would indicate that
in this mutant, at least, the gene effects changes in the embryo which in-
duce germination.
The use of A-B translocations makes possible the systematic production
of embryos and endosperms of differing genetic constitution. In some
strains of maize there may be present, besides the basic set of ten A-type
chromosomes, one or more supernumerary, genetically inert, chromo-
somes which have been designated as B-type. Roman2 has described
the behavior of A-B interchanges in the production of the inale gametes.
In the division of the generative nucleus of the developing pollen grain the
B centromeres usually fail to separate, giving one sperm both B centro-
meres and the other none. Where a portion of an A-type chromosome
is attached to the B centromere, this non-disjunction produces within a
given pollen grain two sperm of different genetic constitution. One sperm
has the portion of the chromosome attached to the B centromere present
in duplicate (hyperploid sperm), whereas the other is deficient for this
region (deficient sperm). If the viviparous gene is located in the trans-
VC)L. 38, 1952 5X1
GENETICS: D. S. ROBERTSON
located section of the A chromosome, two classes of seeds are obtained
from pollination of viviparous by an A-B interchange. These two classes
are shown in table 1. Class A seeds are the result of the hyperploid sperm.
fusing with the polar fusion nucleus, and the deficient sperm fusing with
the egg nucleus; whereas Class B seeds are the result of the reciprocal
fusion. In both classes the endosperm and embryo differ with reference
to their viviparous genotype.
Although these classes are theoretically possible, they are not readily
recognized by the expression of vivipary alone. If one of these classes
of seeds were to germinate prematurely, there is no way to determine a
priori to which class it belongs. However, it is possible to distinguish
these classes in some viviparous mutants which interrupt the normal
carotenoid and chlorophyll development. Seeds of these mutants have
white or pale yellow endosperms and germinate prematurely, producing
albino seedlings. By using such a mutant in combination with the A-B
interchanges, it is possible to recognize the two types of seeds shown in
table 1. Class A seeds should have yellow endosperms because they carry
the normal alleles of vivipary and produce white seedlings, since only the
mutant allele is present in the embryo. The Class B seeds would be recog-
nizable by white endosperms and green seedlings.'
Plants heterozygous for viviparous-5, a mutant which inhibits carote-
noid and chorophyll development as well as inducing premature germina-
tion, was pollinated by pollen of plants carrying A-B interchange TB-lb.
The resulting ears were found to be segregating viviparous and white
seeds. A classification of endosprem and seedling color revealed three
types of seeds: (1) yellow endosprem with albino seedlings, (2) white
endosperm with green seedlings, and (3) yellow endosperm with green
seedlings. Since viviparous-5 affects carotenoid formation, it is possible
to recognize the first type of seeds as those belonging to Class A. The
second type of seeds are those belonging to Class B. The third type re-
sults from the fertilization of ovules carrying the normal alleles of vi-
viparous-5 and are, therefore, not important in this consideration. Thus,
the two classes of seeds shown in table 1 are recognizable. Only seeds of
Class A were found to be viviparous, whereas those of Class B were dor-
mant. As is expected, all seeds of Class B grown to maturity and self-
pollinated have segregated for viviparous-5.
By using TB-lb in combination with viviparous-5, it has been possible
to distinguish between the role of the endosperm and that of the embryo
in the production of premature germinating seeds. The data suggest that
the endosperm does not play an active role in vivipary, since seeds germi-
nate prematurely if they have a normal or mutant endosperm as long as the
embryo is genetically viviparous. Thus, it would appear that vivipary
is determined by the genotype of the embryo and is independent of the
PROC. N. A. S.582
VOL. 38, 1952 GENETICS: SPIEGELMAN AND DELORENZO
genotype of the endosperm. The evidence from hetero-fertilization sup-
ports this conclusion.
The nature of the mechanism responsible for the dormancy of the de-
veloping embryo is not known. Work of La Rue,4 5 Haagen-Smit et al.,6
and others has shown that normal corn embryos are capable of germination
soon after pollination, if removed from the developing caryopsis and
cultured. Thus, the developmental dormancy is not entirely dependent
upon the embryo but is influenced by some environmental factor within
the developing seed. The genetic evidence and that from embryo culture
experiments suggest that viviparous seeds germinate prematurely because
their embryos are capable of germination within the caryopsis in an en-
vironment which will not permit the germination of normal embryos.
* This paper is based on work done at the experimental farm of the California Insti-
tute of Technology. I am indebted to Dr. E. G. Anderson for his advice and encour-
agement.
t Permanent address, The Bible Institute of Los Angeles, 558 South Hope Street, Los
Angeles, Calif.
I Sprague, G. F., Am. Soc. Agronomy, 28, 472-478 (1936).
2 Roman, H., Genetics, 32, 391-409 (1947).
3 The validity of these conclusions is based on the observation that the inhibition of
carotenoid and chlorophyll development by the mutant genes is not dependent on its
first inducing vivipary.
4 La Rue, C. D., Bull. Torr. Bot. Club, 63, 365-382 (1936).
La Rue, C. D., Science, 115, 315 (1952).
6 Haagen-Smit, A. J., Sui, R., and Wilson, G., Science, 101, 234 (1945).
SUBSTRA TE STABILIZA TION OF ENZ YME-FORMING
CAPACITY DURING TIHE SEGREGATION OF A
IIETEROZ YGOTE*
By S. SPIEGELMAN AND W. F. DELORENZOt
DEPARTMENT OF BACTERIOLOGY, UNIVERSITY OF ILLINOIS, URBANA, ILLINOIS
Communicated by M. M. Rhoades, May 23, 1952
Introduction.-In the course of investigating the inheritance of the
capacity to synthesize "galactozymase" Winge and Roberts' discovered
a "slow" adapting phenotype. These authors demonstrated that the
character was determined by a single recessive allele (g,) which segregates
normally in crosses to the wild type bearing the dominant (G).
Analysis by Spiegelman, Sussman and Pinska2 of g,-genotype cultures
revealed the existence of heritable differences in phenotype among cells
carrying this allele. This heterogeneity is easily and simply exhibited by
plating glucose-grown g,-cells on purified galactose agar test plates upon
583


The Genotype of the Endosperm and Embryo as It Influences Vivipary in Maize

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The Genotype of the Endosperm and Embryo as It Influences Vivipary in Maize

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