II. 8. A proposed gene symbol for defective endosperm mutants that express xenia.
R. T. Ramage and Chere L. Crandall. Department of Plant Sciences, University of Arizona, Tucson, Arizona 85721, U.S.A. "R"
Shrunken endosperm in barley may be determined by the maternal genotype or by the genotype of the endosperm (expressing xenia). These mutants have been assigned the gene symbols seg and sex, respectively (1). Shrunken endosperm mutants exhibit a wide range of expressivity. For example, seg2b has a seed weight of about 15 percent of normal and never produces plants under field conditions (3), while seg7h may have a seed size of up to 90 percent of normal and encounters no difficulties in establishing stands under field conditions (8). Likewise, seed of sexla are about 75 percent of normal in size and exhibit normal field establishment and growth (3), while sex2b seed are 80 reduced in size that they are barely visible within the lemma and palea and are, in effect, zygotic lethals (9).
As a rule, the shrunken endosperm mutants, both seg and sex, are also characterized by an increased content of the amino acid lysine in the seed protein (6,10,14,16). The gene symbols sex, for shrunken endosperm, and lys, for high lysine content, have both been used to describe the same mutational event (5,10,12,15).
We have been interested in those shrunken endosperm mutants expressing xenia that are zygotic lethals and have endosperm so defective as to prevent stand establishment under normal field conditions. We have made a sizeable collection of such mutants (7). In general, homozygous recessive seed of this type of mutant grow normally for a few days after fertilization. Then, growth stops and seed begin to shrivel. At maturity, shrunken endosperm seed are so reduced in size that they are barely visible within the lemma and palea. The shrunken endosperm seed do not produce plants under normal field conditions and are, in effect, zygotic lethals.
Since the controversy over the symbolization of sex and lys mutants is likely to continue (2,4,5,11,12,13) and to be confusing for some time, and, because shrunken endosperm mutants that are zygotic lethals are not involved in the controversy, we propose to use the symbol dex to represent mutants expressing xenia that have defective endosperm. We define defective endosperm mutants as those that have endosperm so defective as to prevent stand establishment under normal field conditions.
Accordingly, we propose to change the symbol for the shrunken endosperm mutant sex2b to dexla and to symbolize our collection of similar mutants as dex mutants (7).
References:
1. Eslick, R. F. and E. A. Hockett. 1976. Suggestions for gene symbolization,
g, m, x. Barley Genetics Newsletter 6: 115.
2. Fastnaught, C. E., R. F. Eslick and S. E. Ullrich. 1981. Allelic
relationships of the shrunken endosperm, high lysine mutants sexla, and
Risø 13, 29, and 86. Barley Genetics Newsletter 11:65-66.
3. Jarvi, A. J. and R. F. Eslick. 1975. Shrunken endosperm mutants
in barley. Crop Science 15: 363-366.
4. Jensen, J. 1979. Chromosomal location of one dominant and four recessive
high-lysine genes in barley mutants. Int. Symp. of Seed Prot. Improvement
and Cereals & Grain leg. Germany, 1978.
5. Jensen, J. and H Doll. 1979. Gene symbols for barley high-lysine
mutants. Barley Genetics Newsletter 9: 33-37.
6. Karlsson, K. E. 1977. Linkage studies in a gene for high lysine
content in Risø barley mutant 1508. Barley Genetics Newsletter 7:
40-43.
7. Ramage, R. T. and C. L. Crandall. 1981. Defective endosperm xenia
(dex) mutants. Barley Genetics Newsletter 11:32-33.
8. Ramage, R. T. and J. F. Scheuring. 1976. Shrunken endosperm mutants
seg6 and seg7. Barley Genetics Newsletter 6: 59-60.
9. Scheuring, J. F. and R. T. Ramage. 1976. A tertiary trisomic balanced
for both msg2 and sex2. Barley Genetics Newsletter 6: 60-62.
10. Ullrich, S. E. and R. F. Eslick. 1977a. Inheritance of the shrunken
endosperm character, sex3c, of Bomi Risø mutant 1508 and its association
with lysine content. Barley Genetics Newsletter 7: 66-73.
11. Ullrich, S. E. and R. F. Eslick. 1977b. High-lysine, male sterile
stocks of barley available. Barley Genetics Newsletter 7:120-121.
12. Ullrich, S. E. and R. F. Eslick. 1978a. Allelism evidence for barley
high-lysine, shrunken endosperm xenia (sex) mutants. Barley Genetics Newsletter
8: 109-112.
13. Ullrich, S. E. and R. F. Eslick. 1978b. Chromosome location evidence
from Risø induced high-lysine shrunken endosperm mutants of barley.
Barley Genetics Newsletter 8: 114-125.
14. Ullrich, S. E. and R. F. Eslick. 1978c. Lysine and protein characterization
of spontaneous shrunken endosperm mutants of barley. Crop Science 18: 809-812.
15. Ullrich, S. E. and R. F. Eslick. 1978d. Inheritance of the associated
kernel characters, high-lysine and shrunken endosperm, of the barley mutant
Bomi Risø 1508. Crop Science 18: 828-831.
16. Ullrich, S. E. and R. F. Eslick. 1978e. Lysine and protein characterization
of induced shrunken endosperm mutants of barley. Crop Science 18: 963-166.