--M. S. Scanlon, P. S. Stinard, M. G. James and D. S. Robertson
An earlier report (MNL 64:11) described allelic variation in the endosperm phenotypes of our putative mutator-tagged alleles of the et1 locus. Currently our study has identified 11 independently induced et1 alleles (see mapping article by James et al., this issue), which display great variation in the degree of etching and/or shrinkage of the endosperm. In addition to the endosperm phenotype, the et1 allele is pleiotropic and confers a virescent seedling phenotype. In order to investigate the variation in the seedling virescence of these alleles, representative Mutator-tagged et1 endosperm variants were sandbench tested. The results are given in Table 1; the non-Mutator induced standard et1 allele was included for the sake of comparison.
Table 1. Kernel and seedling phenotypes of putative Mu-induced
et1
alleles.
| Mutant designation | Kernel phenotype | Degree of etching | Seedling phenotype |
| et standard | "normal" etched | moderate | virescent |
| et1-Mu*3328 (a) | severely etched | extreme | virescence extreme, albino |
| et1-Mu*2320 (a) | severely etched | extreme | virescence extreme, albino |
| et1-Mu*24 (a) | mild shrunken | none to slight | mostly green, pale stripes |
| et1-Mu*2457 (a) | severely shrunken | moderate | virescent |
| et1-Mu*2320 (b) | small, sugary, defective | kernel is shriveled | lethal |
| et1-Mu*2162 (b) | small, sugary, defective | kernel is shriveled | lethal |
(a) data from heterozygotes with standard etched (et1/et1-Mu)
(b) data from homozygous mutant kernels (et1-Mu/et1-Mu)
These results indicate that the severity of the virescent phenotype
may be correlated with the degree of etching and not the shrunkenness of
the endosperm. Despite the extreme albino phenotype of the et1-Mu*3328
and et1-Mu*2320 seedlings grown from severely etched seed, these
seedlings do eventually become green, and thus are truly virescent. Cox
(MNL 42:52-56) reported similar results from seedlings grown from severely
etched kernels. The lethality of the et1-Mu*2320 and et1-Mu*2162
sugary defective kernels is attributed to the absence of a germ. The small
defective kernel phenotype is seen on self-pollinated ears of these two
alleles only. It should be noted that variation in seedling and endosperm
phenotypes is exhibited within, as well as between, et1-Mu allelic
families. Possible causes of the phenotypic variations described herein
include: variable expression of et1 due to different Mutator element
insertion sites or Mu-induced deletions; genetic background effects,
although each of the alleles described has been outcrossed to standard
Q60 and standard B70 backgrounds for at least three generations; the presence
of a modifier of etched (Met) as described by Cox in MNL 40:39-42.
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