Early grain development of the seg2 maternal-effect shrunken-endosperm mutant of barley

Abstract

Barley (Hordeum vulgare L.) plants that are homozygous for the seg2 mutation produce shrunken seeds with 15% of normal dry weight regardless of pollen source. Microscopical examination of developing grains sampled from 1 to 8 days after anthesis revealed abnormal endosperm development in seg2 compared with normal barley. Antipodal cells degenerated between 2 and 4 days after anthesis in normal grains, and the amount of endosperm cytoplasm increased and became cellular by 4 days after anthesis. Antipodals persisted beyond 4 days after anthesis in seg2, and the endosperm cytoplasm did not change in appearance or amount until 8 days after anthesis, when thin lobes of endosperm cells developed in the lateral regions. No central endosperm developed in seg2, but rather dorsal nucellar tissue was appressed directly against the ventral nucellar projection, eliminating the usual endosperm cavity. Maternal and embryo tissue of seg2 appeared to develop normally, although the rate of embryo growth was slower than in the normal cultivar. We suggest that seg2 barley would be useful as a genetic probe to study maternal control of endosperm development or antipodal function.