THE MORPHOGENETIC EFFECTS OF THE HOODED GENE IN BARLEY II. CYTOLOGICAL AND ENVIRONMENTAL FACTORS AFFECTING GENE EXPRESSION

Abstract

SUMMARY Hooded barley plants were subjected to either cold treatment or a short-day photoperiod. As a result many of the lemmas elongated and formed awned pheno- copies. The treatment was effective only when given during the developmental period when the hooded gene begins to produce a visible effect on the histological development of the primordium. In every case, the formation of awned pheno- copies was associated with a retardation of development. Short-day treatments, even those applied at the critical developmental stage, which did not retard de- velopment, failed to produce awned phenocopies. These results support the authors’ hypothesis that all of the morphological effects of the hooded gene result from the alteration at a critical stage of a single process, the frequency of cell division relative to cellular elongation. This hypothesis is supported by experi- ments using autoradiography with precursors of DNA and RNA synthesis. An increased frequency of nuclei synthesizing DNA begins before