Effects of the embryonic axis and exogenous growth regulators on sunflower cotyledon storage protein mobilization

Abstract

Cotyledons of sunflower seedlings (Helianthus annuus L. cv. Giant gray stripe) expand and their protein content first rises then begins to decrease during the first three days of growth. Storage protein structures, which are visible with scanning electron microscopy, undergo modification that leads to storage protein disappearance by day 4 post‐imbibition. Expansion of cotyledons detached from seeds prior to imbibition is greatly reduced, total protein levels remain high, and storage protein structures remain visible in cells of these cotyledons. Incubation of excised cotyledons in 1.0 μM benzyladenine or kinetin increases the rates of cotyledon expansion and storage protein loss to levels higher than in intact seedling cotyledons, Incubation in 10 μM indole‐3‐acetic acid inhibits cotyledon expansion and protein mobilization. More rapid hydrolysis of storage proteins in cotyledons of intact seedlings or detached cotyledons treated with cytokinin is further indicated in day 2 specimens by SDS‐polyacrylamide gel electrophoresis. These results suggest a possible mechanism for regulation of cotyledon development by interactions of the promotive effects of cytokinin and inhibitory effects of auxin.