The Effects of Gibberellic Acid on Organelle Biogenesis in the Endosperm of Germinating Castor Bean Seeds

Mature seeds of castor bean (Ricinus communis L.) were imbibed in tap water or 0.3 mM GA3, planted in vermiculite moistened with tap water or 0.3 mM GA3, and incubated at 32 °C. During the course of germination, GA3 promoted marked increases in the activities of the glyoxysomal marker enzyme isocitrate lyase and certain mitochondrial marker enzymes, but did not affect the ER marker enzyme choline phosphotransferase. Glyoxysomal and ER protein and phospholipid were not increased in amount by GA3, whereas mitochondrial protein and phospholipid were. SDS-polyacrylamide gels of the glyoxysomal matrix polypeptides from GA3-treated beans exhibited two polypeptides additional to those found to be common to both GA3-treated and control tissue. Incorporation of CDP-(methyl 14C)-choline into intact endosperm tissue and the distribution amongst the glyoxysomes, mitochondria, and ER of newly synthesized phosphatidyl-(methyl 14C)-choline was unchanged by GA3.