Embryonic control of isocitrate lyase activity in the megagametophyte of Ponderosa pine seeds

Abstract

An earlier publication presented evidence for enhancement of isocitrate lyase (threo-LS isocitrate glyoxylate lyase, EC 4.1.3.1) activity by a factor that diffuses into the megagametopnyte from the embryo of stratified germinating Pinus ponderosa seeds. In contrast, the data reported here indicate the rate of increase in specific activity of embryoless seeds was greater during the first four days than in seeds with embryos left in situ. A similar pattern of activity was observed in seeds which retained their embryos for two days to allow germination to occur prior to excision, but the peak activity was slightly nigher. The highest enzyme activity was achieved in seeds which retained their embryos the longest. A model is included to resolve these apparently diverging effects of the embryo on isocitrate lyase activity. A diffusate prepared from two day germinated embryos had no significant influence on the enzyme activity of embryoless seeds. The phenomena reported here were not dependent on stratification. Imbibition was the only prerequisite for germination and develooment of enzyme activity to occur.