Desiccation and the switch from seed development to germination. Alfalfa embryos can synthesize storage proteins after germination if maturation drying is prevented

Abstract

AbstractStorage proteins (2S, 7S and 11S) are synthesized at the mid- to late stages of development in alfalfa seeds, mainly within the embryos. Mature dry seeds cannot synthesize these proteins upon subsequent germination and growth. When embryos were isolated from the seed during development (stages VII and VIII) and placed on water or nutrient medium, they germinated. They exhibited a pattern of protein synthesis which was identifiable as germinative/post-germinative, and was identical to the pattern synthesized in embryos of germinated dry seeds, and of embryos from seeds that were subjected to drying prematurely at stages VII and VIII. When, after 48 h from the start of imbibition, abscisic acid or osmoticum was introduced to germinated embryos isolated at stage VII and not desiccated, the synthesis of the 11S storage protein was restored to a rate comparable to that of stage-VII embryos before isolation. This was accompanied by an increase in transcription of the 11S storage protein gene. Transfer of germinated stage-VII embryos, which had first been desiccated, to abscisic acid or osmoticum 48 h after imbibition started did not result in any restoration of storage protein synthesis. Thus, desiccation, prematurely or at maturation, off-regulates storage protein synthesis and within the embryos this process is no longer responsive to abscisic acid or osmoticum.