Protein synthesis during rehydration, germination and seedling growth of naturally and precociously matured soybean seeds (Glycine max)

Soybean seeds [Glycine max (L.) Merr.] synthesize de novo and accumulate several non-storage, soluble polypeptides during natural and precocious seed maturation. These polypeptides have previously been coined ‘maturation polypeptides’. The objective of this study was to determine the fate of maturation polypeptides in naturally and precociously matured soybean seeds during rehydration, germination, and seedling growth. Developing soybean seeds harvested 35 d after flowering (mid-development) were precociously matured through controlled dehydration, whereas naturally matured soybean seeds were harvested directly from the plant. Seeds were rehydrated with water for various times between 5 and 120 h. Total soluble proteins and proteins radio-labelled in vivo were extracted from the cotyledons and embryonic axes of precociously and naturally matured and rehydrated seed tissues and analyzed by one-dimensional PAGE and fluorography. The results indicated that three of the maturation polypeptides (21, 31 and 128 kDa) that had accumulated in the maturing seeds (maturation polypeptides) continued to be synthesized during early stages of seed rehydration and germination (5–30 h after imbibition). However, the progression from seed germination into seedling growth (between 30 and 72 h after imbibition) was marked by the cessation of synthesis of the maturation polypeptides followed by the hydrolysis of storage polypeptides that had been synthesized and accumulated during seed development. This implied a drastic redirection in seed metabolism for the precociously matured seeds as these seeds, if not matured early, would have continued to synthesize storage protein reserves.