STARCH GRANULE FORMATION IN DEVELOPING SEEDS OF PISUM SATIVUM L.: EFFECT OF GENOTYPE

Cell development and starch granule formation in seeds of three pea (Pisum sativum L.) genotypes, R/R Rb/Rb, r/r Rb/Rb, and R/R rb/rb, affecting cotyledon starch were compared. Cotyledon cells at 10 days after flowering were highly vacuolated and contained small protein bodies in the vacuoles and small oval starch granules in the cytoplasm in all three genotypes. Gradients of cell development from the center to the periphery of the cotyledon and toward the cotyledon-hypocotyl axis persisted through the cell enlargement, reserve synthesis, and into the maturation stages of cotyledon development. By 14 days after flowering, many small vacuoles lined with protein deposits had been formed. Vacuoles were only observed in peripheral and basal cells by 18 days after flowering. Starch granules were oval and birefringent in all three genotypes at 10 days. Starch granules in R/R Rb/Rb and R/R rb/rb cotyledons expanded regularly remaining nearly oval and birefringent throughout development. In contrast, starch granules from r/r Rb/Rb cotyledons began to fragment by 14 days after flowering. This process began as a single fissure, followed by a second fissure usually at or near right angles. Finally, because of the fragmentation, the granules appeared compound, and only a portion of the granule was birefringent. All genotypes contained nearly equal volumes of liquid endosperm and embryo at 10 days after flowering. In addition, a layer of parenchyma tissue (ovular and/or endospermic) inside the seed coat was observed. Although, thin walled and poorly defined cytologically, the parenchyma cells contained large numbers of starch granules. These granules were a mixture of simple and compound types in all genotypes. By 18 days after flowering, the parenchyma tissue was reduced to a small layer of cell walls and all starch granules had been mobilized.