An Analysis of Seed Development inPisum sativum

Abstract

A method for quantifying changes in the cell population of Pisum sativum cotyledons during development is described. The method is based on determining the frequency distribution for cell area following the random sampling of a single-cell suspension of cotyledon cells. The population profile of these cells changed progressively and systematically from a single population, similar in size to meristematic cells, found in embryos less than 3.0 mg in fresh weight, to a bimodal population in embryos greater than 100 mg fresh weight. This method was used to compare embryos of similar size from two genotypes near-isogenic except for genes at the r locus. No significant differences were found between the cell population profiles of embryos up to 30 mg fresh weight. However, a significant difference was found between embryos with fresh weights of 100 mg, the wrinkled (rr) line having a higher mean and maximum cell area (2 951 μm² and 9 240 μm² respectively) than the round (RR) line (2591 μm²and 6470 μm²respectively). Comparisons were also made between cotyledon cell populations from round (RR) embryos grown in vivo and in vitro. The most obvious differences were the higher mean and maximum cell size of the large cell population of in vitro grown embryos which were twice those found in vivo. Embryos grown to either 30 mg or 100 mg fresh weight in vitro had a much greater proportion of large cells in the population with a corresponding reduction in total cotyledon cell number, compared with similar sized embryos grown in vivo. These data suggest that comparisons between different genotypes, or, between cultured and in vivoembryos, based on morphological similarities between embryos, may be invalid and subject to misinterpretation.