A 28-kDa Pod Storage Protein of Phaseolus vulgaris: Characterization, Induced Accumulation, and Degradation

During fruit development of French bean plants, a proportion of seed nitrogen is temporarily stored in pods as protein, amino acids and probably small peptides, which are then mobilized to support the growth of seeds (Endo et al., 1987). We observed a continued increase of endopeptidase activity throughout the development and subsequent senescence of French bean pods, and this endopeptidase activity is thought to participate in the protein mobilization in pods during fruit maturation (Tanaka et al., 1993). In the course of studies on endopeptidases in pods of French bean plants, we found that, when a large number of pods in early stages of fruit development were removed from a plant, relative levels of a specific 28-kDa protein were enhanced in the newly formed pods. The protein accumulated to high levels in the pods of plants that had been previously depodded, whereas a smaller amount was detected in the pods of non-treated plants. It was postulated that enhanced levels of the 28-kDa protein resulted from a reduction of plant sink size caused by removing pods in early stages of fruit development.