Protein Degradation And Characterization Of Proteases Of Several Vegetables During Senescence

Intracelluar proteases play an important role in the growth, development, senescence and adaptation to environment stress. The enhancement of protease synthesis and increase of their activity have been considered to be responsible for protein degradation during senescence in plants. This study has been focused on the identification and characterization of proteases and degradation of protein related to senescence of leafy greenstuffs during senescence, with pak choi (Brassica. Chinensis), flat cabbage (Brassica. Campestris ssp. Chinensis van rosulari), yubaicai pak choi (Brassica campestris L ssp chinensis L), leaf mustard (Brassica juncea van foliosa), water spinach (Ipomoea aquatica. Forsk) and garland chrysanthemum (Chrysanthemum Coronarium.) used as models. The effects of sample pre-treatment temperature, incubation temperature and pH of the incubation buffer on the activities of proteases were also investigated. And senescence of different leaves regulated by applying gibberellic acid (GA3) or ethylene during storage was investigated too.By modified SDS-gelatin-PAGE assay, we found that the soluble protein contents were declined in all vegetables investigated during senescence. In fact, the declines were significantly retarded by the treatment of GA3 while promoted by the treatment of ethylene. Protease activity increased in parallel with the development of senescence only in the pak choi leaves, but not in yubaicai pak choi, water spinach and garland chrysanthemum leaves. However, there was a surprising decreased trend of proteases in flat cabbage and the leaf mustard leaves during senescence.The contents of free amino acids were measured and found to be decreased in leaves treated by ethylene during storage. The activities of peroxidase (POD) and polyphenol oxidase (PPO) of these materials were measured during storage. POD activities were increased in all leaves. PPO activities were increased at first but then decreased in the leaves, petioles and stems of all vegetables studied except the leaves of pak choi, flat cabbage and the garland chrysanthemum.