Aspartic protease in leaves of common bean (Phaseolus vulgaris L.) and cowpea (Vigna unguiculata L. Walp): enzymatic activity, gene expression and relation to drought susceptibility.

Four cultivars of related species, common bean and cowpea, which exhibit different degrees of drought resistance, were submitted to water stress by withholding irrigation. Drought induced an increase in endoproteolytic activity, being higher in susceptible cultivars (bean) than in tolerant ones (cowpea). An aspartic protease activity was found to be strongly induced especially in bean. From a cowpea leaf cDNA library, a full length aspartic protease precursor cDNA was obtained. Transcript accumulation in response to water stress indicated that the expression of the gene was constitutive in cowpea and transcriptionally up-regulated in bean. The results showed that drought-tolerant and drought-susceptible bean plants differ regarding aspartic protease precursor gene expression.