Relationship between Relative Water Content, Nitrogen Pools, and Growth of Phaseolus vulgaris L. and P. acutifolius A. Gray during Water Deficit

Phaseolus acutifolius A. Gray is a potential source of stress-tolerant traits for Phaseolus vulgaris L. through interspecific hybrids. The objective of this study was to quantify the effects of water-deficit stress on vegetative growth, shoot relative water content (RWC), and leaf concentrations of proline, polyamines, and related metabolites in P. vulgaris compared with P. acutifolius. Stress-induced changes in N metabolism putatively related to stress tolerance have not been investigated previously in P. acutifolius. Replicate pots, each containing three 5-d-old plants in 18.9 L of soil with 4 L of available water, were subjected to water deficit by withholding water (terminal drought) or were maintained under well-watered (control) conditions. Compared with controls, stressed plants of both species accumulated approximately 55% less shoot dry matter. Root dry matter accumulation was inhibited to a greater degree in P. acutifolius (≈ 70% for two genotypes) than in P. vulgaris (14 and 27% for two genotypes). P. acutifolius maintained greater shoot RWC than P. vulgaris. In droughted plants of P. acutifolius, leaf arginine and proline concentrations did not change, total polyamine (Σ agmatine + putrescine + spermidine + spermine) concentrations decreased, and ammonia increased compared with controls. In P. vulgaris, water deficit increased concentrations of arginine (>30%) and proline (>300%), whereas total polyamine and ammonia concentrations did not change compared with controls. In all four genotypes examined, proline concentration was inversely related to RWC (R² 0.90). Leaf proline concentration is an indicator of plant water status in Phaseolus but not of tolerance or sensitivity of vegetative growth to water deficit. This study was supported in part by the Citrus Research Center and Agricultural Experiment Station of the University of California. This paper represents a portion of the dissertation submitted by I. Lazcano-Ferrat in partial fulfillment of the requirements for the Ph.D. in Botany at the University of California, Riverside.