PHOSPHORUS-NUTRITION AND WATER-STRESS EFFECTS ON PROLINE ACCUMULATIONIN SORGHUM AND BEAN

Phosphorus deficiency and drought can reduce plant growth and alter me tabolic processes such as N metabolism. The amino acid proline often a ccumulates in leaves of many plants grown under water stress, but info rmation about effects of P nutrition on proline accumulation is not av ailable. Two sorghum [Sorghum bicolor (L.) Moench] and two bean (Phase olus vulgaris L. and P. acutifolius A. Gray) cultivars with different tolerances to drought were grown in a greenhouse in soil mixes with di fferent levels of P with and without water stress imposed by withholdi ng water to determine the effects of P nutrition and water stress on p roline accumulation. Shoot dry matter of sorghum and bean increased wi th increasing P level regardless of water stress. Leaves of water-stre ssed sorghum had lower P concentrations than non water-stressed plants , while leaves of water-stressed and non water-stressed bean had simil ar P concentrations. Leaf diffusive resistance (r(s)) values became gr eater and leaf water potential (Psi(L)) values became more negative (g reater tension) as severity of water stress increased compared to non water-stressed plants. These traits became lower and less negative (le ss tension), respectively, and nearly comparable to non water-stressed plants 5d after water stress was relieved. Both plant species had hig her proline accumulation during water-stressed than under non water-st ressed conditions, but differed in their response to added P. Sorghum leaves had highest proline when grown with high P, while bean leaves h ad highest proline when grown with low P. Five days after plants were relieved of water stress, proline accumulation in sorghum leaves decre ased extensively yet remained at relatively high levels, while proline accumulation in bean leaves decreased to the level for non water-stre ssed plants. High proline accumulation in leaves of water-stressed pla nts grown at high P levels might be an adaptive response to drought fo r sorghum, but did not appear to be so for bean.