Effect of drought on polyamine metabolism, yield, protein content and in vitro protein digestibility in tepary (Phaseolus acutifolius) and common (Phaseolus vulgaris) bean seeds

The objective of the present study was to investigate the effect of drought on the metabolism of proline, ornithine and polyamines, and the enzymes involved in their synthesis and degradation, in tepary and common bean seeds. Furthermore, the effect on seed yield, protein content and in vitro protein digestibility was also studied. Genotypes of tepary bean (Phaseolus acutifolius) used were: PI-301-801 from Nicaragua; G-400-35 from Oaxaca, Mexico; L-242-24 and L-242-36 from Sonora, Mexico; L-172 from Arizona, USA; and the common bean (Phaseolus vulgaris) variety Flor de Mayo Bajio (FMB) from Mexico. The cultivars were grown in a greenhouse under controlled temperature, light and humidity. Water content in plants (WCP) decreased when irrigation was stopped (1 and 2 weeks after blooming). Common bean had the lowest WCP value (73.75%), while the best genotypes were PI-301-801 (91.62%), G-400-35 (88.70%) and L-242-24 (85.73%). Tepary bean plants had superior water absorption capacity, which helped to increase yield. De novo synthesis of drought proteins may explain the increased protein content present under drought conditions. The results suggest that water stress induced ornithine amino transferase activity and ornithine concentration. Proline also increased under drought conditions (p < 0.05). Genotypes L-242-24 and G-400-35, which had the highest yield, also had a major concentration of polyamines under water stress. The results also suggest that arginase activity participated in amino acid synthesis such as ornithine and, consequently, in the protein concentration under water stress. Genotypes G-400-35 and L-242-24 are good alternatives for cultivation in and zones. (C) 2003 Society of Chemical Industry.