Abstract

We have observed that bean plants grown under water stress conditions develop resistance to high temperature, phenomenon known as cross resistance. Such resistance, however, is observed in one variety: Orfeo Inia (OI), but not another: Arroz Tuscola (AT), the former known as a stress resistant and the latter as a stress sensitive variety in the field. The aim of the present work was to study both varieties grown under water stress and well watered (control) conditions, as a means to gain knowledge on the precise site either structural or physiological which improves resistance of photosynthesis to high temperature. Threshold temperature for non-reversible damage in OI is increased in about 2.5°C but not in AT when plants are gradually exposed to water stress. Also, the water stressed OI plants continue to evolve oxygen at temperatures which causes a strong decrease in photosynthesis in control plants. As for AT, well watered and control plants are negatively affected at a similar temperature. Water stressed plants in the growing chamber does not increase their leaf temperature since bean plants are able to move their leaves upon excess light, therefore, cross resistance is not due to previous heat on leaves. Malondihaldehyde content in leaves, carotenoids, relative leakage rate as well as leaf anatomy and chloroplasts ultra-structure does not reveal differences in OI and AT growing under stress conditions. At present, lipid composition is under examination in which monogalactosyldiacylglycerol (MGDG) decreases and sulpholipids (SQDG) and phosphatidylglycerol (PG) increases in OI.