Non-photochemical quenching and acclimation to high temperature in barley mutants

Abstract

The influence of high temperature on the efficiency of photosystem II was investigated in plants with different pigment content and light harvesting components. The role of zeaxanthin-mediated non-photochemical quenching (NPQ) in high temperature acclimation was also studied. Wild type barley plants and two chlorina mutants, (chlo. f2 and chlo. 126), were exposed to high temperature treatments (38° C) for 7 days. The quantum efficiency of PSII, measured as Fv/Fm, was not significantly different in different barley genotypes. Exposure to 38° C did not cause considerable changes in Fv/Fm in the different barley lines, but caused significant differences in the actual efficiency of PSII electron transport (F PSII). F PSII was higher in the two mutants than in the wild type before high T treatment. Consistently, the two mutants were able to maintain a high electron transport activity at high temperature conditions, whereas F PSII decreased significantly in the wild type after 7 days at 38° C. Decreased PSII photochemical activity in the wild type after prolonged exposure to 38°C correlated with an increased level of NPQ and zeaxanthin content (Z). NPQ, measured in control chlo. f2 leaves, was lower than that of wild type and it increased slightly after 5-7 days at 38° C. However the amount of Z (plus antheraxanthin) expressed on the basis of chlorophyll a content was much higher in the mutants both before and during heat stress. Apparently, these mutants appear perfectly efficient under conditions of high temperature and high light. The role of different photoprotection mechanism in determining this resistance is discussed.