Water stress induced modulation in thylakoid membrane fluidity and loss of D1 protein during development of clusterbean cotyledons

Abstract

Water stress causes significant changes in the accumulation of pigments, thylakoid polypeptide composition, chlorophyll-a fluorescence characteristics and photochemical efficiency of chloroplasts in the cotyledons of clusterbean (Cyamopsis tetragonoloba L.) seedlings. The cotyledons however, respond differently to the stress at their different developmental phases. During stress, a new band appears in the electrophoretic profiles of the thylakoid proteins of the young and developing cotyledons, which disappears during maturity. In contrast, the stress-induced changes in both the developing and mature cotyledons are associated with a loss in the immunologically probed D1 protein indicating a photoinhibitory damage. The stress-induced changes in the thylakoid organisation and function are correlated with relatively a low amount of carotenoids, loss in the activity of super oxide dismutase, enhancement of lipid peroxidation and subsequent increase in the chlorophyll-a fluorescence polarization. These results are suggestive of a free-radical induced alteration in membrane fluidity as reflected in an increase in polarization, leading to thylakoid rigidity as the contributory factor for the dislocation of electron transport and subsequent loss of the D1 protein in the water-stressed cotyledons of clusterbean in absence of sufficient scavenging potential of the chloroplasts.