Differential accumulation ofLhcbgene products in thylakoid membranes ofZea maysplants grown under contrasting light and temperature conditions

Abstract

In higher plants many different genes encode Lhcb proteins that belong to a highly conserved protein family. Evolutionary conservation of this genetic redundancy suggests that individual gene products play different roles in light harvesting and photoprotection depending on environmental conditions. We have tested the hypothesis that expression/accumulation of individual light harvesting complex (Lhc) proteins depends on plant growth conditions. Zea mays plants were grown in different temperature (13°C vs. 24°C) and light (high vs. low) conditions. The thylakoid membranes were isolated and fractionated by sucrose gradient and the protein content of the different bands was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Significant differences were found in the accumulation of both the major light harvesting complex of photosystem II (LHCII) complexes and the minor antenna chlorophyll proteins CP29, CP26 and CP24. In particular, temperature seems to play a major role in driving the expression/accumulation of the different proteins: the LHCII/minor antenna ratio increases with decreasing temperature. The pigment composition and the spectroscopic properties of LHCII complexes isolated from low temperature grown plants are significantly different from those of LHCII purified from high temperature grown plants. Two-dimensional maps show that different LHCII proteins are accumulated at different levels depending on growth conditions. Moreover the low temperature/high light grown plants show an increased value of nonphotochemical quenching. These results suggest a specific role of different LHCII complexes in the organization of the potosystem II and photoprotection.