THE FUNCTION OF THE PsbS PROTEIN IN RELATION TO NON-PHOTOCHEMICAL ENERGY DEPENDENT QUENCHING IN RICE PLANTS

摘要

Plants have a variety of features that make them possible to adapt to changes in the environment (Bjorkman & Demmig-Adams 1995). These features serve to optimize photosynthesis and to provide protection from the damaging effects of absorbed light. Light is one of the most important environmental factors that controls the growth and development of plants, but excess light is harmful for the plant causing photo-inhibition of photosynthetic apparatus. In order to avoid this dangerous situation, plants have evolved a highly efficient strategy. Dissipation of excess light absorbed by light-harvesting complex (LHC) of photosystem II (PS II) provides a dynamic response to changes in light intensity (Niyogi 1999). Energy dissipation is detected as the nonphotochemical quenching (NPQ) of chlorophyll fluorescence and is regulated by the transthylakoid pH gradient (ApH) and the xanthophylls cycle, the reversible de-epoxidation of violoxanthin into zeaxanthin (Demmig-Adams 1990). As a member of LHC proteins superfamily (Kim et al 1992), PsbS protein has homology with other LHC proteins, but it has four transmembrane helices unlike other LHC proteins that have three transmembrane helices (Kim et al 1994), Pigment-binding characteristics of PsbS seems to differ from other LHC proteins (Dominici et al 2002) but is still controversial (Aspinall-O'Dea et al 2002).