Chlorophyll a Fluorescence pp 525-554
Using Mutants to Understand Light Stress Acclimation in Plants
Light stress acclimation in plants is a complex process that involves avoidance responses, passive defenses, and active regulatory mechanisms acting on different timescales at the thylakoid, chloroplast, cell, leaf, and whole plant levels. Molecular and genetic approaches, especially using three model photosynthetic organisms (Arabidopsis thaliana, Chlamydomonas reinhardtii, and Synechocystis sp. strain PCC6803), are powerful tools for the analysis of plant responses to light stress and, more generally, to abiotic stress. Several genetic techniques can be used to dissect photoprotective processes that have been identified by biochemical and physiological methods, as well as to uncover previously unknown mechanisms. By designing appropriate genetic screens or selections, mutants affecting acclimation to light stress can be isolated. One example of a specific screening strategy is the use of chlorophyll fluorescence video imaging to identify mutants affecting nonphotochemical quenching, state transitions, and photoacclimation. Various nonphotochemical quenching, npq, mutants affecting photosynthetic electron transport, xanthophyll metabolism, and the PsbS protein have provided insights into both mechanistic aspects and the physiological significance of nonphotochemical quenching. Other mutants affecting photoreceptors and antioxidant synthesis have also been very useful in studying light stress acclimation. Targeted reverse genetics approaches such as RNA interference, gene knockouts, and overexpression can be used to test the functions of previously identified genes. Relevant examples include transgenic organisms affecting expression of violaxanthin de-epoxidase, the light-harvesting proteins CP29 and CP26, 2-cysteine peroxiredoxin, and other antioxidant enzymes. Implementation of large-scale approaches such as mRNA expression analysis using microarrays and proteomic analysis will identify new targets for functional genomics studies of light stress acclimation.
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