| Description: | When exposed to excess light, plants sustain damage to their chloroplasts. This photodamage is caused largely by the formation of free radicals and reactive oxygen species. These radicals interact with, and destroy proteins of the photosynthetic apparatus and cause lipid peroxidation in the thylakoid membranes. One intensively studied photoprotection mechanism is the dissipation of excess excitation energy, observed as non-photochemical quenching (NPQ) of chlorophyll fluorescence. The xanthophyll cycle, leading to accumulation of zeaxanthin, plays a major role in NPQ. The xanthophylls were also shown to have anti-oxidant function in thylakoid membranes.Characterization of NPQ-deficient mutants of Arabidopsis has shown that acclimation to prolonged high light conditions can occur in the absence of the xanthophyll cycle. Recent studies also show that in young leaves, xanthophyll cycling is not necessary for photoprotection. These finding strongly suggest that other mechanisms of photoprotection are able to compensate for the lack of the xanthophyll-dependent NPQ and anti-oxidant functions. Over-accumulation of tocopherols, changes in the composition of the light-harvesting complexes and thylakoid membrane structure, and chloroplast movement may be involved in acclimation of xanthophyll- and NPQ-deficient mutants to provide the observed compensation in photoprotection.Here we propose to compare the expression pattern of high light-exposed wild-type plants with that of the triple mutant npq1npq4lut2. This triple mutant is deficient in zeaxanthin, PsbS (a PSII subunit that is necessary for NPQ), and lutein (a carotenoid with a structural role in the light harvesting complexes, which may also have NPQ and anti-oxidant activities). We will grow triple mutant and wild-type plants in short days under low light conditions (150 µmol photons m-2 s-1) for 5-6 weeks. Plants will then be exposed to high light conditions (1500 µmol photons m-2 s-1) for 4 hours, after which leaf tissue will be harvested for RNA extraction. This experiment will be repeated a second time. Physiological and biochemical analyses will be performed in parallel. We predict that compensation for the NPQ and anti-oxidant deficiencies of the triple mutant will be evident in the gene expression pattern, compared with that of the wild-type. Genes that show differences in expression will be used for further study of photoprotection in Arabidopsis. |
NASCArrays Information at The BAR
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