Consequences of chlorophyll deficiency for leaf carotenoid composition in tobacco synthesizing glutamate 1-semialdehyde aminotransferase antisense RNA: dependency on developmental age and growth light

suggests a co-regulation between carotenoid and chlorophyll synthesis; the second emphasizes the Transgenic tobacco (Nicotiana tabacum), with a special role of carotenoids for protection against reduced chlorophyll content of up to less than 10% of light stress. the wild-type level due to a different expression of antisense RNA coding for glutamate 1-semialdehyde Key words: Light acclimation, photoprotection, quantum aminotransferase, were used to study the relationship yield, lutein, xanthophyll cycle. between chlorophyll accumulation and changes in carotenoid composition in developing and mature leaves grown either under low (30 mmol photons Introduction m’2 s’1) or high light (300 mmol photons m’2 s’1). Regardless of the extent to which chlorophyll synthesis Like chlorophylls (Chls), carotenoids of leaves are ubiwas reduced, under low light the ratios of total chloro- quitous structural components of the photosynthetic phyll to carotenoids remained constant. In contrast, apparatus. In higher plants, Chls and carotenoids are under high light the content of carotenoids was elev- bound to specific proteins to form either reaction centre ated relative to chlorophyll and increased further with pigment‐protein complexes or light-harvesting pigment‐ progressive inhibition in chlorophyll synthesis. The protein complexes (LHCs) of photosystem (PS) I and xanthophyll-cycle pigment pool was most strongly PSII (LHCII ). Attempts to ascertain the distribution of increased (up to 18-fold) upon supression of chloro- carotenoids within the multiple pigment‐protein comphyll synthesis. Concurrently to the higher pool sizes plexes by detergent fractionation yielded varying results a higher extent of violaxanthin was converted into between research groups, probably due to distinct isolaantheraxanthin and zeaxanthin and this was found to tion procedures and diVerences in both the growth condibe correlated with a decrease in the quantum yield of tions and plant species. Nevertheless, b-carotene was photosystem II photochemistry. While lutein increased consistently found in the reaction centre/core complexes (up to 3-fold) with decreasing chlorophyll contents in of both PSI and PSII, whereas xanthophylls mainly bind