COMPOSITION OF PHOTOSYSTEM-II ANTENNA IN LIGHT-HARVESTING COMPLEX-II ANTISENSE TOBACCO PLANTS AT VARYING IRRADIANCES

Plants with genes coding for chlorophyll a/b-binding proteins of light -harvesting complex II (LHCII) in antisense orientation (Lhcb) that ar e characterized by severely reduced Lhcb transcript levels (below 10% of wild type) do not show a bleached phenotype due to a specific loss of the polypeptide. To produce such a phenotype, a conceptually differ ent antisense approach was tested with a dual-functional transcript en coding the gene for hygromycin phosphotransferase and the transit sequ ence of Lhcb1-2 in the antisense orientation. Using increasing concent rations of hygromycin, transformants with Lhcb steady-state levels as low as 9% of wild type were regenerated and grown in a growth chamber. Together with Lhcb antisense plants obtained in an earlier study, the se antisense plants were analyzed biochemically for their photosystem II (PSII) antenna composition under varying light conditions. All anti sense plants showed a characteristic low-irradiance-induced increase o f their PSII antenna size as determined by higher chlorophyll concentr ations, an increased content of LHCII, and a constant chlorophyll b-to -lutein ratio in comparison with control plants. One to 5% of the tota l Lhcb transcript amount was sufficient to allow unrestricted formatio n of the PSII antenna at low irradiance, suggesting that LHCII biogene sis is not controlled primarily by transcription.