Changes in light sensitivity of photosynthesis in tobacco (Nicotiana tabacum) planes transformed with the antisense gene of glutamate-1-semialdehyde aminotransferase

Chlorophyll fluorescence and thermoluminescence were used to study photosynthesis in tobacco transgenic plants, in which early stages of chlorophyll synthesis were inhibited owing to the expression of the glutamate-1-semialdehyde aminotransferase gene in the antisense orientation. When such plants were grown in weak light (30 mu Einstein/(m(2) s)), the chlorophyll a content was substantially reduced but the proportion of pigments in light-harvesting complexes was little affected; photosystem II retained its activity, as established from fluorescence parameters. At the same time, changes in the optical properties of leaves in transgenic plants, caused by a reduction in chlorophyll content, enhanced light sensitivity. When these transgenic plants were grown under standard illumination conditions (300 mu Einstein/(m(2)s)), they experienced stress associated with partial photoinhibition of photosystem II activity, enhanced nonphotochemical dissipation of light. energy, elevated rates of lipid peroxidation, and the consequent emission of high-temperature (120 degrees C) thermoluminescence of chlorophyll.