摘要
Transgenic tomato （Solanum lycopersicum） plants were generated expressing a fragment of the mitochon- drial NAD-dependent isocitrate dehydrogenase gene （SIIDH1） in the antisense orientation. The transgenic plants displayed a mild reduction in the activity of the target enzyme in the leaves but essentially no visible alteration in growth from the wild-type. Fruit size and yield were, however, reduced. These plants were characterized by relatively few changes in pho- tosynthetic parameters, but they displayed a minor decrease in maximum photosynthetic efficiency （Fv/Fm）. Furthermore, a clear reduction in flux through the tricarboxylic acid （TCA） cycle was observed in the transformants. Additionally, bio- chemical analyses revealed that the transgenic lines exhibited considerably altered metabolism, being characterized by slight decreases in the levels of amino acids, intermediates of the TCA cycle, photosynthetic pigments, starch, and NAD（P）H levels, but increased levels of nitrate and protein. Results from these studies show that even small changes in mitochon- drial NAD-dependent isocitrate dehydrogenase activity lead to noticeable alterations in nitrate assimilation and suggest the presence of different strategies by which metabolism is reprogrammed to compensate for this deficiency.
Transgenic tomato （Solanum lycopersicum） plants were generated expressing a fragment of the mitochon- drial NAD-dependent isocitrate dehydrogenase gene （SIIDH1） in the antisense orientation. The transgenic plants displayed a mild reduction in the activity of the target enzyme in the leaves but essentially no visible alteration in growth from the wild-type. Fruit size and yield were, however, reduced. These plants were characterized by relatively few changes in pho- tosynthetic parameters, but they displayed a minor decrease in maximum photosynthetic efficiency （Fv/Fm）. Furthermore, a clear reduction in flux through the tricarboxylic acid （TCA） cycle was observed in the transformants. Additionally, bio- chemical analyses revealed that the transgenic lines exhibited considerably altered metabolism, being characterized by slight decreases in the levels of amino acids, intermediates of the TCA cycle, photosynthetic pigments, starch, and NAD（P）H levels, but increased levels of nitrate and protein. Results from these studies show that even small changes in mitochon- drial NAD-dependent isocitrate dehydrogenase activity lead to noticeable alterations in nitrate assimilation and suggest the presence of different strategies by which metabolism is reprogrammed to compensate for this deficiency.
