ANTISENSE INHIBITION OF CYTOSOLIC NADP-DEPENDENT ISOCITRATE DEHYDROGENASE IN TRANSGENIC POTATO PLANTS

Cytosolic NADP-dependent isocitrate dehydrogenase (cyt-NADP-ICDH; EC 1 .1.1.42) has been suggested to play a major role in the production of 2-oxoglutarate, an important precursor for amino acid synthesis. Using an antisense RNA approach under the control of the cauliflower mosaic virus 35S promoter, transgenic potato plants were created in which NA DP-ICDH activity was reduced to 8% of the wild-type level in leaves. R esidual activity was almost completely due to mitochondrial and chloro plastic NADP-ICDH iso forms. Activity staining after non-denaturing po lyacrylamide gel electrophoresis revealed the complete absence of a ma jor activity band in leaves of antisense plants. No differences in gro wth or development, including flower formation and tuber yield, were o bserved between transgenic and wild-type plants. Photosynthesis and re spiration were also unchanged. Levels of amino acids were the same in wild-type and cyt-NADP-ICDH antisense plants, even when accumulation o f amino acids was induced by incubation of detached leaves in tap wate r in the dark ('induced senescence'). Consistent with a reduction in N ADP-ICDH activity, however, were slight increases in the levels of iso citrate (up to 2.5-fold) and citrate (up to 2-fold). 2-Oxoglutarate wa s not reduced. Our data indicate that potato plants can cope with a se vere reduction in cyt-NADP-ICDH activity without major shifts in growt h and metabolism.