Overexpression of XXXX reductase in tobacco delays drought-induced decreases in @entity1507 reductase activity and mRNA

@entity8326 @entity1949 @entity1522 @entity3260 @entity1507 @entity515 @entity969
Transformed ( @entity3260 35S promoter [35S]) tobacco (Nicotiana plumbaginifolia L.) plants constitutively expressing @entity1507 reductase (NR) and untransformed controls were subjected to drought for 5 d. Drought-induced changes in biomass accumulation and photosynthesis were comparable in both lines of plants. After 4 d of @entity1949 , a large increase in the ratio of shoot dry weight to fresh weight was observed, together with a decrease in the rate of photosynthetic @entity515 assimilation. Foliar @entity969 increased in both lines during water stress, but hexoses increased only in leaves from untransformed controls. Foliar @entity8326 decreased rapidly in both lines and was halved within 2 d of the onset of @entity1949 . Total foliar @entity1522 decreased in leaves of both lines following @entity1949 . After 4 d of @entity1949 no NR activity could be detected in leaves of untransformed plants, whereas about 50% of the original activity remained in the leaves of the 35S-NR transformants. NR mRNA was much more stable than NR activity. NR mRNA abundance increased in the leaves of the 35S-NR plants and remained constant in controls for the first 3 d of drought. On the 4th d, however, NR mRNA suddenly decreased in both lines. Rehydration at d 3 caused rapid recovery (within 24 h) of 35S-NR transcripts, but no recovery was observed in the controls. The phosphorylation state of the protein was unchanged by long-term drought. There was a strong correlation between maximal extractable NR activity and ambient photosynthesis in both lines. We conclude that drought first causes increased NR protein turnover and then accelerates NR mRNA turnover. Constitutive NR expression temporarily delayed drought-induced losses in NR activity. 35S-NR expression may therefore allow more rapid recovery of N assimilation following short-term water deficit.
