Abstract
The chloroplastic NADP-malate dehydrogenase (MDH) is engaged in indirect export of excess reducing equivalents from the stroma. Using transgenic rice overproducing sorghum MDH (19- and 39-fold increase in activity), we investigated the activation of foreign MDH and the effects of MDH overproduction on photosynthesis. The steady state level of MDH activation under growth light conditions was above 80 % in sorghum, while it was 40 % in both transgenic and non-transgenic rice. However, MDH was rapidly inactivated after transfer to darkness in both sorghum and rice, while its activation by illumination proceeded much slower in transgenic rice. The MDH activity reached maximum within two min in sorghum and non-transgenic rice, while in transgenic rice it continued to increase even after 60 min, probably due to short supply of the reduced thioredoxin. Dependences of CO2 assimilation rate on light intensity and Ci remained unchanged by overproduction of MDH.
