Abstract
Effects of overexpression of Rubisco activase on photosynthesis were studied using transgenic rice expressing barley Rubisco activase. Western blot and SDS-PAGE analyses showed that the transgenic rice expressed barley Rubisco activase at the level higher than endogenous rice Rubisco activase. The activation state of Rubisco under illumination was higher in transgenic rice than that in non transgenic rice (NT). In addition, the relaxation time for light activation of Rubisco was significantly lower in transgenic rice compared with NT. These findings indicate that the overexpression of barley Rubisco activase could enhance Rubisco activation in rice. However, the CO2 assimilation rate was decreased in transgenic rice. This decrease in CO2 assimilation rate was observed in young or matured leaves regardless of supplied N levels. The contents of nitrogen and chlorophyll did not differ between transgenic and NT, whereas Rubisco content was significantly decreased in transgenic rice. These results suggest that the overexpression of Rubisco activase can stimulate Rubisco activation, however, which leads to decrease in the photosynthetic rate by the reduction in Rubisco content.
