Genetic variation in the photosynthetic induction response in rice (Oryza sativaL.)

Crop leaves growing under field conditions experience fluctuating light intensities. The photosynthetic response to a sudden increase in light intensity, which is termed the photosynthetic induction response, can potentially affect crop productivity. In the present study, the genetic variation in the photosynthetic induction response and the related gas exchange parameters in the rice diversity research set of germplasm (RDRS) were evaluated using two reference genotypes: Koshihikari and Takanari. Takanari is known to show superior induction response than Koshihikari. The photosynthetic induction response was found to be highly diverse in 59 rice genotypes. The cumulative CO(2)fixation during the first 10 minutes after a transition from low to high light intensity (CCF10) differed by a factor of four between genotypes. The variation of CCF(10)showed no relationship with light saturated photosynthetic rate (R = 0.21), but was significantly correlated with photosynthetic rate (A) under low light conditions (R = 0.88). Several genotypes showed even more rapid induction responses than that of Takanari. In particular, A of ARC 11094 and Rexmont both increased rapidly during the first two minutes of the induction response. The CCF(10)of these two genotypes was approximately four times greater than that of Koshihikari. The rapid induction responses of Rexmont and ARC 11094 most likely resulted from the activation of CO(2)fixation in mesophyll cells and CO(2)diffusion from the air to the leaves, respectively. This study demonstrates that there is a large genetic variation in and, therefore, much potential for genetic improvement of, the photosynthetic induction response in rice.