Enhancement of rice leaf photosynthesis by crossing between cultivated rice, Oryza sativa and wild rice species, Oryza rufipogon

To study whether wild rice species have genes that may increase potential photosynthetic capacities of rice cultivars, we generated BC sub(2) populations by reciprocally backcrossing Oryza rufipogon (W630) with 0. saliva cv. Nipponbare and IR36; N-BC sub(2) populations and IR-BC sub(2) populations, respectively. We measured the oxygen evolution rates (OER) of single leaves under saturating light and CO sub(2) as the maximum photosynthetic rates and the contents of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) and Rubisco activase. Several lines in each BC sub(2) population had significantly higher OERs than parental cultivars, and 14-25% of plants in BC sub(2) populations had higher OERs than the highest values in parental cultivars. The highest OERs in BC sub(2) populations were about 60% higher than average OERs in parental cultivars. The BC sub(2) populations contained 30~40% more Rubisco than parental cultivars. The Rubisco activase contents in N-BC sub(2) populations were 15~30% lower than that in Nipponbare. Cytoplasms derived from O. rufipogon and O. saliva had different effects on the contents of Rubisco and Rubisco activase particularly in N-BC sub(2) populations. In several lines of each BC sub(2) population the OERs had positive correlations with the contents of Rubisco and/or Rubisco activase. These results suggest that O. rufipogon can be used as a source of germplasm to enhance the photosynthetic capacity of O. sativa.