High photosynthesis rate in two wild rice species is driven by leaf anatomy mediating high Rubisco activity and electron transport rate

Abstract

The importance of increasing photosynthetic efficiency for sustainable crop yield increases to feed the growing world population is well recognized. The natural genetic variation for leaf photosynthesis in crop plants is largely unexploited for increasing genetic yield potential. The genus Oryza, including cultivated rice and wild relatives, offers tremendous genetic variability to explore photosynthetic differences, and underlying biochemical, photochemical, and developmental bases. We quantified leaf photosynthesis and related physiological parameters for six cultivated and three wild rice genotypes, and identified photosynthetically efficient wild rice accessions. Fitting A/Ci curves and biochemical analyses showed that the leaf photosynthesis in cultivated rice varieties, IR64 and Nipponbare, was limited due to leaf nitrogen content, Rubisco activity, and electron transport rate compared to photosynthetically efficient accessions of wild rice Oryza australiensis and Oryza latifolia. The selected wild rice accessions with high leaf photosynthesis per unit area had striking anatomical features, such as larger mesophyll cells with more chloroplasts, fewer mesophyll cells between two consecutive veins, and higher mesophyll cell and chloroplast surface area exposed to intercellular space. Our results show the existence of desirable variations in Rubisco activity, electron transport rate, and leaf anatomical features in the rice system itself that could be targeted for increasing the photosynthetic efficiency of cultivated rice varieties.