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

Abstract

10The importance of increasing photosynthetic efficiency for sustainable crop yield 11 increases to feed the growing world population is well recognized. The natural genetic 12 variation for leaf photosynthesis in crop plants is an overlooked and untapped resource. The 13 genus Oryza, including cultivated rice and wild relatives, offers tremendous genetic 14 variability to explore photosynthetic differences, and underlying developmental, 15 photochemical, and biochemical basis. We quantified leaf photosynthesis and related 16 physiological parameters for ten cultivated and wild rice genotypes to identify 17 photosynthetically efficient wild rice species. Wild rice species with high leaf photosynthesis 18 per unit area had striking anatomical features, such as larger mesophyll cells with more 19 chloroplasts, larger and closer veins, and a smaller number of mesophyll cells between two 20 consecutive veins. In addition, photosynthetically efficient wild rice species showed an 21 efficient Photosystem II as well as higher carboxylation activity of Rubisco compared to less 22 efficient cultivated varieties, such as IR 64. Our results show the existence of desirable 23 variations in mesophyll and vein features, Photosystem II efficiency, and Rubisco activity in 24 the rice system itself that could possibly be targeted for higher leaf photosynthesis. Detailed 25 genetic and molecular understanding of these traits shall be instrumental in increasing 26 photosynthetic efficiency of cultivated rice. 27 28