Breaking limitations: photosynthetic traits contribute to the salt tolerance in wild rice Oryza coarctata

Ping Yun, Lana Shabala, Meixue Zhou, Sergey Shabala
School of Biological Sciences, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia; Tasmania Institute of Agriculture, University of Tasmania, 1 Churchill Avenue, Sandy Bay, TAS, Australia; International Research Center for Environmental Membrane Biology, Foshan University, Foshan 528000, China

Salt-induced limitations of photosynthesis impede the growth and grain yield in rice (Oryza sativa). Oryza coarctata, the only halophyte in the Oryza species, possesses outstanding salt tolerance, while the underlying mechanisms remain unknown. To evaluate the stomatal-related factors in salinity-induced photosynthesis limitations in O. coarctata and understand its coping strategy, we compared stomatal morphology and operation between O. sativa and O. coarctata. With an innate larger stomata aperture (2-fold of O. sativa), O. coarctata could achieve a similar photosynthetic rate with 50% lower stomatal conductance (Gs) under control conditions. After salt treatment, O. sativa developed smaller and denser stomata, which resulted in lower Gs and stomatal opening speed. While O. coarctata maintained relatively steady CO2 assimilation under salinity, with stomatal traits largely unaffected, including unaltered stomatal-related traits (size, density, and opening speed) and the ability to utilize Na+ for stomatal operation. It is suggested that the above traits as potential targets in breeding programs to improve salinity tolerance in cultivated rice.