Learning from nature: photosynthetic traits conferring superior salt tolerance in wild rice <i>Oryza coarctata</i>

This work aimed to reveal a mechanistic basis of differential salinity stress tolerance between cultivated (<i>Oryza sativa</i>) and wild (<i>Oryza coarctata</i>) rice species related to photosynthesis and leaf gas exchange. With an innate larger (twofold) stomata, <i>O. coarctata</i> could achieve a similar net photosynthetic rate with 63% lower stomatal density and show 72% higher intrinsic water use efficiency under control conditions. After salt treatment, cultivated rice developed smaller and denser stomata with decreased aperture, which resulted in lower stomatal conductance and reduced stomatal opening speed. Also, <i>ca</i> twofold decrease in the maximum carboxylation rate of ribulose bisphosphate carboxylase (RuBisCO) and the rate of ribulose 1,5-bisphosphate (RuBP) regeneration were also observed. In addition, Na⁺ accumulation in mesophyll depressed the operation of photosystem II (PSII). At the same time, <i>O. coarctata</i> maintained relatively steady CO₂ assimilation under saline conditions, with both stomatal and photochemical traits largely unaffected. This included unaltered stomatal size, density and opening speed; enhanced ribulose bisphosphate carboxylase carboxylation and RuBP regeneration in the Calvin cycle; and more stable leaf photochemistry. <i>Oryza coarctata</i> also possessed an ability to utilize Na⁺ for stomata operation-a trait lacking in cultivated rice. The above-mentioned traits could be used as potential targets in breeding programmes to improve salinity tolerance in cultivated rice.This article is part of the theme issue 'Crops under stress: can we mitigate the impacts of climate change on agriculture and launch the 'Resilience Revolution'?'.