Abstract
BackgroundRice (Oryza sativa) is one of the world’s most important crops and is especially important in Asia. Because irrigated rice consumes about 34–43% of the total water used for irrigation globally, increasing drought and global temperature will increase the risk of rice crop loss. However, rice is among the least efficient crops in terms of water use, whereby most of the uptaken water is used for transpirational cooling via stomatal pores on the leaf blades and sheaths. To increase the water-use efficiency of rice, alterations in stomatal density and size may help to reduce transpiration and thereby increase water-use efficiency (WUE). ResultsWe identified four stomatal model lines—with either high-density (HD) or low-density (LD) stomata and small-sized (SS) or big-sized (BS) stomata—from the Mutant Core Collection (MCC) of 216 mutants. Gas exchange analysis revealed that the stomatal model lines have similar photosynthetic assimilation (A) and chlorophyll fluorescence. With increasing CO2 concentration, A of all stomatal model lines was observed to respond similarly at 100–600 ppm CO2, but beyond this point, SS was more responsive to increasing CO2 concentration than the other stomatal model lines. HD had higher stomatal conductance (gs) and gsmax than the other stomatal model lines. In response to a mild heat at 30 °C, both SS and LD had higher canopy temperature than HD, BS, and JHN-wt as a result of heat retention. All stomatal model lines are also similar in their rhythmic stomatal responses to ten-minute dark/light transition cycles, except that initial stomata closure in SS was more rapid than in BS. The stomatal model lines did not show any significant differences in the response to short-term water stress. Long-term water stress had less impact on leaf drying, Fv/Fm, grain yield, and harvest index in LD and SS. In the field, all stomatal model lines and JHN-wt had similar WUE in the sufficient-water treatment. LD had the highest WUE and biomass/plant than any stomatal model lines in the long-term restricted-water treatment. ConclusionsTaken together, our results suggest that induced alterations in stomata density and size influence rice WUE and the responses to drought and heat stresses, providing further understanding of the roles of stomata density and size in related processes. The low-density and small stomata lines have high potential as genetic donors for improving WUE and drought in climate-ready rice.
A Genetic Pathway Composed of EDT1/HDG11, ERECTA, and E2Fa Loci Regulates Water Use Efficiency by Modulating Stomatal Density