Heat Waves Coupled with Nanoparticles Induce Yield and Nutritional Losses in Rice by Regulating Stomatal Closure

The frequency, duration, and intensity of heat waves (HWs) within terrestrial ecosystems are increasing, posing potential risks to agricultural production. Cerium dioxide nanoparticles (CeO₂ NPs) are garnering increasing attention in the field of agriculture because of their potential to enhance photosynthesis and improve stress tolerance. In the present study, CeO₂ NPs decreased the grain yield, grain protein content, and amino acid content by 16.2, 23.9, and 10.4%, respectively, under HW conditions. Individually, neither the CeO₂ NPs nor HWs alone negatively affected rice production or triggered stomatal closure. However, under HW conditions, CeO₂ NPs decreased the stomatal conductance and net photosynthetic rate by 67.6 and 33.5%, respectively. Moreover, stomatal closure in the presence of HWs and CeO₂ NPs triggered reactive oxygen species (ROS) accumulation (increased by 32.3-57.1%), resulting in chloroplast distortion and reduced photosystem II activity (decreased by 9.4-36.4%). Metabolic, transcriptomic, and quantitative real-time polymerase chain reaction (qRT-PCR) analyses revealed that, under HW conditions, CeO₂ NPs activated a stomatal closure pathway mediated by abscisic acid (ABA) and ROS by regulating gene expression (PP2C, NCED4, HPCA1, and RBOHD were upregulated, while CYP707A and ALMT9 were downregulated) and metabolite levels (the content of γ-aminobutyric acid (GABA) increased while that of gallic acid decreased). These findings elucidate the mechanism underlying the yield and nutritional losses induced by stomatal closure in the presence of CeO₂ NPs and HWs and thus highlight the potential threat posed by CeO₂ NPs to rice production during HWs.