Multiple strategies for heat adaptation in rice endosperms revealed by on-site cell-specific analysis

Abstract

Plant cells have multiple strategies to adapt to environmental stresses. Rice endosperms form chalkiness in a part of the tissue under heat conditions during the grain-filling stage, although nitrogen supply reduces chalky rice. Air spaces formed in the cells cause an irregular light reflection and create chalkiness, yet what exactly occurs remains unclear at cell level. Through on-site cell-specific analysis, we show that heat-treated cells adjust osmotically and retard protein synthesis to preserve protein storage vacuoles in the cytosol, resulting in air space formation. Application of nitrogen enhances heat tolerance to sustain protein body and amyloplast development during strong osmotic adjustment, which diminishes air spaces to avoid chalkiness. Hence, we conclude that rice endosperm cells could alter organelle compartments spatially during the heat adaptation, depending on the available nitrogen level. Our findings provide new insight into the cellular mechanism of rice chalky formation as a strategy for heat acclimation.