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

Abstract

19Plant cells have multiple strategies to adapt to environmental stresses. Rice endosperms 20 form chalkiness in a part of the tissue under heat conditions during the grain-filling stage, 21 although nitrogen supply reduces chalky rice. Air spaces formed in the cells cause an 22 irregular light reflection and create chalkiness, yet what exactly occurs remains unclear at 23 cell level. Through on-site cell-specific analysis, we show that heat-treated cells adjust 24 osmotically and retard protein synthesis to preserve protein storage vacuoles in the cytosol, 25 resulting in air space formation. Application of nitrogen enhances heat tolerance to sustain 26 protein body and amyloplast development during strong osmotic adjustment, which 27 diminishes air spaces to avoid chalkiness. Hence, we conclude that rice endosperm cells 28 could alter organelle compartments spatially during the heat adaptation, depending on the 29 available nitrogen level. Our findings provide new insight into the cellular mechanism of rice 30 chalky formation as a strategy for heat acclimation.