Increased Ring‐Shaped Chalkiness and Osmotic Adjustment when Growing Rice Grains under Foehn‐Induced Dry Wind Condition

Abstract

ABSTRACTFoehn‐induced dry wind during grain filling increased ring‐shaped chalky kernels in rice (Oryza sativa L.) plants. The objective of this study was to determine physiological mechanisms of the occurrence of ring‐shaped chalky kernels. Rice plants were subjected to water deficit in a paddy field after shade by applying dry high‐speed wind. Additionally, a growth chamber experiment was conducted with plants in pots to measure the water status under the dry wind condition for 24 h by combining in situ turgor (Ψp) assay in developing endosperms with the water potential measurements. The dry (high vapor pressure deficit [VPD]) wind treatment produced the largest number of ring‐shaped chalky kernels due to poor starch accumulation, compared with shade or low‐VPD wind treatment. The inner endosperm cells, where a high frequency of chalkiness was observed, spatially maintained Ψp by osmotic adjustment before the chalky formation with no decline of grain weight. Dry wind reduced photosynthesis due to a partial stomatal closure after water deficit developed. However, these responses, including those related to the plant water status, returned to a level similar to those of the control plants in a day after the dry wind was stopped. We conclude that (i) Ψp maintenance by osmotic adjustment contributes to grain development under water deficit under foehn conditions and (ii) osmotic adjustment has a role in temporally inhibiting starch accumulation in endosperms, resulting in ring‐shaped chalky kernels under foehn‐induced water deficit conditions.