Stem xylem dysfunction causes acute panicle dehydration of rice under flooded conditions in dry winds

Dry winds from typhoons severely dehydrate panicles of paddy rice (Oryza sativa L.) at heading in a single night in flooded fields and markedly decrease grain yield and quality. We reproduced the acute panicle dehydration by using dry-wind treatment in the laboratory and elucidated the dehydration mechanism by focusing on panicle transpiration and water transport to the panicle in cv. 'Koshihikari'. Under dry winds, panicle water potential (Ψpanicle) decreased immediately after the start of the treatment due to an increase in transpiration and then continued to decrease owing to a temporary increase in panicle transpiration. This decrease caused a decrease in hydraulic conductance in the panicle neck (stem internode to panicle) (Kneck), which further decreased Ψpanicle and Kneck, leading to catastrophic xylem dysfunction via a "runaway cavitation" mechanism and to severe panicle dehydration within a few hours. Such panicle dehydration did not occur at ripening in cv. 'Koshihikari' owing to a small decrease in Ψpanicle under dry winds and was less likely even at heading in cultivars with lower xylem vulnerability to cavitation. We demonstrate that even in the absence of soil drought, acute xylem dysfunction causing mortality by cavitation can occur under conditions of high vapor pressure deficit and intense transpiration. The study provides insights into the development of rice cultivars less susceptible to damage by dry typhoon winds, which are expected to become stronger due to climate change.