Defining the limits of differential transpiration

Differential transpiration is a newly discovered acclimation strategy of annual plants to a combination of water deficit (WD) and heat stress (HS). Under these conditions ( i.e., WD+HS), transpiration of vegetative tissues is suppressed in plants such as soybean and tomato, while transpiration of reproductive tissues is not (termed ‘Differential Transpiration’; DT). This newly discovered acclimation process enables the cooling of reproductive organs under conditions of WD+HS, limiting HS-induced damage to plant reproduction. However, at what temperature and WD extremes will this process be active and functional at reducing the internal temperature of reproductive tissues, and at what developmental stages of the plant is it activated, remain unknown. Here, we report that DT occurs at most nodes (leaf developmental stages) of soybean plants subjected to WD+HS, and that it can function under extreme conditions of WD+HS ( i.e., 18% of field water capacity and 42°C combined). Our findings reveal that DT is an effective acclimation strategy that protects reproductive processes from extreme conditions of WD+HS, at almost all developmental stages. In addition, our findings suggest that under field conditions DT could also be active in plants subjected to low or mild levels of WD during a heat wave.