Dynamic thermal imaging confirms local but not fast systemic ABA responses.

Abscisic acid (ABA) signals regulating stomatal aperture and water loss are usually studied in detached leaves or isolated epidermal peels and at infrequent timepoints. Measuring stomatal ABA responses in attached leaves across a time course enables the study of stomatal behaviour in the physiological context of the plant. Infrared thermal imaging is often used to characterize steady-state stomatal conductance via comparisons of leaf surface temperature but is rarely used to capture stomatal responses over time or across different leaf surfaces. We used dynamic thermal imaging as a robust, but sensitive, tool to observe stomatal ABA responses in a whole plant context. We detected stomatal responses to low levels of ABA in both monocots and dicots and identified differences between the responses of different leaves. Using whole plant thermal imaging, stomata did not always behave as described previously for detached samples: in Arabidopsis, we found no evidence for fast systemic ABA-induced stomatal closure, and in barley, we observed no requirement for exogenous nitrate during ABA-induced stomatal closure. Thus, we recommend dynamic thermal imaging as a useful approach to complement detached sample assays for the study of local and systemic stomatal responses and molecular mechanisms underlying stomatal responses to ABA in the whole plant context.