Shade and drought growth conditions strongly impact dynamic responses of stomata to variations in irradiance in Nicotiana tabacum

Recent research has made progress in describing stomatal dynamics in terms of speed, amplitude of response, lag time and response time. However, little is known about the impact of growth conditions on the rapidity of stomatal movements, and their relationship with stomatal morphology within a species. We measured stomatal dynamics during opening and closing in response to changes in irradiance in tobacco plants (Nicotiana tabacum) grown under “Control”, “Drought” and “Shade” treatments. Growth conditions strongly changed the rapidity of stomatal responses to irradiance. The “Drought” treatment considerably accelerated the response and “Shade” treatment slowed it down when compared to “Control”. We confirmed for the “Control” treatment the known asymmetry of response, with closing faster than opening, but interestingly the asymmetry disappeared under both treatments. Only stomatal density and index were affected by the growth conditions, not stomatal size and form. Thus, the observed variation in stomatal closing and opening dynamic parameters (speed, amplitude, lag time, response time) was not due to a variation in the size of the stomata, and only a marginal relationship between speed of the stomatal response and stomatal density was observed. These results suggest that physiological factors might be the main driver of variations in stomatal conductance dynamics within a species grown under different environmental conditions.