An investigation on the possibility of use of chlorophyll fluorescence to study the stomatal behaviour in plants under drought stress

Stomata play a key role in the control of plant water relations and photosynthesis. A rapid non-destructive method to study the stomatal behaviour in aerial parts of plants is important for researchers in plant sciences and agricultural fields. Stomata close in response to drought stress. Stomatal closure causes lower availability of CO2 inside the leaf and thus a decrease in the rate of carboxylation. Thus, a measurement of relative quantum yied for electron transport by photosystem II (ΦPSII) under a non-photorespiratory condition may be used to detect the closure of stomata. In this research we aimed to study the relationship between ΦPSII and stomatal closing behaviour in Tradescantia virginiana under water stress and rehydration using a chlorophyll fluorescence imaging system. Results showed that in leaves from well-watered plants and in an atmosphere of 2% O2 and normal CO2, ΦPSII was high (0.69) before excision, but 2 h dessication after excision ΦPSII decreased significantly (0.33), and with the transition to high CO2 ΦPSII almost completely recovered to the value of the control images (0.66). Moreover, ΦPSII increased significantly from 0.27 to 0.64 during rehydration of the dessicated leaves. Direct measurement of stomatal aperture in control and dessicated plants (7 and 1 µm, respectively) confirmed the high correlation between ΦPSII under low O2 concentration and stomatal closure as well as the effectiveness of chlorophyll fluorescence imaging system in the study of stomatal behaviour. Therefore, this new non-destructive method could be used to study stomatal closing behaviour and patchiness in different parts of a leaf.