To examine the hypothesis that microbes can function as antitranspirants regulating stomatal behavior, we studied the effect of Saccharomyces cerevisiae strain BY4741 on gas exchange and water-use efficiency (WUE) in Vicia faba L. Stomatal aperture and photosynthetic parameters were analyzed every day for 7 days after treatment. In the present study, spraying yeast decreased the stomatal aperture. On the 4th, 5th, 6th, and 7th days after the foliar application of yeast, a decreased in net photosynthetic rate (Pn) was observed. This decrease was accompanied with decreases in stomatal conductance (gs), intercellular CO2 concentration (Ci), and transpiration (Tr). The carboxylation efficiency (CE) was reduced by yeast on the 1st day after treatment. On the 1st, 2nd, and 3rd days of treatment, the yeast dramatically decreased the maximum photochemical efficiency of photosystem (PS) II (Fv/Fm) and increased non-photochemical quenching (NPQ); however, these parameters eventually recovered to their normal levels. The marked decrease of qP was observed on the 1st and 2nd days after yeast treatment. At the beginning of the treatment, the yeast decreased electron the transport rate (ETR), but later increased it. Both concentrations of yeast (1×106 and 1×1010 CFU mL−1) increased the WUE on the 4th, 5th, 6th, and 7th days of treatments. At the concentrations of 1×106 CFU mL−1, yeast acted as a more effective antitranspirant, showing higher WUE, than at the concentration of 1 × 1010 CFU mL−1. Pn was positively correlated with Tr and gs on the 7th day of the treatment. Moreover, Tr was much more sensitive to yeast than was Pn. In general, the foliar application of yeast resulted in decreased Tr and increased WUE. The yeast-induced decrease in photosynthesis is mainly caused by stomatal closure, suggesting that yeast can be used as an antitranspirant or a priming agent for improving drought tolerance in plants.
WATER USE EFFICIENCY AND YIELD FOR DUAL PURPOSE IN FABA BEAN (Vicia faba L.) CULTIVARS
