Bacillus subtilis-regulation of stomatal movement and instantaneous water use efficiency in Vicia faba

Abstract

Microbes- and microbe-associated molecular patterns-induced stomatal closure have been known to be connected with the early defense responses and the improvement of instantaneous water use efficiency (WUEi) in plants. Being a commercially available microorganism, Bacillus subtilis can promote plant growth and induce disease resistance. However, its effects on stomatal movement and WUEi in plants have been largely unexplored. Here, we showed that B. subtilis induced stomatal closure in a dose- and time-dependent manner when applied to isolated epidermal peels and intact leaves of broad bean. Pharmacological study further revealed that the B. subtilis-induced stomatal closure in epidermal peels was mediated mainly by reactive oxygen species production via NADPH oxidases. Furthermore, foliar application of B. subtilis significantly reduced stomatal aperture, stomatal conductance (gs), transpiration rate (E) and net photosynthesis rate (Pn) of leaves of broad bean at 8 and 24 h, reductions in which were reversed after 48 h. As a consequence, the WUEi of plants treated with B. subtilis for 8–144 h was higher than that in the control. The chlorophyll fluorescence and content analysis further demonstrated that B. subtilis could enhance plant photosynthetic activities by increasing leaf photosynthetic efficiency and chlorophyll content. These results suggest that foliar spray of B. subtilis can improve WUEi of crop plant via the regulations of stomatal movement and photosynthetic activity during a special time period.