Salicylic acid-induced stomatal closure differs in vascular plants of various lineages

Salicylic acid (SA) triggering of stomatal closure to prevent pathogen invasion has been widely recognized in angiosperms. However, whether SA-induced stomal closure differs across vascular plants of various lineages remains unclear. In this study, the stomatal responses of 28 species, comprising 13 angiosperms, six gymnosperms, eight ferns, and one lycophyte, to exogenous SA were evaluated, and the stomatal closure signaling pathways of six representative species were subsequently examined. SA-induced stomatal closure was observed in seed plants but not in the ferns or lycophyte. Additionally, SA induced an increase in reactive oxygen species in the guard cells of these six different vascular plants, but nitric oxide accumulation in and K+ efflux from guard cells were detected in seed plants but not in the two ferns or one lycophyte investigated. The application of SA induced large vacuolar compartments in the guard cells of the seed plants to disaggregate, whereas no such changes were observed in the guard cells of the ferns or lycophyte. The differences in the responses of the seed plant, fern, and lycophyte stomata to SA observed in this study were due mainly to the partial absence of the SA signaling pathway in the ferns and lycophyte.