Blue light-induced stomatal opening is associated with species-specific changes in primary metabolism but not with starch breakdown in guard cells.

Blue light (BL)-induced stomatal opening has been associated with starch breakdown within Arabidopsis guard cells (GCs). However, whether this mechanism is conserved in angiosperms and which metabolic pathways are activated downstream of BL perception and/or starch degradation, remains unknown. Here, we performed stomatal and metabolomics analyses to investigate how BL stomatal responses are associated with GC starch and primary metabolisms in Arabidopsis, cowpea, and tobacco. The stomatal aperture increased, but no starch degradation was observed in all species under BL. Guard cell primary metabolism was altered by BL exposition in a species-specific and time-dependent manner. Sucrose was negatively correlated with stomatal aperture in both Arabidopsis and cowpea, resembling previous results during white light (WL)-induced stomatal opening. However, contrasting metabolic changes were observed in tobacco under BL and WL. For instance, malate and fumarate accumulated preferentially in tobacco GCs under BL and WL, respectively. Despite the species-specific BL metabolic responses, sugars were positively correlated with tricarboxylic acid cycle-related metabolites in all species under BL, similar to those previously observed under WL-induced stomatal opening. Our study highlights that both starch breakdown and the changes in primary metabolism within GCs triggered by light depend on the species, environmental condition, and/or light quality.