Illuminating stomatal responses to red light: establishing the role ofCi-dependent vs - independent mechanisms

Abstract

AbstractThe stomatal response to red light appears to link stomatal conductance (gs) with photosynthetic rates. Initially, it was suggested that changes in intercellular CO2(Ci) provide the main cue via aCi-dependent response. However, evidence forCi-independent mechanisms suggests an additional, more direct relationship with photosynthesis. While bothCi-dependent and -independent mechanisms clearly function in stomatal red-light responses, little is known regarding their relative contribution. The present study aimed to quantify the relative magnitude ofCi-dependent and - independent mechanisms on the stomatal red-light response, to characterise their interplay and to assess the putative link between plastoquinone (PQ) redox state andCi-independent stomatal responses. Red light response curves measured at a range ofCivalues for wild-typeArabidopsis thaliana(Col-0) and the CO2hyposensitive mutant,ca1ca4, allowed deconvolution ofCi-dependent and -independent pathways. Surprisingly, we observed that both mechanisms contribute equally to stomatal red-light responses, butCi-independent stomatal opening is suppressed at highCi. The present data are also consistent with the involvement of PQ redox in coordinatingCi-independent stomatal movements. Overall, it seems that whileCi-independent mechanisms are distinct from responses toCi,interplay between these two pathways is important to facilitate effective coordination betweengsand photosynthesis.HighlightBy controlling intercellular CO2(Ci) at a range of values across red-light response curves, we demonstrate independent and interactive roles ofCi-dependent and –independent pathways in coordinating stomatal red-light responses.