Role of Rieske FeS and SBPase in stomatal behaviour

The biomass of a crop depends on the cumulative rate of photosynthesis and the rate of carbon fixation can be limited by the flux of CO2 in to the leaf. Stomata regulate gaseous exchange between the leaf interior and the external air surrounding the leaf, thereby, controlling CO2 uptake for photosynthesis, and simultaneously water loss and evaporative cooling through transpiration. Both stomatal conductance (gs) and photosynthesis (A) respond to changes in environmental conditions and a close correlation between A and gs is often reported. However, the mechanism(s) that co-ordinate stomatal behavior with A is not clear. This study was conducted to investigate the role of guard cell chloroplast in stomatal function and in particular their role in the coordination between stomatal behaviour and mesophyll photosynthesis. For that, we have examined transgenic tobacco (Nicotiana tabacum) plants with altered expression levels of the Calvin cycle enzyme Sedoheptulose-1,7, bis-phosphatase (SBPase), and the electron transport protein, Rieske FeS specifically in guard cells under the control of promoter AGPase. Expression levels were quantified using an epidermal peel enrichment prep for guard cells and qPCR. High-resolution chlorophyll fluorescence imaging and infra-red gas analysis were used to assess the influence of these manipulations on photosynthesis efficiency and stomatal kinetics. Our results revealed that the increase in Rieske FeS in guard cells resulted in a increased operating efficiency of PSII in guard cells when compared to the WT. Moreover, overexpression Rieske FeS plants showed higher stomatal conductance and shoot biomass increased significantly (5%-10%). On other hand, significant variation in the operating efficiency of PSII in guard cells was observed in plants with altered SBPase expression. Furthermore, stomatal conductance and assimilation rates have been affected, this suggests that the greatest effect in terms of stomatal behaviour is realised by manipulation of Calvin cycle enzymes.