The role of guard cell chloroplasts in stomatal function and coordinating stomatal and mesophyll responses .

Guard cells controls the stomata through which exchange of gas takes place by balancing between CO2 uptake for photosynthesis and water loss through transpiration leading to ultimate plant water use efficiency (WUE). Climate change is predicted to lead to greater temperatures and reduced water availability resulting in adverse effect on plant productivity. Sustainable agriculture will therefore require a major reduction in plant water use hence stomata have become potential target for manipulation. Understanding the signal mechanisms of stomata in response to these changing environmental conditions is therefore critically important. In order to facilitate an understanding of stomatal regulation and how it is influenced by the surrounding mesophyll cells, we have used two approaches to find a possible coordination that links mesophyll and guard cell metabolism through the use of stomatal physiology and genetic engineering. The first approach used a novel epidermal mesophyll transfer experiment to monitor stomatal responses to dynamic environmental changes with and without the mesophyll present. The second approach used new molecular tools and techniques to manipulate chloroplast metabolism specifically in the guard cells to elucidate mesophyll-derived signals that coordinate mesophyll CO2 demands with stomatal behaviour towards crop improvement. The results presented have shown guard cells plays a role in stomatal function even though the degree of responsiveness is slower than when the mesophyll is present. Furthermore, the molecular approach demonstrated using Arabidopsis plants overexpressing Rieske and SBPase resulted in substantial and significant impacts on plant development coupled with increases in photosynthetic efficiency of photosystem II in the early stages of seedling development. The result obtained proves more opportunities await the exploitation of guard cells metabolism towards the improvement of plants.