The Importance of Energy Balance in Improving Photosynthetic Productivity

Abstract

Current proposals to improve photosynthesis to meet our energy and food needs include the following: (1) improving the performance of Rubisco; (2) decreasing photorespiration by turning C3 plants into C4 plants, installing algal or cyanobacterial carbon-concentrating mechanisms into higher plant chloroplasts, or redesigning photorespiratory metabolism; and (3) adding new biosynthetic pathways to increase the flow of carbon into useful products, like starch or oils, etc. While introducing or modifying pathways for these processes will be an important step forward, it is important to note that these approaches may also substantially alter the energetic demands placed on photosynthesis. To successfully translate these modifications into enhanced photosynthesis requires that chloroplasts can meet these altered demands. Chloroplasts have already evolved significant energy flexibility mechanisms, as discussed below, but these are activated under specific environmental and metabolic challenges. We need knowledge of the mechanisms regulating these processes in order to modulate them for increased energy efficiency. Ultimately, we could adjust chloroplast performance to meet altered needs by altering gene regulation or by introducing new balancing systems. It is thus useful to review what is known about energy balance in the chloroplast and project how these might be adjusted