Photorespiratory bypasses: how can they work?

Photorespiration has been suggested as a target for increasing photosynthesis for decades. Within the last few years, three bypass pathways or reactions have been designed and tested in plants. The three reactions bypass photorespiration either in the chloroplast or in the peroxisome, or oxidize glycolate completely to CO2 in the chloroplast. The reactions differ in their demand for energy and reducing power as well as in the catabolic fate of glycolate. The design, energy balance, and reported benefits of the three bypasses are compared here, and an outlook on further optimization is given.