increase in photosynthesis rate can, therefore, be achieved by decreasing or eliminating photorespiration. This could be done by increasing the affinity of rubisco for CO2, thereby decreasing its oxygenase activity. The substrate specificity factor determines the relative rates of two reactions at any given CO2 and O2 concentration. A high specificity value indicates greater specificity for CO2. Rubisco enzyme from diverse species showed substantial differences in CO2/O2 specificity and that carboxylase/oxygenase ratio increased during the natural evolution of photosynthesis66. Furthermore, higher temperature increasingly favours oxygenation64. Among chemicals tested, Mn2+ and urea in vitro have been shown to alter the ratio of two activities for greater oxygenation67–69. These studies indicate that balance between RuBP carboxylation and oxygenation is not immutable and alteration in ratio is possible. However, successful manipulation of rubisco is yet to be achieved.