Super-RuBisCO

The Key for Improvement of Plant Photosynthesis

Abstract

Plants receive various kinds of stresses from the environment and are obliged to reduce their productivity. These stresses are often lethal. Changing the present plants to ones resistant to these stresses is important for guaranteeing the next generation the food and the environment. One of the most severe factors that influence the productivity is the shortage of water for growth. Under water limitation, plants close the stomata and the excess light energy captured on the thylakoid membranes is directed to formation of active oxygens. Our previous efforts successfully rendered a model plant, tobacco, to be active oxygen-resistant. However, the active oxygen-resistant tobacco could not grow at all under water deficit because of closure of the stomata. The plant to be created must fix CO₂ for growth even if the stomata is almost closed and the rate of the flow of CO₂ from the atmosphere into the leaf is strongly reduced. Our knowledge in plant physiology tells us plants can fix CO₂ even under water deficit if the active site of the C0₂-fixing enzyme RuBisCO strongly discreminates against dioxygen. The present plant RuBisCO fixes one molecule of dioxygen for every 3 CO₂ fixations. We have found that RuBisCO from Galdieria partita, an acidic, thermophilic red alga, discreminates against dioxygen 3 times more strongly than the plant enzyme. The affinity of the Galdieria enzyme for CO₂ was 2 times higher than the plant enzyme. Physiological calculations tell that the Galdieria enzyme can render tobacco to fix CO₂ at the range of the CO₂ concentration where the natural plants cannot if the genes are successfully introduced into tobacco.