Elevated CO2 concentration alleviates salinity stress in tomato plant

Abstract

Tomato [Solanum lycopersicum (formerly Lycopersicon esculentum) L. cv. Momotarou] plants were grown under potted conditions inside the greenhouse of Hiroshima University, Japan. The effects of salinity stress under either ambient or elevated CO2 atmospheric conditions during the fruit-growth period were compared. Stem was the major sink organ for the carbon assimilates from the source leaves. A simple nondestructive micromorphometric technique was used to measure growth of these organs. The effect of salt stress under ambient air or elevated CO2 concentration was studied on the apparent photosynthesis (source activity), partitioning 13C, Na content, and antioxidative enzymes. Compared with the control (without salt), salt-stress treatment severely decreased whole-plant biomass. The treatment also depressed leaf photosynthesis and transport of 13C assimilates; however, the impact of stress on these activities was alleviated under elevated CO2 concentration and such alleviation was promoted when sink activity relative to source activity was higher, suggesting that sink activity is involved in alleviation of photosynthesis impaired from salinity. Catalase and ascorbate peroxidase activities increased by salinity stress but they decreased by elevated CO2. These results suggested that salinity stress suppresses stem growth in tomato plants; however, the adverse effect is alleviated under elevated CO2 concentration due not to elevation of source activity in leaves but to activation of sink activity, probably owing to improvement of oxidative stress as well as the water status through stomatal closure at high CO2 concentration.