Effects of light irradiance on stomatal regulation and growth of tomato

Light is not only a primary energy source for photosynthesis but also a vital regulator of numerous processes in plants. However, high light intensity always poses a dilemma for plants: to grow or to suffer. Combining physiological techniques at plant, tissue, and cellular levels, we investigated the regulation of stomatal behaviour and cytosolic Ca2+ concentration ([Ca2+]cyt) on growth of tomato plants under different light irradiance. Overall, plants exhibited a distinct short-term (days) and a long-term (weeks) response to high light by significantly increasing shoot biomass, leaf number, leaf temperature, vapour pressure deficit, stomatal index, aperture length and guard cell length. However, most physiological parameters were significantly reduced upon high light treatment, indicating a strong negative impact of high light on photosynthesis and stomatal opening. For instance, Short- and long-term exposure to high light significantly reduced stomatal aperture width by 31.7% and 46.3%, respectively. Moreover, high light treatments significantly decreased [Ca2+]cyt from 252±39 to 52±16nM in stomatal guard cells. Aperture width, guard cell width and stomatal index were the parameters that highly significantly correlated to photosynthesis and growth of tomato plants (P