Effects of light irradiance on stomatal regulation and growth of tomato

• Distinct short- and long-term stomatal closure is induced by high light irradiance.
• Short-term response of high light-induced stomatal closure is modulation via [Ca2+]cyt in guard cells.
• High light (PAR 1000) supply does not improve the biomass production 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 ± 16 nM 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 < 0.01) followed by aperture width/length, guard cell volume and stomatal density. These causal links revealed some insights into the fine-regulation of stomata on plant performance despite some non-stomatal factors. Therefore, stomatal parameters including aperture width/length, guard cell width, stomatal density and index and [Ca2+]cyt could be employed as physiological markers for fast and effective assessment of performance of tomato plants.