Effect of postharvest short-term radiation of near infrared light on transpiration of lettuce leaf

We investigated the physiological effects of short-term postharvest near infrared (NIR) radiation on relative transpiration rates, stomatal apertures, and reactive oxygen species (ROS) levels in guard cells on excised young lettuce leaves and on transpiration of leaf lettuce at commercial maturity. When the young leaves were radiated by NIR of wavelengths longer than 850nm at 100μmolm^-2s^-1 for short duration (10-60)min, relative transpiration rates during subsequent storage were reduced, but not by visible light radiation and by longer radiation (180min) of NIR. The reduction in transpiration rates by the short-term NIR radiation was greater at 10°C than at 25°C under both dark and light conditions during subsequent storage. The short-term NIR radiation enhanced stomatal closure and ROS accumulation in guard cells of young lettuce leaves. These results indicate that the suppression of transpiration by short-term NIR radiation is likely to be mediated through stomatal closure due to NIR-induced ROS accumulation. The reduction of transpiration by short-term NIR radiation was obtained not only in excised young leaves but also in leaf lettuce at commercial maturity, resulting in keeping freshness. The short-term NIR radiation could be an additional means to extend shelf life of leaf vegetables.