ABSTRACT
Stomata are pores in the gastight waxy cuticula that covers the outer surface of aerial parts of plants. They make uptake of CO2 possible, which is needed for photosynthesis. At the same time, water vapor will leave the plant via the stomata. To optimize photosynthesis, while at the same time preventing excess water loss, stomata control their opening by a signaling network of pathways that respond to environmental conditions such as light and darkness, water vapor pressure decit (VPD), temperature, CO2, and ethylene. Water loss is one of the most obvious changes in harvested vegetables, often limiting marketing life, and a negative water balance (uptake of water is insufcient to compensate transpiration) is one of the most important reasons for the end of the vase life of cut owers. Also, the postharvest quality of some fruits is negatively affected by water loss. In leafy vegetables, stomata are portals that make invasion of bacteria into the inner tissue possible and protect in that way bacteria for sanitizers in washing solutions with the risk of food-borne bacterial diseases. This chapter discusses how several environmental factors, during preharvest cultivation as well as postharvest storage, inuence stomata closing control in harvested cut owers, vegetables, and fruits. Also, the role of the number of stomata and their variability between genotypes and due to cultivation conditions are discussed in relation to postharvest life. One of the most striking factors is low VPD (high humidity) during the growth of plants: after exposure of several days to low VPD, the control of stomata closure is largely disturbed; stomata do not respond anymore to stimuli that normally induce closure. This malfunctioning is very persistent and results in high water loss afterward in the harvested products. Fast cooling of produce can close the stomata of some crops, while in others, the stomata stay open until wilting.
