Waterlogging the soil promotes epinastic growth of tomato petioles and increases the concentration of ethylene which can be extracted from various parts of the shoot. These concentrations exceed those normally required to promote epinasty when applied to the shoots of non-waterlogged plants.
Waterlogging also results in a rapid decline in the concentration of dissolved oxygen in the soil water. Low concentrations of oxygen around the roots of plants growing in nutrient solution promote epinastic growth and also increase ethylene concentration in the leaves. Experiments with detached shoots indicate that the root system is required for the response to low O2concentrations to develop.
Ethylene concentrations in the soil can increase during waterlogging to levels which may allow sufficient movement into the shoot to stimulate epinasty.
Treatment with substances which can inhibit the action of ethylene, such as carbon dioxide or 7-chloro-4-ethoxycarbonylmethoxy-5-methyl-2, 1,3-benzothiadiazole also inhibit the epinastic response in waterlogged plants, in plants with low O2 concentrations around the roots and in plants treated with ethylene. The internal level of carbon dioxide in the lower leaves is little affected by waterlogging for up to 96 h.