Effect of flooding on tomato cultivars: The relationship between proline accumulation and other morphological and physiological changes

Flooding of the root system of tomato plants ( Lycopersicon esculentum ) caused cessation of leaf elongation, leaf epinasty, formation of adventitious roots, and increase in diffusive resistance associated with the wilting of leaves at the first stage of the stress. Upon development of adventitious roots, the wilted leaves regained their turgor and the diffusive resistance slowly decreased at a rate slower than that at which water potential increased. In the course of flooding, proline accumulated but after 11 days dropped back to the control level. The extent of proline accumulation in various tomato cultivars was positively correlated with the extent to which their leaf water potential dropped, but was not correlated with the changes in their diffusive resistance. Cultivars which accumulated the highest proline levels were those which showed the most severe injury, with only one cultivar as an exception. However, only in the cultivars producing high levels of proline was the return of leaf turgor followed by resumption of leaf elongation. In cv. 'Hosen', which was severely injured by the stress, but accumulated a low level of proline, leaf elongation was not resumed. The results suggest that proline accumulation is an indicator of the cultivar's sensitivity to dehydration associated with the flooding stress, and confirm the notion that proline may play a role in the post-stress recovery process.