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.     

Thiocyanate content in relation to the quality features of radish Raphanus sativus L

Relationships between radish thiocyanate content and its dry weight, the content of sugar, protein, fibre, ascorbic acid, some minerals, the incidence of plant shooting, the firmness and pithiness of storage-roots, and the ratio of leaves to storageroot (wt/wt) were investigated. The analysis of linear correlation was based on numerous data from the 4-year field experiment with six radish cultivars and different sowing and harvest dates. The content of thiocyanate in radish roots was found to be positively correlated with their dry weight, and the content of total protein, crude fibre, and soluble sugar. A strong relationship was found between the content of thiocyanate and dry weight of radish leaves. The negative correlation between the thiocyanate content in the leaves and the firmness of storageroots and the positive correlation with their pithiness might indicate the translocation of this compounds into green plant parts during the ageing of root tissue. The root thiocyanate content and the percentage of shooting correlated significantly only in the case of Tokinashi. The closeness of relations between the ratio of leaves/storage-root and thiocyanate content, though in general small, was affected also by a cultivar. A similar effect was observed for the correlations between the thiocyanate contents in leaves and storage-roots.     

Stem pithiness in tomato plants: The effect of water stress and the role of abscisic acid

The pith parenchyma in tomato ( Lycopersicum esculentum ) stems was found to be disrupted in response to water stress (stem pithiness). The process of the degradation starts at the upper part of the stem and proceeds downwards as the stress is prolonged. The damage to the stem tissue was found to be irreversible upon rehydration of the stressed plants. Scanning electron microscopy revealed that the protoplast of the affected cells is disrupted first, followed by degradation of the cell wall.
Application of abscisic acid (ABA) induced pithiness in non-stressed plants and also enhanced the effect of a short period of dehydration. Kinetin, although causing severe wilting, did not induce pithiness. However, when given after a short period of water stress or within the period of stress, kinetin enhanced pithiness development.
In the course of the stress, ABA levels in the upper part of the stem and in the young leaves were higher than the levels found in the lower parts of the plant shoot. The increase in ABA levels was detected before any sign of pithiness.
It is suggested that ABA might be the triggering agent of the cellular degradation process initiated by water stress.