SALINITY EFFECTS ON THE NETWORK OF VASCULAR BUNDLES DURING TOMATO FRUIT-DEVELOPMENT

The development and distribution of the conducting tissue of tomato fruit in relation to salinity was studied by recording the number of vascular bundles in different layers of the fruit tissues at different growth stages in fruit grown at three levels of salinity (electrical conductivity, 5, 10 and 15 mS cm-1). The uptake of safranin through the pedicel was used to locate the lignified xylem tissue in the bundles. Pericarp and placenta were supplied by separated vascular networks. Both the number and the density of vascular bundles (per cross sectional area of fruit tissue) were higher in pericarp than in placenta. The number of bundles decreased from the proximal (pedicel) half to the distal (blossom-end) half of the fruit, more so in the placenta than in the pericarp. The average density of bundles decreased from 1.7 and 0.6 bundles mm-2 in pericarp and placenta, respectively, to less than 0.1 bundles mm-2 during fruit expansion from d14 to d31. The average density of bundles in layer 5 of the placenta was 2.5 times lower than that of the pericarp throughout fruit development. Salinity reduced the number of both total and stained bundles especially in the distal layer of the placenta. Therefore, xylem tissue development in the distal fruit tissue was substantially retarded at high salinity and this may be the anatomical basis for the initial Ca deficiency symptom of blossom-end rot in the distal placenta.