The development of xylem within the tomato and its influence on the movement of water and calcium into the fruit

Hudak, Kathi A. (1990) The development of xylem within the tomato and its influence on the movement of water and calcium into the fruit. Masters thesis, Memorial University of Newfoundland.

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Abstract

Functional associations of xylem vascularization, calcium transport, and water flux were studied in Lycopersicon esculentum Mill. "Tiny Tim". Xylem formation of the pedicel and fruit was traced from the emergence of the floral primordia through to the development of mature fruit. Berberine hemi-sulphate, an apoplastically mobile dye, was used to follow water movements through the xylem systems of intact stems and trusses. ⁴⁵Ca was used to identify areas of calcium localization within the plant and correlated with transpiration rates measured for the selected plant parts. -- Water flow and calcium distribution in the plant were not uniform and the pattern was dependent on the extent of xylem vascularization. Leaves, sepals, and the smallest immature fruit (<30 mm³), which were all well supplied with xylem, showed the greatest accumulations of calcium. Fruit in this class also showed the highest transpiration rates. In contrast, calcium concentration was lowest in mature fruit, which also had the lowest proportion of xylem vascularization and lowest transpiration rates. -- These findings bear on the mechanism of induction of blossom end rot, a phytopathological condition regarded as a calcium-deficiency disease of tomatoes. The suggestion that the deficiency might first occur in very small fruit as a result of their early, rapid increase in volume is not supported by the present data which demonstrate that such fruit, due to high water flux and transpiration rate, accumulate large amounts of calcium. The distal portion of larger fruit may become calcium deficient because apoplastic water does not reach the far blossom end of these fruit.

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