Translocation of Calcium in Relation to Tomato Fruit Growth

Regulation of the uptake and distribution of calcium in the tomato plant was investigated in plants grown in recirculating nutrient solutions at electrical conductivities of 2,7,12 and 17 millisiemens (mS). Despite an increased calcium content in the nutrient solution at high conductivity (7–17 mS), the accumulation of calcium by fruit was progressively reduced by increasing salinity, particularly in the distal half. The incidence of blossom-end rot in fruit (BER) also increased with salinity. The uptake of water and 45Ca by plants was substantially reduced in the high salinity treatment (17 mS) and, to a lesser extent, by high relative humidity (90 per cent r.h. at 20 °C). Further, the translocation of 45Ca from roots to shoots was reduced by high salinity, while the percentage distribution of 45Ca to the apex was reduced by high humidity. Only approx. 2 per cent of the 45Ca taken up by a plant was imported by the truss. The uptake of 45Ca and its distribution among pedicel, calyx and berry by detached fruit in 24 h showed that fruit from high salinity plants had a reduced uptake and a lower accumulation of 45 Ca in the berry than in the calyx. In addition, plants grown at high conductivity had a lower rate of xylem sap exudation from decapitated plants. The fruit of these plants had a smaller xylem cross-sectional area in the fruit pedicel and a smaller calyx than those of the low conductivity treatment.