Calcium partitioning and allocation and blossom-end rot development in tomato plants in response to whole-plant and fruit-specific abscisic acid treatments

The mechanisms regulating Ca-2 partitioning and allocation in plants and fruit remain poorly understood. The objectives of this study were to determine Ca-2 partitioning and allocation in tomato plants and fruit in response to whole-plant and fruit-specific abscisic acid (ABA) treatments, as well as to analyse the effect of changes in Ca-2 partitioning and allocation on fruit susceptibility to the Ca-2 deficiency disorder blossom-end rot (BER) under water stress conditions. Tomato plants of the cultivar Ace 55 (Vf) were grown in a greenhouse and exposed to low Ca-2 conditions during fruit growth and development. Starting 1 day after pollination (DAP), the following treatments were initiated: (i) whole plants were sprayed weekly with deionized water (control) or (ii) with 500mg l(1) ABA; or fruit on each plant were dipped weekly (iii) in deionized water (control) or (iv) in 500mg l(1) ABA. At 15 DAP, BER was completely prevented by whole-plant or fruit-specific ABA treatments, whereas plants or fruit treated with water had 1619% BER incidence. At 30 DAP, BER was prevented by the whole-plant ABA treatment, whereas fruit dipped in ABA had a 16% and water-treated plants or fruit had a 3640% incidence of BER. The results showed that spraying the whole plant with ABA increases xylem sap flow and Ca-2 movement into the fruit, resulting in higher fruit tissue and water-soluble apoplastic Ca-2 concentrations that prevent BER development. Although fruit-specific ABA treatment had no effect on xylem sap flow rates or Ca-2 movement into the fruit, it increased fruit tissue water-soluble apoplastic Ca-2 concentrations and reduced fruit susceptibility to BER to a lesser extent.