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

Sergio Tonetto De Freitas,Elizabeth J Mitcham,Andrew J Mcelrone,Kenneth A Shackel

doi:10.1093/jxb/ert364

Sergio Tonetto De Freitas, Elizabeth J Mitcham + Show 2 more

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https://doi.org/10.1093/jxb/ert364

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Abstract

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 16-19% 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 36-40% 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.

Highlights

Calcium (Ca2+) is an essential plant nutrient required for proper plasma membrane function, in storage organelles to counterbalance anionic charges, in the cytosol for cellular signalling responses, and in the apoplast for cell wall structure (White and Broadley, 2003; Taylor and Locascio, 2004; Ho and White, 2005)
Stem water potential (SWP) was less negative in response to whole-plant abscisic acid (ABA) treatment at 15 and 30 day after pollination (DAP) compared with all other treatments (Fig. 2)
Leaf stomatal conductance progressively increased from the base, middle, to the top regions of the plant, and was lower in the whole-plant ABA treatment at 15 and 30 DAP compared with all other treatments (Fig. 3)

Summary

Introduction

Calcium (Ca2+) is an essential plant nutrient required for proper plasma membrane function, in storage organelles to counterbalance anionic charges, in the cytosol for cellular signalling responses, and in the apoplast for cell wall structure (White and Broadley, 2003; Taylor and Locascio, 2004; Ho and White, 2005). Ca2+ deficiency disorders in fruit have been attributed to lower total tissue Ca2+ content, as well as abnormal regulation of cellular Ca2+ partitioning and distribution (Ho and White, 2005; Park et al, 2005; De Freitas et al, 2011a). Consistent with xylem sap flow, the direction and rate of xylemic Ca2+ flow in the plant should be determined by water potential gradients in response to different tissue transpiration and growth rates (Taylor and Locascio, 2004; Ho and White, 2005). The partitioning of Ca2+ flowing from the roots toward leaves and fruit will depend on the xylem sap Ca2+ concentration, as well as leaf and fruit transpiration and growth rates. Leaves have much higher transpiration rates than fruit, which results in much higher Ca2+ content in the leaves than in the fruit (Ho, 1989; Ho and White, 2005; De Freitas et al, 2011b)

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