Developmental changes in tomato fruit composition in response to water deficit and salinity

Processing tomato ( Lycopersicon esculentum Mill. cv. UC82B) plants were subjected to moderate levels of water deficit and salinity (Na₂SO₄/CaCl₂) in sand culture. Fruit water content and the relative contributions of organic and inorganic constituents to fruit solute potential (_Ψ) and soluble solids content were determined throughout development. Fruit _Ψ averaged –0.63, –0.86 and –0.77 MPa in the control, salinity and water deficit plants, respectively. Reduced net water import and maintenance of solute accumulation, irrespective of water import, accounted for the reductions in _Ψ of stressed fruits. Mineral ions (Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻ and SO^2-₄) contributed –0.31 MPa to _Ψ in salinized fruit, compared with –0.19 MPa in control and water deficit treatments. Changes in net carbon accumulation were not observed among treatments, despite considerable differences in fruit K⁺ status. Starch accumulation in immature fruit was increased and hexose accumulation was decreased by both salinity and water deficit. Maximum starch levels were negatively correlated with total fruit _Ψ, but were independent of fruit K⁺. Organic acid levels were generally higher throughout development in salinized plants, relative to control plants, and correlated with increased inorganic cation rather than anion accumulation in these fruits.