Temperature and Temperature Preconditioning on Flux and Chemical Composition of Xylem Exudate from Muscadine Grapevines

Abstract

Abstract Volume flux (Jv), solute flux (Js), and the chemical profile of xylem exudate from cut shoots of ‘Noble’ and ‘Welder’ muscadine grapevines [Vitis rotundifolia (Michx.)] were analyzed as a function of temperature and temperature preconditioning. The effects of short-term (i.e., 2-hr) temperature changes on Jv, xylem fluid osmotic potential (Ψs) and Js from bleeding ‘Noble’ grapevines were determined. The effects of 10 days of preconditioning temperature (4 to 8C or 22 to 28C) on ‘Noble’ and ‘Welder’ were monitored at 25C in relation to Jv, Ψs, Js and inorganic element, amino acid, organic acid, and sugar composition of xylem fluid. Short-term temperature changes induced marked increases in Jv (Q10 = 2.0) and Js but little alteration in Ψs. Temperature-preconditioning effects were cultivar-dependent. Js was enhanced ≈2-fold for both cultivars when preconditioned at 22 to 28C. The stimulation in Js of ‘Noble’ was a result of increased solute concentration (reduced Ψs); increased Js of ‘Welder’ was associated with increased Jv. We propose that the increase in Js with a concomitant increase in Jv of ‘Welder’ was due to a change in hydraulic conductance. Conversely, the increase in Js of ‘Noble’ was due to an increased solute concentration in cells surrounding the xylem vessels and/or to changes in membrane permeability to solutes. Temperature preconditioning had a substantial effect on inorganic ion, amino acid, organic acid, and sugar profile in xylem exudate of ‘Noble’, yet the chemical profile of ‘Welder’ was not altered. The physiological basis for this cultivar-dependent preconditioning response is discussed.