Long Distance Transport of Abscisic Acid in NaCI-Treated Intact Plants ofLupinus albus

Abstract

Plants of Lupinus albus were grown for 51 d under control (M mol m-3 NaCl) and saline (40 mol m-3 NaCl) conditions. Plants were harvested and changes of carbon, nitrogen and abscisic acid (ABA) contents of individual organs were determined 41 d and 51 d after germination. In the period between the two harvests xylem and phloem saps were collected and respiration and photosynthesis of individual organs were measured. Using flows of carbon, C/ABA ratios and increments of ABA flows of ABA in phloem and xylem and rates of biosynthesis and degradation of ABA were calculated. Both under control and saline conditions net biosynthesis occurred in the root, the basal strata of leaves and in the inflorescence. Metabolic degradation of ABA took place in the stem internodes and apical leaf strata. Salt stress increased xylem transport of ABA up to 10-fold and phloem transport to the root up to 5-fold relative to that of the controls. A considerable amount of ABA in the xylem sap originated from biosynthesis in the roots, i.e. 55% in salt-treated and smaller than 28% in control plants. The remaining part of ABA in the xylem sap originated from the shoot: it was translocated in the phloem from fully differentiated leaves towards the root and from there it was recirculated back to the aerial parts of the plant. The data suggest that ABA may serve as a hormonal stress signal from the root system.