Effects of Abscisic Acid Application to Roots on Water and Ion Uptake and Leaf Conductance of Soybean PDF

Keywords

Abscisic acid, roots, leaves, water

Abstract

Reported effects of applied abscisic acid (ABA) on water and ion uptake rates of excised leaves and roots are many and contradictory. Seedlings (8 d) of soybean (Glycine max (L.) Meer. cv Bragg) were trimmed to three uniform root branches and grown in nutrient solution. Seedlings (18 d) were transferred to a continuously aerated circulating nutrient solutions in 3 glass tubes mounted together. An automatic system was used to monitor water and ion uptake at 10 min intervals. Concentrations of ABA from 10^-5 to 5 x 10^-4 M were applied to one root division. The other two divisions were used as controls. Water uptake was enhanced by 10^-4 to 5 x 10^-4 M ABA in the treated root portion for a short time and then reduced throughout the treatment. WHen ABA was replaced with nutrient medium, treated roots began to recover slowly. Complete recovery required more than 24 h. Water uptake of untreated roots was reduced less than treated roots and returned more rapidly to normal water uptake. Reductions of water uptake rates were less during applications of 3.16 x 10^-5 and 10^-5 M ABA. Ion uptake rates were reduced in treated root portions were not affected. Patterns of nutrient uptake reduction were unrelated to ABA concentration. ABA applied to roots reduced stomatal aperture as evidenced by consistent reductions in leaf conductance and in total water uptake