Effect of water stress on transport of [2-C]abscisic acid in intact plants ofPhaseolus coccineus L.

Eight- to 10-day-old plants ofPhaseolus coccineus, which grow on vermiculite with a water content of 12-17% of the water-holding capacity, stop growing completely, whereas water potential and relative water content are almost unaffected. [2-C]Abscisic acid, which is applied to the midrib of a primary leaf, is transported especially to the roots and the apical bud, but not to the second primary leaf and the cotyledons. Water-stressed plants, however, export only negligible amounts of ABA from the donor leaf to the plant. Thus an accumulation of ABA occurs in the donor leaf. Consequently water stress can increase ABA concentration in leaves not only by stimulating ABA synthesis but also by inhibiting ABA transport. Recovery of growth and ABA transport after reirrigation is very weak. Water stress has no effect on ABA metabolism in bean plants.