Factors Affecting Penetration of 1-aminocyclopropane-1-carboxylic Acid (ACC) into Apple Fruit and Leaves

Abstract For plant growth regulators, uptake and physiological performance must be consistent and predictable. The objectives were to establish the uptake behavior of 14 C labeled 1-aminocyclopropane-[1- 14 C]carboxylic acid (ACC) into leaves and fruit of apple from simulated spray droplets (1 µl). Uptake into leaves and fruit increased with time. Uptake through the abaxial leaf surface exceeded fruit uptake two-fold, and adaxial leaf uptake seven-fold. Abaxial leaf and fruit uptakes were log-normally distributed. Uptake into fruit increased up to 17% of the applied dose at 32 days after full bloom, but declined thereafter. Along a shoot, uptake increased continuously from the tip to the tenth leaf. Higher ACC concentrations increased the amount of ACC taken up into leaves but not into fruit. The pH of the solution had no effect. Adding salts having a deliquescence point up to 75%, such as CaCl 2 , enhanced ACC uptake. Tween 20 increased ACC uptake by fruit 9-fold, into young leaves 6-fold and old leaves 2-fold. Uptake of 14 C-ACC into fruit was higher from commercial formulations than from technical grade ACC. Temperature had no effect on ACC uptake, but higher humidity increased uptake. Penetration of 14 C-ACC through isolated cuticles of apple fruit was equally low. Increasing the humidity above the droplet residue increased penetration, particularly when droplets were applied on to lenticels. Removal of cuticular wax increased ACC penetration. Our data demonstrate that the mobility of ACC in the droplet deposit limits uptake and that deposit hydration may overcome this limitation.