Hormonal Balance in Bark and Leaves of Shamouti Orange Trees (Citrus Sinensis (L.) Osbeck) in Relation to Ringing

Seasonal changes in native auxins, gibberellins and inhibitors in leaves and bark of Shamouti orange trees were studied. In December and February some auxin activity was found in the pH 6.0 ether fraction of leaves. Gibberellins were found mostly in the pH 7.0 water residue, with a peak in December. Large amounts of abscisic acid-like inhibitors were found in the pH 6.0 ether fraction of leaves, and the pH 7.0 water residue contained other inhibitors. Auxin activity in the bark was higher than in leaves, and the amount of inhibiting substances detected in the bark was much lower. Auxins were found in both fractions, whereas gibberellins were found in the pH 7.0 water residue as well as in the pH 3.0 ether fraction.

Ringing the trunks of trees in March promoted the accumulation of growth regulators in the bark near the ring and in the leaves. The main effect of ringing in August was an accumulation of acidic gibberellins above the ring during the first three weeks after ringing.