UPTAKE OF C-14 GIBBERELLIC-ACID BY MATURE GRAPEFRUIT (CITRUS-PARADISI MACF) AS AFFECTED BY RELATIVE-HUMIDITY AND METHOD OF APPLICATION

Effects of the method of application and relative humidity on the uptake of 14C‐gibberellic acid (14C‐GA3) by mature grapefruit (Citrus paradisi Macf.) were examined. Uptake was higher when 14C‐GA3 was applied as a ‘drying‐out’ solution than as a ‘non‐drying’ solution. When 14C‐GA, was applied by the ‘drying‐out’ method, which closely imitates field conditions, rates of uptake were very high while the solution was drying out and during the first few hours after drying. Uptake from the dry residue continued in decreasing rates till the end of the experiment (72 h). Uptake from the dry residue was higher when fruits were incubated at 100% than at 50% relative humidity (RH). Transfer of fruits from 50% to 100% RH as late as 48 h after drying still increased the rate of uptake. Drying‐out treatment solutions produced higher uptake rates with neutral (pH 7) as well as acid (pH 4) treatment solutions, and in the presence of triton B‐1956, Triton X‐100 or L‐77 surfactants. Copyright © 1990, Wiley Blackwell. All rights reserved