Acidifying Agents, Uptake, and Physiological Activity of Gibberellin A3 in Citrus

Abstract

Acidification of treatment solutions from pH 7 to 4, with either citrate-phosphate (CP) buffer or with dimethylglutaric acid–NaOH (DMG) buffer, increased [ 14 C]GA 3 uptake by ‘Marsh’ grapefruit ( Citrus paradisi Macf.) peel. Acidification was effective also when wax was removed with organic solvents and under low and high relative humidity. The GA 3 -induced delay of coloration of ‘Minneola’ ( Citrus paradisi × C. reticulata Blanco) tangelo and ‘Ortanique’ ( C. sinensis × C. reticulata) was increased similarly by acidification with either buffer. Acidification with either buffer permitted the use of lower GA 3 concentrations than those required to obtain the same physiological effect with neutral solutions. Acidification also delayed fruit senescence in field trials with ‘Clementine’ ( Citrus reticulata Blanco) tangerines sprayed with 5 ppm GA 3 + 0.1% H 3 PO 4 . Uptake of [ 14 C]GA 3 progressively increased by reducing pH from 7 to 3. With [ 3 H]GA 4 , acidification improved the uptake only in the range of pH 8 to 5. This difference seems to be related to the more lipophilic nature of GA 4 .