Endogenous Growth Regulators in Tracheal Sap of Citrus

Abstract

Tracheal sap was extracted from stem and root segments of ‘Troyer’ ( Poncirus trifoliata × Citrus sinensis ), ‘Volkamer’ lemon ( C. volkameriana ), and sour orange ( C. aurantium L.). Thirty to 100 μl of sap were used for determination of amino acids, cytokinins, and gibberellins. Proline, γ-aminobutyric and aspartic acid, arginine, and serine were the main (90–94%) amino acids found in sap of ‘Troyer’ and ‘Volkameriana’. Cytokinin-like activity was higher in orange ( C. sinensis Osb.) trees on ‘Volkamer’ lemon than on ‘Troyer’ rootstock. Gibberellin activity in alternate-bearing ‘Wilking’ [‘King’ × ‘Willowleaf’ ( C. reticulata Blanco × C. sinensis ) × C. reticulata ] sap was higher in fruiting shoots late in the on-year than in nonfruiting shoots late in the off-year.