STUDIES ON OCTYLPHENOXY SURFACTANTS .9. EFFECT OF OXYETHYLENE CHAIN-LENGTH ON GA3 ABSORPTION BY SOUR CHERRY LEAVES

The effect of a homologous series of octylphenoxy surfactants, alpha-[4-(1,1,3,3-tetramethylbutyl)phenyl]-omega-hydroxypoly-(oxy-1,2-ethanediyl), condensed with 5, 7-8, 9-10, 16, and 30 oxyethylene (EO) units on enhancement of gibberellic acid (GA3) absorption by leaves of Prunus cerasus cv. Montmorency was studied. Increasing EO chain length (5-30 EO) increased surface tension (27.5-35.3 mN m-1) and contact angles on adaxial (21-36-degrees) and abaxial (28-49-degrees) leaf surfaces. With increasing EO content, the form of GA3 deposits from droplets on the leaf surface changed from an annulus shape (5 and 7-8 EO) to globular forms covering increasingly smaller interface areas (9-10 to 30 EO). The surfactants increased GA3 uptake, the magnitude decreased with an increase in oxyethylene chain length. Similar trends were found for both the adaxial and abaxial surfaces. Penetration through the abaxial surface was linearly related to the logarithm of the oxyethylene content of the surfactant molecule (r2 = 0.934**) and to the hydrophilic:lipophilic balance (r2 = 0.926**). Absorption by the abaxial surface was approximately one order of magnitude greater than by the adaxial surface.