Gibberellin-like activity in shoots of Salix pentandra as related to the elongation growth

Abstract

Activities of acidic gibberellin(GA)-like substances in shoots of Salix pentandra trees growing under natural conditions (69°39′ N, 18°37′ E) were studied in relation to shoot elongation and tip abscission. Bioassay after separation on SiO2 partition columns was accomplished with the lettuce hypocotyl and dwarf rice 'Tan-ginbozu' assays. The GA-like activity in the apical part of the shoot greatly decreased before cessation of growth and shoot tip abscission. In the basal part of the shoot the marked reduction of GA-like substances occurred well before shoot tip abscission and even before shoot elongation had ceased. Low GA-like activity in the shoot may be a prerequisite for apical growth cessation and for the development of lateral flower buds.