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Changes in Cytokinins and Gibberellin-Like Substances in Pinus radiata Buds during Lateral Shoot Initiation and the Characterization of Ribosyl Zeatin and a Novel Ribosyl Zeatin Glycoside ¹

Department of Biology, The University of Calgary, Calgary, Alberta, Canada T2N 1N4, Forest Research Institute, Private Bag, Rotorua, New Zealand

Based on detection and quantitation by bioassay, endogenous gibberellin-like substances (GAs) and cytokinins (CKs) in Pinus radiata D. Don buds during sequential shoot initiation shift from less polar to more polar forms (GAs) and from conjugated to free forms (CKs). As the terminal bud moves from the production of "short shoots" (needle fascicles) to "long shoots" (lateral branches or female conebuds), a more polar GA appears while a glucoside-conjugate of zeatin riboside is reduced, and zeatin riboside levels increase markedly.

Permethyl derivatives of the two highly active CK fractions were examined by capillary gas chromatography-mass spectrometry after separation by C₁₈ reverse phase high performance liquid chromatography. The mass spectra indicated the presence of: 9--D-ribofuranosyl-6-(4-hydroxy-3-methyl-but-2-enylamino)purine (zeatin riboside) and 9-[hexosyl(probably glucosyl)--D-ribofuranosyl]-6-(4-hydroxy-3-methyl-but-2- enylamino)purine (a glycoside of zeatin riboside in which the glycosyl moiety is attached directly to the ribosyl moiety at an unknown position).