HISTOLOGICAL AND CHEMICAL COMPARISON OF TRITERPENE AND PHENOLIC DETERRENT CONTENTS OF JUVENILE SHOOTS OF BETULA SPECIES

Defence-related epithelial structures of juvenile stems and their phyt ochemistry were compared between six woody species of Betula from diff erent geographical areas. The shoots of B. pendula, B. papyrifera, B. platypylla and B. ermanii are covered by resin droplets secreted by mu lticellular peltate glands. The seedlings of B. papyrifera and B. pube scens are covered with long epithelial hairs. Closer topical examinati on also revealed smaller glands on B. papyrifera and B. pubescens. The glands of B. ermanii are oval while the other species have a round sh ape. Phenol-specific histochemical staining indicated phenolic compoun ds in the cells in active glands of the resinous birches, but not in t hose of the pubescent birches. The epithelial hairs were strongly posi tive to the phenol stain. Analysis of the triterpenoids (3alpha- and 3 beta-papyriferic acid and pendulic acid) and a phenolic (platyphyllosi de) deterrent indicated that the morphological differences are accompa nied by chemical ones. Pendulic acid was the main triterpene in B. erm anii instead of the 3alpha-papyriferic acid of the other resinous spec ies. Concentrations of the triterpenes ranged from about 0.3 to 12 mg/ g, while the platyphylloside level was around 0.5 mg/g in all of them. Some triterpenes were also detected in B. papyrifera, but none in B. pubescens. The former contained only about 0.05 mg/g of platyphyllosid e, but B. pubescens contained 4 mg/g of this compound.