RELATIONS BETWEEN CYTOKININ LEVEL, BUD DEVELOPMENT AND APICAL CONTROLIN NORWAY SPRUCE, PICEA-ABIES

In conifers such as Norway spruce, the extent of shoot growth is prede termined by the size and number of embryonal organs of the buds laid d own the previous year. As it is known that cytokinins have a key role in bud development a possible hypothesis is that the level of cytokini n in the buds during their formation determines their size and complex ity. As a first step to test this hypothesis we compared cytokinin lev els in buds of different size of annual shoots from 15- to 20-year-old trees of Picea abies (L.) Karst. Apical buds from the leaders, and fr om branches in lower parts of the trees, were collected in April, July and August. The difference in size of the buds and the shoots growing from them was considerable in these three positions. Extracts were pu rified by immunoaffinity columns, and the retained compounds were sepa rated by high-performance liquid chromatography (HPLC). Quantification was made by enzyme-linked immunosorbent assay (ELISA), and the accura cy of this method was checked by measurements with liquid chromatograp hy-mass spectrometry (LC-MS) and UV absorption. Zeatin riboside (ZR) w as the most abundant cytokinin, but isopentenyladenosine (iPA) was als o present in all samples. The large apical bud of the leader contained much higher cytokinin concentrations than the considerably smaller bu ds from lower positions, and during the period of secondary growth in July, similar relationships were found for annual stem tissue from dif ferent positions. The possible role of ZR as a controlling factor in b ud development and apical control is discussed. Our conclusion is that the level of zeatin-type cytokinins appears to play an important role in the establishment of differences in bud size and, thereby, the arc hitecture of the tree crown.