Biotrophic fungal interaction with host plants involve alterations in host metabolism in favour of the fungus, characteristic of perturbations in the levels of plant growth regulators. Pyrenopeziza brassicae mycelia, culture filtrate and spore extracts contained zeatin riboside and iso-pentenyladenisine-type cytokinins as determined using HPLC-ELISA. The significance of cytokinin synthesis by P. brassicae in relation to infection of host plant tissue is discussed.

It was our aim to investigate whether the cytokinin status of Norway spruce seedlings (Picea abies L. Karst.) was changed when the plants were grown under nutritive stress. Cytokinins in shoots and roots from spruce seedlings, grown in various hydrocultural media with complete (control) or poor nutrient supply (stress), were determined by an indirect competitive enzyme-liked immunosorbent assay. The shoots of spruce seedlings grown in a poor acidic culture medium, to which aluminium ions (AlCl3, 0.8 mM) were added, showed up to 5-fold higher concentrations of zeatin riboside and isopentenyladenosine (iPa). When adding naphtylacetic acid to the nutrient medium also higher levels of cytokinin ribosides were measured in the shoots. In the roots however cytokinin riboside levels did not increase significantly under Al- or auxin treatment. Feeding experiments using tritiated iPA have shown that the metabolism of this cytokinin is strongly retarded in the roots of stressed seedlings. The experiments show that acid conditions and nutrient shortage together with aluminium ions in the rhizosphere increase the number of lateral roots in Norway spruce seedlings. It is assumed that the increased number of sites of cytokinin biosynthesis and the reduced metabolism of iPA result in the higher content of cytokinin ribosides in the shoots of seedlings.

Work was carried out to investigate the effect of pollution on the needle cytokinin content of mature Picea abies (L.) Karst individuals. Needles were collected from trees growing at two sites, one polluted and relatively non-polluted, in central Slovenia. After ethanolic extraction and purification, the needle cytokinin extracts were separed by reverse-phase HPLC. Cytokinin content was analysed using four direct ELISA techniques specific for Z-, DHZ- and iP-type cytokinins and the O-glucoside conjugate of Z. Results showed a trend towards the accumulation of cytokinins in needles from trees subject to high levels of atmospheric pollution, particulary with respect to ribotide derivatives. No difference was found in the (OG)Z content between polluted and non-polluted samples. The results are discussed with respect to the origins of the observed accumulation.

Cytokinins were analysed by a combined HPLC-ELISA method in needles of Norway spruce seedlings. The seedlings were grown in vitro on sterile or nonsterile soil substrates from two differently polluted forest research plots. Difference were predominantly found in the isopentenyladenine-type of cytokinins. These were elevated in seedlings, grown on polluted soils in comparison to those, grown on soils from the unpolluted plot. A possible explanation might be in the change of the metabolism in the roots due to pollution stress (when grown on sterilized substrates) or in change of the mycorrhizosphere organisms (when grown on nonsterile soil substrates). The model system using Norway spruce seedlings as tester organisms for soil pollution is discussed.