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Abstract. Seven monoclonal anti-zeatin riboside antibodies were characterized by radioimmunoassay (RIA) and found to measure femtomole (10-15 M) quantities (-20 pg) of this cytokinin. The antibodies had different measuring ranges defined by the linear portion of the logit/log plots; slopes and intercepts of the line varied considerably between the antibodies. Competitive binding trials against cis-zeatin riboside (cZR), dihydrozeatin riboside (diHZR), zeatin (Z), and isopentenyl adenosine (iPA) showed differences among the seven antibodies in their cross-reactivities towards these structurally related cytokinins. It was possible to combine selected antibodies to provide a mixture with a predictable measuring range and cross-reactivity; the ability to prepare a highly specific reagent in this manner with well-defined reactivity was noted and differences between monoclonal antibody and polyclonal antiserum probes for measurement of cytokinins were discussed.Cytokinins play important roles in many plant physiological processes including the regulation of growth and development. Plant hormone research has been hindered by the lack of specific and sensitive methods for qualitative and quantitative assays, in part because cytokinins and other growth regulators

Abstract— Action spectra for light induced sporulation were determined for conidia of Alternaria dauci, and conidia and perithecia of Pleospora herbarum (Imperfect stage is Stemphylium botryosum). Only radiation less than 370 mμ induced formation of conidia, and less than 390 mμ formation of perithecia. The action spectra showed increased effectiveness in the 230 and 290 mμ regions, and possibly in the 260–270 mμ regions. Below 280 mμ these action spectra may not be representative of the “true” absorption spectra of the photoreceptors involved because of possible superimposed effects caused by nucleic acid absorption. Though the action spectra were not identical, the number of characters in common were suggestive of a similar photoreceptor. Similarities between action spectra for sexual and asexual reproduction of P. herbarum indicate the possibility of a single photoreceptor for both processes.