Comparison of cytokinin activities of 9-substituted N6-benzyladenines in the Cucumis and Amaranthus bioassays

9-Substituted N⁶-benzyladenines were tested for their ability to eliminate the lag phase in and promote chlorophyll synthesis in Cucumis sativus cotyledons and for their effectiveness in eliciting the dark biosynthesis of betacyanin in Amaranthus tricolor cotyledon-hypocotyl explants. The following general relationships were established for dose-responses: (a) 9-ribosidation brought about little (in Amaranthus) or no (in Cucumis) decrease in activity relative to the free base, (b) the presence of a 9-ribose 5′-phosphate group moderately depressed activity in Amaranthus but slightly enhanced activity in Cucumis, (c) the presence of a 9-ribose 3′,5′- cyclic phosphate group depressed activity substantially in both systems, more so in Amaranthus, (d) 9-glucosylation greatly decreased activity, as did 7-glucosylation, while 3-glucosylation depressed activity to a much lesser extent, in both systems, (e) 9-substitution with cyclopentyl, methyl, methoxymethyl, and tetrahydropyranyl groups reduced activity, the first two substituents more so than the last two, and (f) alteration of the 9-riboside group to a 9-[2-O-β-hydroxyethylglycerol] moiety by oxidation- reduction led to complete (in Amaranthus) or nearly complete (in Cucumis) inactivation. Responses to hormone treatment were detectable after dark incubation times as short as 4 hr (in Cucumis) or 8 hr (in Amaranthus).