Structure-activity-relationships of Zeatin Cytokinins Produced By Plant Pathogenic Pseudomonades

The naturally occurring new cytokinin 1'-methylzeatin (1'MeZ) with its 9-beta-D-riboside (1''MeZR) and 2'-deoxyzeatin riboside (2'deOZR), as well as their derivatives obtained by chemical or enzymatic modification, were analysed for their ability to stimulate the synthesis of chlorophyll in etiolated cucumber cotyledons. In contrast to 2' deOZR, which showed a very low cytokinin activity, 1'MeZ and 1''MeZR displayed a higher stimulating potency of chlorophyll synthesis when compared to zeatin and zeatin riboside, respectively. With regard to the synthetic analogues, any modification of the carbon skeleton of the side chain proved to influence the activity. In particular, the reduction of the trans-double bond in 1'MeZ and its 9-beta-D-riboside produces two diastereomeric dihydro derivatives, which show respectively a reduction and the complete loss of activity probably due to the stereochemistry of the new chiral carbon (C-3 of side chain). Deoxygenation at C-4 of the side chain in the two dihydro derivatives of 1'MeZ and 1''MeZR, respectively, gives rise to two inactive compounds. The acylation of the hydroxy group (at C-4) of the side chain as well as the acetylation of the hydroxy groups of the ribose moiety did not significantly affect the biological activity.