Role of dehydrodiconiferyl alcohol glucosides in cytokinin-induced plant cell division

Cytokinins are a group of plant hormones which are essential for the division of cultured plant cells. They have a wide range of biological activities, but the biochemical bases for their control of cell division are not known and little is known about the potential signal transduction pathways that are utilized. In the late 1960s, a fraction was isolated from crown gall tumor cells of Vinca rosea which could substitute for cytokinins in plant cell culture systems. The structure of the compounds responsible for this activity were identified recently as six different isomers of dehydrodiconiferyl alcohol glucosides (DCGs). The biologically active isomers A and B were chemically synthesized and their biological activities examined. In cell division assays, the synthetic DCGs mimicked the plant-derived isomers, stimulating dose-dependent growth of tobacco leaf callus at concentrations ranging from 10 $\mu$M through the highest concentrations tested. The synthetic DCGs directly induced cell division of tobacco leaf callus. The DCGs were tested for their activity in other cytokinin bioassays, but were unable to induce shoot organogenesis of tobacco leaf explants nor stimulate betacyanin production in amaranth seedlings, even at concentrations up to 100 $\mu$M. Therefore, the DCGs seemed only to be able to replace the cytokinins in inducing cell division. To determine whether the DCGs have a role in endogenous cell division, DCG A + B levels were measured during cytokinin-induced growth of tobacco pith tissue. It was found that the cells began to divide after 3 to 4 days of cytokinin treatment, which is the same time the DCGs A + B began to accumulate. A block to DCG biosynthesis also correlated with an inhibition of growth suggesting that the DCGs are required for cell division to occur. Taking the pattern of DCG accumulation together with the fact that DCGs A/B can stimulate cell division when applied exogenously to cultured plant cells, it is possible to propose that the DCGs are one signal in the pathway of cytokinin-induced cell division