Cytokinin concentration in relation to mineral nutrition and benzyladenine treatment in Plantago major ssp. pleiosperma

Cytokinins in shoot and root tissue were studied in plants of Plantago major L. ssp. pleiosperma (Pilger) grown on a concentrated and on a dilute nutrient solution. Cytokinins of plants transferred from the concentrated to the dilute solution were compared with plants treated similarly but with 10⁻⁸M benzyladenine (BA) added to the dilute solution. Cytokinin concentrations were also measured in plants that had been grown throughout on one of the two nutrient solutions. A restricted supply of minerals was correlated with low cytokinin concentrations. Transfer from a concentrated nutrient solution to a dilute solution depressed the cytokinin concentration by 50% within two days of transfer. This decline did not appear if similar plants were supplied with 10⁻⁸M BA in the dilute solution. The glucosides were the only major cytokinins enhanced by mineral shortage. This effect of low mineral supply was retarded but not entirely prevented by exogenous BA. The increased synthesis of glucosides in the BA‐treated plants was accompanied by lowered concentrations of free bases and their ribosides and of nucleotides. The sum of cytokinins in BA‐treated plants was thus similar to that in plants grown at the high mineral level. The results are discussed in relation to a possible role of cytokinins in regulating growth responses to changes in mineral nutrition.