The effects of exogenously applied plant growth substances on the physiological plasticity in Plantago major ssp. pleiosperma: Responses of growth, shoot to root ratio and respiration

Growth rates, shoot to root ratios and root respiration were studied in plants of Plantago major L. ssp. pleiosperma (Pilger) at two regimes of mineral nutrition. The responses of plants transferred from one condition to the other were compared with similarly transferred plants supplied with a plant growth substance and also with plants permanently grown at the same nutritional level. The effect of an addition of benzyladenine (BA) depended on the concentration. Changes in the relative growth rates, shoot to root ratios and root respiration as a response to a lowered mineral supply were strongly retarded by 10−8M BA. These effects of BA were very obvious in the first period of 7 days after the transfer of the plants. During the second period of 7 days the hormonal effects disappeared due to limitation of mineral nutrients. Daily spray with abscisic acid or with indoleacetic acid did not significantly affect the measured characteristics. The results from the experiments with BA addition are discussed in relation to a possible regulatory role of cytokinins in physiological plasticity upon mineral nutrition.