[Combined effect of zeatin and hydrogen peroxide on growth of rape and tomato germs as applied to the conditions of biological life support systems].

Cytokine-regulated growth of germs' roots and hypocotyls was investigated on a background of modeled oxidative outbreak caused by the stress from exogenous hydrogen peroxide. Germs of rape (1-d old) and tomato (56-d old) in Petri dishes with solutions containing substances under study were subjected to 24-48 hour incubation in the dark. Exogenous zeatin inhibited growth; in different tests treatment with H2O2 brought about both acceleration and inhibition of root and hypocotyl growth. The combined use of two substances deformed concentration curves. Hydrogen peroxide concentration of 100 microM without cytokines inhibited growth of tomato root significantly, whereas application of 0.003-0.01 and 0.9 microM of zeatin intensified root growth. The series of zeatin concentration-effect curves obtained for rape roots and hypocotyls with gradually increasing H2O2 concentration included the inhibition curve (w/o H2O2), curve with predominant growth stimulation and reliable maximum (1 microM of H2O2), intermediate shape curves (0.3 and 3.3-10 microM). Hence, biological life support systems should be designed with consideration for variability of effects of physiologically active substances under conditions of stress.

[Polyphase character of the dependence of Brassica napus germ root and hypocotyl growth on zeatin and thidiazuron concentrations with view of applicability to biological life support systems].

Physiologically active substances are considered as a potential component of plant cultivation technologies for biological life support systems. In spacelight, plant reactions to growth-regulating agents may be changed by the specific stress factors such as microgravity, radiation, and trace admixtures in cabin air. Complex character of the concentration dependence of PAS efficiency and consequent variability generate a need to optimize plant growth regulating technologies in order to stabilize the wanted effect. Pattern of the concentration dependence of zeatin and tidiazurone effects on roots and hypocotyls growth was analyzed in rape germs. 24-hour Brassica napus germs grown in the dark in thermostat at 24 degrees C were transferred to Petri dishes with solutions of cytokinins under study for continued incubation under the same conditions for the next 24 hours. Roots and hypocotyls were measured. Zeatin concentration curve for roots was multiphase and, in addition to the general trend towards greater inhibition with increase of phyto-hormone concentration and had clearly defined minimum and maximum. The dependence of root growth inhibition on tidiazurone concentration also was not monotonic and had a distinct similarity with the zeatin curve. Gradual increase of tidiazurone concentration used in combination with zeatin brought about a predictable gradual twist of the zeatin curve; however, in most of the instances no additive cytokinin effect was observed. A supposition can be made that PAS interaction with the phytohormone regulation system may be a factor in variability of activity of these substances.