[The role of reactive oxygen species and calcium ions in the implementation of the stress-protective effect of brassinosteroids on plant cells].

The effect of the brassinosteroids (BS) 24-epibrassiniolide and 24-epicastasterone on the thermoresistance of wheat coleoptile (Triticum aestivum L.) and their generation of the superoxide anion radical and antioxidant enzymes activity were investigated. The treatment of coleoptiles with 10 nM solutions of BS caused a transient increase in O2·- generation and a subsequent increase in the activity of superoxide dismutase and catalase and an improvement in heat resistance. Pretreatment of coleoptiles with the NADPH oxidase inhibitor imidazole leveled the increase in production of the superoxide anion radical and prevented an increase in the activity of antioxidant enzymes and the development of cell thermostability. The investigated effects of BS were also depressed by the pretreatment of coleoptile segments with extracellular calcium chelator EGTA and inhibitor of ADP-ribosyl cyclase nicotinamide. A conclusion was made about the participation of calcium ions and reactive oxygen species generated by the action of NADPH oxidase in the implementation of the stress-protective effect of the BS in the cells of wheat coleoptile.

[Reactive oxygen forms and Ca ions as possible intermediaries under the induction of heat resistance of plant cells by jasmonic acid].

The participation of reactive oxygen species (ROS) and calcium ions in realization of influence of exogenous jasmonic acid (JA) on the heat resistance of wheat coleoptiles has been investigated. Influence of 1 microM JA caused the transitional intensifying of generation of superoxide anion-radical (O2*-) and hydrogen peroxide in coleoptiles with the maximum within 15-30 minutes after the treatment beginning. Within the first hour after the beginning of coleoptiles treatment with JA the increase of superoxide dismutase (SOD) activity was noted. Later on (within 5-24 hours after the treatment beginning) there was the lowering of ROS generation by coleoptiles of experimental variant, and the SOD activity approached the control value. Intensifying of generation of superoxide radical induced by JA was suppressed by the antioxidant ionol and was partially levelled by imidazole (inhibitor of NADPH-oxidase), EGTA (chelator of extracellular calcium) and lanthanum chloride (calcium channels blocker). Pretreatment of coleoptiles with the ionol, imidazole, EGTA and LaC3l3 also partially removed the effect of increase of their resistance to the damaging heating caused by exogenous JA. It is supposed that the ROS generated with participation NADPH-oxidase, which activity depends on the receipt of calcium ions from extracellular space in the cytosol, are involved in realization of physiological effects of JA.