L. Kh. Gordon

Superoxide Production and the Activity of Extracellular Peroxidase in Plant Tissues under Stress Conditions

The production of reactive oxygen species on the plant-cell surface is considered. Along with the plasmalemmal redox systems, cell-wall peroxidase is involved in the production of superoxide and hydrogen peroxide. Under stress conditions, some soluble peroxidase isoforms are easily secreted into the apoplast. Various membranotropic compounds, salicylic acid in particular, can also induce this process. Mobile peroxidase forms are supposed to induce the plant defense response.

The effect of melafen on the growth and energy processes in the plant cell.

During the past years, significant success has been reached in understanding the role of phytohormones in life of plants, their metabolism, and molecular mechanism of their action [1, 2]. Because the use of phytohormones in practice is economically disadvantageous, the synthetic preparations that at ultralow concentrations can trigger physiological and genetic programs, thereby leading to the intensification of key physiological processes, have been intensively sought.

Salicylic acid induces dissipation of the proton gradient on the plant cell plasma membrane.

Recently, the role of salicylic acid in plant cell responses to various effects has been intensely studied by many researchers. It was shown that pathogens induce production of large amounts of salicylic acid in plant cells (its concentration may increase by one or two orders of magnitude) [1, 2]. Note that salicylic acid may be released into the apoplast and circulate in the plant [3]. The cause of the production and release of large amounts of salicylic acid from cells remains unknown. Published data describe the phenomenon of salicylic acid-induced activation of gene expression and synthesis of defence proteins [2] (including the synthesis of alternative oxidase [4]). However, one of the simplest mechanisms of the salicylic acid effect on cells (pathogen cells, in particular) is apparently based on its protonophore properties and ability to dissipate the proton gradient across the membrane. The protonophore properties of salicylic acid are described in [5], where it is regarded as a typical agent uncoupling oxidation and phosphorylation. The uncoupling effect of salicylic acid is also described in [4]. In view of this, we attempted to study the effect of salicylic acid on the respiration and growth of wheat seedling root cells, their membrane potential, ä + release from them, pH of the incubation medium, and the effect of salicylic acid on the mitotic index of pea root cells.

Heat production of root cells upon the dissipation of ion gradients on plasma membrane

The dissipation of ion gradients across plasma membranes contributes to the heat production by live cells. The aim of the present research is to determine the dependence of the rate of heat production by plant tissues on ion balance shifts, supposing a priori that the shifts are the beginning mechanism in adaptation to various stresses. Excised wheat roots subjected to prolonged incubation in different solutions served as objects for investigation. Two ion transporters (K + /H + -transporter nigericin and Ca 2+ -ionophore A23187) shifted the ion homeostasis and induced distinct changes in the energy metabolism of plant tissues. Nigericin, which considerably increased the plasmalemma conductivity for protons and potassium, enhanced production of heat by root cells throughout the exposure. Prolonged incubation with A23187 was required to display its ion-transporting properties which were accompanied by a rise in the rate of heat release. The high rate of heat release and respiration in root cells exposed to ion transporters is a reflection of the ion-gradient dissipation and the increased energy expenditure for the activation of ATPase systems necessary for the restoration of ionophore-disturbed ion homeostasis.

A comparative study of the effect of melaphene and kinetin on growth and energy processes in the plant cell.

Earlier, when studying the responses of plants to treatment with certain types of chemicals, we found that melaphene, the melamine salt of bis(methylol)phosphinic acid, at ultralow concentrations exhibits regulatory activity [1]. Studies of the effect of melaphene on the regulation of growth and development of the unicellular alga Chlorella , as well as on the rate of photosynthesis, respiration, and metabolic heat emission as an index of energy status of cells, showed that melaphene had the greatest effect at concentrations of 3 × 10 –9 –3 × 10 –10 å [1]. These results and published data allowed us to conclude that the effect of melaphene on energy processes and metabolism in plants is similar to the effect of phytohormones of the cytokinin series [2].

The energetic stress response of the microalgal Chlorella vulgaris to the mycoplasma, Acholeplasma laidlawii as a model system for plant–pathogen interaction

Loseva, N. L., Alyabyev, A. J., Gordon, L. K., Andreyeva, I. N., Kolesnikov, O. P., Ponomareva, A. A., Chernov, V. M., Kemp, R .B. (2003). The energetic stress response of the microalgal Chlorella vulgaris to the mycoplasma, Acholeplasma laidlawii as a model system for plant-pathogen interaction. Thermochimica Acta, 397, (1-2), 37-47. Sponsorship: INTAS Grant no. 99-1390

Energy exchange and ultrastructure of plant cells under generation of nitric oxide

The effects of nitric oxide (NO) on oxygen consumption, heat generation, and cell ultrastructure were investigated in the seedlings of wheat (Triticum aestivum L.). The experiments were conducted with the excised roots of 5-day-old seedlings grown in the solution of CaCl2 (2.5 × 10−4 M). The source of NO was NaNO2 (5 × 10−3 M) where the roots were incubated. Production of NO was determined by means of EPR, respiration — gasometrically, heat generation — using a microcalorimeter. The results showed that NO was formed in the presence of NaNO2. This was accompanied by a decrease in the respiration rate by about 30%, which lasted for 5–6 h. Apparently, NO inhibited mitochondrial oxidation because stimulation of oxygen consumption induced by 2,4-DNP was completely removed in the presence of NaNO2. When the cells were affected by succinic acid in the presence of NaNO2, respiration was strongly inhibited. The effects of succinic acid and NaNO2 were negated by ascorbic acid. A decrease in the rate of respiration was accompanied by a reduction in heat generation. Moreover, the efflux of potassium ions to the root incubation medium was stimulated, which may point to changes in ionic membrane permeability. The observed changes in energy exchange were accompanied by disturbances in the cell ultrastructure. Nitric oxide induced a clarification of the mitochondrial matrix and a reduction in the number of cristae. It was concluded that NO excess in plant tissues brings about a deceleration of energy exchange, disturbance of the ultrastructural organization, and cell death.

Change in lipid composition of wheat roots on early phase of mechanical stress

Changes of composition of phospholipid fatty acids, free fatty acids and phospholipids including lysophosphatidylcholine in the early stage (until one hour) of mechanical stress of wheat roots were studied. The saturation degree of phospholipid fatty acids sharply increases at expense of the decrease in the content of linoleic and linolenic acids within fifteen minutes after excision of roots from seedlings At the same time the increase of free fatty acids, lysophosphatidylcholine and the decrease of phospholipids were observed. This suggests that the action of phospholipases, in particular phospholipase A2, takes place in early phase of stress of wheat roots. It has been shown that alteration of lipid content in roots after excision depends on membrane fluidity and permeability for ions. It is suggested that early changes in lipid composition of wheat roots after excision may be considered as a response reaction of cells to mechanical stress and can be caused by the action of lipases in particular PLA2. This reaction is probably the unspecified one and is dictated by plasma membrane properties (fluidity, permeability).

Effect of NaNO2, a donor of nitric oxide, on the energy metabolism of plant cells

39 Nitric oxide (NO) has been demonstrated to have a wide spectrum of biochemical effects [1]. NO is one of the messengers involved in the regulation of both intraand intersignaling in plants [2]. NO has also cytotoxic and cytostatic properties along with the regulatory functions [1]. In addition, NO is known to effectively regulate plant respiration owing to its high affinity to a number of enzymes participating in glycolysis and mitochondrial oxidation [3, 4].

Calixarenes: Influence on energy exchange of plant tissues

The distinctive features of the influence of synthetic compounds of a new class, calixarenes, on the energy exchange of the plant tissues and on the ionic permeability of the plant membranes were investigated. Calixarenes of the different chemical structure were shown to sufficiently influence the oxygen consumption by wheat roots, pH of the incubation mixture, and the potassium ions release. Aminomethylated calyx[4]resorcinaren showed the highest effect. The influence of these compounds on the wheat roots was pH dependent.