[The protective action of cytokinins on the photosynthetic apparatus and productivity of plants under stress (review)].

A putative way of the protective action of cytokinins on the photosynthetic processes in crops experiencing various stress factors is considered. Various cytokinins are characterized. Pathways of the multiple effects of cytokinin preparations mediating the protection of the photosynthetic machinery from stress are described. Cytokinins interact with receptor proteins, and then the signal is transduced to primary cellular targets (primary response genes). These genes, which possess receptor domains, induce synthesis of the corresponding mRNAs and photosynthesis-related proteins of chlorophyll-protein complexes, the electron-transport chain, and carbon metabolism, primarily, the key enzyme ribulose bisphosphate carboxylase/oxygenase. The protective action of cytokinins under stress conditions preserves the structure and function of the photosynthetic apparatus. The application of cytokinins to improving crop yields is discussed.

[A protector effect of cytokinin preparations on the photosynthetic apparatus of wheat plants under water deficiency conditions].

The protective effects of the cytokinin 6-benzylaminopurine and the compounds thidiazuron and kartolin, displaying a cytokinin activity, on the photosynthetic apparatus of young seedlings and leaves of adult plants of two wheat (Triticum aestivum L.) cultivars, Mironovskaya 808 (more drought tolerant) and Lutescens 758 (less tolerant to water stress), were compared on the background of an increasing water deficiency. At the stages of drought and subsequent rehydration, cartolin preparations were the most efficient protectors, enhancing a less pronounced decrease in the intensity of photosynthesis, carboxylating activity of the key enzyme of carbon metabolism--ribulose bisphosphate carboxylase/oxygenase (EC 4.1.1.39)-and the activity of NADP-glyceraldehyde phosphate dehydrogenase--the enzyme complex comprising phosphoglycerate kinase (EC 2.7.2.3) and glyceraldehyde phosphate dehydrogenase (EC 1.2.1.13). This effect also included an increase in the leaf specific density and plant productivity. The negative influence of water stress on the photosynthetic apparatus was more pronounced in a less tolerant cultivar Lutescens 758 and in the seedlings as compared with the adult plants.

[Activity of NADP-dependent glyceraldehyde-phosphate dehydrogenase and phosphoenolpyruvate carboxylase in wheat leaves under water stress].

The activities of NADP: glyceraldehyde-phosphate dehydrogenase (GAPDH), an enzyme complex comprising of phosphoglycerate kinase (EC 2.7.2.3) and glyceraldehyde-phosphate dehydrogenase (EC 1.2.1.13), and phosphoenolpyruvate carboxylase (PEPK; EC 4.1.1.31) in seedlings and leaves of wheat (Triticum aestivum L.) plants of the cultivars Mironovskaya 808 and Lutescens 758 have been compared under conditions of normal water supply, water deficiency, and subsequent rehydration. GAPDH activity, which determines the carbohydrate route of photosynthetic metabolism at the initial stages, is decreased by water stress to a greater extent than that of PEPK, on the activity of which non-carbohydrate metabolic pathways depend. Pretreatment of seedlings and mature plants with natural (6-benzylaminopurine) and synthetic (tidiazuron, kartolin-2, and kartolin-4) cytokinins attenuates the loss of enzyme activities during drought and facilitates their recovery within the period of rehydration; both effects are underlain by augmentation of reparation processes. The relative intensification of non-carbohydrate pathways of photosynthetic metabolism, observed under conditions of water deficiency, is accompanied by an increase in the osmotic pressure of cell sap. Possible mechanisms of this protector effect of cytokinin preparations are discussed.

[Effect of water stress on the photosynthetic apparatus of plants and the protective role of cytokinins: a review].

Characteristics of photosynthetic apparatus (the pool of pigments and proteins; the activity of photosystems; the intensities of in vivo photoassimilation of carbon dioxide and in vitro activity of enzymes of carbon metabolism; leaf structure; chloroplast structure), undergoing changes under the conditions of water deficiency, have been reviewed. The protective role of cytokinins is due to their regulatory effects on the renewal of disrupted cellular structures, the condition of the stomata, and de novo synthesis and activation of proteins that are required for increasing plant resistance to water stress.

[Effects of cytokinin preparations on the stability of the photosynthetic apparatus of two wheat cultivars under water deficiency]. / Vliianie tsitokininovykh preparatov na stabil'nost' fotosinteticheskogo apparata dvukh sortov pshenitsy pri vodnom defitsite.

Carboxylase activities of the key enzyme of carbon metabolism, ribulose-bisphosphate carboxylase/oxygenase (RuBisCO; EC 4.1.1.39), and phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31), as well as intensities of carbon dioxide photosynthetic assimilation in young seedlings and adult leaves of the wheat Triticum aestivum L. cultivars Mironovskaya 808 (a more tolerant) and Lyutestsens 758 (a less tolerant), were compared under conditions of progressive water deficiency. The water stress had more pronounced negative effects on all the studied characteristics of photosynthetic apparatus of cultivar Lyutestsens 758 photosynthetic machinery of the cultivar Lyutestsens 758. Its seedlings were more sensitive to water stress. Compounds with a cytokinin activity (6-benzylaminopurine, thidiazuron, cartolin 2, and cartolin 4) played a protective role, increasing the stability of the photosynthetic machinery under conditions of water deficiency. Preparations of cartolins displayed the maximum protective effect.

[Effect of cytokinin preparations on the pools of pigments and proteins of wheat cultivars differing in their tolerance to water stress]. / Vliianie tsitokininovykh preparatov na pul pigmentov i belkov sortov pshenitsy, razlichaiushchikhsia po ustoichivosti k vodnomu stressu.

Contents of chlorophylls, carotenoids, soluble leaf proteins, and the key enzyme of carbon metabolism--ribulose bisphosphate carboxylase/oxygenase (RuBisCO; EC 4.1.1.39)--in young seedlings and adult leaves of the wheat Triticum aestivum L. cultivars Mironovskaya 808 and Lyutestsens 758, contrasting in their water stress tolerances, were compared under conditions of normal available water supply, water deficiency, and subsequent rehydration. It was discovered that compounds displaying a cytokinin activity (6-benzylaminopurine, thidiazuron, cartolin-2, and cartolin-4) reduced the decreases in contents of chlorophylls, carotenoids, soluble leaf proteins, and RuBisCO progressing with development of water stress. These compounds with cytokinin activity also accelerated restoration of the compounds studied to their initial concentrations during rehydration. The cartolin preparations caused a maximal protective effect. Water stress had a more pronounced negative effect on cultivar Lyutestsens 758. Dehydration resulted in a more extensive destruction of seedlings compared to leaves of adult plants.

[Effect of preparations exhibiting cytokinin-like activity on the specific density of leaf in grasses]. / Vliianie preparatov s tsitokininovoi aktivnost'iu na udel'nuiu plotnost' lista zlakov.

The effects of synthetic preparations exhibiting cytokinin-like activity (6-benzylaminopurine, Thidiazuron, and kartolin-2) on the specific leaf area (SLA) were studied in plants of the family Gramineae (wheat, Triticum aestivum L.; meadow fescue, Festuca pratensis Huds.; and reed fescue, F. arindinacea Schreb.). At the early stages of ontogeny (until the leaf area reached 50-60% of the maximum value), treatment of plants of the three species with cytokinin-like preparations caused an increase in SLA. The SLA value in these plants was correlated with the rate of photosynthetic assimilation of carbon dioxide and activities of carbon metabolism enzymes: ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39), NAD-malate dehydrogenase (EC 1.1.1.37), and NADP-glyceraldehydrophosphate dehydrogenase complex, which includes phosphoglycerate kinase (EC 2.7.2.3) and glyceraldehydrophosphate dehydrogenase (EC 1.2.1.13). However, there was no correlation of SLA with the activity of phospho(enol)pyruvate carboxylase (EC 4.1.1.31), an anaplerotic carboxylation enzyme of grasses. SLA is suggested to reflect the state and activity of the photosynthetic apparatus and can be recommended as a characteristic of photosynthesis variability (e.g., caused by cytokinin-like preparations).

[Protective role of kartolin-4 in soil drought in wheat plants]. / Zashchitnaia rol' kartolina-4 pri pochvennoi zasukhe u rastenii pshenitsy.

Parameters of photosynthesis, heat-resistance, and osmotic pressure of cell exudate of leaves of the drought-sensitive cultivar Lyutestsens 758 of wheat, Triticum aestivum, were studied under conditions of normal water supply, soil drought, and subsequent rehydration. The plants preliminarily treated with kartolin-4 were compared to untreated plants. Kartolin-4, a preparation with cytokininlike activity, partially prevented the drought-induced inhibition of the photosynthetic assimilation of carbon dioxide and carboxylation activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39), the key enzyme of carbon metabolism in plants. Upon a subsequent rehydration, kartolin-4 stimulated the reparation reactions and facilitated rapid recovery of normal photosynthetic activity. Kartolin-4 also increased plant resistance to overheating and water deficiency.

[Activity of carbon metabolism enzymes in wheat plants treated with kartolin-4 and exposed to water stress]. / Aktivnost' fermentov uglerodnogo metabolizma rastenii pshenitsy v usloviiakh vodnogo stressa pri obrabotke kartolinom-4.

Enzymatic activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) (EC 4.1.1.39), phospho(enol)pyruvate carboxylase (EC 4.1.1.31), NAD malate dehydrogenase (EC 1.1.1.37), and NADP glyceraldehydephosphate dehydrogenase complex including phosphoglycerate kinase (EC 2.7.2.3) and glyceraldehydephosphate dehydrogenase (EC 1.2.1.13) were comparatively assayed in wheat seedlings of the cultivar Lyutestsens 758 grown under normal conditions, water deficiency conditions, and subsequent rehydration. Water stress was found to decrease the activity of all enzymes tested, the effect being most pronounced in case of Rubisco. The content of Rubisco in wheat plants exposed to water deficiency was reduced less significantly than the activity of the enzyme. Preliminary treatment of plant seeds with kartolin-4 (o-isopropyl-N-2-hydroxyethyl carbamate), a preparation with cytokinin activity, reduced the dehydration-induced inhibition of enzymatic activity. Upon a subsequent rehydration, kartolin-4 facilitated rapid recovery of the photosynthetic activity, the process being based on the kartolin-induced stimulation of reparation reactions. Under conditions of water stress, a partial decrease in the activity of carbon metabolism enzymes in vitro was accompanied by complete inhibition of photosynthesis in vivo, perhaps, as a result of an abrupt increase in the stomatal resistance.

[Ontogenetic changes in the photosynthetic apparatus and effect of cytokinins]. / Intogeneticheskie izmeneniia fotosinteticheskogo apparata i vliianie tsitokininov.

Data on structural and functional changes in the photosynthetic apparatus of agricultural plants are presented. Results of studies on the regulatory effects of cytokinin-like phytohormones on photosynthesis are discussed. Cytokinins were found to be involved in the structural formation and maintenance of the photosynthetic apparatus, conditions of the stomata and the supply of CO2 to carboxylation sites through the leaf mesophyll, the syntheses of pigments and enzyme systems, and the regulation of photoreduction and carbon metabolism. Possible mechanisms mediating the regulatory effects of cytokinins are discussed.

[Acid-soluble nucleotides of the phototrophic bacterium Rhodospirillum rubrum during growth in light and in darkness]. / Kislotorastvorimye nukleotidy fototrofnoi bakterii Rhodospirillum rubrum pri roste na svetu i v temnote

The content of acid-soluble nucleotides was different in the cells of non-sulphur purple bacterium Rhodospirillum rubrum, growing phototrophically under anaerobic conditions and aerobically under conditions of heterotrophic nutrition. The cells of the culture growing in the darkness contained more adenylic and guanylic nucleotides, and the total of reduced and oxidized NADP. The cells of the culture growing in the light contained more FMN. The cells of the "light" and "dark" cultures contained GTP dependent phosphopyruvate carboxylase (E.C. 4.1.1.32). The cells of the "light" culture, contrary to the "dark" culture, contained also pyrophosphate dependent phosphopyruvate carboxylase (E.C. 4.1.1.38).