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The aim of this work was to examine the ability of ABA and proline to counteract the deleterious effect of water deficit stress on cell membrane injuries. Six-day-old seedlings of two barley genotypes (cv. Aramir, line R567) were treated with ABA (2·10⁻⁴ M) or proline (0.1 M) for 24 h, and then subjected to osmotic stress for 24h, by immersing their roots in polyethylene glycol (PEG 6000) solution of osmotic potential of −1.0 MPa and −1.5 MPa or by submerging the leaf pieces in PEG solution of osmotic potential of −1.6 MPa. Pretreatment of plants with ABA and proline caused an increase of free proline level in the leaves. Plants treated with ABA exhibited a lower membrane injury index under water stress conditions than those untreated even when no effect of this hormone on RWC in the leaves of stressed plants was observed. Pretreatment of plants with proline prevented to some extent membrane damage in leaves of the stressed seedlings, but only in the case when stress was imposed to roots. Improvement in water status of leaves was also observed in seedlings pretreatment with proline. The protective effect of both ABA and proline was more pronounced in line R567 that exhibited higher membrane injury under water deficit stress conditions.
Purified proline-specific amino peptidases from Lactobacillus curvatus and from Lactococcus lactis were active on both X-proline dipeptidyl aminopeptidase (PepX) substrates, Gly-Pro-AMC or Gly-PropNA and on proline endopepetidase (PEP) substrates Suc-Gly-Pro-Leu-Gly-Pro, Suc-Gly-Pro-AMC, Z-Gly-Pro-AMC or Suc-Gly-Pro-pNA, however; activity on PEP substrates was markedly less than that on PepX substrates. The enzymes from Lactobacillus and Lactococcus hydrolyzed a number of oligopeptides containing 7-11 amino acids residues and proline at the penultimate position from N-terminus, but hydrolysis of natural PEP oligopeptide substrates containing proline residues at internal positions was negligible. The two proline-specific enzymes were strongly stimulated by NaCl and inhibited by phenylmethylsulfonyl fluoride and organic solvents.
Atmospheric ozone remains depleted which in turn leads to the increase of UV-B radiation reaching the surface of the earth and in the same time more and more nitrogen will be imported into the terrestrial ecosystems through nitrogen deposition. These two factors will operate simultaneously. The photosynthetic and physiological responses of deciduous broad leaved species Swida hemsleyi occurring commonly at 1350–3700 m a.s.l. subjected to enhanced UV-B and to nitrogen supply were studied. The experimental design included two levels of UV-B treatments (ambient UV-B, 11.02 KJ m⁻² day⁻¹ and enhanced UV-B, 14.33 KJ m⁻² day⁻¹) and two nitrogen levels (without supplemental nitrogen supply and with supplemental nitrogen supply). An experiment was conducted in open semi-field condition in Maoxian Ecological Station of Chinese Academy of Sciences, Sichuan province, China at 1820 m a.s.l. Enhanced UV-B caused a marked decline in growth parameters, net photosynthetic rate, stomatal conductance to water vapour, chlorophyll pigments, whereas it induced an increase in rate of reactive oxygen species (ROS) production and ROS accumulation and malondialdehyde (MDA) content. Enhanced UV-B also induced an increase in leaf thickness and antioxidant compounds content, such as carotenoids and proline content. On the other hand, nitrogen supply caused an increase in some growth parameters, chlorophyll pigments and antioxidant compounds, and reduced ROS accumulation. However, nitrogen supply did not affect MDA content under enhanced UV-B, though it increased antioxidant compounds content and reduced the rate of ROS production and ROS accumulation. These results implied that enhanced UV-B brought harmful effects on Swida hemsleyi seedlings and supplemental nitrogen supply could alleviate the adverse effects of UV-B radiation on plants to some extent.
The present study deals with biochemical and physiological methods for assessment of the optimal nutrient supply for the growth and development of garden rocket (Eruca sativa Mill.), edible vegetable. Two nitrate (0.3; 0.6 g N dm⁻³ of medium) and three potassium doses (0.3; 0.6; 0.9 g K dm⁻³ of medium) in the form of sulphate or chloride were examined. At the higher nitrate dose and the sulphate form of potassium the intense green colour of leaves, higher content of nitrates, flavonoids, L-ascorbic acid and lower carbohydrates content correlated with elevated growth parameters, e.g. the number of leaves and partially plant fresh weight. The proline and anthocyanin contents weakly diversified the nutrient supply. Despite the lack of modification in the photosynthetic pigment concentration, the chlorophyll fluorescence parameters were significantly improved when the higher nitrate dose accompanied the sulphate form of potassium (higher values of fluorescence decrease, maximum quantum efficiency of PSII photochemistry in the dark-adapted state, photochemical quenching and lower values of the fraction of absorbed light energy not used for photochemistry). The biochemical and photosynthetic parameters corresponding to the morphological characteristics (leaf colour, number of leaves and plant fresh weight) indicated that better nutrient conditions were provided to plants under the combined fertilization of the higher nitrate dose and the sulphate form of potassium.
Salinization of soils or waters is one of the world’s most serious environmental problems in agriculture. It is necessary to determine the environmental factors under which medicinal and aromatic plants give higher yields and better quality. The problem of salinity is characterized by an excess of inorganic salts and is common in the arid and semi-arid lands, where it has been naturally formed under the prevailing climatic conditions and due to higher rates of evapotranspiration and lack of leaching water. Although more frequent in arid lands, salt-affected soils are also present in areas where salinity is caused by poor quality of irrigation water. Saline soil induces physiological and metabolic disturbances in plants, affecting development, growth, yield, and quality of plants. Plants affects adversely as a result of salinity, seed germination, survival percentage, morphological characteristics, development and yield and its components. In general, salt stress decreases the photosynthesis and respiration rate of plants. Total carbohydrate, fatty acid and protein content were adversely affected due to salinity effect, but increased the level of amino acids, particularly proline. The content of some secondary plant products is significantly higher in plants grown under salt stress than in those cultivated in normal conditions. The salinity tolerance depends on the interaction between salinity and other environmental factors.
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