Xiu-Juan Wang

Effects of long-term chilling on ultrastructure and antioxidant activity in leaves of two cucumber cultivars under low light

Cucumber (Cucumis sativus L.) cv. Xintaimici (a chilling-resistant cultivar) and cv. Jinyan no. 4 (a chilling-sensitive cultivar) were subjected to two temperatures (15/15 and 25/18 degrees C) under low light (100 mumol m(-2) s(-1)) to understand the relationship between ultrastructural changes and the antioxidant abilities caused by low temperature (15/15 degrees C). We also aimed to find indicators for chilling resistance that could be used on a routine basis in breeding programs of greenhouse crops. At the 15/15 degrees C treatment, the membranes of chloroplast, mitochondrion, ER and plasma were not significantly changed in Xintaimici, whereas they were seriously affected in Jinyan no. 4. This result was consistent with the changes of malonaldehyde in chilling-stressed cucumber leaves. The antioxidant activities were changed under low temperature according to cultivar-expected resistance, relating in part to the described ultrastructural changes. The activities of superoxide dismutase (EC 1.15.1.1) and guaiacol peroxidase (EC 1.11.1.7) increased in chilling-stressed leaves of both cultivars, but the two enzymes were not responsible for the difference between cucumber cultivars. At 15/15 degrees C, contents of GSH and activities of glutathione reductase (GR, EC 1.6.4.2) increased more in leaves of Xintaimici than in those of Jinyan no. 4, while catalase (CAT, EC 1.11.1.6) activities decreased less. GSH, GR and CAT were affected by low temperature and cultivars and correlated with the difference in ultrastructure between chilling-stressed cucumber cultivars. We propose that the three antioxidants might be therefore used as biochemical indicators to screen chilling-resistant cucumber cultivars.

Ferulic acid pretreatment enhances dehydration-stress tolerance of cucumber seedlings

To examine whether ferulic acid (FA) could protect plants from dehydration stress and to investigate a mechanism for the protection, cucumber seedlings were pretreated with 0.5 mM FA for 2 d and then were exposed to dehydration induced by 10 % polyethylene glycol 6000. After pretreatment with FA, the activities of antioxidant enzymes (catalase, superoxide dismutase, and quaiacol peroxidase) in leaves were higher than under dehydration treatment alone which was in accordance with the increased transcript levels of respective genes. Moreover, the combination of FA pretreatment and dehydration reduced the content of superoxide radical, hydrogen peroxide, and malondialdehyde, and increased the relative water content and content of FA, proline, and soluble sugars in comparison with dehydration alone. We propose that pretreatment with FA protects cucumbers against dehydration stress by decrease of lipid peroxidation due to activation of antioxidant enzymes and by increase of proline and soluble sugar content in leaves.

Bacillus methylotrophicus isolated from the cucumber rhizosphere degrades ferulic acid in soil and affects antioxidant and rhizosphere enzyme activities

AimsFerulic acid (FA) accumulates in soil and inhibits plant growth. We examined whether the FA-degrading bacterium Bacillus methylotrophicus degrades FA in soil.MethodsB. methylotrophicus strain CSY-F1 was isolated and applied to unplanted soil and soil planted with Cucumis sativus (cucumber). We analyzed the effects of B. methylotrophicus on rhizosphere enzyme activities and antioxidant enzyme activities in cucumber and CSY-F1 exposed to FA.ResultsCSY-F1 degraded FA in culture medium and in soil, giving rise to 4-vinyl guaiacol, vanillin, vanillic acid, and protocatechuic acid. When cucumber seedlings were grown in soil treated with FA, the activities of some soil enzymes decreased, and the malonaldehyde content in cucumber leaves increased. The addition of CSY-F1 to FA-treated soil increased the activities of these soil enzymes, decreased the FA concentration in the soil, and elevated the activities of some antioxidant enzymes in seedlings. Moreover, the levels of superoxide radical, hydrogen peroxide, and malonaldehyde were reduced in cucumber leaves. FA treatment increased the activities of antioxidant enzymes, including superoxide dismutase, catalase, and monodehydroascorbate, in CSY-F1.ConclusionBacillus methylotrophicus CSY-F1 has potential applications as an FA-degrading agent in soil, as it mitigates FA stress in cucumber seedlings by activating several antioxidant and soil enzymes.

Glucose application protects chloroplast ultrastructure in heat-stressed cucumber leaves through modifying antioxidant enzyme activity

To elucidate a physiological mechanism of heat stress mitigation by exogenous glucose, seedlings of Cucumis sativus cv. Jinchun No. 4 were pretreated with glucose and then exposed to normal (25/18 °C) and elevated (42/38 °C) temperatures. We investigated whether glucose can protect cucumber plantlets and chloroplast ultrastructure from heat and whether this protection is associated with antioxidant enzymes, proline, and soluble sugars. Heat inhibited plant growth, disorganized membranes of 86.33 % of chloroplasts, and elevated the content of malondialdehyde (MDA), superoxide radical (O2·−), and hydrogen peroxide (H2O2). An optimum concentration of glucose was 30 mM as it significantly alleviated plant growth inhibition and obviously reduced the content of MDA, O2·−, and H2O2 under the heat stress. The pretreatment with 30 mM glucose mitigated heat-induced damage of chloroplast ultrastructure and changes in leaf morphology more than 30 mM mannitol suggesting that glucose did not act only as osmolyte. Moreover, the glucose pretreatment increased activities of some antioxidant enzymes and enhanced the content of proline and soluble sugars under the heat stress, as well as the transcriptions of Cu/Zn-superoxide dismutase, Mn-superoxide dismutase, catalase, and glutathione reductase genes. We conclude that the pretreatment with 30 mM glucose protected chloroplast ultrastructure and enhanced heat tolerance of the seedlings by the increased activites of antioxidants and the content of proline and soluble sugars, and repressed accumulation of reactive oxygen species.

Exogenous sucrose influences antioxidant enzyme activities and reduces lipid peroxidation in water-stressed cucumber leaves

To investigate whether exogenous sucrose can protect cucumber from water stress, cucumber (Cucumis sativus L.) seedlings were pretreated with 90 mM sucrose or 90 mM mannitol for 1 d and then were dehydrated with 10 % (m/v) polyethylene glycol (PEG) 6000 for further 1 d. Dehydration inhibited plant growth and decreased osmotic potential and relative water content (RWC) in leaves. The pretreatment with 90 mM sucrose further reduced the osmotic potential but increased the RWC and alleviated the growth inhibition. Compared with the PEG treatment alone, the combination of sucrose + PEG increased the activities of superoxide dismutase, guaiacol peroxidase, glutathione reductase, dehydroascorbate reductase, monodehydroascorbate reductase, ascorbate peroxidase, and glutathione peroxidase, and elevated the content of endogenous sucrose, glucose, and fructose together with the activities of soluble acid invertase and neutral invertase. This was in accordance with the enhanced transcription of genes encoding copper/zinc superoxide dismutase, guaiacol peroxidase, and glutathione reductase. Furthermore, the sucrose pretreatment decreased the content of malondialdehyde and hydrogen peroxide and increased the content of ascorbate, reduced glutathione, and proline under the dehydration. Taken together, the pretreatment with 90 mM sucrose, but much less with mannitol, induced antioxidants, proline, and soluble sugars and thus reduced dehydration-caused damage to the cucumber seedlings.

Bacillus methylotrophicus CSY-F1 alleviates drought stress in cucumber (Cucumis sativus) grown in soil with high ferulic acid levels

AimsDrought and ferulic acid (FA) inhibit plant growth. Here, we investigated whether Bacillus methylotrophicus CSY-F1 alleviates drought stress in cucumber (Cucumis sativus) plants grown in high-FA soil.MethodsCucumber seedlings grown in high-FA soil were inoculated with CSY-F1 for 20 d, and then subjected to drought for 3 d.ResultsIn rhizospheric soil of drought-stressed seedlings, CSY-F1 decreased FA levels and increased soil water contents, polysaccharide levels, and catalase, phosphatase, urease, and sucrase activities at low or high FA concentrations. In drought-stressed seedlings grown in FA-containing soil, CSY-F1 improved plant growth, and reduced leaf wilting; CSY-F1 decreased superoxide radical, hydrogen peroxide, and malonaldehyde levels. CSY-F1 increased superoxide dismutase (SOD), catalase, guaiacol peroxidase, ascorbate peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase, and glutathione reductase activities in these seedlings. In addition, CSY-F1 elevated plant relative water content and osmotic potential, and enhanced ascorbate and glutathione contents, proline and soluble sugar levels, and catalase, copper/zinc SOD, manganese SOD, CsPYL1, and CsPYL2 transcript levels.ConclusionCSY-F1 increases the polysaccharide levels and enzyme activities in soil, and enhances antioxidant enzyme activities, proline and soluble sugar levels, and transcript levels of CsPYL1 and CsPYL2 in leaves, thus alleviating drought stress in cucumber under FA conditions.

Acinetobacter calcoaceticus CSY-P13 Mitigates Stress of Ferulic and p-Hydroxybenzoic Acids in Cucumber by Affecting Antioxidant Enzyme Activity and Soil Bacterial Community

Ferulic acid (FA) and p-hydroxybenzoic acid (PHBA) are main phenolic compounds accumulated in rhizosphere of continuously cropped cucumber, causing stress in plants. Microbial degradation of a mixture of FA and PHBA is not well understood in soil. We isolated a strain CSY-P13 of Acinetobacter calcoaceticus, inoculated it into soil to protect cucumber from FA and PHBA stress, and explored a mechanism underlying the protection. CSY-P13 effectively degraded a mixture of FA and PHBA in culture solution under conditions of 39.37°C, pH 6.97, and 21.59 g L-1 potassium dihydrogen phosphate, giving rise to 4-vinyl guaiacol, vanillin, vanillic acid, and protocatechuic acid. During FA and PHBA degradation, activities of superoxide dismutase (SOD), catalase, ascorbate peroxidase, and dehydroascorbate reductase in CSY-P13 were induced. Inoculated into cucumber-planted soil containing 220 μg g-1 mixture of FA and PHBA, CSY-P13 degraded FA and PHBA in soil, increased plant height, and decreased malonaldehyde, superoxide radical, and hydrogen peroxide levels in leaves. CSY-P13 also enhanced SOD, guaiacol peroxidase, catalase, glutathione peroxidase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase activities; increased ascorbate and glutathione contents; and elevated transcript levels of copper/zinc SOD, manganese SOD, and catalase in leaves under FA and PHBA. Moreover, CSY-P13 increased phosphatase, catalase, urease, and sucrase activities and changed bacterial richness, diversity, and community composition by high throughput sequencing in cucumber-planted soil supplemented with the mixture of FA and PHBA. So CSY-P13 degrades the mixture of FA and PHBA in soil and mitigates stress from the two phenolic compounds in cucumber by activating antioxidant enzymes, changing soil bacterial community, and inducing soil enzymes.