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

Abstract

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 (O 2 .-), and hydrogen peroxide (H 2 O 2 ). An optimum concentration of glucose was 30 mM as it significantly alleviated plant growth inhibition and obviously reduced the content of MDA, O 2 .-, and H 2 O 2 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 the repressed accumulation of reactive oxygen species.

Exogenous glutathione improves high root-zone temperature tolerance by modulating photosynthesis, antioxidant and osmolytes systems in cucumber seedlings

“…Huang et al . 19 found that glucose application increases the transcriptions of some antioxidant enzymes under heat stress. The up-regulation of these genes contributed to an enhanced adaptation to high temperature stress in cucumber roots.…”

“…ROS are scavenged by plant antioxidant defense systems which include non-enzymatic antioxidants (such as ascorbic acid, AsA; glutathione, GSH) and antioxidant enzymes (such as superoxide dismutase, SOD; catalase, CAT; ascorbate peroxidase, APX; glutathione reductase, GR; guaiacol peroxidase, G-POD) 16 17 . Proline accumulation has been reported during various stress conditions, including drought 18 and heat 19 . Proline is important in cellular homeostasis (cell proliferation or cell death) and can act as a signaling molecule to modulate mitochondrial functions and trigger specific genes expression, which is essential for plant recovery from stresses 20 .…”

Responses of antioxidant enzymes, photosynthetic pigments and carbohydrates in micropropagated Pitcairnia encholirioides L.B. Sm. (Bromeliaceae) under ex vitro water deficit and after rehydration

“…In comparison, proline contents and POD activity improved in plants previously in vitro cultured in media with 30 g L -1 sucrose and GA 3 , which can be related to drought tolerance of these plants. Studies show that exogenous glucose application enhances tolerance of plants to dehydration and heat stress by increasing the content of proline and activities of antioxidants and repressing ROS accumulation (Huang et al, 2013(Huang et al, , 2015Cao et al, 2015), corroborating this hypothesis. There were no differences in enzymatic activity between the materials submitted to dehydration and the control after rehydration, suggesting a high adaptability of this species to water stress conditions and recovery after the end of stress period.…”

The Role of Chloroplast Gene Expression in Plant Responses to Environmental Stress

“…The chloroplast, a unique plant organelle, is the site of photosynthesis, intracellular signaling, and the production of various compounds important in metabolism, such as amino acids, hormones, nucleotides, vitamins, lipids, and secondary metabolites [ 7 , 8 , 9 ]. Chloroplasts also serve as sensors of the external environment.…”