Study On Protect And Repair Role Of Wheat Seedlings Under Drought Stress And Mechanism With Laser Radiation

The wheat (Triticum aestivum L. cv. Mianyang 26) seeds and seedlings damaged by drought stress were exposed to CO₂ laser (20.1mW·mm^-2) and He-Ne laser (5.23mW·mm^-2) irradiation in order to determine whether or not CO₂ laser and He-Ne laser have protect and repair capacity of the seedlings from drought stress damage. The results were as follows:1. In order to determine the effects of He-Ne laser on wheat (Triticum aestivum L.) exposed to drought stress, protective enzyme activities and lipid peroxidation in wheat seedlings treated with different concentration of PEG6000 were studied. 12-day-old seedlings were treated with drought stress using 5%, 10% and 15% PEG6000 for 3d, 6d, 9d, 12d, 15d, respectively. After 3d, 6d, 9d, 12d, 15d of drought stress, a He-Ne laser was employed to irradiate seedlings of spring wheat for 0min, 1min and 3min, respectively. Leaves and roots were sampled for various analyses. He-Ne laser irradiation significantly decreased malondialdehyde (MDA), hydrogen peroxide (H₂O₂) concentration and the production rate of superoxide radical (O₂) and notably increased peroxidase (POD), ascorbate peroxidase (APX), glutathione reductase (GR) activity and glutathione (GSH), ascorbate (AsA), Proline concentration and root length, root activity in wheat seedlings treated by moderate drought stress. While superoxide dismutase (SOD), catalase (CAT) activity, leaf area and dry weight were not notably influenced by He-Ne laser. It was concluded that 3min laser irradiation enhanced anti-drought of wheat seedlings treated with 5% or 10% PEG6000.2. In order to determine the role of laser in drought stress resistance of spring wheat (Triticum aestivum L.), seed embryos were exposed to CO₂ laser radiation for 0min, 1min, 3min and 5min, respectively, and when the seedlings were 12 days old they were treated with 10% (w/v) PEG6000 solution for 10 days. Changes in the concentration of malondialdehyde (MDA), hydrogen peroxide (H₂O₂), glutathione (GSH), ascorbate (AsA), oxidized glutathione (GSSG), carotenoid, zeaxanthin, the production rate of superoxide radical (O₂^-), the activities of ascorbate peroxidase (APX), peroxidase (POD), catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR), glutathione peroxidase (GP), glutathione-S-transferase (GST) and the growth parameters of seedlings (plant height, leaf area and dry weight) were measured to test the effects of laser pretreatment. The results showed that suitable laser pretreatment of embryos enhanced drought stress resistance in wheat seedlings by decreasing the concentration of MDA and H₂O₂, GSSG, the production rate of O₂^-, leaf area and increasing the activities of APX, GST, GP and POD and AsA, carotenoid and zeaxanthin concentration. It is suggested that those changes in MDA, O₂^- H₂O₂, anti-oxidative enzymes and anti-oxidative compounds were responsible for the increase in drought stress resistance observed in the experiments. The results also showed that the laser had a long-term positive physiological effect on the growth of drought stress seedlings.3. The laser has been widely used in the field of biology with the development of laser technology. Previous studies suggest that suitable doses of laser irradiation improved plant metabolism and enzymatic activities under drought stress and enhanced drought tolerance in wheat seedlings. The objective of this study was to test whether nitric oxide (NO) is involved in laser pretreatment induced drought tolerance in wheat seedlings due to its nature as a second messenger in stress responses. Plant were treated with NO donor (sodium nitroprusside, SNP), 3min CO₂ laser pretreatment, laser pretreatment in combination with 0.5% (w/v) c-PTIO (NO scavenger) and their effects on the lipid peroxidation, the activities of antioxidant enzymes and the concentration of antioxidant compounds and wheat seedlings growth and development were compared. The results showed that 3min laser pretreatment and NO donor SNP could enhance drought tolerance in wheat seedlings by decreasing the concentration of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂), the production rate of O₂^-, and increasing the activities of ascorbate peroxidase (APX), peroxidase (POD), catalase (CAT), superoxide dismutase (SOD) and glutathione reductase (GR) and the concentration of glutathione (GSH) and ascorbate (AsA), and having a positive physiological effect on the growth of drought stress seedlings. But the promotive effect of laser pretreatment induced drought tolerance in wheat seedling was not effectively reversed by the addition of 0.5% (w/v) c-PTIO (NO scavenger). The results suggested that NO was not involved in laser pretreatment induced drought tolerance in wheat seedlings and laser pretreatment did not trigger NO production that may lead to the drought tolerance of wheat seedlings.4. Previous studies suggest that suitable doses of laser irradiation improved plant metabolism and enzymatic activities under drought stress and enhanced drought tolerance in wheat seedlings. The objective of this study was to test whether hydrogen peroxide (H₂O₂) is involved in laser pretreatment induced drought tolerance in wheat seedlings due to its nature as a second messenger in stress responses. Plant were treated with different concentration of H₂O₂, 3min CO₂ laser pretreatment, laser pretreatment in combination with 100U CAT, 2mM AsA (H₂O₂ scavenger) and 5μM DPI (an inhibitor of NADPH oxidase) and their effects on the lipid peroxidation, the activities of antioxidant enzymes and the concentration of antioxidant compounds and wheat seedlings growth and development were compared. The results showed that 3min laser pretreatment could enhance drought tolerance in wheat seedlings by decreasing the concentration of malondialdehyde (MDA) and hydrogen peroxide (H2 O₂), the production rate of O₂^-, and increasing the activities of ascorbate peroxidase (APX), peroxidase (POD), catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR) and the concentration of glutathione (GSH), and having a positive physiological effect on the growth of drought stress seedlings. But the promotive effect of laser pretreatment induced drought tolerance in wheat seedling was effectively reversed by the addition of 100U CAT, 2mM AsA (H₂O₂ scavenger) and 5μM DPI (an inhibitor of NADPH oxidase). The results suggested that H₂O₂ was involved in laser pretreatment induced drought tolerance in wheat seedlings and laser pretreatment triggered H₂O₂ production that may lead to the drought tolerance of wheat seedlings. The data also imply that laser pretreatment-triggered H₂O₂ generation is likely related to NADPH oxidase.