Study On The Alleviatory Effect Of GSH On Limonium Bicolor Under NaCl Stress

The lost of the membrane stability and integrity during salt stress is the primaryreason that salt stress leads to destruction and death of plant. Under salt stress, Na+ isexcessively accumulated in the plant. The balance between producing and scavenging ofreactive oxygen species is destroyed. This can start up the peroxidation and degreasing ofmembrane lipids, consequently destroy the structure of bio-membrane. Thereforeimproving the ability of scavenging system against reactive oxygen species can enhancethe salinity tolerance of the plant. GSH is a reductive substance that containing –SHgroup. It distributes widely in plant. GSH plays a great role in defending membraneperoxidation. Its main function is to eliminate peroxidation and convert R-S-S-R to –SHby the exchanging reaction between GSH and R-S-S-R, consequently reduce enzymesand structural proteins. Plant cell can stabilize –SH and membrane structural proteins bykeeping high concentration of GSH. In this study seedlings of Limonium bicolor under 0,200, 400mmol/L NaCl were treated with or without 20mg/L GSH in the hydroponicculture solution. Then the activities of ROS scavenging enzymes and the content ofantioxidants were determined, meanwhile some other physiological parameters such asgrowth, photosynthesis, oxidative damage and so on were also measured simultaneously.The aim was to determine the alleviatory effect of GSH on the salt-secretary halophyteLimonium bicolor under NaCl stress. The main results were shown as follows:1. Effect of exogenous GSH on the growth of Limonium bicolor under NaCl stressThe growth of Limonium bicolor was significantly enhanced by GSH. The fresh anddry weight, leaf area and leaf succulent extent were all significantly lowered with theincrease of NaCl concentration up to 400mmol/L. When GSH was applied in thehydroponic culture solution, however, the decrease extent was significantly minished.The same phenomenon was found in the root/shoot ratio of the plant treated with NaCland GSH together with.2. Effect of exogenous GSH on the water status of Limonium bicolor under NaClstressThe osmotic potential and water potential both decreased with the increase of NaClconcentration, but osmotic adjustment ability increased with NaCl treatment. When GSHwas added, the osmotic potential and water potential all increase, with the waterpotential increase more significantly than osmotic potential, which implied the increaseof turgor pressure under GSH treatment. However, the osmotic adjustment ability did notincrease significantly under GSH treatment, indicating GSH did not participate in theosmotic adjustment.3. Effect of exogenous GSH on the Na+,K+ content of Limonium bicolor underNaCl stressNa+ contents increased sharply with the increase of NaCl concentration. Under thecondition of 400mmol/L NaCl, Na+ contents in the shoot and root were 5 and 2.3 times ofcontrol respectively. When GSH was applied together with NaCl, Na+ contents in theshoot and root both decreased significantly compared with those treated without GSH,and the decrease extent in the root was more obvious than that in the shoot. On thecontrary, K+ content in the shoot and root decreased sharply with the increase of NaClconcentration, and the decrease extent in the shoot was more remarkable than that in theroot. When treated with GSH, K+ content in both parts increased greatly compared withthose treated without GSH.4. Effect of exogenous GSH on the photosynthetic parameters of Limonium bicolorunder NaCl stressThe net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2concentration (Ci) of Limonium bicolor decreased with the increase of NaClconcentration. When GSH was added, the decrease degree was much lower than whenGSH wasn't added. Under NaCl stress the content of chlorophyll in the leaves increased,and when GSH was applied with NaCl, it decreased on the contrary. This was probablybecause GSH alleviated salt stress and enhanced the expending of leaves.5. Effect of exogenous GSH on the activities of ROS-scavenging enzymes inLimonium bicolor under NaCl stressThe integrity of protection enzymes is key to salinity tolerance of plants. Under NaClstress, the activities of SOD, CAT, APX and GR in Limonium bicolor all increasedsignificantly. This might be the cause of Limonium bicolor's high salt-tolerance ability.Limonium bicolor is a typical salt-secreting halophyte. Unlike non-halophytes, NaCltreatment can activate its ability of ROS scavenging, When GSH was applied toLimonium bicolor, and the activities of the enzymes were further increased significantly.This was probably because GSH can protect the enzymes and the –SH of structuralproteins from being oxidated, and stabilize biomacromolecules. In addition, exogenousGSH may enhance the AsA-GSH cycle.6. Effect of exogenous GSH on the contents of antioxidants of Limonium bicolorunder NaCl stressAsA is an important member of non-enzymic system in ROS scavenging. Under NaClstress, the AsA content in the leaves of Limonium bicolor increased sharply. When GSHwas added, both AsA and GSH in the leaves increased. But the increasing degree of AsAwas higher than that of GSH. The results indicated that exogenous GSH may be absorbedby the root and then transported to the leaves. When GSH is in high concentration, it canbe offered to AsA-GSH cycle, and thus enhanced the AsA content.7. Effect of exogenous GSH on radical damage of Limonium bicolor under NaClstressBeing the index of lipid peroxidation, MDA was determined to indicate thedamaging degree of free radicals. NaCl treatment significantly increased MDA content,While GSH treatment remarkably lowered MDA content. The change of membranepermeability also proved that exogenous GSH can lessen the peroxidation of membraneand protect the membrane from being damaged.8. Effect of exogenous GSH on free radical of Limonium bicolor under NaCl stressAs to reactive oxygen species, H2O2 and O2.-play key roles in damaging plants undersalt stress. Under NaCl stress, the H2O2 content and the O2.-production rate of Limoniumbicolor increased with the concentration of NaCl. Moreover, they increased sharply under400mmol/L NaCl. When GSH was applied, the increasing extent decreased significantly,which suggested that GSH treatment can lower the accumulation of ROS and improve thesalt-tolerance of plants.