Effects Of Exogenous No On The Physiological Characteristics Of Three Ornamental Grasses Under NaCl Stress

Miscanthus sacchariflorus?Pennisetum alopecuroides?Mscanthus sinensis were used as experimental materials in this study.The salt stress environment was simulated by NaCl under pot experiments condition,Sodium nitrine?SNP?were used as the exogenous nitric oxide?NO?donor.Six treatments were set up:CK0?CK1?120mmol/LNaCl??T1?120mmol/LNaCl+0.05mmol/LNO??T2?120mmol/LNaCl+0.1mmol/LNO??T3?120mmol/LNaCl+0.25mmol/LNO??T4?120mmol/LNaCl+0.5mmol/LNO?in this study.In order to provide theoretical basis for improving the salt tolerance of ornamental grass and reveal the sustained release effect of NO on NaCl,different exogenous NO concentration measurement were set to three kinds of ornamental grass growth under NaCl stress and the change of physiological and biochemical indexes were analyzed.The main results are as follows:?1?NaCl stress treatment inhibited the growth of 3 ornamental grass,with the extension of stress time,the growth rate of plant height and leaf length in other treated plants were lower than that of blank control CK0.Applying exogenous NO treatment can alleviate the stress of NaCl on plant.With the extension of processing time,3 species of ornamental grass were higher than 120mmol/L NaCl.With the increase in applying exogenous NO concentration,the growth rate of 3 species of ornamental grass showed a change trend which rose at first and then went down,and reach its maximum under T3treatment.The height and growth rate of the leaves of Miscanthus sacchariflorus under the T3 treatment were 1.20 times and 1.70 times higher than that of CK1.The height and growth rate of the leaves of the Pennisetum alopecuroides were 2.22 times and 1.59 times respectively.The height and growth rate of the leaves of the Miscanthus sinensis were 1.57times and 1.63 times respectively on day 24.?2?Compared with the blank control CK0,the relative water content and moisture saturation deficit in leaves of the three ornamental grass were respectively decreased and increased with the extension of stress time under NaCl stress.The application of appropriate concentration of exogenous NO has different degree of alleviating effect on NaCl stress,and the appropriate concentration of exogenous NO effectively slowed down the loss of water in the leaves.The sustained release of water loss of 3 ornamental grasses was most obvious under the T2 and T3 treatments on day 24.Compared with CK1,the water content of leaves was improved 6.58%?6.77%?31.06%?27.15%?15.44%and11.56%.?3?Under the NaCl continuous stress,the relative conductivity and MDA content in leaves of the three ornamental grass increased significantly.A moderate amount of exogenous NO applying can significantly reduce the relative electrical conductivity and MDA content of 3 kinds ofunder the ornamental grass NaCl stress.With the increased of the exogenous NO concentration,the relative conductivity and MDA content decreased first and then increased.under T3 treatment,the relative conductivity and MDA content of Miscanthus sacchariflorus were reduced by 9.17%and 28.44%respectively compared with CK1 treatment.,the relative conductivity and MDA content of Pennisetum alopecuroides were reduced by 20.11%and 67.95%respectively compared with CK1treatment,the relative conductivity and MDA content of Miscanthus sinensis were reduced by 7.56%and 21.77%respectively compared with CK1 treatment.?4?With the prolongation of NaCl stress,the contents of free proline and soluble sugar in leaves of three ornamental grasses increased continuously under the CK1treatment.Compared with CK1,the application of exogenous NO significantly slowed down the increase of free proline and soluble sugar content in leaves.With the increase of exogenous NO concentration,the content of free proline and soluble sugar in leaves firstly decreased and then increased,and they all went to the lowest contents under the treatment of T3.When treated with 24 days,the free proline content of the leaves of Miscanthus sacchariflorus?Pennisetum alopecuroides?Mscanthus sinensis were 52.99%,48.47%and52.82%of CK1,respectively,and the content of soluble sugar was 79.18%,54.37%and73.95%of CK1,respectively.With the increase of CK1 treatment time,soluble protein first decreased,then rose and then decreased,but the soluble protein content of leaves which were treated with different concentrations of exogenous NO showed different trends.After 24 days,the three ornamental grasses which were treated under the different concentrations of exogenous NO were higher than CK1,and all of them were highest under T3 treatment.The soluble protein content of leaves of Miscanthus sacchariflorus?Pennisetum alopecuroides?Mscanthus sinensis was 135.20%,144.06%and 137.83%of CK1 respectively under T3 treatment.?5?With the prolongation of treatment time,the SOD and POD activities of the three ornamental grasses showed a trend of increasing first and then decreasing,compared with NaCl stress treatment,the application of exogenous NO could maintain the SOD and POD activity of the leaves to a higher level after reaching the limit of tolerance,so as to relieve the damage of plants to NaCl stress.In this experiment,the activities of SOD and POD increased first and then decreased with the increase of the concentration of exogenous NO,and the activity was highest under the treatment of T3.After 24 days of treatment,the activities of SOD and POD in leaves of Miscanthus sacchariflorus were 245.82%and160.88%of CK1,and the activities of SOD and POD in leaves of Pennisetum alopecuroides were 238.88%and 238.00%of CK1,respectively.The activity of Mscanthus sinensis was 167.08%and 176.92%of CK1,respectively.?6?Under NaCl simulated salt stress,the contents of chlorophyll a,chlorophyll b,total chlorophyll,and carotenoids in leaves of three ornamental grasses showed a decreasing trend with the extension of stress time.However,the color difference values L*,a*,b*were rose.After the application of SNP,the decrease trend of each pigment content and the upward trend of color difference value were significantly slower than that of NaCl stress alone.Even the pigment content in Miscanthus sacchariflorus and Pennisetum alopecuroides first decreased and then increased.Overall,the effect is most significant under T3 treatment.?7?NaCl single salt stress resulted in imbalance of ion content in leaves of three ornamental grasses.With the prolongation of stress time,Na⁺and Cl^-will accumulate in large amounts in leaves,and the contents of K⁺,Ca²⁺and Mg²⁺will be greatly reduced,Na⁺/K⁺,Na⁺/Ca²⁺and Na⁺/Mg²⁺increased.However,the addition of exogenous SNP could significantly reduce the Na⁺and Cl^-contents in leaves under the salt stress,and promote the increase of K⁺,Ca²⁺and Mg²⁺contents,they can improve the relative balance of ions in the leaves.With the increase of exogenous NO concentration,the alleviation effect first increased and then decreased,and the T3 treatment had the strongest alleviation effect.?8?There was a dose-effect of exogenous NO on the alleviation of NaCl stress in three species of ornamental grasses,at a certain concentration between 0.05 and 0.25 mmol/L,the mitigation effect of NaCl stress increased with the increase of exogenous NO concentration.However,when the concentration was higher than 0.25 mmol/L,the mitigation effect was significantly reduced or no mitigation when reached 0.5 mmol/L.In a comprehensive analysis,exogenous NO at a concentration of 0.25 mmol/L had the most significant alleviation effect on the NaCl stress of three ornamental grasses,followed by an exogenous NO at a concentration of 0.1 mmol/L,which was able to better weaken the hurt of plants which were caused by NaCl stress.