Study On The Alkali Tolerance Of Nitraria Tangutorum And The Effect Of Exogenous NO On The Relieving Of Alkali Stress

Soil salinization has become a global resource and environmental problem.This ecological disaster seriously restricts the growth of crops and the survival of vegetation,breaking the ecological balance and system stability.Compared with saline soil,alkaline soil has a larger area and more harm.Nitraria tangutorum is a kind of ecological stress resistant and economical shrub with fruit pulp.It has ecological adaptability of wind sand resistance,saline alkali resistance and barren resistance.It plays an active role in soil and water conservation,saline-alkali soil improvement and wind sand fixation.Therefore,it is of great significance to study the response mechanism of Nitraria tangutorum to alkali stress and evaluate its alkali tolerance,and explore the technical ways to improve its growth adaptability in alkaline soil,so as to realize the continuous improvement and efficient utilization of saline-alkali soil.Different concentrations(0,200,300,400,500 mmol·L-1)of Na HCO3 and Na2CO3 were used to treat Nitraria tangutorum seedlings.At the same time,SNP was used as an exogenous NO donor,and five concentration gradients of 0,100,150,200 and 300 μmol·L-1 was set,objective to explore the growth,physiological response and leaf ultrastructure changes of Nitraria tangutorum under alkali stress,and the effect of exogenous NO on the growth and physiological indexes of Nitraria tangutorum under various alkali stress concentrations.The main results are as follows:1)The ultrastructure showed that when the concentration of alkali stress was more than 300 mmol·L-1,the cell wall,plasma membrane and chloroplast morphology of Nitraria tangutorum mesophyll cells changed significantly,and the chloroplast structure was damaged significantly.Among them,the cell wall of mesophyll cells was no longer smooth and there was a tendency of precipitation or dissolution;the folds and protrusions of cell plasma membrane showed vesicles of different shapes;the chloroplast swelled and deformed,accompanied with the separation of plasma wall,the compact structure of grana lamellae was destroyed,and some thylakoids were arranged disorderly,and appeared vesiculation or even disintegration;the outer membrane of chloroplast was sunken or partially broken,and matrix was exosmosis;osmiophilic granules in chloroplast gathered into piles,and the number and volume of osmiophilic granules increased compared with the control,and a small amount of starch granules appeared.2)The plant height,biomass,root shoot ratio,root activity and chl(a+b)of Nitraria tangutorum decreased with the increase of alkali stress concentration,the root activity decreased significantly under200 mmol·L-1 alkali stress,while the biomass and root shoot ratio decreased significantly under 300mmol·L-1 alkali stress;malondialdehyde(MDA),hydrogen peroxide(H2O2)and superoxide anion(SOD)increased with the increase of alkali stress concentration;soluble protein(SP),peroxidase(POD)and catalase(CAT)increased significantly when the concentration of alkali stress was ≤ 300 mmol·L-1,and decreased significantly when the concentration of alkali stress was ≥ 300 mmol·L-1;proline(pro)and superoxide dismutase(SOD)increased significantly when the concentration of alkali stress was ≤ 400mmol·L-1,and decreased significantly when the concentration of alkali stress was ≥ 400 mmol·L-1.3)Under different alkali stress concentrations,plant height,biomass,root shoot ratio,root activity and chl(a+b)of Nitraria tangutorum increased first and then decreased with the increase of exogenous NO concentration;MDA,H2O2 and? 2O decreased first and then increased with the increase of exogenous NO concentration;The content of pro and SP as well as the activities of SOD,POD and CAT increased first and then decreased with the increase of exogenous NO concentration,except that pro increased with the increase of exogenous NO concentration under 400 mmol·L-1 alkali stress.4)The effect of exogenous NO on Nitraria tangutorum under alkali stress was dual.Low concentration of exogenous NO(SNP 100-200 μmol·L-1)could significantly alleviate alkali stress,especially could effectively improve the growth adaptability of plants under high concentration of alkali stress.High concentration of exogenous NO(SNP ≥ 300 μmol·L-1)did not significantly alleviate alkali stress,and even had inhibitory effect.In conclusion,with the increase of alkali stress concentration,the growth inhibition and ultrastructure of Nitraria tangutorum were significantly damaged;when the concentration of alkali stress was ≤ 300mmol·L-1,Nitraria tangutorum showed a certain alkali resistance through its physiological regulation(accumulation of osmotic regulating substances,activation of antioxidant enzyme activity),and structural changes(vesicles formed by protuberance of plasma membrane,and increase of osminophils).Under alkali stress,exogenous NO at a lower concentration(SNP 100-200 μmol·L-1)can maintain the balance of active oxygen in plants with antioxidant enzymes.At the same time,it can maintain the osmotic balance by promoting the accumulation of osmotic adjustment substances,thus changing the distribution pattern of energy and nutrients in plants,and alleviating the growth inhibition caused by alkali stress;exogenous NO at a higher concentration(SNP 300 μmol·L-1)has a weak effect on the alkali stress,and even aggravates the oxidative stress.