| As Lu mian yan 28 was the experimental material, and under the conditions of Hydroponic with interior control, three testing program, from which, were set: the first was studies on the effects of different treatment time of exogenous nitric oxide (NO) donor sodium nitroprusside (SNP) on the growth and physiological changing of cotton seedlings under salt (NaCl) stress; and the second was studies on the effects of SNP on indexes above of cotton seedlings under different concentrations NaCl stress; the third one was to research the effects of SNP on the same indexes of cotton seedlings with no stress. The results show that:1. With the treatment time prolonged, the growth of cotton seedling was inhibited severely in the treatment of 100 mmol·L～（-1）NaCl. Growth on plant height, stem diameter and leaf emergence rate, were all slowed down. Meanwhile, leaf area decreased, cotyledon abscission became earlier, portion of the blade was withered and fade. For SNP treatment under salt stress, cotton seedling height, stem diameter and leaf area were reduced, cotyledon growth time increased, thus making blade damage degree reduced and , leaf senescence delayed. The growth rate of height and the speed of blade appeared of cotton seedling under 50μmol·L～（-1）SNP processing 18-25d in NaCl stress exceeded that in the treatment of only NaCl.2. With the treatment process, chlorophyll (a+b) content of cotton seedling leaf under 100 mmol·L～（-1）NaCl was first increased and then decreased. Comparing with the conrol, only in the initial time (5d) there is no difference, the value of NaCl treatment were significantly lower; the degradation rate of chlorophyll b is higher than the chlorophyll a, chlorophyll a/b ratio increased, and carotenoids content reduced. Under the condition of this experiment, the chlorophyll (a+b) content was increased in the early phase of processing, and then no alleviate effect appeared by 50μmol·L～（-1）SNP under NaCl stress; the chlorophyll content of cotton seedling leaf under NaCl stress increased obviously, and chlorophyll a/b ratio increased slightly in the late phase by 500μmol·L～（-1）SNP. SNP, especially for the concentration of 50μmol·L～（-1）effect better, alleviated NaCl stress, would decreased the fluorescence parameters Fv/Fm,ΦPSⅡand qP. However, the NPQ decreased without remission effect; insteadly, 500μmol·L～（-1）SNP aggravate its reduction. This demonstrated that exogenous nitric oxide alleviated the cotton seedling`s chlorophyll content and chlorophyll fluorescence parameters reducing caused by NaCl stress, which is beneficial to improve the photosynthetic capacity.3. In the early time with the 100 mmol·L～（-1）NaCl, soluble protein content of cotton seedling leaf is slightly higher than that of the control, while the latter was decreased significantly; MDA content changing trend was in accorded with trend of protein; proline content showed a high - low - high - low trend. However, soluble protein content level of cotton seedling with SNP treatment under NaCl stress leaf was constant on the whole, and the decreasing effect caused by NaCl stress on the late was alleviated by SNP. The proline content in leaves of cotton seedling under NaCl stress were reduced by SNP, especially for 500μmol·L～（-1）SNP. At processing 25d, the soluble protein, MDA and proline content in leaves of different parts of the cotton seedling were different: decreasing effect of soluble protein contents in middle and lower leaves of cotton seedling under NaCl were alleviated sifnificantly by SNP; MDA content in top and lower leaves of cotton seedling under NaCl stress was decreased by SNP; proline content all parts are reduced. Thus it can be seen, exogenous nitric oxide have a regulatory effect on some physiological indexes of cotton seedling under NaCl stress.4. With the NaCl treatment time prolonged, IAA content of cotton seedling leaf in the early stage (10d) was higher as much as 56% than that of the control, and followed by a rapid decline; ABA content in the early stage (20d) was higher as much as 64% than that of the control, then the increase (ranged from 7% to 20% higher than that of the control) of ABA content decrease; ZR (one kind of cytokinin) content has been 30%-50% higher than that of the control; GA content were almost always higher than that of the control, but only at 15d when it slightly lower than the control; hormone balance was broken. In the treatment of 50μmol·L～（-1）SNP, IAA content showed increasing then decreasing trend; The content of ABA and GA decreased during the treatment of 20 days; ZR content first decreased and then increased. High concentration of SNP affect IAA content with the first tall hind low change; ABA content slightly lower than that of the salt stress; GA content decreased, but rised occasionally; ZR content was fluctuated and unstable. Low concentrations of SNP lower IAA / ABA ratio, IAA/ZR with the same trend- lower after the first high to the control. In early time, ZR/ABA was higher than salt stress, and decreased at 25d; GA/ABA first tall hind low. Changes in hormone content may be the caused of exogenous nitric oxide on cotton seedling under salt stress in other various physiological changes the incentive.5. In the treatment of 10 days, the degree of cotton seedling inhibited under mild salt stress was lighter than that under high salt stress, the leaf relative water content was improved by NaCl stress. With SNP treatment, the specific leaf weight of cotton seedling under NaCl stress was increased, the relative moisture content of shoot and root of cotton seedling under NaCl stress was decreased significantly, while the biomass has not changed.6. In the treatment of 10 days, no remission effect of SNP on chlorophyll content of cotton seedling under salt stress decreased. But obvious relief effect under high salt stress, especially 50μmol·L～（-1）SNP effect is best. Under mild salt stress, SNP effected on chlorophyll fluorescence parameters Fv / Fm decline without relief, but alleviatedΦPSⅡdecreased, qP decreased and NPQ increases. It suggested that exogenous nitric oxide on cotton seedling chlorophyll fluorescence parameters effect of poor relief in the second scheme condition.7. In the treatment of 10 days, Soluble protion content, SOD activity, POD activity and CAT activity of cotton seedling leaf was significantly decreased with the increasing of NaCl concentration; SNP increased SOD activity of cotton seedling under NaCl stress leaf, reduce the activity of CAT; POD activity was improved by SNP under high concentration NaCl, and was reduced by high concentration SNP under mild NaCl stress. This indicated that exogenous nitric oxide partially alleviates the lower activity of protective enzymes caused by NaCl stress.8 SNP showed concentration effect on the growth of cotton seedling. Stress symptoms would appear on cotton seedling under 200~1000μmol·L～（-1）SNP. Internode enlongation, stem diameter growth and blade expansion of cotton seedling was inhibited, cotton seedling organs moisture content is reduced, and dry weight of leaf, stem and root decreased significantly with 50~1000μmol·L～（-1）SNP.9 leaf chlorophyll content and Fv/Fm of cotton seedling were inversely to SNP concentrations, and chlorophyll a showed larger reduction amplitude than chlorophyll b. Chlorophyll a/b values increased with along SNP concentration, taking on rising and then descending performance. For 200 to 1000μmol·L～（-1）SNP treatment, the content of chlorophyll (a+b) and carotenoid, chlorophyll a/b and Fv/Fm of cotton seedling were all reduced significantly.10. Superoxide anion production rate, MDA and proline content, and the activity of SOD of cotton seedling leaf increased; soluble protein content and CAT activity decreased with the SNP concentration change from 200 to 1000μmol·L～（-1）. So, the concentration range is not conductive to the growth of cotton. The POD activity change is various, which reduced under 50μmol·L～（-1）SNP processing and increased under 1000μmol·L～（-1）SNP. Meanwhile, other treatments did not change significantly. |
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