The Regulation Of Na~+on The Growth And Adaptation In Cotton Under Drought Stress

In this experiment, the material was potted cotton watering with salt water (differentconcentrations of NaCl solution), followed by a sustained drought. Then we measured thedata of photosynthetic rate, chlorophyll fluorescence parameters, photosynthetic gas exchangeparameters,and analyzed the changes of relative water plants, water potential, osmoticpotential, water status, antioxidant enzyme activity in leaves,the content of Na+and K+andosmolyte,which is to explore the effect of Na+in environment to adapt to drought stress incotton. Test results are as follows:(1) The regulating effect of NaCl on the growth and water status of cotton under droughtconditionsThe results showed that the growth of the plantlets was significantly inhibited by thedrought stress, but the plant height, biomass in the cotton plants watered with25~100mmol·L-1NaCl solution under drought stress were significantly higher than those watered with waterunder the same intensity of drought stress. Meanwhile, the soil and leaf relative water content,cell turgor, Na+concentration in plants watered with25~100mmol·L-1NaCl solution were allsignificantly higher compared with those in plants watered with water, but the plant waterpotential and tissue osmotic potential of plants watered with saltwater was significantly lowerthan those watered with water under the same intensity of drought stress. In addition, thedecrease in tissue osmotic potential was significantly correlated with the Na+content. Theseresults indicated that the presence of a moderate amount of Na+in the soil can improve thewater status of both the soil and the cotton plants, accelerate the absorption and accumulationof Na+in the roots, lower the tissue osmotic potential, thereby enhance the suction force ofwater in plant for maintaining a high cell turgor, consequently enable the plants to maintain arelatively higher photosynthetic rate and growth rate. In this sense, it is suggested that theexistence of a certain amount of NaCl in soil can effectively alleviate the adverse effects ofdrought on cotton.（2）The effect of NaCl on the photosynthesis of cotton leavies under drought conditionsIn this experiment, the net photosynthetic rate of cotton leaves under natural droughtconditions drought increases the number of days and continued to decline. Gas exchange parameters, natural cotton plants in arid drought continued rapid increase in intercellular CO2concentration20d after the rapid decline in stomatal limitation; chlorophyll fluorescenceparameters of, Fo began to rise rapidly in the drought continued after10d20d afterdecreased rapidly, Fv, Fv/Fm, Fv/Fo, RC/CSo and PI were10d after the start of thedrought continued rapidly declining (PI in the drought began to decrease after5d), ABS/RCin the drought lasts10d after rising. These results have shown that prolonged drought has ledto lower photosynthetic activity of mesophyll cells, the photosynthetic apparatus from seriousinjury. The cotton plant drought+NaCl treatment, the net photosynthetic rate of decline wassignificantly less than the blades are not treated with NaCl, photosynthetic apparatus by thedegree of injury is also lighter or no significant damage. Thus, under conditions of prolongeddrought soil after watering NaCl solution, cotton plants to increase the absorption andaccumulation of Na+, reducing potential tissue penetration, strong suction power plants tomaintain a certain amount of cell turgor, thereby reducing water shortage due to droughtdamage caused by cotton photosynthetic apparatus (chloroplasts), so that the productioncapacity of the plant material is kept at a relatively high level, mitigate the adverse effects ofdrought on photosynthetic apparatus damage caused to the maximum extent, thus enhancingtheir drought tolerance of plants.(3) NaCl treatment on antioxidant enzyme activity of cotton leaves under drought conditionsIn this study, the SOD, POD, CAT activity and MDA content in cotton leaves wereinvestigated. Within10days of drought treatment, the MDA content and the activity of threeenzymes were not significantly changed when the soil water content was high. However, fromthe10th day on after the drought stress, the MDA content and the activity of three enzymesincreased progressively in a rapid rate, and reached the height in25days after the droughtstress followed by a decline, while the MDA is maintained at a high level. This may implythat the drought stress resulted in the increase in the free radicals that activated theanti-oxidation protection mechanisms but still resulted in the permanent injury in the plants.Although the combined stresses of drought and salt also resulted in the increase in the SOD,POD, MDA content and CAT activity, no sharp decline in activity of the three enzymes, andthe MDA content was less than one third of the treatment. This implies that the addition of25~100mmol·L-1NaCl could effectively alleviate the membrane oxidation.(4) The effect of NaCl treatment on the osmoregulator content in cotton leaves under drought conditionsThere are two categories of osmoregulators, one is the inorganic ions taken by plant cellsfrom the external environment, such as K+, Na+, Ca2+and Cl-and other inorganic ions, theother is the organic compounds synthesized in cells, such as proline, betaine, soluble sugar,soluble protein and amino acids. Osmoregulators is an important strategy in lowering theosmotic potential of plants under water stress, so as to withstand drought, salinity and otherstress. In this experiment, the continuing drought conditions, soluble sugar, proline, betaineand soluble protein content of cotton leaves were significantly increased, indicating that thedrought induced the increase in the osmoregulators in cotton leaves. The addition of25–100mol/L NaCl to the soil resulted in the accumulation of these four kinds of osmoregulatorscompared with cotton plants subjected only drought. The ions could have been absorbed bythe cotton root transported to its upper parts and compartmentalized by the vacuoles so thatthe concentration of the cell sap was raised and the osmotic potential was reduced, this wasfavorable for cells to take water and better adapt to water stress.To sum up,25~100mmol·L-1Na+in the soil could increase the ability of the plants andthe soil to maintain water, as well as the Na+absorption and accumulation in cotton plants,thus reduced the tissue osmotic potential, thereby enhancing the suction force of water inplants, so as to maintain a high cell turgor, a relatively higher photosynthetic rate and a highergrowth rate, thereby reduce the membrane lipid peroxidation. Meanwhile, theinorganic osmoregulators like Na+could significantly reduce the requirement oforganic osmoregulators, such as protein, betaine, soluble sugar and proline accumulation,reducing the consumption of assimilated organics, consequently enhanced the plant growthand drought resistance.