Research On The Compensatory Mechanisms Of Cotton Root Under Drought Stress After Re-watering During The Flowering And Boll-forming Stage

Two cotton varieties(CCRI-45 and CCRI-60) with different drought toleranct were screened to study the changes of cotton root dry weight, root physiological indexes, cotton yield and quality under the different degree and the time of drought stress after re-watering during the flowering and boll-forming stage. The main results were as follows:1、The results showed that the cotton root dry weight and the lint yield of CCRI-45 were highest under the SRWC(45±5)% for 6 days after re-watering treatment, the cotton root dry weight and the lint yield of CCRI-60 were highest under the SRWC(60±5)% for 6 days after re-watering treatment. However, the root dry weight and the lint yield of CCRI-45 and CCRI-60 were significantly lower than in control under SRWC(45±5)% for 9 days after re-watering treatment. The fiber length, uniformity index, elongation rate and fiber strength of CCRI-45 were higher than in control under the SRWC(60±5)% and SRWC(45±5)% for 6 days after re-watering treatment, and the fiber length, uniformity index, elongation rate and fiber strength of CCRI-60 were higher than in control under the SRWC(45±5)% for 3 days and the SRWC(60±5)% for 6 days after re-watering treatment, the index of the fiber quality of CCRI-45 and CCRI-60 were significantly lower than in control under the SRWC(45±5)% for 9 days after re-watering treatment. The increased amplitude of root dry weight and lint yield of CCRI-45 were higher than that in CCRI-60 under the SRWC(45±5)% for 6 days after re-watering treatment, which showed that the CCRI-45 had the high compensation ability than CCRI-60. At the same time, the relationship between the percentage of lint yield increased and the percentage of root dry weight increased were positive correlation.2、With the degree and the time of drought stress increasing, the soluble sugar and proline content of root increased, the soluble protein content of cotton root decreased under drought stress for 3 days treatment, but the soluble protein content of cotton root increased under drought stress for 6 days and 9 days treatment, after re-watering, soluble sugar and proline content of cotton root decreased, the soluble protein content of cotton root increased under the drought stress for 3 days after re-watering treatment, but the soluble protein content of cotton root decreased under the drought stress for 6 days and 9 days after re-watering treatment, and the soluble sugar, proline and soluble protein content of cotton root were still higher than in control under the drought stress for 3 days, 6 days and 9 days after re-watering treatment. The increased amplitude of cotton root soluble sugar and proline and soluble protein content of CCRI-45 were significantly higher than in CCRI-60 under the SRWC((45±5)%) for 6 days after re-watering treatment. This results showed that higher soluble sugar and proline and soluble protein content of CCRI-45 could enhance the osmotic adjustment ability of the cells and improve the ability of drought resistance and compensation.3、With the degree and the time of drought stress increasing, the gibberellin(GA) content of root decreased, the brassinolide(BRs), abscisic acid(ABA) and ethylene(Eth) content of root increasd, after re-watering, the GA content of root increased, but the root BRs and ABA and Eth content of root decreased. The increased amplitude of root GA and BRs content of CCRI-45 were significantly higher than in CCRI-60 under the SRWC((60±5)%) and SRWC((45±5)%) for 6 days after re-watering treatment, the decreased amplitude of root ABA and Eth content of CCRI-45 were significantly higher than in CCRI-60 under the SRWC((60±5)%) and SRWC((45±5)%) for 6 days after re-watering treatment. This results showed that higher GA and BRs content of CCRI-45 could promote the growth of root, make up for the damage during the drought stress, and enhances the compensation ability of root.4、With the degree and the time of drought stress increasing, the superoxide dismutase(SOD) and peroxidase(POD) activity of cotton root increased, however the catalase(CAT) activity of cotton root decreased. After re-watering, the SOD and POD activities of cotton root decreased, and the CAT activities of cotton root increased. The increased amplitude of SOD and POD activity in CCRI-45 were significantly higher than in CCRI-60 under the SRWC((60±5)%) and SRWC((45±5)%) for 9 days after re-watering treatment, the increased amplitude of CAT activity in CCRI-45 were significantly higher than in CCRI-60 under the SRWC((45±5)%) for 6 days after re-watering treatment. This results showed that the root maintaining high antioxidant enzyme activityafter re-watering could ensure the normal root physiological process and improve the compensation ability of cotton root by reducing the content of active oxygen and preventing cell damage.5、With the degree and the time of drought stress increasing, the root dry weight, the total root length, the total root surface area, the total root volume and the average root diameter of CCRI-45 firstly increasd and then decreasd, the root dry weight and the total root length of CCRI-60 showed the same trend as CCRI-45, but the total root surface area, the total root volume and the average root diameter of CCRI-60 showed the decreased trend. The root dry weight, the total root length, the total root surface area, the total cotton volume and the average root diameter of CCRI-45 were significantly higher than in control under the 10%PEG for 24 and 48 hours and 20%PEG for 48 hours treatment, the root dry weight and the total root length of CCRI-60 were significantly higher than in control under the 10%PEG for 24 hours treatment, and the increased amplitude of the root dry weight and the total root length of CCRI-45 were significantly higher than in CCRI-60 under the 10%PEG for 24 hours treatment. With the degree and the time of drought stress increasing, the cytoplasm wall separation of cotton root cell were serious, and the nucleus content degradation and mitochondrial inner structure degradation especially. The degree of disintegration of mitochondria of CCRI-45 were significantly lower than in CCRI-60 under 20% PEG for 48 hours treatment, which showed that mitochondrial structure of drought resistant varieties were stable, and could guarantee the root energy supply stress under the drought stress improving the root drought resistance.