| Cotton production plays an important role in China's agricultural development and has become a pillar industry supporting the economic development of Xinjiang,where is particularly suitable for cotton cultivation.Low temperature is one of the most important abiotic stress factors that limit plant growth,development,survival,distribution,crop yield,and crop quality.Seedling emergence during periods of low temperature restricts the sustained and healthy development of cotton production in Xinjiang.Cotton seed coating can improve the resistance of cotton seedlings to chilling injury,but the mechanism underlying this effect is not well understood.In this study,commercially available cotton seed coatings were applied under low temperature stress in simulated field conditions.The active ingredients of seed coatings on cotton seedling leaf ultrastructure,seedling growth,and physiological and biochemical indexes of seed germination and seedling health were assessed to study the mechanism underlying resistance to chilling in cotton seedlings.The main results are as follows:1.Research on the screen of active ingredientsand formulation.Based on indoor bioassay and effect evaluation test in field,nine of the active ingredients can improve cotton seedling emergence,seed coatings M1,M3 and M4 respectively improved the cotton seedling emergence rate and germination rate by 14.81%,13.41%and 14.37%in comparison with the control treatment.The cotton seedling height,stem diameter,root length,and lateral root number were increased by 0.6cm?4.95cm?0.07mm?0.16mm?2.83cm?6.13cm ? 2.28?23.08%.in comparison with the control treatment.Then,the formulation which consists of M1,M3 and M4 was made.2.Seed coating improved the e?ffect of cotton on chilling resistance.The temperatures were respectively set to 5 ?,10 ?,15 ? and 20 ?,after sowing 1 d,3 d,5 d.In comparison with the germination rate of uncoated seeds,the germination rates of seeds coated with M1 and M4 were significantly increased by 14.98%and 12.45%,respectively,at a temperature of less than 15 ?,whereas the emergence rates of seeds coated with M1 and M4 were significantly increased by 11.8%and 9.35%,respectively,at a temperature of less than 10 ?.The plant height of seedlings from seeds coated with M1 and M3 were increased by 3.3 cm and 3.2 cm,respectively,in comparison with that of control plants.Cotton seedlings that were treated with seed coatings suffered lightly and recovered quickly.Fungicides played an important role in cotton chilling resistance,followed by plant growth regulators.3.Effects of seed coating on the cell ultrastructure of cotton seedling leaves and roots.After sowing 4 d and 7 d,the temperature was set the same with the above.The observation of transmission electron microscopy(sem)showed that,chloroplast ultrastructure was damaged in the leaf cells of uncoated cotton seedlings,while mitochondria growth was abnormal.In seedlings from coated seeds,the leaf cell structure was more complete than that of seedlings from uncoated seeds,while chloroplasts and mitochondria were clearly visible.4.Seed coating increased the physiological and biochemical reaction of cotton seedlings related withchilling resistance.The measurement of cotton seedling leaf cell membrane permeability,protective enzyme activity and osmotic regulation substances showed that,the tested cotton seed coatings significantly improved the antioxidant enzyme activity of cotton seedlings.Seeds coatings M1,M3,and M4 increased superoxide dismutase(SOD)activity by 3%-68%,in comparison with that of seedlings from untreated seeds.The seed coating treatments increased soluble sugar content(7-10-fold),soluble protein content(68-101%),reducing the damage caused by chilling stress on cotton seeds and seedling.5.Seed coating regulated the expression of genes related with chilling resistance.The expression levels of P5CS?SOD?POD?TIP1?AGP31 were measured.Expression levels of P5CS and POD were increased in the leaves and lower axes of the cotton seedlings from coated seeds in comparison with that of seedlings from uncoated seeds.Under low temperature stress(10?),the expression levels of POD,SOD,TIP1,and AGP31 was significantly increased in the leaves and lower axes of the cotton seedlings from coated seeds in comparison with that of seedlings from uncoated seeds.When the temperature was 15?,the expression levels of AGP 31 was significantly increased in the leaves of the cotton seedlings from coated seeds in comparison with that of seedlings from uncoated seeds.In conclusion,during chilling stress at 0-15 ?,the seed coatings protected the biological structure of cells,enhanced expression levels of cold resistance genes,improved the physiological activity of cells,promoted seed germination and seedling growth,and improved seedling resistance to low temperature stress.Enhancement of cold resistance by seed coatings is likely related primarily to their constituent bactericides and growth regulators.Among the tested seed coatings,M1 has the best comprehensive effect with the enhanced the cold resistance of cotton seedling. |
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