摘要:褪黑素是一种有效的抗氧化剂, 能够促进逆境胁迫下植物的生长发育, 减缓逆境胁迫产生的伤害。棉花是我国重要的经济作物, 盐胁迫严重影响其生长发育。为探究褪黑素对盐胁迫下棉花生长发育的调控效应, 本研究以‘国欣棉9号’为材料, 设置不同浓度褪黑素浸种处理, 对盐胁迫下(150 mmol?L?1 NaCl)棉苗根系形态(总根长、总表面积、总体积、侧根数目、主根长、主根表面积、主根平均直径)进行了测定, 筛选出适宜的褪黑素浓度(10 μmol?L?1); 并分析正常生长条件(CK)、10 μmol?L?1褪黑素浸种(MT)、150 mmol?L?1 NaCl处理(S)、10 μmol?L?1褪黑素浸种和150 mmol?L?1 NaCl处理(MS)下棉花幼苗株高、干物重、根系形态、叶和根中抗氧化酶活性、丙二醛(MDA)以及可溶性糖含量的变化。结果表明, 150 mmol?L?1 NaCl胁迫下, 棉苗株高比CK显著降低(P<0.05), 根系不发达, 干物重减少, 抗氧化酶[超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX)]活性及可溶性蛋白质含量显著降低(P<0.05), 而MDA含量增加(P<0.05); 10 μmol?L?1褪黑素浸种后, 提高了盐胁迫下棉苗株高及生物量, 显著增加了根系总根长、侧根数目和主根直径(P<0.05), 并提高了根与叶中的SOD、POD、CAT和APX活性(P<0.05), 增加了可溶性糖含量(P<0.05), 降低了MDA含量(P<0.05); 在无NaCl胁迫下, 10 μmol?L?1褪黑素浸种未能显著增加棉花株高, 但显著提高了主根直径和根中SOD、POD、CAT、APX活性(P<0.05), 增加了可溶性糖含量(P<0.05), 降低了MDA含量(P<0.05)。对19个代表性指标进行Spearman相关分析, 发现棉花幼苗总干重与株高、根系形态(总根长、主根长、根系平均直径、总侧根数目)、抗氧化酶活性(根与叶SOD、POD、CAT、APX)、可溶性糖含量均呈现显著正相关, 而与根和叶中MDA含量呈显著负相关。综合分析认为, 外源褪黑素可通过促进棉苗侧根发育和主根直径增粗以及增加抗氧化酶活性和可溶性糖含量, 减缓盐胁迫对棉花幼苗产生的伤害, 促进株高增加及干物质积累, 提高了棉苗的抗盐性。此外, 外源褪黑素还可促进正常条件下棉花幼苗发育, 这为褪黑素的开发利用及棉花栽培调控提供了理论依据。
关键词:褪黑素/
盐胁迫/
棉花幼苗/
形态特征/
抗氧化酶活性
Abstract:Melatonin is an effective antioxidant that can promote the growth and development of plants under stress and alleviate stress-induced damage. The growth and development of cotton, an important cash crop in China, is severely impacted by salt stress. As such, here, we explored the regulatory effect of melatonin on the growth and development of cotton under salt stress by soaking ‘Guoxin Cotton No. 9’ seeds in different concentrations of melatonin (0, 0.1, 1, 10, 50, 100, 150 mmol?L?1) under 150 mmol?L?1 NaCl. We determined the root morphology (total root length, total surface area, total volume, number of lateral roots, root length, surface area and diameter), seedling height, and dry matter weight; thereafter, the most suitable melatonin concentration, 10 μmol?L?1, was selected. Then, we measured and analyzed the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX), as well as the contents of malondialdehyde (MDA) and soluble sugar in leaves and roots of cotton seedlings and the height, biomass, as well as root morphology indexes under 150 mmol?L?1 NaCl, 10 μmol?L?1 melatonin, and 150 mmol?L?1 NaCl plus 10 μmol?L?1 melatonin. The results revealed that under salt stress, the height of seedlings decreased, root systems were underdeveloped, dry matter weights decreased, the activities of antioxidant enzymes (SOD, POD, CAT, and APX) decreased, and soluble protein content decreased; however, the MDA content was found to increase when compared to normal, salt stress-free condition. After soaking the seeds in 10 μmol?L?1 melatonin and 150 mmol?L?1 NaCl, seedling heights and biomass, total root lengths, number of lateral roots, diameter of taproots, activities of SOD, POD, CAT, APX, and content of soluble sugar all increased, but MDA content decreased in roots and leaves. In the absence of salt stress, soaking the seeds in 10 μmol?L?1 melatonin did not significantly increase the plant heights, but significantly increased taproot diameters, SOD, POD, CAT, and APX activities, as well as soluble sugar content in the cotton plant roots (P<0.05); however, significantly decreased MDA content (P<0.05). Spearman correlation analysis of 19 indices revealed that the total dry weight of seedlings was significantly and positively correlated with plant height, total root length, main root length, root mean diameter, total lateral root number, SOD, POD, CAT, and APX activities in roots and leaves, and soluble sugar content; however, there was a significant and negative correlation between total dry weight and MDA content in roots and leaves. With these comprehensive analyses, we show that exogenous melatonin could alleviate the damage caused by salt stress in cotton seedlings, promote an increase in plant height and dry matter accumulation, improve the resistance of cotton seedlings to salt stress by promoting lateral root development and thickening of main root, and increase the antioxidant enzyme activity and soluble sugar content. In addition, we reveal that exogenous melatonin can promote the development of cotton seedlings under salt stress-free condition; this provides a theoretical basis for the development and utilization of melatonin as well as the regulation of cotton cultivation.
Key words:Melatonin/
Salt stress/
Cotton seedling/
Morphology/
Antioxidant enzymes activity
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