Effects of Drought Stress on Germination and Growth of Rapeseed and Mechanism of Seed Priming to Improve Drought Resistance
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【Author in Chinese】 Mohammad Nauman Khan；
【Author's Information】 华中农业大学， 作物栽培学与耕作学， 2020， 博士
【Abstract in Chinese】 中国食用油的来源很大程度上依赖于油菜生产。然而,秋季干旱的频繁发生对冬油菜的萌发出苗和正常生长造成障碍。干旱是影响作物生长发育的主要因素。水分亏缺导致生物膜氧化和打乱组织水分的平衡状态,进而阻碍了作物生长和发育。幼苗对水分亏缺的抗性是作物在干旱条件下完成整个生命周期生长发育的关键。种子引发是提高油菜逆境条件下萌发出苗和生长发育的有效方法,但是其生理机制研究不太系统。本研究开展了系统的培养箱、盆栽和大田试验,主要目的是阐明种子引发提高作物萌发、苗期长势、产量和品质的机理。得到了如下三个方面的主要结论。(1)干旱胁迫条件下油菜种子萌发和幼苗生长的生理机制为了较好的探索油菜对干旱的适应性,本试验研究了酶促,非酶促抗氧化剂和渗透调节物质在提高油菜耐旱性中的作用。通过比较分析评价了6个油菜品种在对照(0.00 MPa)和干旱胁迫(聚乙烯6000模拟的0.2,-0.3,-0.4,and-0.5 MPa)条件下萌发和幼苗生长阶段的表现。根据种子萌发和幼苗生长阶段的表现,圣光127(SG 127)和中油36(ZY 36)分别被鉴定为抗旱性强和抗旱性弱的品种,并且在-0.3 MPa干旱条件下进行后续胁迫试验。结果表明,干旱胁迫严重阻碍了油菜的发芽和幼苗的早期生长。与抗旱性弱的ZY 36相比,干旱对SG 127幼苗生长影响较小,SG 127细胞内的过氧化氢(H2O2)和丙二醛(MDA)含量较低,电解质泄漏(EL%)和叶绿素(Chl)降解较小。SG 127的耐旱性可能与抗氧化酶活性(过氧化物酶POD,过氧化氢酶CAT和超氧化物歧化酶SOD),非酶抗氧化剂(抗坏血酸As A,谷胱甘肽GSH)的活性增强,脯氨酸的积累,总可溶性糖和总可溶性蛋白有关。此外,我们的研究强调了在干旱胁迫下油菜幼苗中酶促和非酶促抗氧化剂和渗透物质的重要性。(2)有效的种子引发提高了油菜种子发芽和幼苗早期的耐旱性我们研究了在聚乙二醇(PEG)模拟的干旱条件(-0.3 MPa)下的不同种子引发剂(6-BA,ABA,BRs,,GB,IAA,Me Ja,,PA和SA)引发对油菜幼苗形成和生长特性的影响。采用GA3,MT,GB,BRs和IAA等物质进行种子引发处理,可以有效提高油菜在PEG模拟干旱条件下的出苗率和幼苗长势。本试验进一步阐明了应对干旱有效的种子引发剂赤霉素(GA3)和褪黑激素(MT)对PEG模拟干旱胁迫下提高油菜苗期抗旱性的生理机制。赤霉素和褪黑素引发有减轻油菜幼苗的氧化损伤和叶绿素含量的作用,二者通过调节细胞中抗氧化酶(SOD、POD和CAT)的活性和非酶抗氧化剂(GSH和As A)的水平来增强油菜的抗氧化防御系统。同时,赤霉素和褪黑激素也通过增加脯氨酸、可溶性蛋白和可溶性糖含量等渗透调节物质的积累,在干旱胁迫下的渗透调节中发挥重要作用。扫描电镜(SEM)结果表明,气孔数量、气孔长度、气孔宽度等气孔性状在干旱胁迫条件下明显减少。然而,赤霉素和褪黑激素引发显著提高气孔数,气孔长度和宽度。超微结构分析显示,在无引发处理中,叶绿体发生自行消化。在干旱胁迫下,无引发处理也表现出细胞壁的退化。然而,赤霉素和褪黑激素引发保护了叶绿体不被吞噬,使叶绿体保持椭圆形,排列整齐,紧贴细胞壁。同样,在干旱胁迫条件下,赤霉素和褪黑激素引发保护细胞壁不受降解,表现出典型的细胞结构,边缘完整清晰。(3)在干旱和正常条件下,赤霉素和褪黑素引发均显著提高油菜产量和品质通过盆栽和田间试验研究了在干旱和非干旱条件下,种子引发对油菜产量和品质的影响。采用GA3和MT对圣光127和华油杂9号两个油菜品种进行了种子引发处理。在良好控制的温室条件下,开花期通过称重法控制盆栽土壤含水量,使之形成35-40%的严重干旱胁迫条件。同时在大田条件下种植引发处理的种子进行小区试验。在盆栽试验中,油菜植株的形态性状,产量和产量构成因素明显降低;同时也观察到种子的品质指标在干旱胁迫下显著下降。然而,GA3和MT引发的植株在形态性状、产量及产量构成因素、品质指标下降的幅度较小。与正常和干旱胁迫条件下的无引发处理相比较,种子引发处理的植株抗旱性增强,抗氧化酶的活性和脯氨酸含量提高。从而更好地清除了活性氧(ROS)的不良影响。与无种子引发的处理相比,GA3和MT引发改善了大田条件下植株的农艺性状,提高了籽粒产量和品质。综上所述,有效的种子引发处理如GA3和MT引发促进了油菜在萌发和不同生长时期植株的耐旱性,主要的原因是加强了抗氧化防御系统和渗透调节能力,改善了干旱胁迫下叶片的气孔形态和叶绿体超微结构。同时,盆栽试验与大田试验研究表明,GA3和MT引发显著提高了油菜的产量和品质。本研究结果探索了种子引发促进干旱耐受性的可能途径,有助于在缺水和半干旱农业生态系统下提高油菜的产量和品质。
【Abstract】 The edible oil production in China is highly dependent on the successful production of rapeseed.However,the excessive occurrence of autumn drought caused obstacles to the germination and normal growth of rapeseed.Drought stress is the main reason for crop failure.Water stress encumbers the rapeseed growth and development primarily by oxidative alteration to biological membranes and interrupted tissue water status.Seedling tolerance to water stress is vital for better crop development through the entire period under drought stress condition.Priming seed is an approach through which seeds are exposed to numerous unfavorable situations to confer stress variation in seedlings germinating and growing under stressful conditions.However,its physiological mechanism research is not systematic.The present study aimed to elucidate how seed priming affected rapeseed germination,early seedling growth,seed yield and quality by conducting a series of incubator,pot and field experiments.The main findings are summarized below.(1)Drought stress inhibited germination and early seedling growthTo better predict about the adaption of rapeseed to drought stress,the current study explored the presumed roles of enzymatic,non-enzymatic antioxidants and osmolytes in improving rapeseed drought-tolerance.The comparative analysis in terms of germination and early seedling growth of six rapeseed cultivars was assessed under normal(0.00 MPa)and osmotic stresses(-0.1,-0.2,-0.3,-0.4,and-0.5 MPa simulated by polyethylene glycol 6000).Subsequently,based on the process of germination and early seedling growth,Shenguang 127(SG 127)and Zhongyou 36(ZY 36)were chosen as drought-tolerant and-sensitive rapeseed varieties.The results indicated that drought stress rigorously hindered germination and early seedling growth of rapeseed cultivars.On the other hand,SG 127 exhibited less reduction in seedling growth paralleled with ZY 36.SG 127 revealed lower levels of hydrogen peroxide(H2O2),lipids peroxidation(MDA),electrolyte leakage(EL %)and less reduction in chlorophyll(Chl)content than ZY 36.The drought-tolerance of SG 127 may be correlated with enhanced activities of enzymatic(superoxide peroxidase,catalase,and dismutase),non-enzymatic antioxidants(ascorbic acid,glutathione),more accumulation of proline;total soluble sugar and total soluble protein.Furthermore,our study highlighted the significance of enzymatic and non-enzymatic antioxidants and osmolytes in the establishment of rapeseed seedlings under drought stress.(2)Effective priming treatments promoted rapeseed drought-tolerance during germination and early seedling growthWe studied the influences of seed priming(induced by 6-BA,ABA,BRs,GA3,GB,IAA,Me Ja,MT,PA and SA)on subsequent seedling establishment and growth attributes of rapeseed seedlings under the drought stress induced by polyethylene glycol(PEG).Seed priming treatments including GA3,MT,GB,BRs,and IAA were effective at improving seedling establishment and early seedling growth of rapeseed under the PEG simulated drought stress.The effective seed priming treatment such as GA3 and MT were further elucidated from the perspectives of physiological and biochemical mechanisms involved in droughttolerance during early seedlings stage.GA3-and MT-priming tended to alleviate the oxidative damage and the amount of chlorophyll in rapeseed.Seed priming with gibberellic acid and melatonin strengthened the antioxidant defense system in rapeseed by regulating the activities of antioxidant enzymes(SOD,POD,and CAT)and levels of nonenzymatic antioxidants(GSH and As A).Nonetheless,gibberellic acid and melatonin priming also played an important role in osmotic adjustment under drought stress by increasing the accumulation of osmolytes including proline,soluble protein and soluble sugar contents.The results from scanning electron microscopy(SEM)revealed that stomatal traits such as number,stomatal length and width were significantly reduced under drought stress conditions in no-primed treatment.However,GA3-and MT-priming greatly improved stomatal number;stomatal length and width.Ultrastructure analysis showed that in no-primed treatment,chloroplast autopepsia(self-digestion)was observed.Under drought stress,the no-primed treatment also exhibited cell wall degradation.Nonetheless,GA3-and MT-priming preserved the chloroplast from chlorophagy and the chloroplast exhibited ellipse shape,well-arranged and clung to the cell wall.Similarly,under the drought stress conditions,GA3-and MT-priming protected cell wall from degradation and exhibited a typical structure with complete and clear edges;and was well-formed.(3)Gibberellic acid and melatonin priming significantly increased seed yield and improved seed quality under drought stress and normal growing conditionsPot and field experiments were conducted to investigate whether seed priming could improve rapeseed yield and quality under drought-stress and non-stress conditions.We primed the seeds of two rapeseed cultivars viz.,Shenguang 127(SG 127)and Huayouza 9(HZ 9)with gibberellic acid(GA3)and melatonin(MT).The potted plants were subjected to a severe drought stress of 35-40% at flowering stage in well-controlled glasshouse conditions;while in the field experiment,the plants were grown under the open field conditions.In the pot experiment,significant reduction in morphological traits,yield and yield components;and deterioration in seed qualitative attributes was recorded under the drought stress in both cultivars.However,the GA3 and MT-primed plants exhibited less reduction in morphological traits,yield and yield components;and deterioration in seed qualitative attributes under the drought stress compared to no-primed plants.The results of our study reveals that the better performance of primed-issued plants was associated with better scavenging of ROS through the activation of antioxidant enzymes and more accumulation of proline as compared to no-primed plants both under normal and drought stress conditions.Nonetheless,GA3 and MT-priming also improved the morphological traits,seed yield,and seed qualitative attributes under the open field conditions compared to no-primed treatment.Conclusively,effective priming treatments such as GA3 and MT promoted rapeseed drought-tolerance during germination and different growth stages.GA3 and MT-priming potentially regulated antioxidant defense system and osmotic adjustment which ultimately modulated stomatal morphology and chloroplast ultrastructure under drought stress.Meanwhile,GA3 and MT-priming significantly increased seed yield and improved seed quality.Taking together,the finding of our study may explore new avenues and advancing priming-induced drought tolerance helping to improve rapeseed productivity and quality under water scarcity and semi-arid cropping system.