【作者】 康云艳；

【导师】 郭世荣；

【作者基本信息】 南京农业大学 ， 蔬菜学， 2008， 博士

【摘要】 洪水、冬季冰封、过多的降雨、灌溉不均匀、土壤紧实以及无土栽培生产实践中管理不当等均易使农作物根系供氧不足,造成低氧胁迫,并最终导致其生长和产量的下降。油菜素内酯(Brassinolide, BR)是广泛存在于植物中的类似于动物和昆虫甾醇类激素的一种天然产物,已证明其在植物的种子休眠与萌发、器官分化、维管组织发育、开花和衰老以及向性建成等各个生长发育的过程中起到重要调控作用。目前已被公认为第六大类植物激素。同时,研究表明BR在植物抗逆境胁迫中发挥着重要作用。然而,关于BR与蔬菜作物低氧耐性的关系以及BR在此过程中发挥的生理调节功能至今尚未阐明。本文以低氧耐性具有明显差异的两个黄瓜(Cucumis sativus L.)品种(耐低氧较强的‘绿霸春4号’和耐低氧较弱的‘中农8号’)为试材,采用营养液栽培,通过营养液添加1μg.L-124-表油菜素内酯(EBR),研究营养液溶氧浓度1mg.L-1的根际低氧胁迫下黄瓜植株生长、碳代谢以及活性氧代谢的变化,探讨其与植株低氧耐性的关系,以及外源EBR在提高黄瓜低氧耐性中发挥的生理调节功能。主要研究结果如下：1.根际低氧胁迫下,黄瓜地上部和根系生长均显著受抑而下降,抗低氧能力较强的‘绿霸春4号’地上部鲜重、干重、根的总长、总表面积、总体积以及总根尖数降低幅度均低于抗低氧能力较弱的‘中农8号’2.低氧胁迫下,两品种黄瓜根系三羧酸循环显著受阻,无氧呼吸代谢被促进。与耐低氧能力较弱的品种‘中农8号’相比,耐低氧能力较强的品种‘绿霸春4号’根系SDH、IDH活性降低幅度以及LDH活性、乳酸含量增加幅度较小,PDC、 ADH活性以及乙醇、丙氨酸含量增加幅度较大,两品种幼苗根系AlaAT活性以及乙醛含量没有显著差异。表明低氧胁迫下根系乙醇发酵的增强和丙氨酸的积累有利于植株防御低氧伤害。3.低氧胁迫下,耐性不同的两品种幼苗中显著积累了不同类型的碳水化合物,根系中淀粉和葡萄糖含量表现出显著差异。耐低氧能力较强的品种‘绿霸春4号’根系中淀粉含量维持不变,葡萄糖含量显著提高；相反,耐低氧能力较弱的品种‘中农8号’根系中淀粉和葡萄糖含量均显著降低。同时,耐性不同的两品种幼苗中糖酵解代谢酶活性变化也表现出明显的品种差异,‘绿霸春4号’根系中AI活性略有降低,PFK活性呈先上升后下降的变化趋势,试验期间高于对照；相反,‘中农8号’根系中AI活性持续降低,PFK活性在整个试验期间缓慢降低,且低于对照水平。表明低氧条件下,黄瓜根系淀粉和葡萄糖含量以及AI和PFK活性的变化特性可用来区别品种的耐性。4.低氧胁迫下,黄瓜幼苗叶片和根中活性氧、MDA和抗氧化剂含量以及SOD、CAT、APX和DHAR活性均显著提高；耐低氧性较强的‘绿霸春4号’叶片和根中活性氧和MDA含量的上升幅度小于耐低氧性较弱的‘中农8号’,而保护酶活性和还原型抗氧化剂含量的提高幅度大于‘中农8号’。5.营养液添加EBR显著缓解了根际低氧胁迫对黄瓜幼苗生长的抑制：低氧胁迫下,EBR处理后‘绿霸春4号’和‘中农8号’幼苗根系总长度分别提高23%和37%,总表面积分别提高26%和29%；EBR处理后‘中农8号’幼苗根系总根尖数显著提高,‘绿霸春4号’无明显变化；外源EBR对低氧胁迫伤害的缓解效果‘中农8号’大于‘绿霸春4号’6.EBR参与低氧胁迫下黄瓜根系呼吸代谢的调节：外源EBR处理显著提高了低氧胁迫下两品种黄瓜幼苗根系SDH、IDH和ADH活性,降低了两品种根系LDH、AlaAT活性及‘中农8号’根系PDC活性,降低了两品种根系乳酸含量,而对‘绿霸春4号’根系PDC活性及两品种根系乙醛、乙醇和丙氨酸含量无明显影响。表明低氧胁迫下,外源EBR处理可通过部分恢复有氧呼吸、增强乙醇发酵及根系乳酸分泌能力提高植株抗低氧胁迫的能力。7.EBR参与低氧胁迫下黄瓜体内碳水化合物代谢的调节：低氧条件下,EBR处理进一步提高了两品种根系蔗糖和果糖含量以及大部分的糖酵解代谢酶活性,而对叶片中大部分碳水化合物含量和糖酵解代谢酶活性均无显著影响。表明EBR处理直接参与调节黄瓜幼苗体内碳水化合物代谢,通过促进低氧胁迫下碳水化合物从叶片向根系的分配以及根系糖酵解代谢酶活性增强了黄瓜植株抵抗低氧胁迫的能力。8.EBR参与低氧胁迫下黄瓜体内活性氧代谢的调节：低氧胁迫下,外源EBR处理显著提高了SOD、APX、GR活性及AsA、GSH含量,降低了O2·-、H2O2及MDA含量。表明外源EBR处理通过促进低氧胁迫下黄瓜幼苗叶片和根系中抗氧化酶活性和抗氧化剂含量的提高,降低ROS含量,增强植株抗低氧胁迫的能力。更多还原

【Abstract】 Plant hypoxia frequently occurs when internal oxygen levels fall below a critical value. Spring floods, winter ice encasement, excess rainfall, irrigation followed by poor drainage, soil compaction and bad management in soilless cultivation are common conditions that lead to root-zone hypoxia or anoxia. These deleterious effects are responsible for the slower growth and reduced yield observed in many agricultural crops after flooding and other hypoxia-induced conditions. Brassinosteroids (BRs) are a class of plant polyhydroxysteroids similar to animal and insect steroid hormones that have been recognized as a new kind of phytohormones and play an essential role in plant development. Intensive research conducted on BRs reveals that they elicit a broad spectrum of physiological responses in plants, including germination and breaking of seed dormancy, organ differentiation, vascular tissue development, flowering and senescence, and tropisms. Besides that, BRs can protect plants from various biotic and abiotic stresses. However, the relationship between brassinolide and hypoxia tolerance of vegetables and the physiological regulation function of brassinolide is still not well known.In the present study, two cultivars of cucumber (Cucumis sativus L.), cvs. Lubachun No.4and Zhongnong No.8, were used. It has been reported that cv. Lubachun No.4is hypoxia-resistant as in most cucumber cultivars, whereas cv. Zhongnong No.8is comparatively sensitive to root-zone hypoxia. Cucumber seedlings were hydroponically grown for8days in normoxic and hypoxic nutrient solutions with and without addition of24-epibrassinolide (EBR) at1μg.L-1The objectives of the present study were to investigate the effects of root-zone hypoxia with dissolved oxygen (DO) at1mg.L-1on plant growth, carbon and ROS metabolism, to elucidate the relationship between the changes of carbon and ROS metabolism in cucumber plants and hypoxia tolerance, and the physiology regulation function of exogenous EBR in improving hypoxia tolerance of cucumber plants. Main research results were as follows:1. Root-zone hypoxia caused severe inhibition of shoots and roots growth of cucumber (expressed by shoot fresh weight, shoot dry weight, total root length, total root surface, total root volume and total root tip numbers). The inhibition was more marked in cv. Zhongnong No.8than in cv. Lubachun No.4.2. Root-zone hypoxia significantly inhibited TCA cycle but accelerated anaerobic respiration of cucumber roots. Under root-zone hypoxia stress, compared with Zhongnong No.8seedling roots, the extent of decrease in SDH, IDH activities and increase in LDH activity, lactate and pyruvate contents were less in Lubachun No.4seedling roots, conversely, the extent of increase in PDC and ADH activities and alcohol, alanine contents in Lubachun No.4seedling roots was greater than that in Zhongnong No.8; all these response of respiratory metabolism to root-zone hypoxia were the reasons for two cucumber cultivars of different hypoxia tolerance; there was no difference about AlaAT activity and acetaldehyde content between two cultivars.3. Two genotypes cucumber accumulated different types of carbohydrates under hypoxia and showed significantly diverse changes on contents of starch and glucose in roots; stable starch contents and increased glucose contents were observed in Lubachun No.4roots; on the contrary, these two types of sugars were significantly reduced in Zhongnong No.8roots. Furthermore, changes of glycolytic enzymes activities showed obviously different between two genotypes cucumber in response to root-zone hypoxia; AI activity slightly decreased during hypoxia, and PFK activities were higher than control level throughout the entire experiment, but they increased during the first4days of hypoxic treatment, and then declined in subsequent days in Lubachun No.4roots; on the contrary, AI activity rapidly reduced during hypoxia, and slightly decreased PFK activities were observed in Zhongnong No.8roots. These results suggest that changes of contents of starch and glucose and activities of AI and PFK are some of primary characteristic for cultivar difference.4. Under hypoxia stress, the contents of ROS, MDA and antioxidants, and the activities of SOD, CAT, APX, and DHAR were enhanced in cucumber seedlings roots of both two cultivars. The extent of increase in ROS and MDA contents in Lubachun No.4roots was less than those in Zhongnong No.8roots, however, the extent of increase in activities of SOD, CAT, APX, DHAR and AsA and GSH contents in Lubachun No.4roots was greater than those in Zhongnong No.8roots.5. Application of EBR to hypoxic nutrient solution alleviated the inhibition of plant growth. For example, EBR treatment increased the total root length by23%and37%, and the total root area by26%and29%, respectively, in cv. Lubachun No.4and cv. Zhongnong No.8seedling roots; the EBR application significantly increased the number of the total root tips of cv. Zhongnong No.8seedling, but had no effect on cv. Lubachun No.4seedling roots. Greater promotion by EBR treatment was observed in cv. Zhongnong No.8seedling roots than in cv. Lubachun No.4.6. EBR takes part in the regulation of respiratory metabolism of cucumber plants under hypoxia. EBR treatment significantly enhanced activities of SDH, IDH and ADH, decreased activities of LDH and AlaAT, contents of lactate in roots of both two cultivars and PDC activity in cv. Zhongnong No.8seedling roots. However, EBR treatment had no effect on PDC activity in cv. Lubachun No.4roots and contents of acetaldehyde, alcohol and alcohol in roots of two cultivars. These results suggest that EBR added to hypoxic nutrient solution may partly resume aerobic respiration, stimulate the shift from lactate fermentation to alcohol fermentation in hypoxic roots, and eventually enhanced tolerance of cucumber plants to root-zone hypoxia.7. EBR takes part in the regulation of carbohydrate metabolism of cucumber plants under hypoxia. EBR added to hypoxic nutrient solution caused an increase in the concentrations of fructose and sucrose and activities of major glycolytic enzymes in the roots but not in the leaves. These results suggest that EBR added to hypoxic nutrient solution may stimulate the photosynthate allocation down to roots and activities of major glycolytic enzymes, and eventually enhanced tolerance of cucumber plants to root-zone hypoxia.8. Under hypoxia, EBR takes part in the regulation of ROS metabolism of cucumber plants. Application of EBR to hypoxic nutrient solution significantly increased activities of SOD, APX, GR, and contents of AsA and GSH, however, the chemical rapidly reduced the accumulation of O2·-,H2O2and MDA. From the results obtained in this work, it can be concluded that oxidative damage on cucumber plants caused by hypoxia stress can be considerably alleviated by adding EBR to nutrient solution and the tolerance of plants was elevated.更多还原