【作者】 陈万超；

【导师】 石德成；

【作者基本信息】 东北师范大学 ， 植物学， 2011， 博士

【摘要】 目前,土壤盐碱化已成为制约农业发展的全球性问题,并影响到生态系统的稳定和生物的多样性。然而,直到现在研究者更多关注的是土壤盐化问题,对碱化问题的报道很少。事实上,盐碱是两种不同的胁迫,二者不仅对植物的胁迫作用不同,而且植物对其适应机制也不同。本文选择了三种具有一定耐盐碱能力的经济植物(棉花、沙棘和苜蓿)作为研究对象,在人工控制的盐碱胁迫条件下,研究并比较了盐、碱两种胁迫对它们的影响及它们的抗碱生理机制。主要结果与结论如下:1.碱胁迫对三种植物的胁迫作用机制。对三种植物的测定结果均表明,碱胁迫对植物生长和光合的抑制均远远大于相同浓度的盐胁迫。碱胁迫与盐胁迫相比,均具有渗透胁迫和离子毒害作用,不同在于碱胁迫还涉及高pH伤害。这种高pH伤害可能是植物生长受抑制作用明显大于盐胁迫的主要原因。因为高pH不仅会直接伤害植物的根部,破坏根系的生长与细胞的分化,改变细胞的结构与膜的稳定性,干扰跨膜电位的形成,致使根细胞功能及代谢紊乱,而且还会导致磷、钙和镁等重要矿质元素大量沉淀,造成植物的营养匮乏。碱胁迫下植物若要生存下去,除了必须进行渗透调节,维持离子稳态外,还必须抵抗这种高pH值胁迫。因此,碱胁迫对植物的胁迫伤害比盐胁迫要更为严重,更为复杂。2.碱胁迫下Na~+大量积累是三种植物生长和光合低于盐胁迫的主要原因。离子含量的分析结果表明:在pH值相对较低时,茎叶中Na~+含量在盐、碱胁迫之间并无显著差异,但在高pH值时,碱胁迫远远高于盐胁迫。其原因可能是三种植物对高pH值胁迫均具有一定的调节能力,在胁迫强度较低时能将高pH值危害抵御在体外,使体内环境不受影响,因而此时植物对碱胁迫的响应与盐胁迫类似。但是,随着胁迫强度的增大,当强度超过了根系调节能力后,就造成Na~+大量涌入到植物的茎叶之中。虽然液泡能贮存Na~+,但超过阈值时原生质中也不得不积累Na~+,从而造成叶绿体片层结构破坏、叶绿素含量降低、各种酶失活,气孔导度下降等等。因此,碱胁迫下Na~+的大量积累可能就是植物生长和光合低于盐胁迫的主要原因。根据本文的实验结果,并结合已有研究报道,我们推测,碱胁迫下Na~+大量积累可能与高pH值胁迫抑制Na~+外排有关,这一点值得进一步研究。3.碱胁迫下有机酸积累是三种植物细胞离子平衡和pH调节的关键生理机制。实验结果表明,三种植物在盐胁迫下均不积累有机酸,而碱胁迫下均大量积累有机酸。三种植物在碱胁迫下,Na~+含量不断增加,而无机阴离子总量却在减少,这导致了细胞内负电荷亏缺,水分子解离平衡破坏,最终造成细胞内pH值不稳定,各种代谢受到干扰。碱胁迫下有机酸的大量积累可能正是对细胞内负电荷亏缺的适应性响应,它在维持细胞内离子平衡和pH值稳定方面发挥了极其重要的作用。因此,有机酸积累可能是植物抗碱的关键生理机制。另外,碱胁迫下三种植物有机酸代谢调节有所不同,不同的有机酸在不同的植物中可能起不同的作用。棉花根茎叶中主要积累苹果酸和柠檬酸,未检测到乙酸;沙棘茎叶中主要积累苹果酸、柠檬酸和草酸,而根中苹果酸和柠檬酸含量相对较少,显著积累的是乙酸;苜蓿根茎叶中主要积累苹果酸和柠檬酸,酒石酸虽含量不多,但随胁迫时间的增加不断增加,棉花和沙棘中未见酒石酸积累。有机酸的具体调控机制极其复杂,可能涉及三羧酸循环、光合碳固定、无氧呼吸等诸多基础代谢途径,其调控过程可能发生在转录、翻译和相关蛋白质活性调节等不同层面,这些还都需要进一步的研究。更多还原

【Abstract】 At present, soil salinization has restricted the development of the global issues of agriculture, and affected the stability of global ecosystems and biological diversity. However, to date, more attention has been given to the problem of soil salinization, and few alkalization problems have been reported. In fact, salt and alkali stresses are two different stresses, which damaging actions to plants are different, and there are special responses to two stresses for plants. In present study, we chose three common economic plants (cotton, alfalfa, Sea buckthorn) which have certain salt-alkali-tolerant ability as the objects of study, under salt and alkali stresses in manual control, and compared effects of salt and alkali stress on both of them and physiological mechanisms by which they resist alkali stress. The main results and conclusions are as follows:1. The mechanism of alkali stress on three plantsThe findings of the three plants indicated that alkali stress on the inhibition of plant growth and photosynthesis was much greater than salt stress at the same salinity.. Alkali stress significantly inhibited root growth, leaf gas exchange disturbances and reduced the photosynthetic rate and transpiration rate, thereby inhibiting the growth and metabolism. Compared to alkali stress and salt stress, both stresses generally involves osmotic and ion stresses, but the difference is that alkali stress adds the high pH effect. This high pH damage caused by alkali stress might be major factor why alkali stresses are more destructive to plants growth than salt stress. This high pH can not only directly harm plant roots, root growth and damage to cell differentiation, alter the cell structure and stability of membrane, and interfere with the formation of transmembrane potential , resulting in root cell function and metabolism disorders, but the high pH can also cause phosphorus and calcium, magnesium and other important mineral elements to precipitate, and lead to lack of plant nutrients. To survive under alkali stress, plant species must carry out osmotic adjustment and maintain ion homeostasis, but also must resist this high pH. Therefore, the injury of alkali stress on the plant is more serious and complex than salt stress.2. A large of Na~+ accumulation under alkali stress might be main reason why the three plants growth and photosynthesis was lower than that of under salt stressThe results about contents of inorganic ion analysis showed that Na~+ content in shoot existed no significant difference between salt and alkali stresses when pH was low, but under the high pH stress the content under alkali stress was much higher than that of under salt stress. Because all three plants had certain pH regulation ability, under low-intensity stress, the harmful effect of high pH was resisted outside the roots and consequently the intracellular environment was not affected, here the response of plants to alkali stress was similar to salt stress. However, with increasing stress intensity, when stress exceeded the capacity of root adjustment, a large number of Na~+ influx into shoot of plants. Although the vacuole can store a certain amount of Na~+, when Na~+ content was more than the threshold value, protoplasm had to accumulated Na +, which resulted in the destruction of chloroplast lamellar structure, the decrease of chlorophyll content, the inactivation of enzymes, the decrease of stomatal conductance. It can be argued that Na~+ accumulation under alkali stress might be main reason why the plant growth and photosynthesis was lower than that of under salt stress. According to the results of this experiment, combined with existing research reports, we hypothesized that Na~+ accumulation under alkaline stress might also be related to possible decreased Na~+ exclusion, which deserves further study.3. Organic acids accumulation in three plants cells under alkali stress was a key physiological mechanism on ionic balance and pH regulationThe experimental results showed that none of the three plants under salt stress accumulated organic acids, but all of them accumulated a large of organic acids under alkali stress. For three plants under alkaline stress, Na~+ content increased, the total amount of inorganic anions decreased, which led to deficiency of intracellular negative charge, the damage of water molecular dissociation, eventually led to instability in the intracellular pH and interference of various metabolic activities. The large number of organic acids accumulation under alkaline stress might be a passive response to deficit of negative charge in cells, which played an important role in maintaining ionic balance and pH stability. Organic acids accumulation was the key physiological mechanism which decided the alkali tolerance of plants. In addition, organic acid metabolism regulation pathways in three different plants under alkali stress were different and different organic acids in the different plants might play different roles. Roots and leaves of cotton mainly accumulated malic acid and citric acid, but acetic acid was not detected; shoots of sea buckthorn mainly accumulated malic acid, citric acid and oxalic acid, but the contents of malic acid and citric acid were relatively small, acetic acid accumulation was enhanced significantly; roots and leaves alfalfa, mainly accumulated malic acid and citric acid, the content of tartaric acid was not many, but increased with increasing stress time, and no tartaric acid accumulation in cotton and sea buckthorn.However, the regulatory mechanism of organic acids may be extremely complex, possibly involving the citric acid cycle, photosynthetic carbon fixation, anaerobic respiration, and many other basic metabolic pathways. The regulatory process may occur in the transcription, translation and the proteins regulating the activity of various levels, which deserves further study.更多还原