【作者】 郭立泉；

【导师】 石德成；

【作者基本信息】 东北师范大学 ， 植物学， 2009， 博士

【摘要】 根据中国东北地区盐碱化草原土壤所含的可溶性盐分的组成特点,分别将中性盐NaCl、Na2SO4和碱性盐NaHCO3、Na2CO3以1:1的摩尔比混合,模拟出0-240mmol/L的盐胁迫和碱胁迫条件。选用天然高抗盐碱牧草星星草为材料,对其8周龄苗进行盐胁迫和碱胁迫处理。通过检测胁迫苗在生长、干物质积累、氮代谢、有机酸代谢、抗氧化系统、渗透调节及离子平衡等方面的生理响应,以探讨并比较星星草适应盐碱两种胁迫的生理机制及其差异。所获主要实验结果与结论如下:1.盐、碱胁迫对星星草生长及氮代谢的影响星星草幼苗在盐、碱胁迫下,总生物量、RGR和总氮量均表现出先升高后降低的变化趋势。即低浓度的中性盐(≤120mmol/L)和碱性盐(≤60mmol/L)对星星草的生长、干物质积累及氮素吸收具有明显的促进作用,而后转为抑制作用,而且随着盐度的增高抑制作用逐渐增强,就抑制幅度而言,碱胁迫大于盐胁迫。可见,盐碱两种胁迫对星星草氮代谢的影响与对其生长的影响密切相关。2.星星草抗氧化系统与其抗盐碱性的关系盐胁迫与碱胁迫均造成了丙二醛的积累和电解质外渗率的增加,就变化幅度而言,碱胁迫大于盐胁迫,这说明,碱胁迫对质膜结构的破坏程度更大,伤害更加显著。盐胁迫下超氧化物歧化酶(SOD)、过氧化物酶酶(POD)和过氧化氢酶(CAT)这三种抗氧化酶活性均增强;而在碱胁迫下,CAT活性逐渐降低,但是SOD活性增加了1.4倍～1.6倍,POD活性增加了3.5倍。这一现象表明了:星星草特殊的抗氧化酶系统是决定其抗盐碱性的因素之一。3.以柠檬酸为主的有机酸积累是星星草适应碱胁迫的关键生理响应结果表明,盐胁迫下星星草体内有机酸含量无明显变化甚至稍有降低,而当碱胁迫达到一定强度后(≥60 mmol/L)则引起有机酸急剧积累,而且不管是茎叶还是根中所积累的有机酸均以柠檬酸为主。可见以柠檬酸为主的有机酸积累是星星草针对碱胁迫的特异生理响应。碱胁迫下星星草体内特异积累以柠檬酸为主的有机酸的生理作用可能与其体内pH的调节及离子平衡密切相关。只有碱胁迫才能引起了星星草体内有机酸的特异积累,这一现象充分证明了植物对碱胁迫和盐胁迫有着不同的生理适应机制。4.碱胁迫下星星草根系有机酸积累和分泌的特点碱胁迫下星星草根部的有机酸含量很低而且变化不明显,其原因一方面是根部代谢特点所决定,另外也与根系的分泌作用有关。在碱胁迫下的根系分泌物中,柠檬酸是唯一可以检测出来的有机酸,其数量较少,仅仅为5.92微摩尔/株/天。但是星星草根系对碱性环境的适应能力及pH调节作用却非常显著。据此可以认为,星星草对碱胁迫引起的环境高pH的调节作用可能是通过分泌有机酸和呼吸释放CO2来完成,作用部位可能是根尖部皮层的质外体空间而非根表皮之外。5.盐、碱胁迫下的渗透调节和离子平衡作用结果表明:在盐、碱胁迫下脯氨酸含量明显增加,但是其含量对于总溶质含量来说却非常低,因此它对渗透调节的作用是非常有限的。盐胁迫下星星草的主要渗透调节剂是Na+、K+和Cl-,而碱胁迫下则是Na+、K+和有机酸。从有机酸含量与其它溶质含量的相关性分析结果来看,碱胁迫下有机酸积累与Na+含量增加密切正相关。碱胁迫造成植物体内Na+含量急剧的上升,导致细胞内离子平衡破坏,这可能就是引起有机酸相应大量积累的主要原因。盐碱两种胁迫下,不同阴离子对总阴离子的贡献率差异明显,有机酸在碱胁迫下的贡献率高达68%,而在盐胁迫下仅为39%,可见两种胁迫下星星草体内的离子平衡特点明显不同。总之,在碱胁迫下,星星草通过在体内积累有机酸,进行渗透调节、维持离子平衡,通过根系分泌有机酸来调节外部环境的高pH造成的胁迫。因此,在碱胁迫下,有机酸是调节植物体内外环境的最关键物质。更多还原

【Abstract】 According to the soluble components of salt-alkaline grassland of the Northeast of China, eight-week-old seedlings of Puccinellia tenuiflora were stressed by exposure to 1:1 molar-ratio mixtures either of the two neutral salts NaCl and Na2SO4 or of the two alkali salts NaHCO3 and Na2CO3, which were simulated conditions of 0-24mmol/L salt stress or alkali stress. To identify the physiological mechanisms involved in this plant’s resistance to alkali stress, the relative growth rates, dry matter accumulation, nitrogen metabolism, organic acid metabolism, anti-oxidative system, osmotic adjust and ionic balance to salt or alkaline stress were detected and measured.The experimental results and conclusions were as follows:1. Effects on Growth and Nitrogen Metabolism of P. tenuiflora under Salt and Alkali Stresses.The total biomass, relative growth rates, total nitrogen of P. tenuiflora under salt or alkali stress initially increased and then decreased. The results showed that lower salinity of neutral salts (≤120mmol/L) or alkali salts promoted the growth, dry matter accumulation, nitrogen absorption of P. tenuiflora, while higher salinity of neutral salts or alkali salts inhibited its growth and nitrogen absorption evidently, and their inhibition became more and more obvious with the salinity increased although alkali stress was more inhibitory than salt stress. Therefore, the effects of salt stress and alkali stress on nitrogen metabolism in P. tenuiflora correlated with effects on its growthe under salt stress and alkali stress.2. Relation between Anti-oxidative System and Salt- or Alkali- Resistance. in P. tenuifloraBoth salt stress and alkali stress led to the accumulation of malonaldehyde and the increasing of osmosis of electrolytes outside the membrane, however, alkali stress was predominantly obvious than salt stress. This demonstrated that the alkali stress was more destructive to membrane.The activities of superoxid dismutase (SOD), perodidase (POD) and catalase (CAT) increased under salt stress, while the activity of catalase decreased gradually although SOD activity increased by 1.4～1.6times of it and POD activity increased by 3.5 times of it. This demonstrated that the unique anti-oxidative system was one of main factors related to its salt or alkali resistance. 3. Accumulating Large Quantities of Organic Acids with Citric Acid As a Dominant Component were the Key Physiological Responses of P. tenuiflora to Alkali StressThe results indicate that organic acid concentrations in P. tenuiflora have no obviously changes and even decreased slightly. However, organic acids accumulate in detectable quantities only under alkali stress above 60 mM. Citric acid is always the dominant component of the accumulating organic acids in both the shoots and the roots. Therefore, the accumulation of organic acids, mostly citric acid, appears to be a specific physiological response of P. tenuiflora to alkali stress. Therefore, accumulating large quantities of organic acids with citric acid as a dominant component in P. tenuiflora under alkali Stress is closely related to the pH regulation and iron balance. Only alkali stress caused organic acids to accumulate, plants clearly shows that they have different physiological mechanisms under alkali stress and salt stress.4. The Characteristics of Organic Acid Accumulation in P. tenuiflora Roots Under Alkali StressThe organic acid concentration in the roots of P. tenuiflora under alkali stress was very low and has no obviously changes. The one of reasons is decided by the metabolism character in P. tenuiflora roots, and another reason is relative with is related to the secretary activity of the roots. Under alkali stress, the roots secreted citric acid which was the only organic acid detected. Calculation showed that the average amount of organic acid secreted each day was 5.92μmol per seedling. But it very obviously that P. tenuiflora roots adapt to alkali environment and pH regulation. Above all, the regulation roles of P. tenuiflora roots to high pH under alkali stress, perhaps were secretes organic acids and produce CO2 by respiration. The site of action is apoplast in cortex of root tips, instead of outside root epidermis5. Osmotic Adjust and Ionic Balance Roles under Salt and Alkali StressesThe result show that proline concentration under salt and alkali stresses increased obviously, but proline concentration was very low compared to total concentration. So proline contributed in a very limited way to total osmotic adjustment. Under salt stress, important osmolytes include Na+, K+, and Cl- are all, but under alkali stress, include Na+, K+, and organic acid.From the result of correlation analysis between organic acid concentration and other solute concentration, organic acid accumulation is closely correlated with Na+ concentration. Na+ concentration increased sharply under alkali stress, it induced iron balance was destroyed. Perhaps, these were primary reasons caused by organic acid accumulation. Percentage of the contribution of various free anions to total anions is deferent obviously. Under alkali stress, organic acid contributed 67.8% of total negative charge, while the total contribution of the inorganic anions was only 39%.So, the character of iron balance in P. tenuiflora is obviously different.Above all, organic acid accumulation, osmotic adjustment and maintaining ionic balance in P. tenuiflora under alkali stress, and adjust high pH by secreted organic acids from Rhyzosphere. Therefore, organic acid is the most key to regulate vivo and vitro.更多还原