Abstract:

At present, there is a lack of systematic research on the physiological differences of tolerant and susceptible rice varieties in response to alkali stress. The method of calculating the stress index and determining the stress level based on physiological and biochemical indexes is also rarely seen. This study aims at elucidating the physiological mechanism of rice alkali resistance and providing a theoretical basis for improving alkali resistance and classifying alkali resistance levels in rice. The alkali-sensitive cultivar ‘Zhonghua 11’ and alkali-tolerant cultivar ‘Ninggeng 52’ were used as materials, and three alkali concentrations (10 mmol∙L^-1, 20 mmol∙L^-1, and 30 mmol∙L^-1) and three pH levels (pH 8.65, pH 9.55, and pH 10.50) were set to explore the effects of alkali stress on the leaves of rice seedlings. A series of indicators were investigated, including the relative water content, chlorophyll (Chla, Chlb, Chl) content, chlorophyll a/b (Chl a/b), malondialdehyde (MDA) content, lipoxygenase (LOX) activity, reactive oxygen species (O₂^{∙ -} and H₂O₂) content, osmotic adjustment substances (Pro, SS, SP) content, antioxidant enzymes (SOD, POD and CAT) activity, reduced ascorbic acid (ASA) and reduced glutathione (GSH) content. The key physiological parameters were extracted by principal component analysis and the alkali stress levels were established. The results showed that, (1) Under alkali stress, ‘Ninggeng 52’ could maintain higher levels of Chla, Chlb and Chl content, Chl a/b and leaf relative water content, SOD, POD and CAT activity, Pro, SS, SP, ASA and GSH content, and maintain lower levels of MDA content, LOX activity, O₂^{∙ -} and H₂O₂ content. (2) Through principal component analysis, the key indexes such as Chla, SOD, MDA, H₂O₂, SS and ASA were selected for calculation of the stress index Z. The damages in rice were classified into five grades: normal (0≤Z<1), mild (1≤Z<4), moderate (4≤Z<7), severe (7≤Z<10) and extremely severe (10≤Z). (3) The MDA content, LOX activity, active oxygen content and stress indexes of the tested materials decreased under the 30A (alkali concentration 30 mmol∙L^-1 and pH 8.65) treatment compared with that under 20C (alkali concentration 20 mmol∙L^-1 and pH 10.50), indicating that when the alkali concentration was greater than 20 mmol∙L^-1, the damage of low alkali concentration and high pH to rice was greater than that of high alkali concentration and low pH. Therefore, the effects of total saline-alkali concentration and pH on rice growth should be considered in the cultivation of rice in saline-alkali soils.

Key words: rice, alkali stress, pH, seedling, physiology, stress index

摘要：

目前关于不同耐碱水稻品种响应碱胁迫的生理差异缺乏系统性的研究,依据生理生化指标计算胁迫指数并确定胁迫等级的方法较少见。为进一步阐明水稻耐碱的生理机制、提高水稻耐碱性和明确水稻抗碱等级,以碱敏感品种“中花11”和耐碱品种“宁粳52”为材料,设3个碱浓度水平（10、20和30 mmol∙L^-1）和3个pH水平（pH 8.65、pH 9.55和pH 10.50）,探究碱胁迫对不同耐碱水稻品种幼苗叶片相对含水量、叶绿素（Chla、Chlb、Chl）含量、叶绿素a/b（Chla/b）、丙二醛（MDA）含量、脂氧合酶（LOX）活性、活性氧（O₂^∙-和H₂O₂）含量、渗透调节物质（Pro、SS、SP）含量、抗氧化酶（SOD、POD和CAT）活性、还原型抗坏血酸（ASA）和还原型谷胱甘肽（GSH）含量的影响,通过主成分分析提取关键生理参数并建立碱胁迫等级。结果表明,（1）在碱胁迫条件下,耐碱品种“宁粳52”能维持更高的Chla、Chlb和Chl含量、Chla/b和叶片相对含水量,保持较低的MDA含量、LOX活性、O₂^∙-和H₂O₂含量,合成更多的SOD、POD和CAT活性、Pro、SS、SP、ASA和GSH含量。（2）通过主成分分析,挑选出Chla、SOD、MDA、H₂O₂、SS、ASA等关键指标,并计算胁迫指数Z,将水稻受害划分为正常（0≤Z<1）、轻度（1≤Z<4）、中度（4≤Z<7）、重度（7≤Z<10）、特重度（10≤Z）5个等级。（3）与20C（碱浓度为20 mmol∙L^-1、pH 10.50）相比,供试材料在30A（30 mmol∙L^-1、pH 8.65）处理下MDA含量、LOX活性、活性氧含量和胁迫指数均下降,说明在碱浓度大于20 mmol∙L^-1时,低碱浓度与高pH对水稻的伤害大于高碱浓度低pH。因此,在碱化土种植水稻时应考虑总盐碱浓度和pH共同对水稻生长的影响。

关键词: 水稻, 碱胁迫, pH, 幼苗, 生理, 胁迫指数