耐盐和盐敏感型小麦品种对NaCl胁迫的生理响应及耐盐性差异

Abstract

为探究小麦品种类型对盐胁迫的生理响应及敏感性差异，以耐盐型品种济麦22和盐敏感型品种河农6425为材料，对幼苗期植株施以不同浓度的NaCl胁迫处理，比较分析了两个品种幼苗在胁迫条件下的生长、生理生化和叶绿体荧光特征等方面的差异。结果表明，NaCl胁迫对幼苗地上和地下部分的生长表现浓度依赖性的抑制效应，对耐盐型品种的抑制程度较小。在生理响应方面，幼苗体内的Na⁺含量随NaCl 浓度的增加而上升，K⁺和Ca²⁺含量则表现相反的变化趋势，耐盐型品种幼苗在胁迫处理前、后均具有较高的K⁺/Na⁺比和Ca²⁺/Na⁺比；NaCl胁迫导致幼苗的光系统Ⅱ受损，表现在Fv/Fm、Fv/Fo、qP 和YⅡ 等叶绿体荧光参数数值下降，降幅在耐盐性品种上相对较小。在氧化胁迫和抗氧化系统方面，NaCl胁迫导致幼苗体内活性氧水平的上升和过氧化物酶（POD）、过氧化氢酶（CAT）等抗氧化酶的响应；POD活性在处理后的0-12 d范围内呈先下降后上升的趋势，CAT活性则呈先上升后下降的趋势。耐盐品种的POD活性在胁迫早期受抑制时间较短，随后的响应更迅速且上升幅度更高；耐盐品种的CAT活性上升幅度更高，且在胁迫后期对高浓度NaCl和长时间胁迫导致的酶活性抑制的耐受性更强。耐盐品种抗氧化酶的这一响应特征与其较低的活性氧上升幅度一致，也与其较低水平的代表膜损伤程度的丙二醛（MDA）积累一致。耐盐型品种根部的MDA积累经200 mmol/L NaCl处理1 d后达到峰值，而盐敏感品种根部的MDA积累经150 mmol/L NaCl处理1 d后即达到峰值。以上研究结果表明，耐盐型小麦品种济麦22可分别通过其较强的K⁺/Na⁺、Ca²⁺/Na⁺调节能力和抗氧化酶体系缓解盐胁迫所导致的渗透胁迫和活性氧伤害，从而表现出耐盐的特征。;Soil salinity is a major abiotic stress inhibiting plant growth, development, and productivity, especially in case of crop. Wheat is an important cereal crop affected by high salinity. A better understanding of the physiological mechanisms underlying salt tolerance will facilitate efforts to improve crop performance under salinity. This study used two general wheat varieties as experimental materials to explore the growth physiological response and sensitivity difference of different cultivated wheat types to salt stress and their salt tolerance. Jimai 22 is salt-tolerant and Henong 6425 is salt-sensitive. In a hydroponic experiment, the effects of different concentrations (0, 50, 100, and 200 mmol/L) of NaCl stress on both Jimai 22 and Henong 6425 seedlings were investigated. The seedlings growth, salt tolerance index, main ion content, physiological and biochemical index, and chloroplast fluorescence parameters were compared. The results showed that NaCl stress inhibited the growth of aboveground and underground parts of wheat seedlings in a concentration dependent manner. The higher the concentration of NaCl was, the greater the toxicity on wheat seedlings would become. And the inhibition degree on Jimai 22 seedlings was smaller than that on Henong 6425 seedlings. In terms of physiological response, the Na⁺ contents in both Jimai 22 and Henong 6425 were increased with the increase of NaCl concentration, while the contents of both K⁺ and Ca²⁺ exhibited opposite trend of changing. The salt tolerance variety Jimai 22 had higher both K⁺/Na⁺ and Ca²⁺/Na⁺ before and after NaCl stress than those on salt sensitive Henong 6425. NaCl stress damaged the photosystem II of both Jimai 22 and Henong 6425 leaves. The concrete manifestation of damage effect was the decrease of chloroplast fluorescence parameters containing Fv/Fm, Fv/Fo, qP and YⅡ under different NaCl concentration. And the lowered range of these parameters in Jimai 22 induced by NaCl stress was lower than that in Henong 6425. In terms of oxidative stress and antioxidant system, the reactive oxygen species (ROS) level was increased with NaCl concentration stress increased. And the activities of peroxidase (POD) and catalase (CAT) were also changed. In 12 d after NaCl treatment, the POD activity was decreased firstly and then increased, while CAT activity was increased firstly and then decreased. The activities of both POD and CAT induced by NaCl stress in Jimai 22 were higher than those in Henong 6425. In the early stage of NaCl stress, the POD activity was temporally suppressed and the rising amplitude of POD activity was very large subsequently. The CAT activities induced by NaCl stress in Jimai 22 were higher than those in Henong 6425. In later days of NaCl stress, Jimai 22 had stronger tolerance to high NaCl concentration and inhibition of antioxidant system induced by long term NaCl stress. The rising range of antioxidant enzyme was consistent with lower ROS and lower malondialdehyde (MDA) which represents the degree of membrane damage in Jimai 22 under NaCl stress. The MDA content of salt tolerant Jimai 22 roots reached the peak after 200 mmol/L NaCl stress for 1 d. While the MDA content of salt sensitive Henong 6425 roots reached the peak after 150 mmol/L NaCl stress for 1 d. Overall, these results suggested that salt tolerant Jimai 22 had higher salt tolerance. Under NaCl stress, Jimai 22 can not only alleviate the damage of both active oxygen and osmotic stress due to the increasing activities of both POD and CAT, but also alleviate the ion stress by maintaining higher level of both K⁺/Na⁺ and Ca²⁺/Na⁺ after different concentrations of NaCl stress. Results from this study could be helpful for further understanding the physiological mechanism of severe NaCl stress in crop, and may be useful for elucidating the salt-tolerant mechanism of different cultivated crop types.