海岸不同生态断带植物根叶抗逆生理变化与其Na+含量的关系

以烟台海岸生态断带滨麦(Leymus mollis)和肾叶打碗花(Calystegia soldanella)为材料,在远离高潮线不同位置上取土样和植物材料,通过测定土壤Na+和两植物根叶Na+含量、丙二醛(MDA)含量、抗氧化酶(SOD、POD、CAT)活性和渗透调节物含量,以揭示滨麦和肾叶打碗花根叶中Na+在其适应海岸盐环境中的生理调控机制。结果表明,在高潮线土壤Na+含量最高,滨麦根叶Na+含量较高,两植物根叶中MDA和水分含量、抗氧化酶活力均较低,但渗透调节物含量均较高。随远离高潮线土壤Na+含量下降,滨麦根叶Na+含量下降,而肾叶打碗花根中Na+含量上升,其根叶Na+含量较滨麦分别高637%和319%。同时两植物根叶MDA含量、叶片含水量增加;两植物根中POD和SOD活力增加;两植物根叶可溶性糖和脯氨酸含量下降。但不同生态断带滨麦叶片平均含水量相对较低,MDA含量、POD和CAT和SOD活力、脯氨酸和可溶性糖含量相对较高。在盐土环境中滨麦通过降低Na+的吸收和提高抗氧化酶活力和有机渗透调节物含量维持氧自由基代谢平衡和水分平衡。而肾叶打碗花是泌盐植物,在不同生态断带其叶片Na+含量、平均含水量相对较高,叶MDA含量、POD和CAT活力、脯氨酸和可溶性糖含量均相对较低。泌盐植物的肾叶打碗花依赖根叶中积累的Na+作为无机渗透调节剂维护其离子平衡和水分平衡及正常生长。因此,积累在根叶中的Na+离子既作为无机渗透调节剂维护细胞离子平衡和水分平衡,又引发细胞生理干旱促进有机渗透调节物合成;另外还作为氧自由基诱发剂促使活性氧自由基(ROS)积累,通过积累的ROS激活抗氧化保护酶系统抑制膜脂过氧化、维护氧自由基代谢平衡。海岸沙地土壤中高浓度Na+是海滨滨麦和肾叶打碗花能长期在盐土环境中生存的依靠元素,其对植物的生理调控作用可能是滨麦和肾叶打碗花适应盐土生存的重要生理适应机理。

The relationship between concentrations of Na+ and changes of physiological response to salt in the leaves and roots of plants

The dominant species of the halophytes Leymus mollis(dune grass) and Calystegia soldanella (beach bindweed) grown in the coastal dunes of the coast of Yantai, China were chosen as materials for this study. Soil and plant materials were sampled from the high tide line, and 10, 20, 30, 40, and 50 metres off the high tide line of the coast. Na⁺ concentrations, activities of the antioxidant enzymes superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), and malondialdehyde (MDA), proline, soluble protein, and sugar contents in the roots and leaves of L. mollis and C. soldanella were determined to understand the role that Na⁺ accumulation in the roots and leaves played in the physiological adaption to saline environments. Na⁺ concentration in the soil was highest at high tide line, and declined with distance, with the sharpest decrease between the high tide line and 20 m further inland. L. mollis and C. soldanella both grew between 10 m and 20 m off the high tide line and further inland. At distances close to the high tide line, the roots and leaves of L. mollis had higher Na⁺ concentrations than did those of C. soldanella;both species had low contents of MDA and water and lower activities of antioxidant enzymes but higher concentrations of the osmoregulatory substances in leaves and roots.Farther from the high tide line, Na⁺ concentration also increased in the roots of C. soldanella; at 50 m, Na⁺ was 637% higher in roots and 319% higher in leaves than in those tissues in L. mollis. Far away from the high tide line, the contents of water and MDA increased in the leaves and roots of both plants; the activities of POD and SOD increased in the roots; and the contents of soluble sugar and proline decreased in the roots of both plants. However, at different distances from high tide, L. mollis had lower average water content, higher contents of MDA, proline, and soluble sugar, and higher POD, CAT, and SOD activity. At the saline seashore soil, L. mollis maintained free radical metabolic balance and water balance by controlling Na⁺ uptake and increasing the activity of antioxidant enzymes and the content of organic osmoregulatory substances. However, C. soldanella is a salt-secreting halophyte with higher Na⁺ and average water content in its leaves and roots, lower MDA content, activities of POD and CAT, and lower contents of proline and soluble sugar on different locations away from high tide, which indicated that the Na⁺ accumulated in the leaves and roots of C. soldanella played a very importance role in maintaining ion balance. Na⁺ accumulated in the roots and leaves of L. mollis and C. soldanella can induce the accumulation of oxygen free radicals to activate the antioxidant enzyme system which in turn would inhibit lipid peroxidation to maintain the balance of oxygen free radical metabolism. Na⁺ accumulated in the roots and leaves of two plants not only can be an inorganic osmotic adjustment substance to maintain cellular water balance, but plants also can increase organic osmotic adjustment substances such as proline and soluble sugars to maintain water balance. Results imply that Na⁺ in the leaves and roots of both plants plays a very important role in physiological regulation of the balance of oxygen free radical metabolism and water balance, allowing these two plants to survive seashore saline conditions.