红树植物耐盐机理研究进展

从形态、生理生化和分子水平综述了红树植物的耐盐机理。红树植物具有盐腺、叶片肉质化等形态特征,通过离子选择性积累、盐分区域化、泌盐和拒盐等机制降低体内的盐分浓度,积累或合成渗透调节物质（主要是松醇和甘露醇）来维持渗透平衡,增强抗氧化系统以清除活性氧。在分子水平上,红树植物的耐盐能力与参与合成渗透调节物质关键酶和抗氧化酶等基因的表达相关。     

Investigations on the antioxidative defence responses to NaCl stress in a mangrove, Bruguiera parviflora: Differential regulations of isoforms of some antioxidative enzymes

Two-month-old healthy seedlings of a true mangrove, Bruguiera parviflora, raised from propagules in normal nursery conditions were subjected to varying concentrations of NaCl for 45 d under hydroponic culture conditions to investigate the defence potentials of antioxidative enzymes against NaCl stress imposed oxidative stress. Changes in the activities of the antioxidative enzymes catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (POX), glutathione reductase (GR) and superoxide dismutase (SOD) were assayed in leaves to monitor the temporal regulation. Among the oxidative stress triggered chemicals, the level of H₂O₂ was significantly increased while total ascorbate and total glutathione content decreased. The ratio of reduced to oxidized glutathiones, however, increased due to decreased levels of oxidized glutathione in the leaf tissue. Among the five antioxidative enzymes monitored, the APX, POX, GR and SOD specific activities were significantly enhanced at high concentration (400 mM NaCl), while the catalase activities declined, suggesting both up and downregulations of antioxidative enzymes occurred due to NaCl imposed osmotic and ionic stress. Analysis of the stress induced alterations in the isoforms of CAT, APX, POX, GR and SOD revealed differential regulations of the isoforms of these enzymes. In B. parviflora one isoform of each of Mn-SOD and Cu/Zn-SOD while three isoforms of Fe-SOD were observed by activity staining gel. Of these, only Mn-SOD and Fe-SOD2 content was preferentially elevated by NaCl treatment, whereas isoforms of Cu/Zn-SOD, Fe-SOD1 and Fe-SOD3 remained unchanged. Similarly, out of the six isoforms of POX, the POX-1,-2,-3 and -6 were enhanced due to salt stress but the levels of POX-4 and -5 remained same as in control plants suggesting preferential upregulation of selective POX isoforms. Activity staining gel revealed only one prominent band of APX and this band increased with increased salt concentration. Similarly, two isoforms of GR (GR1 and GR2) were visualized on activity staining gel and both these isoforms increased upon salt stress. In this mangrove four CAT-isoforms were identified, among which the prominent CAT-2 isoform level was maximally reduced again suggesting differential downregulation of CAT isoforms by NaCl stress. The results presented in this communication are the first report on the resolutions of isoforms APX, POX and GR out of five antioxidative enzymes studied in the leaf tissue of a true mangrove. The differential changes in the levels of the isoforms due to NaCl stress may be useful as markers for recognizing salt tolerance in mangroves. Further, detailed analysis of the isoforms of these antioxidative enzymes is required for using the various isoforms as salt stress markers. Our results indicate that the overproduction of H₂O₂ by NaCl treatment functions as a signal of salt stress and causes upregulation of APX, POX, GR and deactivations of CAT in B. parviflora. The concentrations of malondialdehyde, a product of lipid peroxidation and lipoxygenase activity remained unchanged in leaves treated with different concentrations of NaCl, which again suggests that the elevated levels of the antioxidant enzymes protect the plants against the activated oxygen species thus avoiding lipid peroxidation during salt stress.     

植物耐盐性机理研究进展

在盐胁迫下环境中某些植物会在发生一些变化。从生理学、生物化学、盐胁迫分子学机制的角度对植物对盐胁迫的反应研究进行了回顾,并提供了一些目前知识水平上能增加植物盐耐性的方法。解释了在盐胁迫下植物的离子吸收、相溶性物质、抗氧化酶、植物激素、光合作用等方面的变化规律,其中也有耐盐植物功能调节的研究,这有助于从多学科研究的角度评估盐胁迫的生态重要性。     

Defense potentials to NaCl in a mangrove, Bruguiera parviflora: differential changes of isoforms of some antioxidative enzymes

In order to assess the role of the antioxidative defense system against salt treatment, the activities of some antioxidative enzymes and levels of antioxidants were monitored in a true mangrove, Bruguiera parviflora, subjected to varying levels of NaCl under hydroponic culture. In the leaves of B. parviflora, salt treatment preferentially enhanced the content of H2O2 as well as the activity of ascorbate peroxidase (APX), guaiacol peroxidase (GPX), glutathione reductase (GR), and superoxide dismutase (SOD), whereas it induced the decrease of total ascorbate and glutathione (GSH+GSSG) content as well as catalase (CAT) activity. Analysis of isoforms of antioxidative enzymes by native PAGE and activity staining revealed that leaves of B. parviflora had one isoform each of Mn-SOD and Cu/Zn-SOD and three isoforms of Fe-SOD. Expression of Mn-SOD and Fe-SOD-2 was preferentially elevated by NaCl. Similarly, out of the six isoforms of GPX, the GPX-1, 2, 3 and 6 were enhanced by salt treatment but the levels of GPX-4 and -5 changed minimally as compared to those of a control. Activity staining gel revealed only one prominent isoform of APX and two isoforms of GR (GR-1 and GR-2), all of these isoforms increased upon salt exposure. Four CAT-isoforms were identified, among which the prominent CAT-2 isoform level was maximally reduced, suggesting differential down regulation of CAT isoforms by NaCl. The concentrations of malondialdehyde (MDA), a product of lipid peroxidation, remained unchanged in leaves of the plant treated with different concentrations of NaCl. This suggests that plants are protected against activated oxygen species by the elevated levels of certain antioxidative enzymes, thus avoiding lipid peroxidation during salt exposure. The differential changes in the levels of the isoforms due to NaCl treatment may be useful as markers for recognizing salt tolerance in mangroves.     

Antioxidative defense under salt stress

Salt tolerance is a complex trait involving the coordinated action of many gene families that perform a variety of functions such as control of water loss through stomata, ion sequestration, metabolic adjustment, osmotic adjustment and antioxidative defense. In spite of the large number of publications on the role of antioxidative defense under salt stress, the relative importance of this process to overall plant salt tolerance is still a matter of controversy. In this article, the generation and scavenging of reactive oxygen species (ROS) under normal and salt stress conditions in relation to the type of photosynthesis is discussed. The CO₂ concentrating mechanism in C4 and CAM plants is expected to contribute to decreasing ROS generation. However, the available data supports this hypothesis in CAM but not in C4 plants. We discuss the specific roles of enzymatic and non enzymatic antioxidants in relation to the oxidative load in the context of whole plant salt tolerance. The possible preventive antioxidative mechanisms are also discussed.Key words: salt stress, generation of ROS, type of photosynthesis, scavenging of ROS, preventive antioxidative defense     

Physiological and proteomic analysis of salinity tolerance in Puccinellia tenuiflora

Soil salinity poses a serious threat to agriculture productivity throughout the world. Studying mechanisms of salinity tolerance in halophytic plants will provide valuable information for engineering plants for enhanced salt tolerance. Monocotyledonous Puccinellia tenuiflora is a halophytic species that widely distributed in the saline-alkali soil of the Songnen plain in northeastern China. Here we investigate the molecular mechanisms underlying moderate salt tolerance of P. tenuiflora using a combined physiological and proteomic approach. The changes in biomass, inorganic ion content, osmolytes, photosynthesis, defense-related enzyme activities, and metabolites in the course of salt treatment were analyzed in the leaves. Comparative proteomic analysis revealed 107 identities (representing 93 unique proteins) differentially expressed in P. tenuiflora leaves under saline conditions. These proteins were mainly involved in photosynthesis, stress and defense, carbohydrate and energy metabolism, protein metabolism, signaling, membrane, and transport. Our results showed that reduction of photosynthesis under salt treatment was attributed to the down-regulation of the light-harvesting complex (LHC) and Calvin cycle enzymes. Selective uptake of inorganic ions, high K(+)/Na(+) ratio, Ca(2+) concentration changes, and an accumulation of osmolytes contributed to ion balance and osmotic adjustment in leaf cells. Importantly, P. tenuiflora plants developed diverse reactive oxygen species (ROS) scavenging mechanisms in their leaves to cope with moderate salinity, including enhancement of the photorespiration pathway and thermal dissipation, synthesis of the low-molecular-weight antioxidant α-tocopherol, and an accumulation of compatible solutes. This study provides important information toward improving salt tolerance of cereals.     

海南红树林群系及分子生物技术在其研究中的应用

红树林是生长在热带亚热带海岸潮间带的木本植物群落。海南红树林是中国种类最多,分布和保存面积最大的区域之一,具有极为重要的研究价值。综述了海南红树林在种类、群落组成及红树林资源引种恢复以及分子生物技术等方面的研究,重点综述了分子生物技术在海南红树林植物研究中的应用,包括等位酶的应用、随机扩增多态DNA技术(RAPD)的应用和红树林植物耐盐性研究。     

Hydrogen peroxide pre-treatment induces salt-stress acclimation in maize plants

The effect of exogenously applied H2O2 on salt stress acclimation was studied with regard to plant growth, lipid peroxidation, and activity of antioxidative enzymes in leaves and roots of a salt-sensitive maize genotype. Pre-treatment by addition of 1 microM H2O2 to the hydroponic solution for 2 days induced an increase in salt tolerance during subsequent exposure to salt stress. This was evidenced by plant growth, lipid peroxidation and antioxidative enzymes measurements. In both leaves and roots the variations in lipid peroxidation and antioxidative enzymes (superoxide dismutase, ascorbate peroxidase, guaiacol peroxidase, glutathione reductase, and catalase) activities of both acclimated and unacclimated plants, suggest that differences in the antioxidative enzyme activities may, at least in part, explain the increased tolerance of acclimated plants to salt stress, and that H2O2 metabolism is involved as signal in the processes of maize salt acclimation.     

Differentiation between true mangroves and mangrove associates based on leaf traits and salt contents

Aims Mangrove species are classified as true mangroves and mangrove associates. However, as for some fringe species found mainly on the landward transitional zones of mangroves, no consensus among scientists could be reached in favor of this classification and much debate arises. We hypothesized that true mangroves differ from mangrove associates physiologically and ecologically in their ability to survive in mangrove environment.Methods To test this hypothesis, leaf structural traits and osmotic properties were used to describe variation in 33 mangrove species (17 true mangroves, 6 mangrove associates and 10 controversial species).Important findings Specific leaf area (SLA) of true mangroves as well as leaf nitrogen concentration on a leaf mass (Nmass) were lower than that of mangrove associates; leaf succulence was, in general, twice as high in true mangroves compared to mangrove associates; true mangroves accumulated 8–9 times more Na and Cl than mangrove associates and the former had K/Na ratios <0.5, but the latter had K/Na ratios>0.5. These results indicated that true mangroves differed reliably from mangrove associates in leaf traits and osmotic properties. True mangroves are true halophytes and mangrove associates are glycophytes with certain salt tolerance. Combining distribution pattern information, the 10 controversial species were reclassified.     

丛枝菌根真菌提高盐胁迫植物抗氧化机制的研究进展

土地盐渍化是在自然环境和人为活动的双重作用下形成的全球性的重要生态问题,其会对植物造成渗透失衡、离子胁迫、氧化损伤等危害,导致植物生长缓慢、生物量减少甚至是绝产。丛枝菌根真菌(AMF)是一种普遍存在于土壤中的有益微生物,能够与大多数植物根系形成共生关系,其共生关系在多种逆境生态系统中均具有重要生态意义。AMF-植物共生体具有高效抗氧化系统,能够提高植物在盐胁迫下的抗氧化反应进而增强耐盐性。本文从氧化损伤、渗透调节、抗氧化机制和生物活性分子等角度,系统地阐述了丛枝菌根真菌提高植物抗氧化机制的研究进展,并提出了研究展望,以期为利用菌根生物技术提高植物耐盐性提供理论参考。     

大豆耐盐机理及相关基因分子标记

大豆耐盐涉及多种生理代谢途径.耐盐大豆能够通过Cl-排除、控制Na 的吸收和转运、合成渗透调节物质、改变细胞膜膜脂组分及相关酶类的活性等多种形式来适应盐胁迫;野生大豆群体具有盐腺,从形态结构上适应盐逆境;大豆-根瘤菌共生体在盐胁迫下通过互作来提高整体的耐盐性.分子生物学技术应用于大豆耐盐研究,已获得了一些与耐盐相关基因连锁的分子标记.广泛搜集筛选大豆栽培种和野生种资源,利用分子生物学技术和基因工程提高大豆耐盐性,将成为未来大豆耐盐研究的主要内容.     

Salt tolerance is unrelated to carbohydrate metabolism in cowpea cultivars

Under salinity stress, plants commonly accumulate carbohydrates for osmotic adjustment to balance the excess accumulated ions and to protect biomolecules. We selected two cowpea cultivars with contrasting response to salinity, Pitiúba (salt-tolerant) and TVu (salt-sensitive), to investigate whether the salt tolerance could be associated with changes in carbohydrate accumulation and metabolism in leaves and roots during a long-term experiment. Two salt treatments (0 and 75 mM NaCl) were applied to 10-day-old plants grown in nutrient solution for 24 days. Despite some changes in carbohydrate accumulation and carbohydrate metabolism enzymes induced by salt stress, no consistent alterations in carbohydrates could be found in leaves or roots in this study. Therefore, we suggest that tolerance to salt stress is largely unrelated to carbohydrate accumulation in cowpea.     

Zinc improves salt tolerance by increasing reactive oxygen species scavenging and reducing Na+ accumulation in wheat seedlings

Salt decreases the uptake of Zn and other minerals and causes nutritional disorders in plants. Zn is an essential micronutrient for all organisms and it is reasonable to hypothesize that Zn status is essential for maintaining salt tolerance in plants. In this study, the physiological and molecular mechanisms of Zn-based alleviation of salt stress in wheat seedlings were investigated. Our results indicate that sufficient Zn nutrition maintained antioxidative enzyme activities and decreased a reactive oxygen species over-accumulation in wheat seedlings. Our data also reveal that sufficient Zn nutrition improved the expression of Na⁺/H⁺ antiporter genes, TaSOS1 and TaNHX1, thereby decreasing the Na⁺ accumulation and subsequently improving salt tolerance in wheat seedlings.     

大豆耐盐机理及相关基因分子标记

大豆耐盐涉及多种生理代谢途径。耐盐大豆能够通过Cl-排除、控制Na+的吸收和转运、合成渗透调节物质、改变细胞膜膜脂组分及相关酶类的活性等多种形式来适应盐胁迫;野生大豆群体具有盐腺,从形态结构上适应盐逆境;大豆-根瘤菌共生体在盐胁迫下通过互作来提高整体的耐盐性。分子生物学技术应用于大豆耐盐研究,已获得了一些与耐盐相关基因连锁的分子标记。广泛搜集筛选大豆栽培种和野生种资源,利用分子生物学技术和基因工程提高大豆耐盐性,将成为未来大豆耐盐研究的主要内容。     

三种红树植物对盐胁迫的生理适应

无瓣海桑（Sa）、海桑（Sc）、红海榄（Rs）都属于乔木红树植物。这3种红树植物对盐度的敏感程度存在着差异,因此对不同标准的盐度的适应性也大不相同。通过对这3种红树植物用不同的盐度的水3个月的处理,发现Sa和Sc叶片的净光合作用速率、气孔导度、蒸腾速率都随着盐度的增加而降低。Sa,Sc,Rs叶片中的可溶性总糖含量随着盐度的升高整体上有上升趋势。Sa和Sc茎、叶中丙二醛（MDA）含量在低盐度时（〈10）略有降低,随着盐度升高,MDA含量急速升高,而Rs茎、叶中MDA只是在盐度超过40时才会有明显增长,3种红树植物根部的MDA含量变化都不明显。Rs可以依靠超氧化物歧化酶（SOD）来消除活性氧自由基,而红树植物Sa和Sc的耐盐性稍差,SOD对膜的保护能力不强。根据实验结果,可以得出对3种红树植物对盐度的适应范围,这将为指导中国南海海岸线上的红树造林计划提供依据。     

Stress‐induced pyruvate accumulation contributes to cross protection in a fungus

It is commonly observed that microorganisms subjected to a mild stress develop tolerance not only to higher doses of the same stress but also to other stresses – a phenomenon called cross protection. The mechanisms for cross protection have not been fully revealed. Here, we report that heat shock induced cross protection against UV, oxidative and osmotic/salt stress conditions in the cosmopolitan fungus Metarhizium robertsii. Similarly, oxidative and osmotic/salt stresses also induced cross protection against multiple other stresses. We found that oxidative and osmotic/salt stresses produce an accumulation of pyruvate that scavenges stress‐induced reactive oxygen species and promotes fungal growth. Thus, stress‐induced pyruvate accumulation contributes to cross protection. RNA‐seq and qRT‐PCR analyses showed that UV, osmotic/salt and oxidative stress conditions decrease the expression level of pyruvate consumption genes in the trichloroacetic acid cycle and fermentation pathways leading to pyruvate accumulation. Our work presents a novel mechanism for cross protection in microorganisms.