盐生植物种子萌发对环境的适应对策

盐生环境是一种严峻的胁迫环境,对植物的生长、发育、繁殖等生活史的各阶段都产生着重要的影响。盐生植物是生长在盐渍土壤上的一类天然植物区系,它们在长期的进化过程中形成了一系列适应盐生生境的特殊生存策略。一般情况下,盐生植物种子对环境的适应能力,是植物对盐生环境适应性的重要体现;而植物发育早期对盐度的适应能力又是决定物种分布和群落组成的关键因素。在对国内外相关文献进行分析归纳的基础上,从盐分对种子萌发的影响机理及植物种子萌发对盐生环境的适应对策两个方面综述了植物种子休眠萌发与盐生环境的关系。     

盐生植物耐盐分子机制的研究进展

盐生植物是研究植物耐盐分子机制和分离耐盐基因的良好材料,可以反映植物对盐胁迫的适应策略。综述盐生植物响应盐胁迫的转录因子、渗透平衡调节、离子平衡调节、氧化还原平衡调节、光合作用调节及代谢变化,反映盐生植物在多个方面适应盐胁迫的策略。此外,还对盐生植物耐盐分子机制的研究前景作了展望。     

盐分和水分胁迫对两种盐生植物盐爪爪和盐穗木种子萌发的影响

采用不同浓度NaCl和等渗PEG(分子量为6000)处理2种盐生植物种子(盐爪爪Kalidiumfoliatum、盐穗木Halostachys caspica)。结果表明,(1)NaCl和等渗PEG对种子的萌发均产生抑制作用,且PEG的抑制程度大于等渗NaCl,说明渗透胁迫是影响盐生植物种子萌发的主要因素;(2)盐胁迫和水分胁迫对盐生植物种子的萌发具有明显的抑制作用,降低了种子的萌发率,推迟了种子的初始萌发时间、延长了种子的萌发时间;(3)根据2种盐生植物种子萌发耐盐性比较,两种盐生植物均具有较强的耐盐性,在0~300 mmol.L-1NaCl盐溶液范围内,盐穗木种子相对萌发率达到95%以上,盐爪爪达到80%以上,说明盐穗木比盐爪爪具有更强的耐盐性。盐穗木种子耐盐适宜值为332.5 mmol.L-1,临界值为540 mmo.lL-1,极限值为749 mmo.lL-1;盐爪爪种子耐盐适宜值为246.5 mmol.L-1,临界值为391.8 mmo.lL-1,极限值为537 mmol.L-1;(4)低浓度的NaCl溶液对种子萌发的幼苗生长起着促进作用。在100 mmo.lL-1NaCl处理时,两种盐生植物幼苗的胚...     

不同类型盐生植物适应盐胁迫的生理生长机制及Na+逆向转运研究进展

盐生植物是指能在离子浓度至少200 mmol/L以上的生境中生长并完成生活史的植物。盐生植物可分为稀盐盐生植物、泌盐盐生植物、拒盐盐生植物三类。本文从生长形态、生理和分子3个方面总结三类盐生植物响应盐胁迫的不同策略及研究进展,发现盐生植物在分子水平上主要通过Na⁺转运蛋白和为其提供能量的两类基因应对体内过高Na⁺,这可能是引起盐生植物生理和生长形态异于非盐生植物的重要因素。其中稀盐盐生植物主要通过液泡离子区隔化应对盐胁迫,并表现出肉质化生长形态;泌盐盐生植物通过将体内盐分排出体外应对盐胁迫,并进化出特有的生理结构——盐腺或盐囊泡;拒盐盐生植物通过将盐离子积累在皮层细胞液泡和根部木质部薄壁细胞中减少向上运输Na⁺,同时根部多栓质化减少Na⁺吸收。本综述旨在为今后研究盐生植物及其耐盐机制提供相关依据,为植物耐盐分子育种奠定基础。     

藜科盐生植物的形态特征与耐盐分子机理研究进展

在非生物环境胁迫因子中,盐胁迫是造成农作物减产的主要因素之一.从藜科植物耐盐的形态生理学机制和分子生物学角度入手,讨论了藜科植物耐盐基因工程的新进展,探讨藜科盐生植物的盐胁迫机理,为利用基因工程手段培育耐盐植物奠定基础.     

盐生植物角果碱蓬种子二型性对环境的适应策略

角果碱蓬(Suaeda corniculata)是藜科一年生盐生植物, 在我国分布于北方盐碱滩涂和盐碱荒漠地区。角果碱蓬具有棕色和黑色两种异型体种子(简称棕色和黑色种子)。对采自内蒙古鄂托克前旗盐渍化生境的角果碱蓬二型种子的形态、休眠和萌发特性开展对比研究, 测定了二型种子休眠和萌发行为对温度、光照和盐分(NaCl)的响应, 以揭示盐生植物异型种子对温带盐漠生境的适应对策。结果表明: (1)二型性种子在大小、种皮特性和结实比例方面有显著差异。与黑色种子相比, 棕色种子个体较大, 种皮透水性强。黑色种子与棕色种子的结实比例约为5.6 : 1。(2)新成熟的棕色种子的萌发对各温度梯度和光照条件不敏感, 萌发率较高(84%-100%); 而新成熟的黑色种子萌发率较低(8%-78%), 萌发对光照敏感。(3)黑色种子具有浅度生理休眠, 种皮划破、赤霉素处理和低温层积均可有效地提高种子的萌发率。(4)二型种子萌发对土壤盐分的胁迫具有不同的响应。与黑色种子相比, 棕色种子对盐分胁迫不敏感, 在较高的盐分浓度下仍有较高的萌发率, 低温层积处理能够降低黑色种子对盐胁迫的敏感性, 有效地提高种子的初始萌发率、萌发恢复率和最终萌发率。角果碱蓬二型种子不同的形态、休眠和萌发特性, 提高了该物种在高度异质性生境中的适合度, 对种群成功地适应温带盐漠环境具有重要的意义。     

盐土和沙土对新疆常见一年生盐生植物生长和体内矿质组成的影响

选用古尔班通古特沙漠南缘荒漠-绿洲交错带常见的一年生盐生植物盐角草、刺毛碱蓬、叉毛蓬、猪毛菜和碱地肤为材料,比较了它们在原状盐土和沙土中的生长及体内矿质元素组成的差异。结果表明：① 原状盐土0—100 cm各土层的pH值低于沙土,但电导率和含水量明显高于沙土;② 原状盐土中生长的植物干重是沙土中生长植物干重的7—118倍,后者的根冠比是前者的2—6倍。③ 体现肉质化程度的地上部含水率为52%—81%,中低耐盐植物含水率在两种土壤中差异显著,强耐盐植物差异不显著;④ 5种一年生盐生植物地上部氮浓度为11—34 g/kg,在有效氮含量高的盐土上植物氮浓度也高;磷浓度为1—4 g/kg,在有效磷高的盐土上植物磷浓度也较高（盐角草除外）;但沙土中的植物地上部钾浓度明显高于盐土中植株的地上部钾浓度,这与两种土壤在0—60 cm土层中的钾浓度差异相反;⑤ 尽管原状盐土0—100 cm土层中的水溶性钙、镁、钠、氯、硫浓度显著高于沙土,盐土与沙土中生长的植物地上部钠、水溶性氯和硫的浓度比值远远低于土壤中的相应元素浓度的比值,甚至盐土中的植株钙、镁浓度等于或显著低于沙土中生长的植物。表明盐土不仅影响一年生盐生植物的生长,也显著影响这些植物对矿质元素的吸收和累积。一年生盐生植物能够选择性吸收不同生境中的矿质元素。本研究期望为进一步深入研究盐生植物耐盐的适应机制提供依据,也可为植物修复盐碱土的品种选择提供参考。     

植物盐腺泌盐及发育研究进展

盐腺是泌盐盐生植物抵御盐胁迫的重要表皮结构，泌盐盐生植物可以通过盐腺将体内多余的盐离子排出体外，从而避免盐胁迫。盐腺作为泌盐盐生植物实现高效抗盐的重要结构，在逆境生理、发育和进化等领域都引起了关注和讨论，集中在盐腺的超微结构、生理功能、泌盐机制以及发育模式等不同层面已有广泛的研究报道。本文综述了盐腺结构、分泌机制、盐腺发育的研究进展，总结了盐腺泌盐的可能途径以及盐腺发育的调控方式和关键基因，对未来盐腺泌盐和发育的研究提出了相关见解，讨论了盐腺这一独特形态学结构对于植物耐盐性的作用，并对提高植物耐盐性、培育耐盐品种提出了理论依据和建议，有利于深入解析植物耐盐适应演化、培育抗盐作物和高效利用盐碱地。     

盐芥响应盐胁迫的分子机制研究进展

盐生植物盐芥是拟南芥的近缘物种,具有极强的耐盐能力,是很有研究前景的新兴耐盐模式植物.该文主要从离子平衡(Na+的吸收、外排、区隔化)、渗透平衡和过氧化物清除3个方面对近年来国内外有关盐芥耐盐分子机制的研究进展进行综述,以阐述盐芥植物对于盐胁迫反应的生理及分子机制.     

盐胁迫对花生种子际细菌菌群结构的调控

盐胁迫影响种子萌发和植株形态建成,提高盐胁迫下花生种子萌发速率和成苗健苗率是盐碱地花生高产高效栽培的重要环节之一,花生种子际土壤细菌菌群结构与种子萌发关系密切。为揭示盐胁迫对花生种子际微生物菌群结构的影响,以耐盐花生品种（花育25号,HY25）和盐敏感花生品种（花育20号,HY20）为试验材料,采用盆栽实验和高通量测序技术,研究不同耐盐性品种种子萌发吸胀吸水阶段种子际细菌菌群结构的变化。结果表明,种子际土壤细菌群落以变形菌门（Proteobacteria）、厚壁菌门（Firmicutes）、放线菌门（Actinobacteria）、拟杆菌门（Bacteroidetes）及芽单胞菌门（Gemmatimonadetes）等为优势菌门,盐胁迫处理可以不同程度的提高厚壁菌门和放线菌门的相对丰度。在属水平上,盐胁迫可以增加有益菌芽胞杆菌属（Bacillus）的相对丰度,增强盐胁迫下种子存活能力,提高萌发率。细菌功能预测结果显示,信号转导机制、免疫系统和防御机制等相关功能在盐胁迫处理后明显增强,可能是促进花生萌发并增强花生胁迫应答的重要原因之一。种子际优势菌群的鉴定及机理分析可为通过改良种子际土壤微生物环境,提高花生耐盐性和出苗健苗率提供重要的借鉴意义,同时为开发利用盐碱地提供参考。     

Population ecology of halophyte seeds

Some aspects of the population biology of halophytes are considered in this review. Persistent seed banks have been reported for a number of inland- and coastal-salt marsh plant communities. Seeds of perennial grasses are often under-represented, while annuals and some perennial forbs may be over-represented in the seed bank. The persistent seed bank of annual halophytes appears adaptive, and provides multiple seed germination opportunities which may prevent local extinction when environmental stress increases. Somatic seed polymorphism provides a mechanism by which parent plants can respond to changing environments by partitioning their resources into reproductive units which have distinct germination responses. Parental effects may influence either seed morphology and/or physiological requirements of seeds when they are exposed to environmental stress. A prolonged germination period can provide plant populations with numerous opportunities to establish seedling cohorts. Early cohorts will have a selective advantage under moderate conditions because mortality will be low and plants will survive until maturity. However, fluctuations in salinity levels and tidal activity can cause high mortality in early cohorts in salt marsh habitats, providing later cohorts with an opportunity for establishment. Resource allocation to reproductive structures is related to plant size, which itself can be affected by both abiotic and biotic factors. Larger plants were found to produce more seeds than smaller plants in a population, but the mean seed weight was greater in small plants.     

Halophyte Improvement for a Salinized World

It is more important to improve the salt tolerance of crops in a salinized world with the situations of increasing populations, declining crop yields, and a decrease in agricultural lands. Attempts to produce salt-tolerant crops have involved the manipulation of existing crops through conventional breeding, genetic engineering and marker-assisted selection (MAS). However, these have, so far, not produced lines growing on highly saline water. Hence, the domestication of wild halophytes as crops appears to be a feasible way to develop agriculture in highly saline environments. In this review, at first, the assessment criteria of salt tolerance for halophytes are discussed. The traditional criteria for the classification of salinity in crops are less applicable to strong halophytes with cubic growth curves at higher salinities. Thus, realistic assessment criteria for halophytes should be evaluated at low and high salinity levels. Moreover, absolute growth rather than relative growth in fields during a crop's life cycle should be considered. Secondly, the use of metabolomics to understand the mechanisms by which halophytes respond to salt tolerance is highlighted as is the potential for metabolomics-assisted breeding of this group of plants. Metabolomics provides a better understanding of the changes in cellular metabolism induced by salt stress. Identification of metabolic quantitative trait loci (QTL) associated with salt tolerance might provide a new method to aid the selection of halophyte improvement. Thirdly, the identification of germplasm-regression-combined (GRC) marker-trait association and its potential to identifying markers associated with salt tolerance is outlined. Results of MAS/linkage map-QTL have been modest because of the absence of QTLs with tight linkage, the non-availability of mapping populations and the substantial time needed to develop such populations. To overcome these limitations, identification by GRC-based marker-trait association has been successfully applied to many plant traits, including salt tolerance. Finally, we provide a prospect on the challenges and opportunities for halophyte improvement, especially in the integration of metabolomics- and GRC-marker-assisted selection towards new or unstudied halophyte breeding, for which no other genetic information, such as linkage maps and QTL, are available.     

Plant salt tolerance: adaptations in halophytes

Background Most of the water on Earth is seawater, each kilogram of which contains about 35 g of salts, and yet most plants cannot grow in this solution; less than 0·2 % of species can develop and reproduce with repeated exposure to seawater. These ‘extremophiles’ are called halophytes.Scope Improved knowledge of halophytes is of importance to understanding our natural world and to enable the use of some of these fascinating plants in land re-vegetation, as forages for livestock, and to develop salt-tolerant crops. In this Preface to a Special Issue on halophytes and saline adaptations, the evolution of salt tolerance in halophytes, their life-history traits and progress in understanding the molecular, biochemical and physiological mechanisms contributing to salt tolerance are summarized. In particular, cellular processes that underpin the ability of halophytes to tolerate high tissue concentrations of Na⁺ and Cl⁻, including regulation of membrane transport, their ability to synthesize compatible solutes and to deal with reactive oxygen species, are highlighted. Interacting stress factors in addition to salinity, such as heavy metals and flooding, are also topics gaining increased attention in the search to understand the biology of halophytes.Conclusions Halophytes will play increasingly important roles as models for understanding plant salt tolerance, as genetic resources contributing towards the goal of improvement of salt tolerance in some crops, for re-vegetation of saline lands, and as ‘niche crops’ in their own right for landscapes with saline soils.     

What is known about phytohormones in halophytes? A review

Phytohormones participate in many aspects of the plant life cycle, including responses to biotic and abiotic stresses. They play a key role in plant responses to the environment with direct bearing on a plant’s fitness for adaptation and reproduction. In recent years, there have been major advances in our understanding of the role of phytohormones in halophytic plants. The variability in maximal salinity level that halophytes can tolerate makes it difficult to characterize the specific traits responsible for salt tolerance. However, the most evident effect of salinity is growth disturbance, and growth is directly governed by phytohormones. Phytohormones such as abscisic acid, salicylic acid ethylene and jasmonates are traditionally related to stress responses, while the involvement of cytokinins, gibberellins and auxins has started to be analyzed. Polyamines, although they can’t be considered phytohormones because of the high concentrations required for cell responses, have been proposed as a new category of plant growth regulators involved in several plant processes and stress responses. This review integrates the advances in the knowledge about phytohormones in halophytes and their participation in salt tolerance.     

Assessing the role of endophytic bacteria in the halophyte Arthrocnemum macrostachyum salt tolerance

• There is an increasing interest to use halophytes for revegetation of salt affected ecosystems, as well as in understanding their mechanisms of salt tolerance. We hypothesized that bacteria from the phyllosphere of these plants might play a key role in its high tolerance to excessive salinity.
• Eight endophytic bacteria belonging to Bacillus and closely related genera were isolated from phyllosphere of the halophyte Arthrocnemum macrostachyum growing in salty agricultural soils. The presence of plant‐growth promoting (PGP) properties, enzymatic activities and tolerance towards NaCl was determined. Effects of inoculation on seeds germination and adult plant growth under experimental NaCl treatments (0, 510 and 1030 mM NaCl) were studied.
• Inoculation with a consortium including the best performing bacteria improved considerably the kinetics of germination and the final germination percentage of A. macrostachyum seeds. At high NaCl concentrations (1030 mM), inoculation of plants mitigated the effects of high salinity on plant growth and physiological performance and, in addition, this consortium appears to have increased the potential of A. macrostachyum to accumulate Na⁺ in its shoots, thus improving sodium phytoextraction capacity.
• Bacteria isolated from A. macrostachyum phyllosphere seem to play an important role in plant salt tolerance under stressing salt concentrations. The combined use of A. macrostachyum and its microbiome can be an adequate tool to enhance plant adaptation and sodium phytoextraction during restoration of salt degraded soils.

     

Using euhalophytes to understand salt tolerance and to develop saline agriculture: Suaeda salsa as a promising model

Background As important components in saline agriculture, halophytes can help to provide food for a growing world population. In addition to being potential crops in their own right, halophytes are also potential sources of salt-resistance genes that might help plant breeders and molecular biologists increase the salt tolerance of conventional crop plants. One especially promising halophyte is Suaeda salsa, a euhalophytic herb that occurs both on inland saline soils and in the intertidal zone. The species produces dimorphic seeds: black seeds are sensitive to salinity and remain dormant in light under high salt concentrations, while brown seeds can germinate under high salinity (e.g. 600 mm NaCl) regardless of light. Consequently, the species is useful for studying the mechanisms by which dimorphic seeds are adapted to saline environments. S. salsa has succulent leaves and is highly salt tolerant (e.g. its optimal NaCl concentration for growth is 200 mm). A series of S. salsa genes related to salt tolerance have been cloned and their functions tested: these include SsNHX1, SsHKT1, SsAPX, SsCAT1, SsP5CS and SsBADH. The species is economically important because its fresh branches have high value as a vegetable, and its seed oil is edible and rich in unsaturated fatty acids. Because it can remove salts and heavy metals from saline soils, S. salsa can also be used in the restoration of salinized or contaminated saline land.Scope Because of its economic and ecological value in saline agriculture, S. salsa is one of the most important halophytes in China. In this review, the value of S. salsa as a source of food, medicine and forage is discussed. Its uses in the restoration of salinized or contaminated land and as a source of salt-resistance genes are also considered.     

Macroevolutionary patterns of salt tolerance in angiosperms

Background Halophytes are rare, with only 0·25 % of angiosperm species able to complete their life cycle in saline conditions. This could be interpreted as evidence that salt tolerance is difficult to evolve. However, consideration of the phylogenetic distribution of halophytes paints a different picture: salt tolerance has evolved independently in many different lineages, and halophytes are widely distributed across angiosperm families. In this Viewpoint, I will consider what phylogenetic analysis of halophytes can tell us about the macroevolution of salt tolerance.Hypothesis Phylogenetic analyses of salt tolerance have shown contrasting patterns in different families. In some families, such as chenopods, salt tolerance evolved early in the lineage and has been retained in many lineages. But in other families, including grasses, there have been a surprisingly large number of independent origins of salt tolerance, most of which are relatively recent and result in only one or a few salt-tolerant species. This pattern of many recent origins implies either a high transition rate (salt tolerance is gained and lost often) or a high extinction rate (salt-tolerant lineages do not tend to persist over macroevolutionary timescales). While salt tolerance can evolve in a wide range of genetic backgrounds, some lineages are more likely to produce halophytes than others. This may be due to enabling traits that act as stepping stones to developing salt tolerance. The ability to tolerate environmental salt may increase tolerance of other stresses or vice versa.Conclusions Phylogenetic analyses suggest that enabling traits and cross-tolerances may make some lineages more likely to adapt to increasing salinization, a finding that may prove useful in assessing the probable impact of rapid environmental change on vegetation communities, and in selecting taxa to develop for use in landscape rehabilitation and agriculture.