VA菌根降低植物对重金属镉的吸收

高等植物在漫长的进化过程中对环境产生种种适应机制。菌根的形成即是对自然土壤中有效磷不足的一种适应。菌根真菌与寄主根系共生形成菌根后,真菌的菌丝可以远远伸出根际范围从而扩大了植物对土壤中难以移动的磷元素的吸收范围而改善植物的磷素营养。因此,地球上90％的陆生植物都可形成菌根。菌根的形成,不仅促进了植物对磷的吸收,而且也影响到植物对其它元素包括重金属的吸收。在重金属污染的土壤中,菌根对植物重金属的吸收将影响到植物对重金属的抗性和农产品品质。本文拟研究在添加镉的土壤上菌根对植物吸收Cd的影响。     

既主内政, 又辖外交——以PHR为中心的基因网络调控植物-菌根真菌的共生

磷是植物生长发育必需的大量矿质营养元素, 但自然界大部分土壤都存在严重缺磷的问题。为了适应这一营养逆境, 植物演化出一系列低磷胁迫应答反应。通过改变基因的转录水平调控低磷胁迫应答反应, 而转录因子PHR1在调控植物对低磷胁迫的转录响应中起关键作用。此外, 大部分陆生植物还能与丛枝菌根真菌建立共生关系, 通过丛枝菌根真菌更有效地从土壤中获取磷元素。最近, 中国科学院分子植物科学卓越创新中心王二涛研究组发现, 以PHR为中心的转录调控网络控制植物-丛枝菌根真菌共生的建立。因此, PHR不但在维持植物细胞自身的磷稳态中发挥作用, 而且参与植物与外界微生物的相互作用, 为植物有效地从环境中获得磷元素提供了另外一条途径。     

丛枝菌根形成过程及其信号转导途径

丛枝菌根是由一类土壤中古老的丛枝菌根真菌与植物根系形成的互利互惠共生体。通过共生作用丛枝菌根真菌帮助宿主植物提高水和矿质营养（特别是磷）的吸收效率。作为回报,大约20%的光合作用产物被转移到丛枝菌根真菌中,供其完成自身的生活史。丛枝菌根形成的过程中,需要植物与丛枝菌根真菌之间进行一系列信号分子的识别、交换以及信号转导作用,这一过程由一系列植物和菌根真菌的基因控制。首先,植物会分泌一种植物激素——独角金内酯来诱导菌根真菌加速分支,而菌根真菌也会分泌脂质几丁寡糖促进植物与其形成菌根。加速分支的菌根真菌接触到植物根部以后,会附着在植物根的表皮并形成附着胞,通过附着胞穿透植物根的表皮,最后进入维管组织附近的皮层细胞并在其中不断进行二叉分支,形成特有的丛枝结构。通过对模式植物共生现象的研究,已经发现很多植物基因参与到共生形成的信号转导过程中,包括早期植物反应的基因、菌根与根瘤共生共同需要的转导因子以及菌根特异的信号分子等。本文对菌根的形成过程及信号转导途径进行详细的介绍,为人们深入研究菌根关系提供参考。     

菌根真菌是唱响生物共生交响曲的主角——菌根真菌专辑序言

地球上任何生物都不是单独进行生命活动和进化的,即生物之间更多的是依靠密切联合、共生互助、需求互补和共同发展。其中,陆地生态系统中的强大分解者真菌和强大生产者植物关系密切,特别是以菌根真菌(mycorrhizal fungi)为代表的植物共生真菌自始至终与植物共生,这一强-强共生联合在维持生态平衡、保存生态系统可持续生产力与生态系统综合服务功能体系中,其分布之广、作用之多、功能之强和贡献之大,可谓名副其实的生物共生体系中的主导者。近年来,中国在真菌与植物共生研究领域成绩斐然,占据世界重要地位。本期《菌物学报》"菌根真菌专刊"刊登了2篇综述和20篇研究报告。综述分别对丛枝菌根(AM)真菌在煤矿区生态修复应用研究和兰科植物与菌根真菌的营养关系进行了总结和热点论述;研究报告分别对菌物界球囊菌门AM真菌全球公认种的中文学名给予了全面规范正确的描述、对中国部分林区红桦外生菌根真菌多样性、华山松印度块菌菌根中的块菌交配型基因、AM真菌对枳吸收磷和分泌磷酸酶的影响、转Bt基因棉叶片腐熟物抑制AM真菌定殖及菌根对磷的吸收、低pH影响AM真菌丛枝发育和磷的吸收、接种AM真菌与间作对红壤上玉米和大豆种间氮素竞争的影响、AM真菌及其菌种组合对植物根结线虫病害的影响以及接种AM真菌和施加铁可协同降低水稻砷累积等方面进行了研究。本期内容基本体现了中国菌根真菌分类、物种多样性、生理学、生态学、生理生态效应与作用机制研究的最新进展,对当前和今后开展植物共生真菌的研究具有重要的引领作用。     

营养液强度对AM真菌生长发育的影响

研究了在贫营养基质中不同强度 Hoagland 营养液对丛枝菌根(Arbuscular mycorrhizae,M) 真菌 Glomus versiforme 生长发育的影响。结果表明：本试验条件下,菌根侵染率、菌丝量、孢子数间呈显著正相关。在施加5％～50％强度。Hoagland 营养液时,菌根真菌的生长与宿主植物高粱根中磷浓度、可溶性糖浓度密切相关,而与氮浓度无显著相关。由此认为：在盆栽生产菌根菌剂时,基质中存在一个临界磷浓度,在这个临界浓度之下,菌根真菌的生长发育随磷浓度的提高而增长,超过该临界浓度则会随磷浓度的提高而下降。施用20％、50％强度 Hoagland 营养液对菌根真菌生长最为有利,其菌根侵染率、菌丝量、孢子数均高于其它处理,因此认为：宿主植物一菌根真菌之间共生关系的基础是营养条件,基质中养分的高低会影响互惠共生关系的建立和发展。在高质量菌剂生产中,菌根共生体双方的生长发育完全可以由人工控制。施加营养液是一种有效的调控手段,有可能使共生平衡向有利于菌根真菌生长发育的方向倾斜,使真菌得到最大程度的生长。     

丛枝菌根真菌对植物生长影响的研究

菌根是自然界中一种极为普遍和重要的共生现象,其中分布最为广泛的菌根类型就是丛枝菌根,可以增强植物从土壤中获取水分的能力,改善植物根系对磷、镉等矿质元素及养分的吸收,从而促进植物的生长。本文综述了丛枝菌根真菌对植物生长影响的概况。有关丛枝菌根真菌对植物水分和矿质营养的利用,尤其是磷素营养的研究较为深入,而对植物光合特性的研究较少,这些研究工作为深入理解菌根真菌与植物的相互关系提供基础资料。     

植物磷稳态的调控机制

磷是植物必需的重要营养元素之一,是生物大分子的重要组成部分,在植物生命过程中发挥着不可或缺的作用。维持体内磷稳态对于植物的生长发育和环境应答至关重要。多种信号分子参与调控植物对磷的吸收和转运。植物维持磷稳态主要包括土壤磷的活化、磷的吸收、转运、存储和再利用等过程,涉及磷胁迫响应、转录因子调节、miRNA调节、菌根共生、细胞器间转移等磷调节机制。未来的磷营养机制研究需要跨学科知识的融合,由模式植物研究转向栽培作物。全面总结了植物细胞磷吸收和转运的核心分子及其作用机制的研究进展,旨在为作物品种改良和遗传育种提供重要借鉴。     

营养液强度对AM真菌生长发育的影响*

研究了在贫营养基质中不同强度Hoagland营养液对丛枝菌根(Arbuscular mycorrhizae, M)真菌Glomus versiforme生长发育的影响。结果表明:本试验条件下,菌根侵染率、菌丝量、孢子数间呈显著正相关。在施加5%~50%强度Hoagland营养液时, 菌根真菌的生长与宿主植物高粱根中磷浓度、可溶性糖浓度密切相关,而与氮浓度无显著相关。由此认为:在盆栽生产菌根菌剂时,基质中存在一个临界磷浓度,在这个临界浓度之下,菌根真菌的生长发育随磷浓度的提高而增长,超过该临界浓度则会随磷浓度的提高而下降。施用20%、50%强度Hoagland营养液对菌根真菌生长最为有利,其菌根侵染率、菌丝量、孢子数均高于其它处理,因此认为:宿主植物—菌根真菌之间共生关系的基础是营养条件,基质中养分的高低会影响互惠共生关系的建立和发展。在高质量菌剂生产中, 菌根共生体双方的生长发育完全可以由人工控制。施加营养液是一种有效的调控手段,有可能使共生平衡向有利于菌根真菌生长发育的方向倾斜,使真菌得到最大程度的生长。     

营养液强度对AM真菌生长发育的影响

研究了在贫营养基质中不同强度Hoagland营养液对丛枝菌根(Arbuscularmycorrhizae,M)真菌Glomus versiforme生长发育的影响.结果表明本试验条件下,菌根侵染率、菌丝量、孢子数间呈显著正相关.在施加5%～50%强度Hoagland营养液时,菌根真菌的生长与宿主植物高粱根中磷浓度、可溶性糖浓度密切相关,而与氮浓度无显著相关.由此认为在盆栽生产菌根菌剂时,基质中存在一个临界磷浓度,在这个临界浓度之下,菌根真菌的生长发育随磷浓度的提高而增长,超过该临界浓度则会随磷浓度的提高而下降.施用20%、50%强度Hoagland营养液对菌根真菌生长最为有利,其菌根侵染率、菌丝量、孢子数均高于其它处理,因此认为宿主植物-菌根真菌之间共生关系的基础是营养条件,基质中养分的高低会影响互惠共生关系的建立和发展.在高质量菌剂生产中,菌根共生体双方的生长发育完全可以由人工控制.施加营养液是一种有效的调控手段,有可能使共生平衡向有利于菌根真菌生长发育的方向倾斜,使真菌得到最大程度的生长.     

亚热带典型树种根毛特征及其与共生真菌的关系

根毛和共生真菌增加了吸收面积,提高了植物获取磷等土壤资源的能力。由于野外原位观测根表微观结构较为困难,吸收细根、根毛、共生真菌如何相互作用并适应土壤资源供应,缺乏相应的数据和理论。该研究以受磷限制的亚热带森林为对象,选取了21种典型树种,定量了根毛存在情况、属性变异,分析了根毛形态特征与共生真菌侵染率、吸收细根功能属性之间的关系,探讨了根表结构对低磷土壤的响应和适应格局。结果表明:1)在亚热带森林根毛不是普遍存在的, 21个树种中仅发现7个树种存有根毛, 4个为丛枝菌根(AM)树种, 3个为外生菌根(ECM)树种。其中,马尾松(Pinus massoniana)根毛出现率最高,为86%;2)菌根类型是理解根-根毛-共生真菌关系的关键,AM树种根毛密度与共生真菌侵染率正相关,但ECM树种根毛直径与共生真菌侵染率负相关; 3) AM树种根毛长度和根毛直径、ECM树种根毛出现率与土壤有效磷含量呈负相关关系。该研究揭示了不同菌根类型树种根毛-共生真菌-根属性的格局及相互作用,为精细理解养分获取策略奠定了基础。     

Arbuscular mycorrhiza can depress translocation of zinc to shoots of host plants in soils moderately polluted with zinc

There is increasing and widespread interest in the maintenance of soil quality and remediation strategies for management of soils contaminated with organic pollutants and trace metals or metalloids. There is also a growing body of evidence that arbuscular mycorrhizal (AM) fungi can exert protective effects on host plants under conditions of soil metal contamination. Research has focused on the mechanisms involved and has raised the prospect of utilizing the mutualistic association in soil re-vegetation programmes. In this short paper we briefly review this research, summarize some recent work and highlight some new data which indicate that the alleviation of metal phytotoxicity, particularly Zn toxicity, by arbuscular mycorrhiza may occur by both direct and indirect mechanisms. Binding of metals in mycorrhizal structures and immobilization of metals in the mycorrhizosphere may contribute to the direct effects. Indirect effects may include the mycorrhizal contribution to balanced plant mineral nutrition, especially P nutrition, leading to increased plant growth and enhanced metal tolerance. Further research on the potential application of arbuscular mycorrhiza in the bioremediation or management of metal-contaminated soils is also discussed.     

Biotrophic transportome in mutualistic plant–fungal interactions

Understanding the mechanisms that underlie nutrient use efficiency and carbon allocation along with mycorrhizal interactions is critical for managing croplands and forests soundly. Indeed, nutrient availability, uptake and exchange in biotrophic interactions drive plant growth and modulate biomass allocation. These parameters are crucial for plant yield, a major issue in the context of high biomass production. Transport processes across the polarized membrane interfaces are of major importance in the functioning of the established mycorrhizal association as the symbiotic relationship is based on a ‘fair trade’ between the fungus and the host plant. Nutrient and/or metabolite uptake and exchanges, at biotrophic interfaces, are controlled by membrane transporters whose regulation patterns are essential for determining the outcome of plant–fungus interactions and adapting to changes in soil nutrient quantity and/or quality. In the present review, we summarize the current state of the art regarding transport systems in the two major forms of mycorrhiza, namely ecto- and arbuscular mycorrhiza.     

Cracking the code of plant central phosphate signaling

Phosphate (Pi) is involved in numerous metabolic processes and plays a vital role in plant growth. Green plants have evolved intricate molecular bases of Pi signaling to maintain cellular Pi homeostasis. Here, we summarize recent advances in the molecular and structural bases of central Pi signaling and discuss pending questions.     

Molecular mechanisms regulating Pi-signaling and Pi homeostasis under OsPHR2, a central Pi-signaling regulator, in rice

Phosphorus (P) is one of the most important major mineral elements for plant growth and metabolism. Plants have evolved adaptive regulatory mechanisms to maintain phosphate (Pi) homeostasis by improving phosphorus uptake, translocation, remobilization and efficiency of use. Here we review recent advances in our understanding of the OsPHR2-mediated phosphate-signaling pathway in rice. OsPHR2 positively regulates the low-affinity Pi transporter OsPT2 through physical interaction and reciprocal regulation of OsPHO2 in roots. OsPT2 is responsible for most of the OsPHR2-mediated accumulation of excess Pi in shoots. OsSPX1 acts as a repressor in the OsPHR2-mediated phosphate-signaling pathway. Some mutants screened from ethyl methanesulfonate (EMS)-mutagenized M2 population of OsPHR2 overexpression transgenic line removed the growth inhibition, indicating that some unknown factors are crucial for Pi utilization or plant growth under the regulation of OsPHR2.     

OsSPX1 suppresses the function of OsPHR2 in the regulation of expression of OsPT2 and phosphate homeostasis in shoots of rice

Phosphate (Pi) homeostasis in plants is required for plant growth and development, and is achieved by the coordination of Pi acquisition, translocation from roots to shoots, and remobilization within plants. Previous reports have demonstrated that over‐expression of OsPHR2 (the homolog of AtPHR1) and knockdown of OsSPX1 result in accumulation of excessive shoot Pi in rice. Here we report that OsPHR2 positively regulates the low‐affinity Pi transporter gene OsPT2 by physical interaction and upstream regulation of OsPHO2 in roots. OsPT2 is responsible for most of the OsPHR2‐mediated accumulation of excess shoot Pi. OsSPX1 suppresses the regulation on expression of OsPT2 by OsPHR2 and the accumulation of excess shoot Pi, but it does not suppress induction of OsPT2 or the accumulation of excessive shoot Pi in the Ospho2 mutant. Our data also show that OsSPX1 is a negative regulator of OsPHR2 and is involved in the feedback of Pi‐signaling network in roots that is defined by OsPHR2 and OsPHO2. This finding provides new insight into the regulatory mechanism of Pi uptake, translocation, allocation and homeostasis in plants.     

丛枝菌根在退化土壤恢复中的生态学作用

土壤退化 (包括土壤侵蚀、贫瘠化、盐碱化、沙化、酸化 )不仅为全球所关注 ,而且是关系到我国农业可持续发展的重大问题。全球 1.3× 10 8ｋｍ2 的总土地面积中 ,因人为原因引起的退化面积为 2 0×10 7ｋｍ2 ,这些退化土壤中 ,耕地近 5× 10 8ｈａ ,约占总耕地面积的 1/ 3。我国南方丘陵区土壤退化问题也突出 (水土流失面积 8 0× 10 7ｈａ ,养分贫瘠化 1 9×10 7ｈａ ,污染土壤 3 2× 10 6ｈａ ,酸化土壤 3 2×10 6ｈａ) ,因而探讨恢复和重建退化土壤的途径已成为该地区农业持续发展的重要内容[5] 。菌根 (ｍｙｃｏｒｒｈｉｚａ)是土…     

Nitrate transporter NPF7.3/NRT1.5 plays an essential role in regulating phosphate deficiency responses in Arabidopsis

AtNPF7.3/AtNRT1.5, which is a nitrate transporter that drives root-to-shoot transport of NO₃^?, is also involved in modulating the response to K⁺ deprivation in Arabidopsis by affecting root development and K⁺ transport. However, whether NPF7.3/NRT1.5 functions in regulating plant responses to deficiencies of other nutrients remains unknown. In this study, we found that the expression of AtNPF7.3/AtNRT1.5 was predominant in the roots and was substantially induced by phosphate (Pi) starvation. The atnrt1.5 mutants displayed conspicuously longer primary roots along with a significantly reduced lateral root density under Pi-deficient conditions than did the wild-type plants, and these morphological differences in the roots were eliminated to a certain extent by the ethylene synthesis antagonist Co²⁺. Further analyses revealed that the expression of important Pi starvation-induced genes, which are directly involved in Pi transport, mobilization and distribution, were significantly higher in the atnrt1.5 mutants than that in the wild-type plants under Pi-starvation conditions; therefore, the atnrt1.5 mutants retained higher tissue Pi concentrations. Taken together, our results suggest that NPF7.3/NRT1.5 is an important component in the regulation of phosphate deficiency responses in Arabidopsis.