植物高效吸收和利用磷营养的遗传学研究进展

近些年来 ,人们对植物营养性状的遗传学背景日益了解 ,特别是磷素营养。随着分子生物学的快速发展 ,磷素营养的研究已深入到分子水平并且取得了可喜的成绩。本文从植物体内调控磷吸收利用的相关QTLs定位 ,缺磷诱导的基因表达 ,植物体内的磷调控系统 ,磷转运子及与磷有关的突变体的研究作一概括。     

植物与低磷环境研究进展——诱导、适应与对策

自从20世纪70年代人们发现适应低磷土壤的作物根际磷的有效性明显增加的现象之后。植物与低磷环境的研究便引起了人们的重视。植物如何适应低磷环境和如何有效利用土壤磷素资源的问题已成为国内外当前的研究热点之一。研究表明,低磷条件下,植物根系形态结构会发生适应性变化,根冠间的物质分配会向根部倾斜使根冠比增加;植物根际酸度变化、有机酸分泌和磷酸酶释放有利于活化和利用土壤中的磷素资源;不同种类或品种的植物具有不同的磷营养效率基因型,具有不同亲和力的磷转运体,也具有不同的磷活化机制。人类对植物适应低磷机制的研究还将继续,揭示植物对低磷环境的响应对策和发掘植物有效利用磷素资源的潜力,在经济上和环保上均有非常现实的意义。     

外生菌根真菌及其菌根辅助细菌协同解磷的研究进展

磷素是植物生长发育所必需的大量营养元素,参与植物体内多数生物代谢过程。然而,土壤中矿物对无机磷的强吸附性以及有机磷的难降解性都大大降低了磷素对植物的有效性。植物与外生菌根真菌形成外生菌根共生体,能够显著提高土壤磷素的植物有效性,促进植物对磷素的高效吸收。在此过程中,外生菌根辅助细菌也发挥着十分重要的作用,但对其综述性分析还鲜有报道。本文介绍了外生菌根真菌及其菌根辅助解磷细菌的相互作用;解析了外生菌根真菌及其菌根辅助解磷细菌溶解无机磷和水解有机磷的协同作用,并分析了其溶磷机制;阐明了外生菌根真菌对磷素的吸收过程;展望了外生菌根真菌及其菌根辅助解磷细菌互作促进植物磷素吸收的研究前景。     

土壤解磷微生物促进植物磷素吸收策略研究进展

随着全球磷肥需求增加和磷矿资源储量短缺矛盾逐渐加重,土壤解磷微生物在促进磷循环方面的重要性日益突显,因此有必要对其种类和促进植物磷素吸收策略进行全面梳理总结。荟萃分析了土壤解磷微生物种类并构建了系统进化树,重点论述了土壤解磷微生物促进植物磷素吸收主要策略。土壤解磷微生物主要通过矿化和溶解作用直接活化难溶性磷,但其也能与植物根系互作间接活化磷素。其间接途径主要包括解磷微生物与根系分泌物和丛枝菌根真菌互作,它们通过碳磷交换间接活化磷素;其次包括一些解磷微生物可以通过固氮作用使植物生长受到磷的限制,从而调节植物磷酸盐转运系统间接活化土壤磷;解磷微生物也能通过分泌植物激素和生物防治剂促进植物根系生长间接促进植物磷素吸收。解磷微生物还能通过磷素固定减少磷流失,也可以通过加速自身磷素周转促进植物磷素吸收。对完善和发展解磷微生物主导的土壤磷循环和植物磷素吸收利用理论体系具有重要意义。     

土壤溶磷微生物溶磷、解磷机制研究进展

土壤磷素存量大,但其中约95%不能被植物直接吸收利用,土壤中磷素供给不足常常是制约作物生长发育的重要原因之一。活化土壤中的难溶性磷、增强土壤有效磷的供给能力,一直是人们关注的重要问题,并对农业可持续性发展具有重要意义。土壤溶磷微生物(phosphate solubilizing microorganisms, PSMs)是土壤磷循环中的重要一员,能够通过酸解作用、酶解作用等将无效磷转化为有效磷供植物吸收,从而促进植物生长发育。通过PSMs改善土壤磷素营养是一项有利于资源节约、环境友好的重要农业措施,其应用前景十分广阔。因此,深入了解PSMs溶磷、解磷机制对于提高土壤磷素利用效率和提高作物产量具有十分重要的作用。本文对土壤溶磷微生物的种类、无机矿物磷溶解途径以及溶磷微生物依靠酶解作用对有机磷的矿化等方面进行了综述,并对该领域的研究发展方向进行了展望。     

模拟不同春季降雨量下典型草原土壤微生物磷周转特征

春季降雨是内蒙古典型草原生产力最重要的影响因素之一,土壤湿度与微生物活性密切相关,但春季降雨对土壤微生物量磷周转的影响目前知之甚少。本研究2015年4月底在内蒙古锡林浩特毛登牧场,设立不降雨(W0)、一次模拟降雨20 mm(W1)和两次模拟降雨,每次20 mm(W2)试验,旨在比较不同模拟降雨量条件下,典型草原土壤微生物量磷季节变化特征,了解土壤微生物量磷周转特征及其与植物磷素营养的关系。结果表明:(1)模拟春季降雨显著地提高了土壤微生物量磷,W1和W2分别从W0的6.91μg/g提高到7.47μg/g和8.29μg/g(全年平均值),尤其是模拟2次降雨,土壤微生物量磷周转期缩短至0.53年,周转通量增大至33.16 kg hm~(-2) a~(-1),而W0分别为0.59年和26.82 kg hm~(-2) a~(-1);(2)模拟春季降雨总体上降低了土壤酸性磷酸酶活性,但提高了碱性磷酸酶活性;(3)模拟降雨显著地提高了植物生物量和全磷含量,但是植物生物量和全磷含量与土壤微生物量磷、酸性和碱性磷酸酶活性及土壤有效磷含量之间没有显著的相关性。这可能反映出内蒙古典型草原土壤微生物量磷周转、土壤磷素供给及牧草磷素营养之间存在复杂的关系;土壤微生物与牧草竞争土壤磷素,从而影响牧草磷素营养。     

不同改良方法对盐碱土壤磷素营养的影响

采用浅耕翻、施用磷石膏、施用糠醛渣、施用有机肥、建植星星草人工草地或星星草+羊草人工草地等不同改良方法对盐碱土壤磷素营养影响的研究结果表明, 不同改良方法能不同程度的提高土壤全磷、速效磷、有机磷、无机磷含量和磷酸酶活性, 其中浅耕+有机肥+星星草+羊草处理与浅耕相比土壤磷素各指标增加显著, 盐碱土壤磷素营养各指标间存在着一定的相关关系。     

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。     

植物响应低磷胁迫的功能基因组研究进展

磷对植物的生长发育起着重要的作用,但土壤有效磷含量不足已成为世界范围内制约作物产量和品质提高的重要因素。植物在遭受低磷胁迫时,体内会形成适应性机制,因此解析调控植物对低磷胁迫适应性的分子机制也成为科学领域的一大热点。从功能基因组的角度,包括磷胁迫诱导的差异基因表达谱、差异基因的功能类别、基因调控网络、非编码RNA以及植物激素参与的植物耐低磷调控机制等方面综述了近年来植物响应低磷胁迫的分子机制。     

植物高效利用磷机制的研究进展

缺磷是限制目前农林业产量的一个重要因子,传统的农林业生产主要通过施肥和土壤改良来满足植物对磷的需求,近年来人们开始发掘磷高效利用植物来替代传统方法提高磷的利用效率。本文综述了国内外有关植物高效利用磷的形态学、生理学及遗传学作用机制,植物高效利用磷的机制主要包括：(1)磷高效利用植物能通过根系形态变化(包括根伸长、根轴变细、根毛数量和密度增大、侧根幼根数量增加及形成排根等)和根冠问的物质分配改变等形态学机制来适应磷胁迫;(2)在缺磷环境下磷高效利用植物能通过根系分泌物增加、菌根侵染、根系吸收动力学特征变化及植物磷素内循环加强等生理学机制来适应磷胁迫;(3)在磷亏缺的长期选择压力下,植物可通过某些“沉默”基因的诱导表达或DNA序列的特定形成相对稳定的磷营养遗传性状,由此通过遗传学机制来增加对土壤难溶态性磷的利用,使植物表现出较高的磷素利用效率。     

植物磷营养高效的分子生物学研究进展

挖掘利用植物自身的磷高效营养遗传资源是农业可持续发展的关键.磷高效营养性状涉及根形态、根分泌物、膜与体内磷转运以及菌根等许多方面,表现为数量遗传性状及受多基因控制.近年来,许多高亲和磷转运子基因已被克隆,磷向地上部转运和磷吸收负反馈调节的控制基因也被发现,对于根系分泌有机酸和酸性磷酸酶的基因的控制也有了一定的了解,但目前对于根毛、排根、根构型以及菌根的营养学意义性状的分子生物学研究进展缓慢.     

植物磷营养高效的分子生物学研究进展

挖掘利用植物自身的磷高效营养遗传资源是农业可持续发展的关键。磷高效营养性状涉及根形态、根分泌物、膜与体内磷转运以及菌根等许多方面,表现为数量遗传性状及受多基因控制。近年来,许多高亲和磷转运子基因已被克隆, 磷向地上部转运和磷吸收负反馈调节的控制基因也被发现, 对于根系分泌有机酸和酸性磷酸酶的基因的控制也有了一定的了解, 但目前对于根毛、排根、根构型以及菌根的营养学意义性状的分子生物学研究进展缓慢。     

Screening Arabidopsis for mutants in mineral nutrition

Arabidopsis thaliana is a small herbaceous plant which is used as a model plant for defining the molecular basis of many plant processes. The advantages of this plant for genetic studies are its small, well-characterized genome, a short life cycle, large seed set and small seed size. The analysis of mutants of this plant has proved useful in understanding basic plant processes. To isolate Arabidopsis mutants in mineral nutrition, we have devised a method of screening based on X-ray fluorescence spectrometry (XRFS) analysis of leaves. We have identified three mutants in P and Mn nutrition after screening over 100 000 seedlings. These mutants show either excessive accumulation of P or Mn in shoots or an inabilty to accumulate normal concentrations of P.     

Algivore or Phototroph? Plakobranchus ocellatus (Gastropoda) Continuously Acquires Kleptoplasts and Nutrition from Multiple Algal Species in Nature

The sea slug Plakobranchus ocellatus (Sacoglossa, Gastropoda) retains photosynthetically active chloroplasts from ingested algae (functional kleptoplasts) in the epithelial cells of its digestive gland for up to 10 months. While its feeding behavior has not been observed in natural habitats, two hypotheses have been proposed: 1) adult P. ocellatus uses kleptoplasts to obtain photosynthates and nutritionally behaves as a photoautotroph without replenishing the kleptoplasts; or 2) it behaves as a mixotroph (photoautotroph and herbivorous consumer) and replenishes kleptoplasts continually or periodically. To address the question of which hypothesis is more likely, we examined the source algae for kleptoplasts and temporal changes in kleptoplast composition and nutritional contribution. By characterizing the temporal diversity of P. ocellatus kleptoplasts using rbcL sequences, we found that P. ocellatus harvests kleptoplasts from at least 8 different siphonous green algal species, that kleptoplasts from more than one species are present in each individual sea slug, and that the kleptoplast composition differs temporally. These results suggest that wild P. ocellatus often feed on multiple species of siphonous algae from which they continually obtain fresh chloroplasts. By estimating the trophic position of wild and starved P. ocellatus using the stable nitrogen isotopic composition of amino acids, we showed that despite the abundance of kleptoplasts, their photosynthates do not contribute greatly to the nutrition of wild P. ocellatus, but that kleptoplast photosynthates form a significant source of nutrition for starved sea slugs. The herbivorous nature of wild P. ocellatus is consistent with insights from molecular analyses indicating that kleptoplasts are frequently replenished from ingested algae, leading to the conclusion that natural populations of P. ocellatus do not rely on photosynthesis but mainly on the digestion of ingested algae.     

Engineering the root-soil interface via targeted expression of a synthetic phytase gene in trichoblasts

For biochemical modification of the root-soil interface, the engineered secretion of stable enzymes from trichoblasts (= root hair bearing rhizodermal cells) is proposed. As a reporter activity, we chose to express a synthetic gene encoding a secretory phytase (PHY) directed by a trichoblast-specific promoter in root hair cells of the crop plant potato. Transgenic plants produced and secreted phytase in sufficient amounts to release phosphate from phytate in liquid medium. When grown in an unsterile substrate containing phytate, transgenic plants accumulated 40% more P in leaves than wild-type plants. The improved P nutrition driven by trichoblast-targeted expression and subsequent secretion of PHY illustrates the potential of using trichoblast-targeted expression of suitable enzymes for future applications in plant nutrition, phytoremediation and molecular farming.     

Functional biology of plant phosphate uptake at root and mycorrhiza interfaces

Phosphorus (P) is an essential plant nutrient and one of the most limiting in natural habitats as well as in agricultural production world-wide. The control of P acquisition efficiency and its subsequent uptake and translocation in vascular plants is complex. The physiological role of key cellular structures in plant P uptake and underlying molecular mechanisms are discussed in this review, with emphasis on phosphate transport across the cellular membrane at the root and arbuscular-mycorrhizal (AM) interfaces. The tools of molecular genetics have facilitated novel approaches and provided one of the major driving forces in the investigation of the basic transport mechanisms underlying plant P nutrition. Genetic engineering holds the potential to modify the system in a targeted way at the root-soil or AM symbiotic interface. Such approaches should assist in the breeding of crop plants that exhibit improved P acquisition efficiency and thus require lower inputs of P fertilizer for optimal growth. Whether engineering of P transport systems can contribute to enhanced P uptake will be discussed.     

Ectomycorrhizal fungi: the symbiotic route to the root for phosphorus in forest soils

Many forest trees have evolved mutualistic symbioses with ectomycorrhizal (ECM) fungi that contribute to their phosphorus (P) nutrition. Forest productivity is frequently limited by P, a phenomenon that is likely to become more widespread under future conditions of elevated atmospheric CO₂ concentration [CO₂]. It is thus timely that this review considers current understanding of the key processes (absorption, translocation and transfer to the plant host) in ECM fungus-mediated P nutrition of forest trees. Solubilisation of inorganic P (P_i) and hydrolysis of organic P by ECM fungi in soil occurs largely at the growing mycelial front, where P_i absorption is facilitated by high affinity transporters. While large gaps remain in our understanding of the physiological and molecular mechanisms that underpin movement of P in ECM mycelia in soil and P transfer to the plant, host P demand seems likely to be a key driver of these processes. ECM fungi may make considerable contributions to meeting the likely increased P demand of trees under elevated [CO₂] via increased colonization levels, shifts in ECM fungal community structure and changed patterns of EMM production. Further research into the spatial scale of ECM-mediated P movements in soil, along with the interplay between ECM fungi and other soil microflora is advocated.     

Molecular phylogeny of siboglinid annelids (a.k.a. pogonophorans): a review

Siboglinid, or pogonophoran, annelids are tubicolous worms that rely on chemoautotrophic endosymbionts for nutrition. Three clades within the siboglinids are recognized: Frenulata, Vestimentifera, and Monilifera. As a group, these worms have received considerable attention from molecular phylogenetists. Most studies have focused either on the evolutionary origins of the group or on the relationships within vestimentiferans, which live at hydrocarbon seeps and hydrothermal vents. Here I review the literature to date on siboglinid molecular phylogeny and summarize the clade’s evolution. The vestimentiferans have been well studied, especially in the eastern Pacific. The seep taxon Lamellibrachia is basal in the clade with vent species being more derived. Recent studies of seeps are finding new species and suggest that habitat depth can be correlated with species boundaries. In contrast to the vestimentiferans, frenulate evolution has been poorly studied. Despite their greater apparent diversity, frenulate specimens have not been sampled so extensively, and thus little is known about their evolution. Sclerolinum, also referred to as Monilifera, is a recognized genus of siboglinids that forms the sister group to Vestimentifera. Like the frenulates, little is known about the history of this group. Our present understanding of siboglinid phylogeny has, in large part, been dictated by insufficient sampling effort.     

Influence of commercial inoculation with Glomus intraradices on the structure and functioning of an AM fungal community from an agricultural site

The use of commercial arbuscular mycorrhizal (AM) inoculants is growing. However, we know little about how resident AM communities respond to inoculations under different soil management conditions. The objective of this study was to simulate the application of a commercial AM fungal inoculant of Glomus intraradices to soil to determine whether the structure and functioning of that soil’s resident AM community would be affected. The effects of inoculation were investigated over time under disturbed or undisturbed soil conditions. We predicted that the introduction of an infective AM fungus, such as G. intraradices, would have greater consequences in disturbed soil. Using a combination of molecular (terminal restriction length polymorphism analysis based on the large subunit of the rRNA gene) and classical methods (AM fungal root colonization and P nutrition) we found that, contrary to our prediction, adding inoculant to soil containing a resident AM fungal community does not necessarily have an impact on the structure of that community either under disturbed or undisturbed conditions. However, we found evidence of positive effects of inoculation on plant nutrition under disturbed conditions, suggesting that the inoculant interacted, directly or indirectly, with the resident AM fungi. The inoculant significantly improved the P content of the host but only in presence of the resident AM fungal community. In contrast to inoculation, soil disturbance had a significant negative impact on species richness of AM fungi and influenced the AM fungal community composition as well as its functioning. Thus, we conclude that soil disturbance may under certain conditions have greater consequences for the structure of resident AM fungal communities in agricultural soils than commercial AM fungal inoculations with G. intraradices.