无距虾脊兰营养器官解剖结构及其生态适应性

采用石蜡切片法对无距虾脊兰(Calanthe tsoongiana T.TangetF.T.Wang)营养器官解剖结构进行研究。结果显示,无距虾脊兰叶为等面叶,与一般植物相比,表皮毛和气孔器较少,均分布在下表皮,气孔器稍外凸,叶片维管束分化程度不一,木质部厚度远大于韧皮部。假鳞茎由表皮、基本组织和维管束组成,基本组织发达,含有丰富的内含物。维管束散生于基本组织中;根主要由根被、皮层和中柱组成,根被通常可见4层,皮层由8~10层薄壁细胞组成,菌丝体通过破坏根被细胞侵入皮层。除正对木质部脊的中柱鞘细胞外,其余中柱鞘通道细胞全面增厚,维管束类型为辐射维管束,中柱中央为薄壁细胞组成的髓。无距虾脊兰营养器官的解剖特征表现出阴生植物的特点,引种栽培过程中应注意适当遮荫和通风。     

无距虾脊兰营养器官解剖结构及其生态适应性

采用石蜡切片法对无距虾脊兰（Calanthe tsoongiana T.Tang et F.T.Wang）营养器官解剖结构进行研究。结果显示,无距虾脊兰叶为等面叶,与一般植物相比,表皮毛和气孔器较少,均分布在下表皮,气孔器稍外凸,叶片维管束分化程度不一,木质部厚度远大于韧皮部。假鳞茎由表皮、基本组织和维管束组成,基本组织发达,含有丰富的内含物。维管束散生于基本组织中;根主要由根被、皮层和中柱组成,根被通常可见4层,皮层由8~10层薄壁细胞组成,菌丝体通过破坏根被细胞侵入皮层。除正对木质部脊的中柱鞘细胞外,其余中柱鞘通道细胞全面增厚,维管束类型为辐射维管束,中柱中央为薄壁细胞组成的髓。无距虾脊兰营养器官的解剖特征表现出阴生植物的特点,引种栽培过程中应注意适当遮荫和通风。     

密花石斛等六种兰科植物菌根的显微结构研究

本文对密花石斛等六种兰科植物根的显微结构进行了比较观察。结果表明,它们具有典型的兰科植物根,具根被和发达的皮层组织,皮层细胞内分布有针状结晶和菌根真菌形成的菌丝结,发现菌根真菌通过外皮层薄壁通道细胞或破坏根被组织和外皮层细胞侵入皮层细胞,形成内生菌根。     

密花石斛等六种兰科植物菌根的显微结构研究

本文对密花石斛等六种兰科植物根的显微结构进行了比较观察。结果表明,它们具有典型的兰科植物根,具根被和发达的皮层组织,皮层细胞内分布有针状结晶和菌根真菌形成的菌丝结,发现菌根真菌通过外皮层薄壁通道细胞或破坏根被组织和外皮层细胞侵入皮层细胞,形态内生菌根。     

人工栽培铁皮石斛菌根的细胞学研究

从细胞学水平上研究了人工栽培铁皮石斛的菌根特征。结果表明:真菌与铁皮石斛根成功地形成了菌根,真菌菌丝穿透根被细胞,并在根被的某个细胞中定殖,然后经由外皮层的通道细胞进入皮层薄壁细胞;皮层薄壁细胞层正是真菌与植物体相互作用的活跃部位;真菌侵染大多数的皮层薄壁细胞,并不能侵染内皮层及中柱细胞,从而使根仍然保持生活力。     

墨兰菌根的结构及酸性磷酸酶定位研究

利用光学显微镜、电子显微镜及细胞化学方法,对墨兰菌根的结构和酸性磷酸酶定位进行了初步研究。结果表明墨兰具有典型的兰科植物根结构,发现该兰花的根的外皮层不具薄壁通道细胞,菌根真菌通过破坏部分根被和外皮层细胞而侵入根的皮层细胞并在细胞内形成菌丝结,侵入的菌丝被染菌皮层细胞质膜和电子透明物质包围,进一步被消化并聚集成衰败菌丝团块。酸性磷酸酶在染菌皮层细胞及包围菌丝的皮层细胞质膜和衰败菌丝细胞壁上有强烈的酶反应,衰败菌丝周围分布有许多单层膜的含酶小泡,它们可相互愈合形成大的含酶泡或与包围菌丝的质膜融合,类似于兰科植物共生原球茎中观察到的现象。说明皮层细胞可主动释放水解酶参与对菌丝的消化     

七叶一枝花根的显微结构及其内生真菌分布研究

本文采用石蜡永久制片和光学显微摄像的方法对七叶一枝花Parispolyphylla根的显微结构及其内生真菌的分布进行了研究。结果表明,七叶一枝花的根茎由栓皮层、薄壁组织及维管组织组成,其中栓皮层由4层细胞组成;薄壁组织的细胞含有丰富的营养物质,其内有时分布有针状结晶束。不定根由表皮层、皮层、内皮层及维管束构成,表皮上有根毛,皮层所占根径的比例达80%以上;木质部为三原型。在七叶一枝花的根茎和不定根的皮层细胞中均有内生真菌的分布。真菌由表皮、外皮层侵入到皮层薄壁组织,在皮层薄壁细胞中形成菌丝结,并扩展成一定的侵染区域,部分皮层细胞中菌丝结已被消化吸收。内生真菌只侵染皮层薄壁细胞,不侵染维管柱。七叶一枝花可以通过消化细胞内的菌丝作为营养的来源之一。     

三种白及属植物不同生长发育时期的菌根显微结构

采用石蜡切片技术对白及Bletilla striata、黄花白及B. ochracea和小白及B. formosana的栽培种在生长期、花期、果期和休眠期的菌根解剖结构特征、菌根真菌入侵方式和菌丝特征等进行观察研究,以进一步了解菌根真菌与白及属植物的共生关系。结果表明,3种白及属植物的菌根真菌均是通过通道细胞侵入根皮层薄壁细胞,侵入后菌丝靠近皮层细胞的细胞核分布,最终在皮层细胞形成菌丝团;真菌侵染率和菌丝形态随着植物生长发育变化而变化,3种白及属植物均表现为花期和生长期的真菌侵染率较高,以丝状菌丝团为主,而果期和休眠期较低,以团块状菌丝团居多;同一时期不同植物类型的菌根特征无显著差异。     

濒危药用植物桃儿七根的显微结构及其菌根真菌分布研究

本文研究了桃儿七Sinopodophyllum hexandrum根的显微结构及其真菌分布。结果表明,桃儿七的根为根状茎,节状,不定根形成的须根系发达。根的结构主要由表皮、皮层、维管柱三部分构成,其中,皮层所占比例最大,超过80%。根的木质部有四原型和五原型两种类型,五原型较为常见;四原型的根和五原型的根在皮层细胞形态上存在一定差异。在桃儿七的不定根和其上的侧根观察到真菌菌丝分布,其数量和种类与根的直径有关,在不定根较细(先端)的部位真菌以暗色有隔内生真菌(DSE真菌)为主,侵染率为77.9%;而较粗根中真菌菌丝为无隔菌丝为主,分布很少且仅存在于皮层细胞的一至二层,不侵染皮层深部和维管柱。不定根侧根中真菌以丛枝菌根真菌为主,丛枝菌根常常占据大部分的皮层细胞,侵染率高达90%以上。桃儿七根中没有发现根毛存在,因此,侧根中共生的丛枝菌根真菌可能是桃儿七养分和水分吸收的主要途径。     

卡特兰与丝核菌共培养体系的建立及卡特兰菌根显微结构的研究*

用3个分离自野生卡特兰的丝核菌菌株接种卡特兰组培幼苗,对幼苗生长有不同程度的促进作用,处理苗的鲜重增长率(%)分别是67.5、67.3和62.4,而不接菌的对照仅为49.5,其中KW214菌株处理苗与对照差异达显著水平(α=0.05)。接菌处理后植株的N、P、K含量没有明显增加。在三个接菌处理苗的营养根中均分离获得了原接种真菌,并观察了接种KW214菌株的卡特兰营养根。真菌先侵入根被组织,经通道细胞最后侵染皮层组织细胞,并通过菌丝穿越细胞壁不断地向内延伸扩展。菌丝在皮层组织细胞内形成大量着色较深形状不规则的菌丝结等兰科菌根典型结构,菌丝结在皮层组织中分布不均,多出现在靠外侧的几层皮层细胞内,在被侵染的细胞中,菌丝结常出现在细胞核附近。菌丝结、针状晶体和细胞核在形态和着色反应上有明显区别。菌丝结和细胞核常常相互靠近。从生物量增长、显微结构、重分离接种菌株等三个方面获得的证据表明,已成功建立了卡特兰组培幼苗和丝核菌KW214的共培养体系。     

Root Anatomy and Mycotrophy of the Achlorophyllous Voyria tenella Hook. (Gentianaceae)

The central cylinder of the root of Voynet tenella consists of up to ten central, non-lignified, tracheidal xylem elements surrounded by some parenchymatic tissue and 5–7 groups of phloem. A pericycle could not be discerned. Even though the endodermis carries a faint suberin lamella it cannot be discerned anatomically without special staining. The cells of the 1–3 cortex layers next to the endodermis are elongated longitudinally, the subsequent cortex parenchyma is multi-layered and consists of isodiametric cells. The cells of the 2–3 layered outer dermal tissue are smaller than those of the adjacent cortex, their walls carry a suberin lamella and the outermost of them constantly scale off. The dermal tissue is interpreted as a multilayered exodermis. The fungal colonization in roots of Voyria tenella remarkably differs from any known mycorrhizal pattern. After having penetrated the dermal tissue, the always intracellularly-growing hyphae head straight towards the inner cortex layers, where they spread along the central cylinder. Ramifications from these inner-spreading hyphae then colonize the cortex parenchyma from the inside and they develop dense hyphal coils. Eventually, the coiled hyphae swell and collapse, resulting in amorphous clumps of fungal material. This mycorrhizal pattern is referred to as an intraradical fungus garden. Arguments are given to call the mycorrhiza in Voyria tenella a specialized arbuscular mycorrhiza. Phylogenetic and ecological implications of the observations and the results are discussed.     

Root structure and arbuscular mycorrhizal colonization of the palm Serenoa repens under field conditions

Serenoa repens (Bartr.) Small is a palm native to the southeastern USA. It is a common understory plant in pine communities on both acid sands and alkaline limestone. Roots have only primary growth and range in thickness from 8.0 mm (first order roots from the stem) to 0.8–2.9 mm (ultimate roots of third to fifth order). The thickest roots occur at soil depths >20 cm; fine roots (<1.2 mm) occur at all depths (1–60 cm). Some second and third order roots are negatively geotropic and grow up to the mineral soil surface. The epidermis of all roots has a thick, eventually lignified outer wall. Except for the thinnest, all roots have a single-layered, thick-walled exodermis, which is first suberized and later lignified. Root hairs are never present. A hypodermis composed of several layers of lignified cells (up to 8-cells-thick) is next to the exodermis and forms the outer cortex. Radial series of thin walled and slightly lignified cells sporadically occur in the outer cortex of the thinnest roots, but there are no passage cells in the exodermis, which is continuous. The remaining inner cortex is composed of unlignified parenchyma with air canals and a completely lignosuberized endodermis in old roots. Passage cells were seen the the endodermis of the some of the thinnest roots. Arbuscular mycorrhizal (AM) fungi occur in the outer one-third of the cortical parenchyma adjacent to the hypodermis. Fungal coils, arbuscules and vesicles are found most frequently in the thinnest roots, but also occur sporadically in all root orders. Cells a few mm from the apical meristem are sometimes colonized. At sites of appressoria, coils of AM hyphae occur within an epidermal cell and exodermal and hypodermal cells beneath. Intercellular hyphae with intracellular branch arbuscules (Arum-type) are common in the inner cortex. There is evidence of a dieback of the highest order roots during the winter dry season. Profiles of soil and roots have the highest density of AM spores in the surface 10 cm layer. Total AM spore density ranged from 130 to 1100 spores per 50 g soil in different samples. Glomus spp. dominated followed by Gigaspora spp. The findings are related to a more general understanding of growth and AM colonization in long-lived roots of tropical woody monocotyledons. Palm roots, in particular, are slow growing and are protected by massive hypodermal layers. This revised version was published online in June 2006 with corrections to the Cover Date.     

Studies on fungi in the root region

Summary Fungal isolations were made from roots ofPhaseolus vulgaris after washing in sterile water, at monthly intervals throughout the life of the plant, and from other roots after dissection and after surface sterilization at certain plant ages only. A table is provided showing the relative importance of the most common species isolated in each of four clearly distinct microhabitats — the root surface, the cortex, the outer stele and the inner stele.Fusarium oxysporum andCylindrocarpon radicicola were the most frequently isolated fungi from the roots.Fusarium oxysporum was most abundant on young roots and seemed to be associated, particularly, with the root surface and cortical tissues.Cylindrocarpon radicicola, although common on young roots, was more abundant on older roots and was an important initial colonist of the stelar tissues. Sterile mycelia were isolated mainly from older roots and seemed to be responsible, withC. radicicola, for the initial colonization of the stele. Microscopic examination of roots showed the cortical tissues to be increasingly penetrated by fungal hyphae with plant age but extensive fungal penetration of the endodermis and stelar tissues did not occur until the plants were at least five months old.     

Colonisation patterns of root tissues byPhytophthora nicotianae var.parasitica related to reduced disease in mycorrhizal tomato

Tomato plants pre-colonised by the arbuscular mycorrhizal fungusGlomus mosseae showed decreased root damage by the pathogenPhytophthora nicotianae var.parasitica. In analyses of the cellular bases of their bioprotective effect, a prerequisite for cytological investigations of tissue interactions betweenG. mosseae andP. nicotianae v.parasitica was to discriminate between the hyphae of the two fungi within root tissues. We report the use of antibodies as useful tools, in the absence of an appropriate stain for distinguishing hyphae ofP. nicotianae v.parasitica from those ofG. mosseae inside roots, and present observations on the colonisation patterns by the pathogenic fungus alone or during interactions in mycorrhizal roots. Infection intensity of the pathogen, estimated using an immunoenzyme labelling technique on whole root fragments, was lower in mycorrhizal roots. Immunogold labelling ofP. nicotianae v.parasitica on cross-sections of infected tomato roots showed that inter or intracellular hyphae developed mainly in the cortex, and their presence induced necrosis of host cells, the wall and contents of which showed a strong autofluorescence in reaction to the pathogen. In dual fungal infections of tomato root systems, hyphae of the symbiont and the pathogen were in most cases in different root regions, but they could also be observed in the same root tissues. The number ofP. nicotianae v.parasitica hyphae growing in the root cortex was greatly reduced in mycorrhizal root systems, and in mycorrhizal tissues infected by the pathogen, arbuscule-containing cells surrounded by intercellularP. nicotianae v.parasitica hyphae did not necrose and only a weak autofluorescence was associated with the host cells. Results are discussed in relation to possible processes involved in the phenomenon of bioprotection in arbuscular mycorrhizal plants.     

Interaction between an isolate of dark-septate fungi and its host plant <Emphasis Type="Italic">Saussurea involucrata</Emphasis>

A dark-septate endophytic (DSE) fungus EF-M was isolated from the roots of an alpine plant Saussurea involucrata Kar. et Kir. ex Maxim. The fungus was identified by sequencing the PCR-amplified rDNA 5.8S gene and ITS regions. The sequence was compared with similar sequences in the GenBank, and results showed that EF-M was congeneric to Leptodontidium. Resynthesis study was conducted to clarify the relationship between the root endophyte EF-M and the host plant S. involucrata using the material grown in sterile culture bottle. In roots recovered 6 weeks after inoculation, epidermal cells were colonized by intercellular and intracellular hyphae and “microsclerotia” formed within individual cells in the epidermis layers. However, hyphae did not invade the cortex and the stele. There were no profound effects of endophyte EF-M on plant root development, but significant differences were detected in plant height and shoot dry weight between the treatments. The present study is the first report hitherto on DSE fungi in S. involucrata.     

Medicago truncatula Vapyrin is a novel protein required for arbuscular mycorrhizal symbiosis

Arbuscular mycorrhizal (AM) symbiosis is a widespread mutualism formed between vascular plants and fungi of the Glomeromycota. In this endosymbiosis, fungal hyphae enter the roots, growing through epidermal cells to the cortex where they establish differentiated hyphae called arbuscules in the cortical cells. Reprogramming of the plant epidermal and cortical cells occurs to enable intracellular growth of the fungal symbiont; however, the plant genes underlying this process are largely unknown. Here, through the use of RNAi, we demonstrate that the expression of a Medicago truncatula gene named Vapyrin is essential for arbuscule formation, and also for efficient epidermal penetration by AM fungi. Vapyrin is induced transiently in the epidermis coincident with hyphal penetration, and then in the cortex during arbuscule formation. The Vapyrin protein is cytoplasmic, and in cells containing AM fungal hyphae, the protein accumulates in small puncta that move through the cytoplasm. Vapyrin is a novel protein composed of two domains that mediate protein–protein interactions: an N‐terminal VAMP‐associated protein (VAP)/major sperm protein (MSP) domain and a C‐terminal ankyrin‐repeat domain. Putative Vapyrin orthologs exist widely in the plant kingdom, but not in Arabidopsis, or in non‐plant species. The data suggest a role for Vapyrin in cellular remodeling to support the intracellular development of fungal hyphae during AM symbiosis.     

Comparative study of mycorrhizal susceptibility and anatomy of four palm species

A morphological and anatomical study of the root systems of the palm species Brahea armata S. Watson, Chamaerops humilis L., Phoenix canariensis Chabaud and Phoenix dactylifera L. has been carried out to determine possible mycorrhizal colonization sites. Furthermore, the arbuscular mycorrhizal (AM) anatomical types formed by the four palm species in association with Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe have been examined. The presence of a continuous sclerenchymatic ring in the outer cortex and aerenchyma in the inner cortex that are anatomical indicators of mycorrhizal nonsusceptibility in all four palm species is observed. The root systems of B. armata and C. humilis present only one group of third-order roots, while the third-order roots of P. canariensis and P. dactylifera may be divided into five different groups: short thick roots, mycorrhizal thickened roots, fine short roots, fine long roots, and pneumatorhizas. Third-order and some second-order roots of B. armata and C. humilis are susceptible to colonization by AM fungi, while only the mycorrhizal thickened roots form mycorrhizas with arbuscules in the Phoenix species. The root system of the Phoenix species also presents AM colonization in fine roots with only intraradical hyphae and spores, but without arbuscules, and pseudomantles of spores anchored in the pneumatorings of the second-order roots, which are described for the first time. The mycorrhizas formed by the four palm species are of an intermediate type, between the Arum and the Paris types, and are characterized by intercalary arbusculate coils and not only by intracellular but also by intercellular fungal growth. Our study suggests that a different degree of adaptation may exist among palm mycorrhizas toward the slow growth of palms and low spore numbers in the soil where they grow.