Size and morphology of root systems of perennial grasses from contrasting habitats as affected by nitrogen supply

This paper discusses interspecific differences and phenotypic responses to nitrogen supply in various root parameters of five perennial grasses from contrasting habitats. The following root parameters were studied: root:shoot ratio, specific root length, specific root area, mean root diameter, frequency of fine roots, and the length and density of root hairs. Significant between-species variation was found in all of these features. Species from fertile sites had higher root:shoot ratios at high nitrogen supply than species from infertile habitats. All species growing at low nitrogen supply showed a significant increase in root:shoot ratio. Specific root length, specific root area, mean root diameter and frequency of fine roots were not affected significantly by nitrogen supply. Species from infertile sites responded to low nitrogen supply by a significant increase in root hair length and root hair density.     

入侵植物水花生解剖学和组织化学染色研究

水花生(Alternanthera philoxeroides)因其表型可塑性、高生长速率和快速无性繁殖能适应水、陆生境.该文利用光学显微镜和荧光显微镜对水、陆生境的水花生不定根、茎解剖结构、组织化学特征及质外体通透性进行了研究.结果表明:(1)水生境下,其不定根皮层中具较大裂生型通气组织,无次生生长,内皮层具凯氏带且...     

勃氏甜龙竹不同部位根的解剖结构比较

该研究选择勃氏甜龙竹7月份(雨季)和11月份(干季)地面以下10 cm处土壤中秆基处生的根,秆下部节内(地上部分3~4节)和秆上部枝条基部在空气中自然生的根,以及7月份枝条高空压条产生的伸长阶段和成熟阶段的根作为实验材料,采用树脂切片和徒手切片法,对不同部位根的根尖和根毛区进行横切,甲苯胺蓝O和苏丹红7B染色,研究不同起源根的形态解剖结构,为竹子根解剖学研究提供新的理论信息。结果显示:(1)不同来源根的皮层宽度占根直径的比例、周缘纤维组织宽度及其细胞层数、内皮层细胞壁厚度均随生长时间延长而增加。(2)所有起源根的外皮层和内皮层细胞壁均有显著的木栓质沉积,但环内皮层木栓化程度存在显著差别。(3)测量不同来源根的后生木质部导管数目和直径发现,7月份采集的根导管数目更多、直径更大。(4)枝条基部自然生根的根尖与其他起源部位的根相比更为钝平,但根冠面积较小;秆下部节内自然生根非常硬,所以未能成功观察其根尖结构特点。研究认为,勃氏甜龙竹4种不同起源根的基本结构一致,但在各自的具体结构上还存在显著差别,可能与其生长的环境以及发育状况密切相关。     

Interaction of Pratylenchus penetrans and Rhizoctonia fragariae in Strawberry Black Root Rot

A split-root technique was used to examine the interaction between Pratylenchus penetrans and the cortical root-rotting pathogen Rhizoctonia fragariae in strawberry black root rot. Plants inoculated with both pathogens on the same half of a split-root crown had greater levels of root rot than plants inoculated separately or with either pathogen alone. Isolation of R. fragariae from field-grown roots differed with root type and time of sampling. Fungal infection of structural roots was low until fruiting, whereas perennial root colonization was high. Isolation of R. fragariae from feeder roots was variable, but was greater from feeder roots on perennial than from structural roots. Isolation of the fungus was greater from structural roots with nematode lesions than from non-symptomatic roots. Rhizoctonia fragariae was a common resident on the sloughed cortex of healthy perennial roots. From this source, the fungus may infect additional roots. The direct effects of lesion nematode feeding and movement are cortical cell damage and death. Indirect effects include discoloration of the endodermis and early polyderm formation. Perhaps weakened or dying cells caused directly or indirectly by P. penetrans are more susceptible to R. fragariae, leading to increased disease.     

Transport of Water and Solutes across Maize Roots Modified by Puncturing the Endodermis (Further Evidence for the Composite Transport Model of the Root)

The effects of puncturing the endodermis of young maize roots (Zea mays L.) on their transport properties were measured using the root pressure probe. Small holes with a diameter of 18 to 60 [mu]m were created 70 to 90 mm from the tips of the roots by pushing fine glass tubes radially into them. Such wounds injured about 10-2 to 10-3% of the total surface area of the endodermis, which, in these hydroponically grown roots, had developed a Casparian band but no suberin lamellae. The small injury to the endodermis caused the original root pressure, which varied from 0.08 to 0.19 MPa, to decrease rapidly (half-time = 10-100 s) and substantially to a new steady-state value between 0.02 and 0.07 MPa. The radial hydraulic conductivity (Lpr) of control (uninjured) roots determined using hydrostatic pressure gradients as driving forces was larger by a factor of 10 than that determined using osmotic gradients (averages: Lpr [hydrostatic] = 2.7 x 10-7 m s-1 MPa-1; Lpr [osmotic] = 2.2 x 10-8 m s-1 MPa-1; osmotic solute: NaCl). Puncturing the endodermis did not result in measurable increases in hydraulic conductivities measured by either method. Thus, the endodermis was not rate-limiting root Lpr: apparently the hydraulic resistance of roots was more evenly distributed over the entire root tissue. However, puncturing the endodermis did substantially change the reflection ([sigma]sr) and permeability (Psr) coefficients of roots for NaCl, indicating that the endodermis represented a considerable barrier to the flow of nutrient ions. Values of [sigma]sr decreased from 0.64 to 0.41 (average) and Psr increased by a factor of 2.6, i.e. from 3.8 x 10-9 to 10.1 x 10.-9 m s-1(average). The roots recovered from puncturing after a time and regained root pressure. Measurable increases in root pressure became apparent as soon as 0.5 to 1 h after puncturing, and original or higher root pressures were attained 1.5 to 20 h after injury. However, after recovery roots often did not maintain a stable root pressure, and no further osmotic experiments could be performed with them. The Casparian band of the endodermis is discontinuous at the root tip, where the endodermis has not yet matured, and at sites of developing lateral roots. Measurements of the cross-sectional area of the apoplasmic bypass at the root tip yielded an area of 0.031% of the total surface area of the endodermis. An additional 0.049% was associated with lateral root primordia. These areas are larger than the artificial bypasses created by wounding in this study and may provide pathways for a "natural bypass flow" of water and solutes across the intact root. If there were such a pathway, either in these areas or across the Casparian band itself, roots would have to be treated as a system composed of two parallel pathways (a cell-to-cell and an apoplasmic path). It is demonstrated that this "composite transport model of the root" allows integration of several transport properties of roots that are otherwise difficult to understand, namely (a) the differences between osmotic and hydrostatic water flow, (b) the dependence of root hydraulic resistance on the driving force or water flow across the root, and (c) low reflection coefficients of roots.     

Posidonia oceanica seedling root structure and development

The seedling root system of the seagrass Posidonia oceanica consists of a primary root and up to four adventitious roots. Under culture, germination and early growth began with the emergence of the primary root in the first week. Then the two adventitious root primordia originally present in the seed emerged at 3 and 5 weeks respectively, followed successively by further adventitious roots. Primary roots reached 17 mm at 4 weeks, but then their growth decreased markedly. In contrast the adventitious roots showed a pattern of continued elongation. Anatomical observations of both primary and adventitious roots revealed a multilayered hypodermis of thick-walled cells enclosing a wide cortex (99% of the root transverse area) and narrow stele. A well-distinguished endodermis was only observed in the primary roots, while differentiated xylem elements were found solely in the adventitious roots, but it is unclear to what degree differences between the two root types are due to different root maturity or to their role in water and nutrient uptake. Overall, the P. oceanica seedling root system is composed of multiple, rapidly formed roots which are strong yet flexible due to a large proportion of cortical tissue and further strengthened by a multilayered hypodermis, characteristics which could potentially facilitate initial anchorage and establishment.     

蜈蚣草的解剖结构与组织化学特征

蜈蚣草（Pteris vittata）是多年生的超积累砷植物,并用于修复受重金属污染的土壤。利用光学显微镜和荧光显微镜来研究蜈蚣草的解剖结构及组织化学特征,以此明确该物种适应干旱岩生环境,以及具有离子超富集作用的特点。结果表明（：1）蜈蚣草孢子体的根状茎、不定根和叶的结构均为初生结构,不定根的结构由内而外包括维管柱、内皮层、皮层、木质化厚壁组织层和表皮。（2）根状茎结构由内而外包括网状中柱、内皮层、皮层、表皮外覆盖的角质层。（3）羽状复叶的总叶柄的结构由内而外包括维管束、内皮层、皮层、厚壁组织层、表皮外覆盖的角质层。叶片为异面叶,表皮内方具厚壁层,叶表皮具角质层,仅下表皮有气孔。（4）蜈蚣草根表皮、皮层与根毛的表面富含果胶,皮层木质化;黄连素离子通透性试验结果显示,根毛、根表皮和皮层滞留大量黄连素离子。综上,植物体的内皮层、木质化厚壁组织层、异面叶和厚的角质层结构说明蜈蚣草适应岩生环境,根具木质化皮层和富含果胶的组织化学特点,以及离子通透性试验表明其与离子超积累功能有关。     

From birth to death — Populus trichocarpa fibrous roots functional anatomy

The main task of annually grown fibrous roots is to supply aboveground organs with water and nutrients. The key for this function, the development and mortality of primary tissues during a root lifespan is still poorly understood, especially in plants grown under field conditions. The goal of this study was to investigate the differentiation and maturation of fibrous roots from the initial appearance until the senescence and death. We monitored the histogenesis and anatomy of first order fibrous roots of black cottonwood (Populus trichocarpa Torr. & Gray) sampled at a known age. The daily examination of the first order fibrous roots revealed that only primary tissues were differentiated during the first seven days after their initiation and were maintained during the root lifespan. We observed all stages of exodermis and endodermis formation regulation a fibrous root water and nutrients uptake capacity. A cytological analysis, examined if any cellular symptoms of autophagy could be detected in senescent roots, indicated that vacuolar cell death was involved in root mortality. Our results are the first report strongly suggesting that programmed cell death (PCD) could be engaged in the senescence of ephemeral fibrous roots. The anatomical results advance our understanding of how roots absorptive ability is related to precise timing of tissue development during primary growth and of fibrous root senescence after fulfilment of its tasks.     

The Casparian Strip of Clivia miniata Reg. Roots: Isolation,Fine Structure and Chemical Nature*

The root endodermis of Clivia miniata Reg. was successfully isolated using the cell wall degrading enzymes cellulase and pectinase. The enzymes did not depolymerize those regions of the primary cell walls of anticlinal endodermal root cells where the Casparian strips were located. Since the endodermis of C. miniata roots remained in its primary developmental state over the whole root length, endodermal isolates essentially represented Casparian strips. Thus, sufficient amounts of isolated Casparian strips could be obtained to allow further detailed investigations of the isolates by microscopic, histochemical and analytical methods. Scanning electron microscopy revealed the reticular structure of the Casparian strips completely surrounding the central cylinder of the roots. Whereas in younger parts of the root only the anticlinal cell walls of the endodermis remained intact in the isolates, in older parts of the root the periclinal walls also restricted enzymatic degradation due to the deposition of lignin. Extracts of the isolates with organic solvents did not reveal any wax-like substances which might have been deposited within the cell wall forming a transport barrier, as is the case with cutin and suberin. However, several histochemical and analytical methods (elemental analysis and FTIR spectroscopy) showed that the chemical nature of the Casparian strips of C. miniata roots can definitely be a lignified cell wall. These findings are in complete agreement with studies carried out at the beginning of this century on the chemical nature of the Casparian strips of several other plant species. The implications of these results concerning apoplasmatic transport of solutes and water across Casparian strips are discussed.     

Histopathology of Pea Roots Axenically Infected by Pratylenchus penetrans

The histological changes in pea roots axenically infected by Pratylenchus penetrans were studied and described. Roots of pea seedlings growing aseptically on the surface of nutrient agar slants were inoculated with axenized nematodes. Six hours after inoculation most of the nematodes introduced were probing the root epidermis, but none had completely entered though a few were observed with their anterior section already in the root. Most of the nematodes penetrated the roots after 12 hr inoculation. From 18 to 24 hr after inoculation the nematodes were mostly in the mid-cortex. Invaded regions of the cortex often showed orange discoloration. As incubation continued, the number of nematodes in these roots increased, and feeding and reproductive activities extended deeper into the cortex. These activities resulted in extensive breakdown of the cortex. No nematodes were observed within the stele of infected roots; however, the endodermis of infected roots stained dark-brown. Gravid female nematodes probed the root endodermis and some endodermal cells appeared to collapse after prolonged probing by the nematode. All stages in the life cycle of the nematode were observed in infected roots; the female to male ratio inside the root was about 5:1.     

Soybean root suberin: anatomical distribution, chemical composition, and relationship to partial resistance to Phytophthora sojae

Soybean (Glycine max L. Merr.) is a versatile and important agronomic crop grown worldwide. Each year millions of dollars of potential yield revenues are lost due to a root rot disease caused by the oomycete Phytophthora sojae (Kaufmann & Gerdemann). Since the root is the primary site of infection by this organism, we undertook an examination of the physicochemical barriers in soybean root, namely, the suberized walls of the epidermis and endodermis, to establish whether or not preformed suberin (i.e. naturally present in noninfected plants) could have a role in partial resistance to P. sojae. Herein we describe the anatomical distribution and chemical composition of soybean root suberin as well as its relationship to partial resistance to P. sojae. Soybean roots contain a state I endodermis (Casparian bands only) within the first 80 mm of the root tip, and a state II endodermis (Casparian bands and some cells with suberin lamellae) in more proximal regions. A state III endodermis (with thick, cellulosic, tertiary walls) was not present within the 200-mm-long roots examined. An exodermis was also absent, but some walls of the epidermal and neighboring cortical cells were suberized. Chemically, soybean root suberin resembles a typical suberin, and consists of waxes, fatty acids, omega-hydroxy acids, alpha,omega-diacids, primary alcohols, and guaiacyl- and syringyl-substituted phenolics. Total suberin analysis of isolated soybean epidermis/outer cortex and endodermis tissues demonstrated (1) significantly higher amounts in the endodermis compared to the epidermis/outer cortex, (2) increased amounts in the endodermis as the root matured from state I to state II, (3) increased amounts in the epidermis/outer cortex along the axis of the root, and (4) significantly higher amounts in tissues isolated from a cultivar ('Conrad') with a high degree of partial resistance to P. sojae compared with a susceptible line (OX760-6). This latter correlation was extended by an analysis of nine independent and 32 recombinant inbred lines (derived from a 'Conrad' x OX760-6 cross) ranging in partial resistance to P. sojae: Strong negative correlations (-0.89 and -0.72, respectively) were observed between the amount of the aliphatic component of root suberin and plant mortality in P. sojae-infested fields.     

Structural and Histochemical Features of the Slow-Growing Perennial <i>Coptis chinensis</i> Franch. (Ranunculaceae)

Huanglian (Coptis chinensis Franch.) is a slow-growing perennial medicinal herb with considerable economic value. This study aimed to determine the structural characteristics and the levels of berberine deposits in the organs and tissues of Huanglian using light and epifluorescence microscopy. The adventitious roots are composed of primary and secondary structures with endodermis, exodermis, and phellem. The rhizome structures are composed of primary and secondary structures with cuticle and phellem. The leaves are composed of sclerenchymatous rings, isolateral mesophyll, and thin cuticles. We detected berberine in the xylem walls of the roots and rhizomes as well as in the sclerenchymatous rings of the petioles. We postulate that as the exodermis is developed, the deposition of berberine in the xylem closest to the root tips may affect water and nutrient absorption and transfer. Leaf blades had a thin cuticle and isolateral mesophyll, suggesting shade tolerance. These structural and histochemical features suggest that Huanglian is adapted to the slow growing nature of a shady environment.     

Development of the root system in<Emphasis Type="Italic">Spirodela polyrhiza</Emphasis> (L.) schleiden (Lemnaceae)

The root structure in members of the Lemnaceae is important to plant researchers, because changes during cell differentiation can more easily be monitored in short roots with determinate growth. Here, the structural organization and cellular differentiation of the root system was assessed in the highly reducedSpirodela polyrhiza. While protected by a prophyllous sheath, rapid cell division occurred in the apical and vascular regions of the immature roots. Concentric rings of endodermis with Casparian strips, cortex, and epidermis enclosed a single vascular strand. The cytoplasmic density of the cortex was high at the apex, but decreased progressively along the root. The root root cap junction, closely attached at initiation, later became a distinct boundary layer filled with fibrillar materials. Chloroplasts were well distributed. Numerous plasmodesmata indicated the likely symplastic movement of ions and metabolites in the root system as well as further into the reduced plant body. A high cytoplasmic density at the apex and extreme vacuolization along the cortex provided possible explanations for the considerable distribution of weight along the roots of the plant body. These conditions probably enable the root tip to serve as a pendulum against water motion.     

DEVELOPMENTAL ANATOMY IN ROOTS OF IPOMOEA PURPUREA. II. INITIATION AND DEVELOPMENT OF SECONDARY ROOTS

In seedlings of Ipomoea purpurea secondary roots are initiated in the primary root pericycle opposite immature protoxylem. Cells derived from immature endodermis, pericycle, and incipient protoxylem and stelar parenchyma contribute to the primordium. The derivatives of the endodermis become a uniseriate covering over the tip and flanks of the primordium and emerged secondary root; the endodermal covering is sloughed off when the lateral root reaches 1–5 mm in length. A series of periclinal and anticlinal divisions in the pericycle and its derivatives gives rise to the main body of the secondary root. The initials for the vascular cylinder, cortex, and rootcap-epidermis complex are established very early during primordium enlargement. After emergence from the primary root, the cortical initials undergo significant structural modifications related to enlargement of the ground meristem and cortex, and the rootcapepidermal initials are partitioned into columellar initials and lateral rootcapepidermal initials. Procambium diameter increases by periclinal divisions in peripheral sectors. The mature vascular cylinder is comprised of several vascular patterns, ranging from diarch to pentarch, that are probably related ontogenetically. Cells derived from incipient protoxylem and stelar parenchyma cells of the primary root form the vascuar connection between primary and secondary roots.     

野葛地下器官的解剖学研究

野葛（Ｐｕｅｒａｒｉ９ａ ｌｏｂａｔａ（ｗｉｌｌｄ．）Ｏｈｗｉ．）的地下器官包括初生根、块根、不定根和根状茎４部分。初生根为四原型,内皮层明显,可见到凯氏带。块根的次生木质部发达,民管周转存在额外形成层。成熟块根中积累丰富的淀粉。不定根为三原型,具次生结构。根状茎作为营养繁殖器官,产生不定根,其中不定根可发展成蓼根。无论初生根、收缩不定根或根状茎的细胞中均示发现淀粉积累,这可能与贮藏器官块根的发达     

The role of nodal roots in prostrate clonal herbs: ‘phalanx’ versus ‘guerrilla’

The influence of nodal rooting on branching was studied in three evolutionarily and morphologically diverse species of prostrate clonal herbs: Tradescantia fluminensis (a monocotyledonous extreme ‘phalanx’ species), Calystegia silvatica (a dicotyledonous extreme ‘guerrilla’ species) and Trifolium repens (a dicotyledonous intermediate species). In all three, branch development from axillary buds is regulated by a positive signal produced by roots together with inhibitory influences from both pre-existing branches and shoot apical buds (apical dominance). Responses to nodal roots are cumulative and increased root activity leads to more vigorous bud outgrowth. In the absence of nodal roots, a single basal root system is unable to maintain continued extension growth of the shoot. We suggest that as individual nodal roots and stem internodes are both short-lived in these nodally-rooting clonal species, the plants’ investment in them is minimal. Thus, in contrast to perennial species lacking nodal roots, individual root systems in prostrate clonal herbs are small and stems have little secondary thickening and development of long-distance transport tissues. Hence the decline in extension growth of the shoot in the absence of nodal roots could be linked to the weak development of long-distance transport tissues in their relatively thin horizontal stems and to resource sharing between primary stems and lateral branches (as suggested by the greater retardation of primary stem growth in the more profusely branched ‘phalanx’ species (Trifolium and Tradescantia) than in the weakly branched ‘guerrilla’ species, Calystegia). These findings are consistent with the view that the long-term persistence of genotypes of nodally-rooting prostrate species is dependent upon them encountering the moist conditions required to facilitate the continual development of new young nodal root systems.     

Aerenchyma formation in roots of maize during sulphate starvation

Young maize ( Zea mays L., Poaceae) plants were grown in a complete, well-oxygenated nutrient solution and then deprived of their external source of sulphate. This treatment induced the formation of aerenchyma in roots. In addition to the effect of sulphate starvation on root anatomy, the presence and location of superoxide anions and hydrogen peroxide, and changes in calcium and pH were examined. By day 6 of sulphate deprivation, aerenchyma started to form in the roots of plants and the first aerenchymatous spaces were apparent in the middle of the cortex. S-starvation also induced thickening of the cell walls of the endodermis. Active oxygen species appeared in groups of intact mid-cortex cells. Formation of superoxide anion and hydrogen peroxide was found in degenerating cells of the mid-cortex. Very few nuclei in the cortex of S-starved roots fluoresced, being shrunken and near to the cell wall. By day 12 of S-deprivation, a fully developed aerenchyma was apparent and there were only a few 'chains' of cells bridging hypodermis to endodermis and stele of roots. Cell walls of endodermis of S-starved roots increased 68% in thickness. Intensive fluorescence in the cell walls of the endodermal, hypodermal and to a lesser extent of epidermal cells was observed due to the formation of active oxygen species, while there was no fluorescence in the cortical cells. There was a higher Ca concentration in the cells walls of the endodermis and epidermis, compared to the rest of the S-starved root tissues. A higher pH was observed, mainly in the cell walls of the hypodermis and to a lesser extent in the cell walls of the endodermis. Superoxide anion and hydrogen peroxide was found in degenerating cells of the root cortex. There was no fluorescence of nuclei in the cortex of S-starved roots.     

Structure of Hair Roots in Lysinema ciliatum R. Br. and its Implications for their Water Relations

The fine lateral roots ofLysinema ciliatum R. Br., an epacridfrom habitats subject to periodic drought in Western Australia,are hair roots resembling those of Ericaceae. The finest (ultimate)hair roots have a cortex consisting only of an endodermis andan exodermis. Both layers have Casparian strips on the radialwalls. The exodermis develops to state III very close to theroot tip, showing wall thickening and a suberized lamella encirclingeach cell. In many roots collected after tip-growth had ceasedand the tip had fully differentiated this suberized exodermiscompletely encircled the apex. In older hair roots the epidermiscollapses or is sloughed off leaving the suberized exodermisas the outermost layer. The very fine hair roots have a verysmall stele containing only one xylem tracheid, and phloem consistingof a single sieve element with companion cell. The very smalldiameter of the single tracheid indicates a high resistanceto water flow along the hair roots. This may tend to conservesoil moisture in the region of the hair roots, leading to improvedsurvival and prolonged function of mycorrhizas in the field. Lysinema ciliatum R. Br.; hair root; endodermis; exodermis; water; xylem     

Root Endodermis and Exodermis: Structure,Function, and Responses to the Environment

Roots of virtually all vascular plants have an endodermis with a Casparian band, and the majority of angiosperm roots tested also have an exodermis with a Casparian band. Both the endodermis and exodermis may develop suberin lamellae and thick, tertiary walls. Each of these wall modifications has its own function(s). The endodermal Casparian band prevents the unimpeded movement of apoplastic substances into the stele and also prevents the backflow of ions that have moved into the stele symplastically and then were released into its apoplast. In roots with a mature exodermis, the barrier to apoplastic inflow of ions occurs near the root surface, but prevention of backflow of ions from the stele remains a function of the endodermis. The suberin lamellae protect against pathogen invasion and possibly root drying during times of stress. Tertiary walls of the endodermis and exodermis are believed to function in mechanical support of the root, but this idea remains to be tested. During stress, root growth rates decline, and the endodermis and exodermis develop closer to the root tip. In two cases, stress is known to induce the formation of an exodermis, and in several other cases to accelerate the development of both the exodermis and endodermis. The responses of the endodermis and exodermis to drought, exposure to moist air, flooding, salinity, ion deficiency, acidity, and mechanical impedance are discussed.