Movement of fluorescent dyes Lucifer Yellow (LYCH) and carboxyfluorescein (CF) in Medicago truncatula Gaertn. roots and root nodules

Lucifer Yellow (LYCH) and carboxyfluorescein (CF) served in Medicago truncatula roots and root nodules as the markers of apoplastic and symplastic transport, respectively. The aim of this study was to understand better the water and photoassimilate translocation pathways to and within nodules. The present study shows that in damaged roots LYCH moves apoplastically through the vascular elements but it was not detected within the nodule vascular bundles. In intact roots, the outer cortex was strongly labeled but the dye was not present in the interior of intact root nodules. The inwards movement of LYCH was halted in the endodermis. When the dye was introduced into a damaged nodule by infiltration, it spread only in the cell walls and the intercellular spaces up to the inner cortex. Our research showed that in addition to the outer cortex, the inner tissue containing bacteroid-infected cells is also an apoplastic domain. Our results are consistent with the hypothesis that nodules do not receive water from the xylem but get it and photoassimilates from phloem. A comparison between using LYCH and LYCH followed by glutaraldehyde fixation indicates that glutaraldehyde is responsible for fluorescence of some organelles within root nodule cells. The influence of the fixation on nodule fluorescence has not been reported before but must be taken into consideration to avoid errors. An attempt was made to follow carboxyfluorescein (6(5) CF) translocation from leaflets into roots and root nodules. In root nodules, CF was present in all or a couple of vascular bundles (VB), vascular endodermis and some adjacent cells. The leakage of CF from the VBs was observed, which suggests symplastic continuity between the VBs and the nodule parenchyma. The lack of CF in inner tissue was observed. Therefore, photoassimilate entry to the infected region of nodule must involve an apoplastic pathway.     

Root meristems in Medicago truncatula tissue culture arise from vascular-derived procambial-like cells in a process regulated by ethylene

Leaf explants of Medicago truncatula were used to investigate the origins of auxin-induced root formation. On the application of auxin there is some callus formation (not the massive amount that occurs in response to auxin plus cytokinin) and roots appear shortly after the first visible callus. Histological examination reveals morphologically distinctive sheets of callus cells that emanate from the veins of the leaf explants and, within this cell type, root primordia are produced as well as some vascular tissue cells. What is suggested is that the vein-derived cells (VDCs) are procambial-like and function as pluripotent stem cells with a propensity to form root meristems or vascular tissues in response to added auxin. The development of root primordia from these pluripotent cells was clearly up-regulated by the use of the sickle (skl) mutant, which is a mutant impaired in ethylene signal transduction while the wild type and the sunn mutant, defective in auxin polar transport, produced similar numbers of roots. The skl mutant in generating many more roots concomitantly formed fewer vascular tissues. The root meristems differentiate similarly to normal roots producing a central cylinder of vascular tissue, which connects with the leaf explant veins. The VDCs appear to be derived from the cells of or near the phloem. The leaf observations suggest that a pool of stem cells exist in vascular tissue that, in combination with auxin and perhaps other factors, drive a diversity of plant development outcomes that is species specific. The way auxin interacts with other hormones is a key factor in determining the stem cell fate. The histological data in this study also assist in the interpretation of the molecular analysis of auxin-induced root formation in cultured leaves of M. truncatula.     

Meristem Initial Cells in Irradiated Roots of Vicia faba: With one Figure in the Text

Beans (Vicia faba) were germinated for 24 hours and irradiatedwith X-rays. Primary roots were fixed after 9, 11, and 21 days.Aberrant chromosome complements, the result of chromosome changesinduced by irradiation, were present. They were used as cellmarkers to estimate the number of cell types present in themeristem initial cells of the growing root and the number ofprimordium initial cells from which root regeneration occurred.Up to 9 cell types occur as meristem initials. From the relativefrequencies of the different cell types, it is estimated thatthere are at least 32 actual meristem initial cells in regeneratingirradiated primary roots. This result is compatible with observationsmade on normal roots. The chimaerical nature of the regeneratingroot apparently does not interfere with the normal organizationof the meristem, but it serves to reveal what part of the organizationis.     

银州柴胡根的发育解剖学研究

本研究采用常规石蜡切片结合荧光显微镜技术对银州柴胡根的发育解剖学进行了研究。结果表明:（1）银州柴胡根顶端分生组织由原分生组织及其衍生的初生分生组织组成。原生分生组织细胞体积小、排列紧密、细胞质浓厚、细胞核大而明显,具有典型的分生组织的特点;（2）初生分生组织由根冠原、表皮原、皮层原和中柱原组成。在根发育过程中,表皮、皮层和维管柱共同组成其初生结构。银州柴胡根初生木质部为二原型或三原型,外始式;同时在根表皮细胞的径向壁观察到径向壁的细胞壁加厚;（3）在根次生生长过程中,位于初生木质部和初生韧皮部之间的原形成层恢复分裂能力产生维管形成层,维管形成层不断地向外产生次生韧皮部,向内产生次生木质部;同时位于根内皮层内方的中柱鞘细胞恢复分裂能力产生木栓形成层,木栓形成层向外形成木栓层,向内形成栓内层。在维管形成层和木栓形成层分裂的过程中,在次生韧皮部和中柱鞘组织中产生形态大小不同的分泌道,均为次生的裂生型分泌道。研究认为,银州柴胡根的结构类似于药典收录的北柴胡和红柴胡根的结构特点,但其根表皮细胞径向壁加厚、木纤维的分布、分泌道的大小和数量等有别于柴胡属其它植物,可作为柴胡属植物重要的分类鉴定依据。     

Consequences of root growth kinetics and vascular structure on the distribution of lateral roots

It has been proposed that the acropetal initiation of lateral roots is a built‐in process specified as part of the general process of cell division and differentiation in the parent root tip. Conversely, it is commonly reported that root branching is essentially a variable feature. In the present study, the interlateral distance along the parent root has been investigated using three banana varieties (Musa spp.) grown in two substrates. The pattern of lateral root initiation was obscured by variations of root growth patterns and vascular structure among roots, genotypes and substrates. A framework model is formulated showing the influence of growth pattern and vascular structure on branching density. The model raises a distinction between growth components which should not affect the branching density (i.e. rate of cell division) and which may affect it (i.e. size of mature cells and number of transverse divisions performed by cells executing their trajectory in the meristem). It appears also that lateral root density and root growth rate might be independently modulated by appropriate changes of root growth patterns, in banana and presumably many other taxa.     

桤木插穗不定根发生与发育的解剖学观察

采用常规石蜡切片法对桤木插穗进行解剖观察,研究茎的次生结构及不定根的起源和发生发育过程,探讨影响不定根发生的因素。结果表明:桤木茎的次生构造从外至内由周皮、皮层和次生维管组织3部分组成。皮孔有2种类型。不定根的发育过程可分为4个阶段:(1)维管形成层与髓射线交叉处的细胞活动,产生具有典型分生组织特点的薄壁细胞团;(2)薄壁细胞不断分裂,形成不定根原基发端细胞;(3)分裂分化形成的不定根沿着韧皮射线向皮层延伸;(4)随着不定根内部的维管系统的发育,不定根从皮孔或下切口伸出。     

THE COMPARATIVE AND DEVELOPMENTAL MORPHOLOGY OF THE ROOT SYSTEM OF SELAGINELLA SELAGINOIDES (L.) LINK

All of the roots of Selaginella selaginoides are attached laterally to the base of the shoot, which has monopolar growth as is characteristic of Selaginella. The first three roots are produced by meristematic activity in the cortex of the hypocotyl as in several other species of Selaginella. The fourth root is produced in the same way as the first three, except that not all of the cortical cells which become meristematic mature into root tissue. Some of the meristematic tissue remains undifferentiated and continues to produce additional roots. Potentially an unlimited number of roots could be produced, but no plant was found to have more than eight. There is some secondary growth in the cortex of the basal swelling on the hypocotyl, but no secondary vascular tissue is produced and no cambium of any sort is ever organized. On the basis of comparisons with other living species of Selaginella. the centralized root system of S. selaginoides is interpreted as having been modified from a noncentralized type of root system by the persistence of the juvenile mode of root production.     

SEQUENCE AND PATTERN OF LATERAL ROOT FORMATION IN FIVE SELECTED SPECIES

The proximal-distal distribution of the lateral roots of five species was studied. A detailed investigation was carried out on two of the five species, Ceratopteris thalictroides and Cucurbita maxima. A definite pattern of lateral root arrangement, with a degree of variability related to the number of protoxylem poles, was found in all of the species studied. In the fern Ceratopteris, lateral root initiation was found to be related to the segmentation of the apical cell, which in turn determines the distribution of the laterals. In this species the lateral roots occur in a predictable sequence and they are grouped in pairs. In the angiosperms studied, the pattern of lateral root distribution seemed to depend primarily upon a rather strict longitudinal relationship between the lateral root primordia formed opposite any one protoxylem pole. In Cucurbita maxima, 93.7 ± 5.02% of the lateral root primordia observed were in a specific sequence. The laterals of this species are also arranged in groups. In the other plants studied, Arachis hypogaea, Victoria trickeri, and Eichhornia crassipes, the laterals were not as regularly arranged, but nevertheless they were found to be arranged in groups along the main root axis and not randomly dispersed. Factors controlling the spacing of lateral root primordia include their relationship with the developing vascular system, a direct effect of the parent root apex, and an effect of older lateral root primordia in the same sector of the root.     

Aquaporin-facilitated water uptake in barley (Hordeum vulgare L.) roots

It is not known to what degree aquaporin-facilitated water uptake differs between root developmental regions and types of root. The aim of this study was to measure aquaporin-dependent water flow in the main types of root and root developmental regions of 14- to 17-d-old barley plants and to identify candidate aquaporins which mediate this flow. Water flow at root level was related to flow at cell and plant level. Plants were grown hydroponically. Hydraulic conductivity of cells and roots was determined with a pressure probe and through exudation, respectively, and whole-plant water flow (transpiration) determined gravimetrically in response to the commonly used aquaporin inhibitor HgCl(2). Expression of aquaporins was analysed by real-time PCR and in situ hybridization. Hydraulic conductivity of cortical cells in seminal roots was largest in lateral roots; it was smallest in the fully mature zone and intermediate in the not fully mature 'transition' zone along the main root axis. Adventitious roots displayed an even higher (3- to 4-fold) cortical cell hydraulic conductivity in the transition zone. This coincided with 3- to 4-fold higher expression of three aquaporins (HvPIP2;2, HvPIP2;5, HvTIP1:1). These were expressed (also) in cortical tissue. The largest inhibition of water flow (83-95%) in response to HgCl(2) was observed in cortical cells. Water flow through roots and plants was reduced less (40-74%). It is concluded that aquaporins contribute substantially to root water uptake in 14- to 17-d-old barley plants. Most water uptake occurs through lateral roots. HvPIP2;5, HvPIP2;2, and HvTIP1;1 are prime candidates to mediate water flow in cortical tissue.     

牛膝根的结构发育与三萜皂苷积累的关系

应用植物解剖学、组织化学定位及植物化学技术,研究了不同发育时期牛膝根的结构特征与三帖皂苷积累的关系。结果表明:牛膝根的初生结构和次生结构类似于一般双子叶植物,其根的加粗主要是由于三生结构的发生和分化。第一圈额外形成层产生于次生韧皮部外侧的薄壁组织细胞和射线细胞,以后的每一圈由前一圈向外衍生的薄壁组织细胞产生。额外形成层无纺锤状原始细胞和射线原始细胞之分,在切向纵切面上呈叠生排列。三生维管束以离心方式排成整齐的同心环状,由薄壁结合组织将其彼此分开,其圈数与额外形成层的圈数是一致的,随着根的个体发育而不断增加。在根的初生结构中,三萜皂苷主要分布于中柱鞘、初生韧皮部及初生韧皮部和初生木质部之间的薄壁组织细胞内;在根的次生结构中,主要分布于次生韧皮部及栓内层的薄壁组织细胞内。当三生结构形成后,除次生韧皮部及栓内层细胞外,在额外形成层和三生维管束韧皮部细胞内均有皂苷类物质积累。三生结构在牛膝根中占主要地位,是三萜皂苷积累与分布的主要场所。在牛膝根的生长发育过程中,三萜皂苷元齐墩果酸的百分含量呈“S”型曲线增长,其根的增长、加粗、三生维管束圈数、三萜皂苷总量及根中干重的积累量都在出苗后约120天达到高峰,此时应为牛膝根的最佳采收期。     

温度对马尾松组培单芽不定根发生的影响

马尾松( Pinus massoniana)组织培养生根困难,该研究在严格控制光温条件的光照培养中,以马尾松无性系组培继代芽为材料,分析了在不同温度处理下马尾松组培单芽生根率、生根时间、根系条数和移栽成活率等生根能力指标以及生根解剖构造的变化。所有数据均采用SPSS 19.0统计分析软件,进行单因素分析(ANOVA)的显著性检验及最小显著性差异法(LSD)的多重比较。结果表明：在25℃最适温度培养下,马尾松组培生根效果较佳,移栽成活率最高,可达98.1％。低温处理下,生根时间显著延长,根系条数减少,生根率偏低;高温处理下,根茎愈伤组织明显,移栽成活率显著降低。从生根解剖构造来看,马尾松不定根主要由维管形成层细胞分化而成。与25℃适温处理相比较,在20℃较低温处理下,细胞分裂活动缓慢,不定根原始体诱发较少;而在30℃较高温处理下,细胞活动旺盛,但髓射线与维管组织细胞染色颜色加深、排列紧密,将诱发的不定根原基细胞团区隔成带状或片状。该研究结果探讨了培养环境温度对马尾松组培单芽生根能力的影响,为马尾松组培苗生产提供了参考。     

Apical organization and maturation of the cortex and vascular cylinder inArabidopsis thaliana (Brassicaceae) roots

Developmental and physiological studies of roots are frequently limited to a post-germination stage. In Arabidopsis, a developmental change in the root meristem architecture during plant ontogenesis has not previously been studied and is addressed presently. Arabidopsis thaliana have closed root apical organization, in which all cell file lineages connect directly to one of three distinct initial tiers. The root meristem organization is dynamic and changes as the root ages from 1 to 4 wk post-germination. During the ontogeny of the root, the number of cells within the root apical meristem (RAM) increases and then decreases due to changes in the number of cortical layers and number of cell files within a central cylinder. The architecture of the initial tiers also changes as the root meristem ages. Included in the RAM's ontogeny is a pattern associated with the periclinal divisions that give rise to the middle cortex and endodermis; the three-dimensional arrangement of periclinally dividing derivative cells resembles one gyre of a helix. Four- or 5-wk-old roots exhibit a disorganized array of vacuolated initial cells that are a manifestation of the determinate nature of the meristem. Vascular cambium is formed via coordinated divisions of vascular parenchyma and pericycle cells. The phellogen is the last meristem to complete its development, and it is derived from pericycle cells that delineate the outer boundary of the root.     

核桃试管不定根的组织学研究

以核桃品种‘新早丰’试管嫩茎为试材,采用二步生根法诱导生根,对其试管苗不定根发生发育过程进行了解剖学研究。结果表明:核桃试管嫩茎内未发现潜伏根原基;诱导生根后,不定根原基起源于形成层,特别是髓射线正对的形成层部分,属于诱生根原基型;不定根上的侧根起源于中柱鞘细胞。核桃试管嫩茎不定根的发育过程可分为4个阶段:(1)形成层细胞分裂;(2)转变为分生组织细胞群(即根原始细胞);(3)细胞群发育成可见的根原基; (4)根原基内细胞继续分裂分化形成根尖的外形,其内发育出维管束,并向外生长,穿过皮层,突破茎表皮。在组织培养条件下长出的不定根内部解剖构造为典型的初生构造,移栽后68 d出现次生构造。另外,试管苗根毛出现与否及其发育状况受基质理化性质的影响,即生态条件可以改变组织发生及其形状。     

珍稀植物扇脉杓兰营养器官的解剖学研究

采用石蜡切片技术对扇脉杓兰营养器官的解剖结构进行了研究。结果表明：根状茎的薄壁细胞中含丰富的淀粉粒,维管柱中分布着排列紧凑的周木维管束;根的皮层发达,有的皮层细胞中存在真菌菌丝团,木质部与韧皮部呈辐射状相间排列,根和根状茎的内皮层细胞都形成马蹄形加厚结构。茎的表面分布气孔,皮层面积较小,皮层内部的基本组织发达,外韧维管束散生分布其中,茎和叶上都附有非腺性毛;叶为等面叶,叶肉细胞排列疏松,气孔主要分布于远轴面,略外凸,保卫细胞中含有叶绿体,叶缘处的叶肉组织中含有气腔结构。扇脉杓兰营养器官的这些特征与其荫蔽湿润的生境是相适应的。     

Changes in leaf,stem, and root anatomy of Chrysanthemum cv. Lillian Hoek following paclobutrazol application

Plants ofChrysanthemum cv. Lillian Hoek were treated with a paclobutrazol (PBZ) soil drench and histologically examined after 3 months. PBZ application resulted in thicker leaves, reduced stem diameter, and roots with an increased diameter and an unusual segmented appearance. Increased leaf thickness was partly due to an additional layer of palisade mesophyll, although individual palisade cells were shorter, of smaller diameter, and more tightly packed. Spongy mesophyll depth was also greater and the individual cells were more rounded and the volume of intercellular space was reduced. The narrower stems had an increased development of secondary xylem, but had a marked reduction in the number of sclerenchyma bundle caps. Increased root diameter was due to an increase in the number of rows and diameter of cortical cells. In PBZ-treated plants, root cortical cell length was 50–70% less than in untreated plants, and this reduction appeared to be associated with the segmentation of the roots. PBZ inhibited secondary vascular development in the roots. This study is similar to other relevant studies in recording thicker leaves and roots with PBZ application; however, many of the underlying anatomical changes described above have not been previously reported.     

In vitro cultured primary roots derived from stem segments of cassava (Manihot esculenta) can behave like storage organs

BACKGROUND AND AIMS: Cassava (Manihot esculenta) has three adventitious root types: primary and secondary fibrous roots, and storage roots. Different adventitious root types can also regenerate from in vitro cultured segments. The aim of this study was to investigate aspects of in vitro production of storage roots. METHODS: Morphological and anatomical analyses were performed to identify and differentiate each root type. Twenty-nine clones were assayed to determine the effect of genotype on the capacity to form storage roots in vitro. The effects of cytokinins and auxins on the formation of storage roots in vitro were also examined. KEY RESULTS: Primary roots formed in vitro and in vivo had similar tissue kinds; however, storage roots formed in vitro exhibited physiological specialization for storing starch. The only consistent diagnostic feature between secondary fibrous and storage roots was their functional differentiation. Anatomical analysis of the storage roots formed in vitro showed that radial expansion as a consequence of massive proliferation and enlargement of parenchymatous cells occurred in the middle cortex, but not from cambial activity as in roots formed in vivo. Cortical expansion could be related to dilatation growth favoured by hormone treatments. Starch deposition of storage roots formed in vitro was confined to cortical tissue and occurred earlier than in storage roots formed in vivo. Auxin and cytokinin supplementation were absolutely required for in vitro storage root regeneration; these roots were not able to develop secondary growth, but formed a tissue competent for starch storing. MS medium with 5 % sucrose plus 0.54 microM 1-naphthaleneacetic acid and 0.44 microM 6-benzylaminopurine was one of the most effective in stimulating the storage root formation. Genotypes differed significantly in their capacity to produce storage roots in vitro. Storage root formation was considerably affected by the segment's primary position and strongly influenced by hormone treatments. CONCLUSIONS: The storage root formation system reported here is a first approach to develop a tuberization model, and additional efforts are required to improve it. Although it was not possible to achieve root secondary growth, after this work it will be feasible to advance in some aspects of in vitro cassava tuberization.     

Experimentelle Modifikationen des Leitungssystems bei beginnender Wurzelbildung an Sprosstecklingen von Pappeln

In rooting poplar shoot cuttings of identical morphogenetic characteristics at the same time, the author succeeded to evoke differences in the radial arrangement of the vascular system by different environment influences. More favourable rooting conditions in the green-house, when comparing with the less favourable field conditions, caused root formation with a higher number of alternating xylem and phloem poles. The representants observed (I 214,Populus deltoides var.monilifera, P. pyramidalis) did not react in the same way on the different onvironment. The hybrid I 214 was the most sensible. It was also possible to induce differences by indoleacetic acid (IAA) exogenous application. Not only the number of the roots formed increased in a highly significant manner in the cuttings influenced by IAA, but also the number of poles in the radial vascular bundles of the induced roots was higher in a highly significant way. From the results given above it can be deduced that external conditions affecting activation of dormant root primordia in poplars influence also the pattern of vascular tissue differentiation in formed roots.