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1.
The morphology of the hypogeous root holoparasite Hydnora triceps is highly reduced, and as with many holoparasites, the vegetative body is difficult to interpret. The vegetative body of H. triceps has been historically considered a "pilot root" studded with lateral appendages known as "haustorial roots." We found the vegetative body of H. triceps to consist of a rhizome with a thickened root-cap-like structure that covered a vegetative shoot apical meristem. From the apical meristem, procambial strands originated and developed into endarch collateral vascular bundles arranged radially around a pith without an interfascicular cambium. Xylem vessels had scalariform pitting and simple perforation plates. A continuous periderm without root hairs was observed. Increase in girth was attributed to cork and fascicular cambia. "Haustorial roots" or bumps on the surface of the vegetative body were exogenous, contained meristems and were the origins of vegetative branching, budding, and haustoria. The haustoria of H. triceps were cylindrical and penetrated the host root stele. Phloem and xylem elements were observed within the endophyte, and direct xylem to host-xylem contacts were observed. The arrangement of vascular tissues and xylem anatomy of H. triceps are likely plesiomorphic features in light of Hydnoraceae's placement in the Piperales.  相似文献   

2.
Plants continuously extend their root and shoot systems through the action of meristems at their growing tips. By regulating which meristems are active, plants adjust their body plans to suit local environmental conditions. The transport network of the phytohormone auxin has been proposed to mediate this systemic growth coordination, due to its self-organising, environmentally sensitive properties. In particular, a positive feedback mechanism termed auxin transport canalization, which establishes auxin flow from active shoot meristems (auxin sources) to the roots (auxin sinks), has been proposed to mediate competition between shoot meristems and to balance shoot and root growth. Here we provide strong support for this hypothesis by demonstrating that a second hormone, strigolactone, regulates growth redistribution in the shoot by rapidly modulating auxin transport. A computational model in which strigolactone action is represented as an increase in the rate of removal of the auxin export protein, PIN1, from the plasma membrane can reproduce both the auxin transport and shoot branching phenotypes observed in various mutant combinations and strigolactone treatments, including the counterintuitive ability of strigolactones either to promote or inhibit shoot branching, depending on the auxin transport status of the plant. Consistent with this predicted mode of action, strigolactone signalling was found to trigger PIN1 depletion from the plasma membrane of xylem parenchyma cells in the stem. This effect could be detected within 10 minutes of strigolactone treatment and was independent of protein synthesis but dependent on clathrin-mediated membrane trafficking. Together these results support the hypothesis that growth across the plant shoot system is balanced by competition between shoot apices for a common auxin transport path to the root and that strigolactones regulate shoot branching by modulating this competition.  相似文献   

3.
BACKGROUND: Vascular continuity is established between a host plant and the root parasite broomrape. It is generally accepted that the direction of vascular continuity results from polar flow of auxin. Our hypothesis was that chemical disruptions of auxin transport and activity could influence the infection of the host by the parasite. METHODS: A sterile system for the routine infection of Arabidopsis thaliana seedlings in Nunc cell culture plates by germinated seeds of Orobanche aegyptiaca was developed. This method permitted a quantitative assay of the rate of host infection. The three-dimensional structure of the vascular contacts was followed in cleared tissue. IAA (indole acetic acid) or substances that influence its activity and transport were applied locally to the host root. RESULTS: The orientation of the xylem contacts showed that broomrape grafts itself upon the host by acting hormonally as a root rather than a shoot. Local applications of IAA, PCIB (p-chlorophenoxyisobutyric acid) or NPA (naphthylphthalamic acid) all resulted in drastic reductions of Orobanche infection CONCLUSIONS: Broomrape manipulates the host by acting as a sink for auxin. Disruption of auxin action or auxin flow at the contact site could be a novel basis for controlling infection by Orobanche.  相似文献   

4.
Roles for Class III HD-Zip and KANADI genes in Arabidopsis root development   总被引:1,自引:0,他引:1  
Hawker NP  Bowman JL 《Plant physiology》2004,135(4):2261-2270
Meristems within the plant body differ in their structure and the patterns and identities of organs they produce. Despite these differences, it is becoming apparent that shoot and root apical and vascular meristems share significant gene expression patterns. Class III HD-Zip genes are required for the formation of a functional shoot apical meristem. In addition, Class III HD-Zip and KANADI genes function in patterning lateral organs and vascular bundles produced from the shoot apical and vascular meristems, respectively. We utilize both gain- and loss-of-function mutants and gene expression patterns to analyze the function of Class III HD-Zip and KANADI genes in Arabidopsis roots. Here we show that both Class III HD-Zip and KANADI genes play roles in the ontogeny of lateral roots and suggest that Class III HD-Zip gene activity is required for meristematic activity in the pericycle analogous to its requirement in the shoot apical meristem.  相似文献   

5.
Y. E. Choi  M. Katsumi  H. Sano   《Plant science》2001,160(6):1183-1190
The effect of auxin polar transport inhibitor on somatic embryo development and postembryonic growth in Siberian ginseng (Eleutherococcus senticosus) was examined. In the presence of 2,3,5-triiodobenzoic acid (TIBA), an auxin polar transport inhibitor, embryo formation from embryogenic cells was suppressed, while cell division was not affected. When globular embryos at different stages were transferred onto medium containing TIBA, development of axial and bilateral polarity was suppressed in a stagespecific manner. In abnormal embryos induced by TIBA, further development of shoot and root apical meristems and vascular differentiation was also suppressed. Thus, abnormal development of embryos induced by inhibition of auxin polar transport resulted in plantlets without shoots and roots.  相似文献   

6.
The Role of the Root in the Induction of Xylem Differentiation in Peas   总被引:2,自引:1,他引:1  
SACHS  T. 《Annals of botany》1968,32(2):391-399
It is known that growing parts of the shoot induce the differentiationof vascular tissues below them and that this induction is dueto the production of auxin. The problem dealt with here is whythe formation of xylem proceeds in the growing roots. The redifferentiationof parenchyma to tracheary elements in grafts of pea plantswas used in this study. It is proved that this is not due tostimuli coming from the root tip but rather to the movementof a stimulus coming from the shoot into the root. The polarityof movement is maintained even in thin sections, but it canbe reversed by a strong shoot influence.  相似文献   

7.
The effects of two auxin polar transport inhibitors, N-1-naphthylphthalamic acid (NPA) and 3,3[prime],4[prime],5,7-pentahydroxyflavone (quercetin), on attaining bilateral symmetry from radial symmetry during early wheat embryogenesis were investigated by using an in vitro culture system. Although NPA and quercetin belong to two different classes of auxin transport inhibitors, the phytotropins and the flavonoids, respectively, they induced the same specific abnormal phenotypes during embryo development. These abnormal embryos differentiated multiple meristems (i.e., multiple shoot and root meristems) and multiple organs (i.e., multiple coleoptiles and scutella). Multiple shoot apical meristem phenotypes were characterized by partly multiplied embryonic axes and supernumerary scutella. The differentiation of multiple primary roots in addition to multiple shoot meristems and multiple scutella led to the formation of polyembryos. The occurrence of multiple shoot meristem phenotypes depended on the concentration of the inhibitor and the developmental stage of the isolated embryo. Embryos treated with NPA or quercetin developed multiple radicle phenotypes less frequently than they developed multiple shoot meristem phenotypes. Our observations suggest that the root meristem differentiates later than the shoot meristem. Our data support the hypothesis that polar transport of auxin has a determining influence on the differentiation of the embryonic axis and the scutellum.  相似文献   

8.
Using the facultative root hemiparasiteRhinanthus minor andHordeum vulgare as a host, the flows and partitioning of mannitol in the parasite, and of sucrose in the host have been studied during the period of 41 to 54 days after planting, i.e, about 30 to 43 days after successful attachment of the parasite to the host. The biosynthesis of mannitol inRhinanthus shoots increased 16-fold by parasitism, resulting in a 15-fold higher mannitol flow in the phloem and a 10-fold higher deposition in the shoot. Under reduced nitrogen supply and with ammonium as the only N-form the concentrations of mannitol tended to be increased by approximately 2-fold. Xylem flows of mannitol were increased 10-fold after attachment. No mannitol was found in barley roots even in the direct vicinity of the haustoria. Compared to unparasitized barley, the net biosynthesis and deposition in the shoot and the phloem flow was decreased substantially. No sucrose has been detected in barley xylem sap and consequently there was no indication of a sucrose transfer from the host to the parasite. A possible involvement of mannitol in the abscisic acid relations of the parasite is discussed.  相似文献   

9.
Composite bundles are not simply a type of vascular bundles, but an integrated host/parasite interface. We investigated their structure in tubers of Langsdorffia and Balanophora. Composite bundles in both genera have similar components: 1) a central mass of host vascular tissues among which are located large parasite transfer cells; 2) a sheath of parasite parenchyma surrounding the central host vascular tissues; 3) specialized conducting tissues in the sheath; and 4) apical meristems composed of both host and parasite meristematic cells. Sheath parenchyma is recognizable from parasite tuber matrix by having thinner cell walls, and, especially in Langsdorffia, by the presence of collapsed matrix cells between the bundle sheath and tuber matrix. Sheath-conducting tissues consist of densely cytoplasmic transfer cells and small sieve tube members; in Langsdorffia, tracheary elements are also present. These sheath bundles connect with vascular bundles of the tuber matrix. Direct host/parasite contact only occurs by means of parasite transfer cells in the composite bundles. There is no xylem-xylem contact at the host/parasite interface. Abundance of parasite transfer cells suggests that they play an important role in nutrient absorption and translocation.  相似文献   

10.
The overall morphology of a plant is largely determined by developmental decisions taken within or near the terminally positioned apical meristems of shoots and roots. The spatial separation of these developmental centers emphasizes the need for long-distance signaling. The same signaling events may simultaneously coordinate differentiation within meristems and in the connecting vascular tissues. Recent genetic and molecular analyses not only confirm the proposed role of auxin as a coordinating signal across the plant, but also implicate auxin as a patterning signal in embryo and meristem organization.  相似文献   

11.
Mitogen-activated protein kinase (MAPK) cascades consist ofmembers of three families of protein kinases: the MAPK family,the MAPK kinase family, and the MAPK kinase kinase (MAPKKK)family. Some of these cascades have been shown to play centralroles in the transmission of signals that control various cellularprocesses including cell proliferation. Protein kinase NPK1is a structural and functional tobacco homologue of MAPKKK,but its physiological function is yet unknown. In the presentstudy, we have investigated sites of expression of the NPK1gene in a tobacco plant and developmental and physiologicalcontrols of this expression. After germination, expression ofNPK1 was first detected in tips of a radicle and cotyledons,then in shoot and root apical meristems, surrounding tissuesof the apical meristems, primordia of lateral roots, and youngdeveloping organs. No expression was, however, observed in matureorgans. Incubation of discs from mature leaves of tobacco withboth auxin and cytokinin induced NPK1 expression before thedivision of cells. It was also induced at early stages of thedevelopment of primordia of lateral roots and adventitious roots.Thus, NPK1 expression appears to be tightly correlated withcell division or division competence. Even when an inhibitorof DNA synthesis was added during the germination or the inductionof lateral roots by auxin, NPK1 expression was detected. Theseresults showed that the NPK1 expression precedes DNA replication.We propose that NPK1 participates in a process involving thedivision of plant cells. (Received January 26, 1998; Accepted April 9, 1998)  相似文献   

12.
13.
Auxin is an essential hormone for plant growth and development. Auxin influx carriers AUX1/LAX transport auxin into the cell, while auxin efflux carriers PIN pump it out of the cell. It is well established that efflux carriers play an important role in the shoot vascular patterning, yet the contribution of influx carriers to the shoot vasculature remains unknown. Here, we combined theoretical and experimental approaches to decipher the role of auxin influx carriers in the patterning and differentiation of vascular tissues in the Arabidopsis inflorescence stem. Our theoretical analysis predicts that influx carriers facilitate periodic patterning and modulate the periodicity of auxin maxima. In agreement, we observed fewer and more spaced vascular bundles in quadruple mutants plants of the auxin influx carriers aux1lax1lax2lax3. Furthermore, we show AUX1/LAX carriers promote xylem differentiation in both the shoot and the root tissues. Influx carriers increase cytoplasmic auxin signaling, and thereby differentiation. In addition to this cytoplasmic role of auxin, our computational simulations propose a role for extracellular auxin as an inhibitor of xylem differentiation. Altogether, our study shows that auxin influx carriers AUX1/LAX regulate vascular patterning and differentiation in plants.  相似文献   

14.
Ingvardsen C  Veierskov B  Joshi PA 《Planta》2001,213(3):333-341
This study provides an immunohistochemical demonstration of the involvement of the ubiquitin- and proteasome-dependent pathway during differentiation and organogenesis in plants. The localisation of ubiquitin and the proteasome was studied in meristems, leaves, stems and roots of sunflower (Helianthus annuus L. cv. Giganteus). By using a new technique that enhances very low antigen signals, we obtained information on the structural distribution of the ubiquitin- and proteasome-dependent pathway, and of the importance of this pathway during organogenesis and plant development. Ubiquitin and the proteasome showed overall similarities in their cellular localisation. The highest antigenic signal was observed in the root and shoot apical meristems, in leaf primordia and vascular tissue. The cambium showed less expression than the apical meristems. During adventitious root formation in cuttings, no sign of increased expression was observed within dedifferentiating tissue, but as organogenesis progressed, the antigenic signal of ubiquitin and the proteasome gradually increased in the developing roots. Comparison of immunochemical results and Western blots demonstrated that important changes in the cellular antigen signal could only be detected by immunochemistry.  相似文献   

15.
Rhamphicarpa fistulosa (Hochst.) Benth. (Scrophulariaceae), a parasite of African cereals, develops secondary haustoria which penetrate the roots of the host plant. Light and electron microscopy have been used to study the structure and development of haustoria in this species, which, until now, have not been well characterized. Haustoria are initiated in the hypodermis of the parasite roots. A meristematic strand is developed between the parasite root stele and the host-parasite interface. From this strand, cells differentiate into xylem elements after penetration of the host root. Xylem differentiation follows an acropetal pattern. Mature haustoria are characterized by a continuous xylem bridge between water conducting elements of parasite and host. A detailed study of the hostparasite interface revealed the presence of collapsed and compressed host cells at the lateral interface (between parasite cells and host cortex), whereas the central interface between parasite cells and the host stele is almost devoid of host cell remnants. Implications of these observations for the penetration mechanisms are discussed.  相似文献   

16.
Sucrose-phosphate synthase (SPS; E.C. 2.4.1.14) was studied in 1-year-old leaves of the xylem-parasitic mistletoe (Viscum album L.), growing on Abies alba. Glucose-6-phosphate served as an allosteric activator of mistletoe SPS, increasing the affinity for both substrates, fructose-6-phosphate and UDP-glucose. The activation state of SPS, i.e. the ratio of substrate limited versus non-limited activity, showed two clear peaks between February and July which coincided with increased rates of net photosynthesis of the parasite. Periods of decreased SPS activity were accompanied by a transient accumulation of sucrose and starch. In samples exhibiting a high activation state, activity was decreased by incubation of the extract with ATP; however, ATP did not affect SPS activity in samples exhibiting a low activation state of SPS. In parallel to the first increase of the activation state in March, pool sizes of the positive effector glucose-6-phosphate were high, whereas pool sizes of fructose-2,6-bisphosphate, an inhibitor of sucroneogenesis, were low. The decline in the activation state in April occurred in parallel with increased rates of transpiration of the parasite. This could have increased the availability of host-derived sugars, although the xylem sap of A. alba showed rather consistent concentrations of total soluble sugars throughout the vegetation period (1.1-3.9 mM). We thus speculate that sugar availability in the host xylem controls carbohydrate metabolism in the parasite.  相似文献   

17.
McHale NA  Koning RE 《The Plant cell》2004,16(7):1730-1740
Leaf initiation in the peripheral zone of the shoot apical meristem involves a transition to determinate cell fate, but indeterminacy is maintained in the vascular cambium, a tissue critical to the continuous growth of vascular tissue in leaves and stems. We show that the orientation of cambial growth is regulated by microRNA (miRNA)-directed cleavage of mRNA from the Nicotiana sylvestris ortholog of PHAVOLUTA (NsPHAV). Loss of miRNA regulation in semidominant phv1 mutants misdirects lateral growth of leaf midveins and stem vasculature away from the shoot, disrupting vascular connections in stem nodes. The phv1 mutation also expands the central zone in vegetative and inflorescence meristems, implicating miRNA and NsPHAV in regulation of meristem structure. In flowers, phv1 causes reiteration of carpel initiation, a phenocopy for loss of CARPEL FACTORY/DICER LIKE1, indicating that miRNA is critical to the termination of indeterminacy in floral meristems. Results point to a common role for miRNA in spatial and temporal restriction of HD-ZIPIII mediated indeterminacy in apical and vascular meristems.  相似文献   

18.
The objectives of this research were to identify auxin gene, AUX1, and to determine the plant auxin content and their role in conferring branching on Kenaf. PCR analysis using AUX1 primer capable to amplify the DNA of non branching (KR11) and branching kenaf mutant, resulting in 800 bp PCR product. The sequence of the PCR product showed high degree of homology with the sequence of AUX1 gene of other plants in the NCBI GenBank database, confirming kenaf possession of the gene AUX1. However, some variation on the DNA sequence was found between branching and non branching phenotype indicated allele differences of the same gene which were responsible for the variation in the type of branching. Identification of auxin content in the roots, apical shoot, and axillary branches using spectrophotometry method showed that the branching plant has higher auxin content in the apical shoot compared to the content in the branches. This indicate that AUX1 controls the formation of branches by controlling either the content of auxin in the apical shoot and branches, or the ratio of auxin content in the shoot and branches.  相似文献   

19.
Aciculosporium take causes continuous shoot growth but maintains normal leaf-arrangement and branching patterns in the host plant, which eventually resulting in witches'' broom disease of bamboo. An in situ hybridization technique with a species-specific oligonucleotide probe was recently used to demonstrate that endophytic mycelia of A. take is predominantly distributed in the intercellular spaces of the shoot apical meristem of the host. Endophytic hyphae in meristematic tissues, which may produce auxin, are responsible for continuous primordium initiation within the shoot apex. Here I examine another bamboo witches'' broom causal fungus, Heteroepichloë sasae. Both species are biotrophic and belong to family Clavicipitaceae: however, H. sasae does not cause continuous shoot growth. Histological study showed that H. sasae mycelia were distributed superficially, even on shoot apical meristems. These observations suggest that when their stromata develop, endophytic A. take destroys shoot apical meristem and epiphytic H. sasae chokes the shoot apex of the host. Stromata formation consequently causes lateral bud out-growth because of release from apical dominance. This process repeats and eventually results in the witches'' broom symptoms.Key words: apical dominance, endophyte, epiphyte, histology, shoot development, witches'' broom symptom  相似文献   

20.
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