Naturally Occurring Regenerative Differentiation of Xylem Around Adventitious Roots in Luffa cylindrica Seedlings

Regeneration of xylem induced by adventitious root formationin the hypocotyl of Luffa cylindrica Roem. seedlings is described.This naturally occurring form of xylem regeneration involvesthe formation of a bypass of regenerated tracheary elementsaround a root without external severance of the vascular strands.The regeneration of xylem around an adventitious root is polarand is very similar in its developmental pattern to the well-knownxylem regeneration induced by wounding vascular strands. Adventitious root formation, Luffa cylindrica Roem, regenerated tracheary elements, vascular differentiation, xylem regeneration     

Naturally Occurring Regenerative Differentiation of Xylem Around Adventitious Roots in Luffa cylindrica Seedlings

Regeneration of xylem induced by adventitious root formationin the hypocotyl of Luff a cylindrica Roem. seedlings is described.This naturally occurring form of xylem regeneration involvesthe formation of a bypass of regenerated tracheary elementsaround a root without external severance of the vascular strands.The regeneration of xylem around an adventitious root is polarand is very similar in its developmental pattern to the well-knownxylem regeneration induced by wounding vascular strands. Adventitious root formation, Luffa cylindrica Roem, regenerated tracheary elements, vascular differentiation, xylem regeneration.     

Execution of the auxin replacement apical dominance experiment in temperate woody species

The classic Thimann-Skoog or auxin replacement apical dominance test of exogenous auxin repression of lateral bud outgrowth was successfully executed in both seedlings and older trees of white ash, green ash, and red oak under the following conditions: (1) decapitation of a twig apex and auxin replacement were carried out during spring flush, (2) the decapitation was in the previous season's overwintered wood, and (3) the point of decapitation was below the upper large irrepressible lateral buds but above the lower repressible lateral buds. Although it has been suggested that neither auxin, the terminal bud, nor apical dominance have control over the outgrowth of the irrepressible buds during spring flush, there is evidence in the present study that indicates that such control over the repressible buds exists. In seedlings, second-order branching, which resulted from decapitation of elongating current shoots, was also inhibited by exogenous auxin in the three species. Hence, the auxin replacement experiments did work on year-old proleptic buds (of branches of older trees) that would have entered the bud bank and also on current buds of seedlings. Cytokinin treatments were ineffectual in promoting bud growth.     

Translocation of14C-abscisic acid from roots into the aboveground part of pea (pisum sativum L.) seedlings

The translocation of¹⁴C-ABA from roots into other parts of the plant was followed in intact and decapitated pea seedlings. In intact plants ABA from roots was translocated above all into the apical part of epicotyl. In decapitated plants the regulative ability of intact apex can be partly simulated by exogenous IAA. The growth of lateral buds occurring after decapitation was associated with an intensive flow of¹⁴C-ABA from roots into released lateral buds as late as 72 h after decapitation,i.e. in the stage of intensive elongation growth of buds.     

Vessel origins in Nymphaeaceae: Euryale and Victoria

Metaxylem tracheary elements of roots have differentiation between end walls and lateral walls in both Euryale and Victoria End walls have narrower, more closely spaced bars and scalariform plates. primary walls of end walls (and, to a lesser extent, lateral walls) have striations that are thickened primary wall portions orientated in an axial direction. These striations are less common in Victoria than in Euryale. Although secondary wall strands between perforations occur in some dicotyledons, the report of primary wall striations is new; these can be seen with scanning electron microscopy (SEM) but not with light microscopy. Perforations occur irregularly and sometimes sparsely on end walls of tracheary elements of Victoria , but perforations were not observed in Euryale. Thus, Euryale satisfies one criterion for the presence of vessel (end wall different from lateral wall), whereas Barclaya satisfies another (perforations in end walls) and Victoria satisfies both. Vessel origins in Nymphaeaceae are important in illustrating that there may be multiple vessel origins in dicotyledons.     

Spatial and temporal changes in multiple hormone groups during lateral bud release shortly following apex decapitation of chickpea (Cicer arietinum) seedlings

Although the co-ordination of promotive root-sourced cytokinin (CK) and inhibitory shoot apex-sourced auxin (IAA) is central to all current models on lateral bud dormancy release, control by those hormones alone has appeared inadequate in many studies. Thus it was hypothesized that the IAA : CK model is the central control but that it must be considered within the relevant timeframe leading to lateral bud release and against a backdrop of interactions with other hormone groups. Therefore, IAA and a wide survey of cytokinins (CKs), were examined along with abscisic acid (ABA) and polyamines (PAs) in released buds, tissue surrounding buds and xylem sap at 1 and 4 h after apex removal, when lateral buds of chickpea are known to break dormancy. Three potential lateral bud growth inhibitors, IAA, ABA and cis -zeatin 9-riboside (ZR), declined sharply in the released buds and xylem following decapitation. This is in contrast to potential dormancy breaking CKs like trans -ZR and trans -zeantin 9-riboside 5'phosphate (ZRMP), which represented the strongest correlative changes by increasing 3.5-fold in xylem sap and 22-fold in buds. PAs had not changed significantly in buds or other tissues after 4 h, so they were not directly involved in the breaking of bud dormancy. Results from the xylem and surrounding tissues indicated that bud CK increases resulted from a combination synthesis in the bud and selective loading of CK nucleotides into the xylem from the root.     

Vessels in the roots of Barclaya rotundifolia (Nymphaeaceae)

Scanning electron microscope (SEM) studies of paraffin-sectioned material of stems and roots of Barclaya rotundifolia Hotta revealed perforations on tracheary elements of roots, but not on those of stems. End walls of vessels are identical with lateral walls except for the presence of perforations. Perforations can only be clearly revealed with SEM, and this method is advocated for further study of tracheary elements of Nymphaeaceae in particular, and primary xylem of ∗∗∗angiosperms in general. Vessel presence may be related to the habitat of this species, which unlike other members of the Nymphaeaceae (sensu stricto) has only aerial leaves and a rhizomatous system that is not inundated for prolonged periods.     

The role of endogenous cytokinins in correlation between cotyledon and its axillary bud and in hypocotyl regeneration of flax

When flax seedlings are decapitated above cotyledons and three days later one of the two cotyledons is removed then the remaining cotyledon stimulates in four to five days growth of its axillary bud. It has been found that content of endogenous cytokinins was higher in the stimulated bud as compared with the other one already 12 h after the cotyledon removal. Flax seedlings decapitated under cotyledons regenerate adventitious buds on thy hypocotyl stump during 5–6 days. The endogenous fytohormonal preparation of this regeneration was investigated in the 20 mm apical part of the hypocotyl stump. Decrease in auxin and increase in gibberellins was already found during the first day after decapitation while the level of cytokinins increased as late as three days after the apex removal.     

Study on the Convergent Passages of Water Conducting Elements in Secondary Xylem of Fagaceae

Structural variations in the convergent passages of water conducting elements were described in secondary xylem of 70 species of Fagaceae. Two types of water conducting systems were recognized on the ground of water-flow directions. The convergent passages of the longitudinal system mainly exhibited in the forms as perforations between the ends of Vessel elements, lateral wall pitting between the lateral walls of vessel elements, pitting be-tween vessel elements and imperforate tracheary elements, and pitting between imperforate tracheary elements. The convergent passages in the transverse system consisted of pitting between vessel elements and ray cells, pitting between imperforated tracheary elements and ray cells and simple pitting between ray cells. In addition, the roles of vasicentric tracheids and broad rays played in terms of conducting effectiveness and efficiency as proposed by Zimmermann were discussed.     

The haustorium of the root parasite Triphysaria (Scrophulariaceae), with special reference to xylem bridge ultrastructure

Haustoria of Triphysaria pusilla and T. versicolor subsp. faucibarbata from a natural habitat were analyzed by light and electron microscopy. Secretory trichomes (root hairs) participate in securing the haustorium to the surface of the host root. The keel-shaped intrusive part of the secondary haustorium penetrates to the depth of the vascular tissue of the host. Some of the epidermal interface cells differentiate into xylem elements. A significant number of haustoria do not differentiate further, but in most haustoria one to five of the epidermal xylem elements terminate a similar number of xylem strands. The strands mostly consist of vessel members and they connect host xylem or occasionally host parenchyma to the plate xylem adjacent to the stele of the parasite root. Each strand of this xylem bridge is accompanied by highly protoplasmic parenchyma cells with supposed transfer cell function. Increased surface area of the plasmalemma occurs in these cells as it does in interface parenchyma cells. Graniferous tracheary elements are restricted to the haustorium and occur most frequently in the plate xylem. The plate xylem is also accompanied by highly protoplasmic parenchyma cells. Hyphae of mycorrhizal fungi of the host root occasionally penetrate into the distal part of the xylem bridge. We combine structural observations and physiological facts into a hypothesis for translocation of water and nutrients between host and parasite. Some evolutionary aspects related to endogeny/exogeny of haustoria are discussed, and it is argued that the Triphysaria haustorium represents a greatly advanced and/or reduced condition within Scrophulariaceae.     

壳斗科次生木质部水分输导分子间连接通道结构的研究

壳斗科次生木质部水分运输聚合体及其连接通道结构,根据水分运输方向可分纵向和横向两大系统。水分纵向运输通道有导管分子间的穿孔,导管分子侧壁间的管间纹孔,导管分子与无穿孔管状分子间的侧壁纹孔,无穿孔管状分子与无穿孔管状分子间的侧壁纹孔。     

Abnormal root and nodule vasculature in R50 (sym16), a pea nodulation mutant which accumulates cytokinins

BACKGROUND AND AIMS: R50 (sym16) is a pea nodulation mutant with fewer and shorter lateral roots (LR), fewer nodules and high levels of cytokinins (CK). Because a link exists between CK imbalance and abnormal vasculature, the vasculature of the primary root (PR) and LR of R50 was studied and it was compared with that of the wild-type 'Sparkle'. Also nodule vasculature was investigated to correlate R50 low nodulation phenotype with CK accumulation. METHODS: PR and first-order LR were hand-sectioned transversely in different locations and at different ages. Vascular poles were counted and root and stele diameters measured. To evaluate LR primordia number, roots were cleared. Nodules obtained from inoculated plants were either fixed and sectioned or cleared; numbers of vascular strands and of tracheary elements in the strands were counted. KEY RESULTS: 'Sparkle' PR is triarch, whereas that of R50 can be triarch, tetrarch or pentarch. Furthermore, as the R50 roots developed, supernumerary vascular strands appeared but, as they aged, the new growth of more roots displayed the triarch pattern. LR vasculature differed from that of PR: whereas 'Sparkle' LR had three or four poles, those of R50 had two or three. No differences in PR or PR stele diameters existed between the two lines. Whereas 'Sparkle' nodules had two vascular strands, most R50 nodules possessed three; however, because R50 nodules were variable in size, their vasculature was highly diverse in terms of strand length. A strong correlation was found between nodule length and number of tracheary elements in strands. CONCLUSIONS: R50 displays an additional number of vascular poles in its PR, a smaller number of vascular poles in its first-order LR and an altered vasculature in its nodules. It appears that these three characteristics are linked to the high levels of CKs that the mutant accumulates over its development.     

Ultrastructure of the haustorial interface and apoplastic continuum between host and the root hemiparasiteOlax phyllanthi (Labill.) R. Br. (Olacaceae)

Summary Structural features of haustorial interface parenchyma of the root hemiparasiteOlax phyllanthi are described. Walls contacting host xylem are thickened non-uniformly with polysaccharides, not lignin, and show only a thin protective wall layer when abutting pits in walls of host xylem vessels or tracheids. Lateral walls of interface parenchyma exhibit an expanded middle layer of open fibrillar appearance, sometimes with, but mostly lacking adjoining layers of dense wall material. Free ribosomes and rough endoplasmic reticulum are prominent and occasional wall ingrowths present. Experiments involving transpirational feeding of the apoplast tracers lanthanum nitrate or uranyl acetate to host roots cut below haustorial connections, indicate effective apoplastic transfer from host to parasite root via the haustorium. Deposits of the tracers suggest a major pathway for water flow through host xylem pits, across the thin protective wall layer, and thence into the haustorium via the electronopaque regions of the terminal and lateral walls of the contact parenchyma. Graniferous tracheary elements and walls of parenchyma cells of the body of the haustorium appear to participate in tracer flow as do walls of cortical cells, stele parenchyma and xylem conducting elements of the parasite root, suggesting that both vascular and non-vascular routes are involved in extracytoplasmic transfer of xylem sap from host to parasite. The Casparian strip of the endodermis and the suberin lamella of the exodermis of theOlax root act as barriers to flow within the system.     

Spread of beet necrotic yellow vein virus in infected seedlings and plants of sugar beet (Beta vulgaris)

Summary Infection of sugar beet roots by beet necrotic yellow vein virus (BNYVV) was investigated with transmission electron microscopy, immunogold labelling and enzyme linked immuno sorbent assay (ELISA). Here we show that infection of sugar beet roots is very fast, occurring during germination. Seedlings grown directly in infected soil showed higher BNYVV infection than plants transplanted into infected soil after seven days of initial growth in sterilized soil. The earlier the initial infection, the faster was its spread. The study showed that a few differentiated cells of the cortex and of the xylem parenchyma were the preferred sites of viral multiplication. The spread of viral infection was slow through differentiated tissues. Intact virions were frequently found in undifferentiated and mature vessel elements and xylem parenchyma, whereas they were rare in sieve elements. Virus particle number in the differentiating tracheary elements was high, suggesting that infection of the vessel elements preceded their differentiation. This would explain increased infection after early inoculation. Even the xylem tissue of the primary root was highly infected, the seedlings lacked virus particles in their hypocotyls and leaves.     

Rapid increases in cytokinin concentration in lateral buds of chickpea (Cicer arietinum L.) during release of apical dominance

We examined the role of cytokinins (CKs) in release of apical dominance in lateral buds of chickpea (Cicer arietinum L.). Shoot decapitation or application of CKs (benzyladenine, zeatin or dihydrozeatin) stimulated rapid bud growth. Time-lapse video recording revealed growth initiation within 2 h of application of 200 pmol benzyladenine or within 3 h of decapitation. Endogenous CK content in buds changed little in the first 2 h after shoot decapitation, but significantly increased by 6 h, somewhat later than the initiation of bud growth. The main elevated CK was zeatin riboside, whose content per bud increased 7-fold by 6 h and 25-fold by 24 h. Lesser changes were found in amounts of zeatin and isopentenyl adenine CKs. We have yet to distinguish whether these CKs are imported from the roots via the xylem stream or are synthesised in situ in the buds, but CKs may be part of an endogenous signal involved in lateral bud growth stimulation following shoot decapitation. To our knowledge, this is the first detailed report of CK levels in buds themselves during release of apical dominance. Received: 12 December 1996 / Accepted: 7 January 1997     

The Possible Role of Potassium in the Activation of Axillary Buds of Bidens pilosus L. after Decapitation of the Apex: AN EXAMINATION BY X-RAY MICROANALYSIS

Growth of axillary buds in Bidens pilosus L. can be inducedby decapitation of the shoot apex. By means of X-ray microanalysisit is demonstrated that immediately after decapitation K⁺ isapparently accumulated in the stem tissue around the node. Conventionalelectron microscopy on sections of this part of the tissue revealedthat xylem parenchyma cells of those bundles that lead intothe cotyledons are differentiated as transfer cells. The possiblerole of K⁺ transport processes in growth initiation and regulationis discussed.     

Patterns of protein synthesis in dormant and growing vegetative buds of pea

Lateral buds on intact pea plants (Pisum sativum L. cv. Alaska) remain dormant until they are stimulated to develop by decapitating the terminal bud. Using two-dimensional gel electrophoresis, we have examined the protein content of terminal and lateral buds from intact plants and from plants at various times after decapitation. Silver-staining and in-vivo-labeling demonstrated very different sets of proteins. The level of expression of 18 stained and 25 labeled proteins was altered when growth was stimulated; this represents 3.4% and 9.1% of the total proteins detected by each method, respectively. Within 24 h of being stimulated, lateral buds doubled in length and their protein content was qualitatively nearly the same as that of terminal buds. Six hours after decapitation, before the onset of detectable growth, the overall pattern of protein synthesis in lateral buds was more like that of growing lateral buds or of terminal buds than that of dormant lateral buds. Direct application of N⁶-furfurylaminopurine (kinetin) to buds on intact plants stimulated their growth and resulted in the same pattern of protein synthesis as did decapitation. Inhibition of bud growth by addition of indole-3-acetic acid to the stumps of decapitated plants resulted in the synthesis of dormancy-related proteins. Lateral buds at all stages of development incorporated labeled amino acids at similar rates, indicating that metabolic activity is not a component of dormancy in these buds.Abbreviations IAA indole-3-acetic acid - IEF isoelectric focusing - KIN kinetin (N⁶-furfurylaminopurine) - SDS sodium dodecylsulfate - TCA trichloroacetic acid - 2D-PAGE two-dimensional polyacrylamide gel electrophoresis     

Distribution of 14C-labelled sucrose in seedlings of Pisum sativum L. Treated with indoleacetic acid and kinetin

Summary The influence of decapitation and treatment with IAA and/or kinetin on the pattern of distribution of ¹⁴C-labelled sucrose applied to the third leaf of 14-day old dwarf pea seedlings was investigated. Decapitation resulted in a diversion of the labelled metabolites to the lateral buds, and greatly increased the radioactivity present in the root system indicating that in these seedlings the roots and apex actively competed for translocates from the third leaf. Application of IAA to the decapitated internode prevented the growth of the lateral buds for the duration of the experiment and restored the pattern of distribution of labelled metabolites found in the intact plant. Application of kinetin alone resulted in a marked accumulation of labelled materials in the lateral buds, but when kinetin was applied with IAA metabolites were once again diverted from the lateral buds to the treated internode. Neither of these treatments had any influence on the proportion of the translocated materials which accumulated in the root system when compared with intact plants. The results are discussed in relation to current concepts of hormone-directed transport of nutrients in plants.     

In vitro induction of secondary xylem-like tracheary elements in calli of hybrid poplar (Populus sieboldii × P. grandidentata)

The formation of tracheary elements was induced in calli derived from petioles of hybrid poplar (Populus sieboldii × P. grandidentata) after 10 days of culture on medium that lacked auxin but contained 1 μM brassinolide. Some differentiated cells formed broad regions of cell walls and bordered pits, which are typical features of tracheary elements of secondary xylem. Other differentiated cells resembled tracheary elements of primary xylem, with spiral or reticulate thickening of cell walls. The tracheary elements that developed in calli were formed within cell clusters. This induction system provides a new model for studies of the mechanism of differentiation of secondary xylem cells in vitro.     

Apical Dominance Control in Ipomoea nil: The Influence of the Shoot Apex, Leaves and Stem

The outgrowth of lateral buds is known to be controlled by theupper shoot tissues, which include the apex, the young leavesand the upper stem. An analysis of the influence of these plantparts on axillary bud elongation in Ipomoea nil was carriedout by various treatments on these specific tissues. A restriction of elongation in the main shoot due to eitherdecapitation or shoot inversion resulted in the release of apicaldominance A non-linear type of compensating growth relationshipwas observed between the 13 cm apical growing region of thestem and the lateral buds. It was determined by decapitation,defoliation and AgNO₃ treatments that both the 13 cm stem-growthregion and the young leaves (1–5 cm in length) had a muchgreater inhibitory influence on the outgrowth of specified lateralbuds than did the stem apex (consisting of the terminal 0.5cm of the shoot). The specified lateral buds which were analyzedfor outgrowth were located a number of nodes below the shootapex. The intervening nodes were debudded. Although the importanceof young leaves in the control of apical dominance has beenpreviously recognized, the most significant result from thepresent study with Ipomoea was the strong influence of the 13cm apical growth region of the stem on the out growth of thelateral buds. Apical dominance, Ipomoea nil L., Pharbitis nil, growth region, lateral bud outgrowth, decapitation, defoliation, shoot inversion