The Induction of Fibre Differentiation in Peas

The problem studied in this work was that of the internal controlof the formation of strands of fibres in Pisum sativum. It isshown that fibre differentiation is dependent on stimuli originatingin young leaf primordia. Removing these primordia early enoughprevents fibre differentiation; changing the position of theleaves experimentally changes the position of the fibres aswell. It was demonstrated that some stimuli for fibre differentiationmust flow through the strands at the time they differentiate.The evidence for this flow is in experiments concerning theability of very young fibre strands to regenerate after cutsas well as in experiments concerning their pattern of joining.The stimuli which originate in the leaves and control the differentiationof fibres and xylem are shown to differ in at least one component:auxin does not cause fibre differentiation and no surgical treatments,carried out on very young tissues, caused the replacement ofpart of a strand of fibres byor xylem or vice versa.     

Changes of Plastids During Xylem Differentiation in Barley Root

Plastids (eoplasts) are present in meristematic cells of prospectivecentral metaxylem in the barley root. Starch starts to be formedin plastids precisely after the cessation of mitotic activityand at the beginning of endomitotic growth. During secondarywall formation, the starch is gradually lost. Cavities are formedin plastids and signs of plastid degeneration are present fromthis stage of cell development. However, some intact globularplastids without starch are present until shortly before thefinal step of ontogeny, i.e. total destruction of protoplast. Hordeum distichum L., root, xylem, plastids, endomitotic growth, starch     

The Development of Root Nodule Xylem Transfer Cells in Trifolium repens

Stereological analysis of micrographs of developing and functioningxylem transfer cells of Trifolium repens indicates that theER and dictyosomes may be involved in wall ingrowth deposition,and the ER in intracellular solute transport.     

Mechanism of Xylem Differentiation in Pinus silvestrisL.

The duration and daily rate of radial growth and secondary-wallformation of all consecutive, radially-formed tracheids throughoutthe season were investigated in stems of adult trees of Pinussilvestris L. It was found that (1) the variation in radial diameter of tracheidswas probably dependent on seasonal changes in the rate of growthduring the phase of radial enlargement, (2) the daily rate ofcell-wall formation determined the final cell-wall thicknessof tracheids only at the beginning and the end of the season,(3) both rates were affected by temperature, (4) seasonal changesin cell-wall thickness were dependent mostly upon seasonal changesin the duration of the maturation period, (5) the changes inthe duration of the maturation period which brought about transitionfrom early to late wood were determined mostly by the delayin onset of autolysis of cytoplasm which terminates the phaseof tracheid maturation. This process, unlike the xylem productionfrom cambium and the termination of radial enlargemnt, was foundnot to be affected by the seasonal variation of temperature. An attempt to correlate these processes with the activity ofnatural auxin extracted from the cambial region gave negativeresults. On the basis of the results obtained, auxin and environmentalfactors such as precipitation and temperature seem not to bespecific for xylem differentiation. They may seriously affectwood differentiation if they become limiting or exceed the limitof tolerance, but probably they do not determine differentiationof the annual ring of conifers into early and late wood.     

Some Constituents of Xylem Sap and their Possible Relationship to Xylem Differentiation

Bleeding sap of Actinidia chinensis and Betula populifolia andguttation fluidof Avena sativa were analysed for sugars, amino-acids,auxin, and certain enzymes. A wide range of amino-acids wasfound in all three. Auxin was not detected in the bleeding sap,but was present in Avena guttation fluid (5.1 µg IAA equivalent/l).‘IAA oxidase’, acid phosphatase, ribonuclease, deoxyribonuclease,and protease were detected in the bleeding sap and guttationfluid. The possibility that some of the substances found insap and guttation fluid are products of autolysing, differentiatingxylem cells in the roots is discussed.     

木质部细胞分化的研究进展

本文主要从研究木质部细胞分化常用的实验系统,木质部分的诱导,木质部细胞的编程性死亡以及次生壁的构建4个方面阐述了木质细胞分的研究进展,并对目前研究的热点也是难点问题进行了展望,希望引起同行的兴趣。     

Field Estimates of Root and Xylem Resistances in Pinus contorta using Root Excision

A root excision technique was used to estimate the proportionof total resistance to water flux residing in the soil, theroot, and the xylem of lodgepole pine (Pinus contorta Douglex. Loud.) trees in the field. Root excision at mid-day alwaysresulted in rapid recovery of leaf water potential when waterwas supplied to the cut stem, suggesting a high soil-root resistance.Transpiration was unaffected if leaf water potential beforecutting was not limiting leaf conductance. By mid-June wateruptake by the excised stem always exceeded calculated crowntranspiration indicating recharge of internal sapwood storage.Predawn leaf water potential before root excision was highlycorrelated with total soil-plant resistance (r² = 0·89)and calculated root water uptake (r² = 0·92).     

Proteins and Carbohydrates in Xylem Sap from Squash Root

The xylem sap from squash roots was collected from the cut surfaceof stems, and the proteins and carbohydrates in the sap wereanalyzed. The sap contained 18.6 µg ml^–1 proteinand the major polypeptides were as follows: 1) two polypeptides,of 75 and 40 kDa, with high-mannose glycans, the levels of whichincreased for about 24 h after cutting and then decreased; 2)a 32-kDa polypeptide, which appeared soon after cutting, disappearedand then reappeared again 48–64 h after cutting; and 3)a 19-kDa and a 14-kDa polypeptide, which were present constitutively.The carbohydrates contained in the xylem sap were fractionatedinto 80% ethanol-soluble and -insoluble material, and whichwere analyzed by high-performance liquid chromatography, gaschromatography and enzymatic mathods. The former fraction containedconsiderable amounts of myo-inositol and fructose as free sugarsand oligosaccharides composed mainly of galactose, arabinoseand glucose. The latter contained polysaccharides composed mainlyof uronic acids, galactose and arabinose. The possible significanceof these substances, which may mediate the interactions betweenthe root and the aerial organs, is discussed. (Received April 20, 1992; Accepted July 4, 1992)     

Nitrate Reductase Activity: Phytochrome Mediation of Induction in Etiolated Peas

THE extractable activity of nitrate reductase from higher plant leaves is inducible by light and shows, under natural growth conditions, a pattern of diurnal variation¹. Studies on the nature of light involvement have generally used the green leaf as experimental material, implying that photosynthesis supports the induction process^1,2. We have examined the role of light for the induction of nitrate reductase activity in the etiolated terminal buds of field peas (Pisum arvense cv. Century). Treatments consisted of brief exposure of intact plants to broad bands of light, followed by a period in darkness before extraction for enzyme assay. These light treatments exclude the possibility of photosynthesis as a process contributing to induction. Under these conditions, induction is shown to be reversibly controlled by red and far red light, an effect ascribable to the pigment phytochrome.     

The Differentiation of Contact Cells and Isolation Cells in the Xylem Ray Parenchyma of Populus maximowiczii

A histochemical analysis was made of the differentiation ofcontact cells and isolation cells in the xylem ray parenchymaof Populus maximowiczii. The contact cells formed secondarywalls at approximately the same time as adjoining vessel elements.The lignification of the cell walls of contact cells and vesselelements began earlier than that of wood fibres and isolationcells. Thus, the formation of the secondary wall, includinglignification, of the contact cells might occur at the sametime as that of the vessel elements to which they are directlyconnected. By contrast, the isolation cells began to form secondarywalls later than the vessel elements and wood fibres in thevicinity of the isolation cells. After the deposition of thesecondary wall, a protective layer was formed in contact cellsbut no isotropic layer was observed in isolation cells. Theresults suggest the importance of vessel elements in the determinationof the differentiation of adjoining ray parenchyma cells.Copyright1999 Annals of Botany Company Contact cell, isolation cell, vessel element, xylem differentiation, Populus maximowiczii Henry.     

Studies of Root Function in Zea mays: III. Xylem Sap Composition at Maximum Root Pressure Provides Evidence of Active Transport into the Xylem and a Measurement of the Reflection Coefficient of the Root

The cut ends of excised Zea mays roots were sealed to a pressure transducer and their root pressures recorded. These rose approximately hyperbolically to a maximum value of 4.21 ± 0.34 bar after 30 to 40 minutes. Xylem exudate could not be collected at this pressure since the flow rate was zero. Samples of exudate were collected at lower applied pressures (ΔP), however, and Δπ, the osmotic pressure difference between them and the solution bathing the root, was measured by freezing point depression. A plot of ΔP/Δπ against J_v/Δπ, where J_v is the volume flux, proved to be a straight line whose intercept, equal to σ, the reflection coefficient, was 0.853 ± 0.016. The maximum xylem concentrations of various chemical species were found by a similar extrapolative method and compared with those in the cell sap. This indicated that (a) Ca²⁺, Mg²⁺, NO₃²⁻, SO₄²⁻, and most amino acids move from the cells to the xylem down an electrochemical potential gradient; (b) relative to these ions H⁺, NH₄⁺, glutamine and asparagine are actively transported into the xylem; and (c) H₂PO₄⁻, and K⁺ are actively retained in the symplasm.     

Investigation of Growth Hormones in Xylem Exudate and Root Tissue 1

Infection of the root system in tomato by the root-knot nematodewas found to alter the gibberellins and cytokinina extractedfrom root tissue and xylum exudate. Gibberellins from the roottissue and xylem exudate of healthy plants occurred in the neutral,acidic, and aqueous fractions. With increasing levels of infection,gibberellins were primarily extracted in the slightly acidicfraction. Gibberellin activity in the neutral, acidic, and aqueousfractions was decreased in diseased plants. Cytokinins, whichwere also extracted from root tissue and xylem exudate, werelower in diseased plants than in uninfected plants.     

土壤干旱条件下木质部汁液成分变化及其在根冠信号传递中的作用

介绍了植物木质部汁液收集方法和干旱条件下 ,蒸腾流中碳水化合物、蛋白质、pH等的变化 ,并对这些成分变化在根冠信号传递中的可能作用进行了讨论     

Properties of Two Outward-Rectifying Channels in Root Xylem Parenchyma Cells Suggest a Role in K+ Homeostasis and Long-Distance Signaling

Xylem parenchyma cells (XPCs) control the composition of the transpiration stream in plants and are thought to play a role in long-distance signaling as well. We addressed the regulation, selectivity, and dependence on the apoplastic ion concentrations of two types of outward rectifiers in the plasma membrane of XPCs, to assess the physiological role of these conductances. In whole-cell recordings, the membrane conductance at depolarization was under the control of cytosolic Ca2+: at physiological Ca2+ levels (150 nM) the K+ outward-rectifying conductance (KORC) predominated, whereas at elevated Ca2+ levels (5 [mu]M), only the nonselective outward-rectifying conductance (NORC) was active. No such regulatory effect of Ca2+ was observed in inside-out experiments. The voltage dependence of whole-cell KORC currents strongly depended on apoplastic K+ concentration: an increase in apoplastic K+ resulted in a positive shift of the current-voltage curve, roughly following the shift in Nernst potential of K+. KORC is impermeable to Na+, but does translocate Ca2+ in addition to K+. In contrast to KORC, NORC selected poorly among monovalent cations and anions, the relative permeability PC+/PA- being about 1.9. Gating of NORC was largely unaffected by the level of K+ in the bath. Under all ionic conditions tested, NORC tail currents or single-channel currents reversed close to 0 mV. Using an in vivo xylem-perfusion technique, tetraethylammonium (an inhibitor of KORC) was shown to block K+ transport to the shoot. These data support the hypothesis that release of K+ to the xylem sap is mediated by KORC. The molecular properties of these two conductances are discussed in the light of the distinct physiological role of XPCs.     

杜仲次生木质部分化过程中的细胞编程死亡

通过电子显微镜观察、DNA断裂检测及类似半胱氨酸蛋白酶（caspase-like proteases,CLPs)降解检测等技术,对杜仲（Eucommia ulmoides Oliv.）次生木质部分化过程的细胞编程死亡进行了研究。分化中的次生木质部细胞总DNA凝胶电泳检测到DNA ladder,并通过TUNEL检测进一步确定了DNA被降解。Western blot结果表明：caspase-8和caspase-3状蛋白酶（caspase-8-和caspase-3-like proteases,CLPs)及多聚ADP-核糖聚合酶（poly(ADP-ribose) polymerase,PARP)在次生木质部分化过程中被降解。这些研究结果表明,杜仲次生木质部的细胞分化是一个典型的编程性死亡（Programmed cell death,PCD)过程,CLPs可能参与了此过程。     

Tenascin-C Induction in Whitlock-Witte Culture: A Relevant Role of the Thiol Moiety in Lymphoid-Lineage Differentiation

The extracellular matrix (ECM) glycoprotein tenascin-C is expressed in a temporally and spatially restricted pattern during embryogenesis and carcinogenesis in association with stromal-epithelial interactions. First, we investigated the production of tenascin-C and other ECM glycoproteins in the established in vitro model system specific for the lymphoid-lineage hemopoiesis, i.e., the Whitlock-Witte (W-W) culture system. In murine primary long-term bone marrow cultures, tenascin-C was produced constitutively and was expressed significantly in higher amounts in this system than in the other established in vitro model system specific for the myeloid-lineage hemopoiesis, i.e., the Dexter culture system. 2-Mercaptoethanol (2-ME), a component of the W-W system, induced the secretion of tenascin-C and upregulated the expression of its mRNA. Furthermore, the reduced glutathione, which, like 2-ME, contains a thiol moiety, induced tenascin-C glycoprotein and its mRNA. By contrast, hydrocortisone (HC), a component of the Dexter system, inhibited the secretion of ECM glycoproteins. 2-ME and TGF-β1, the latter of which is known as an inducer of ECM glycoproteins, had an additive effect on the induction of tenascin-C when they were simultaneously added to the W-W system. The TGF-β receptor binding analysis demonstrated that this induction by 2-ME was not mediated by the cell-surface TGF-β receptors, suggesting that it was regulated independently of TGF-β1. Then, the role of thiol compounds in the lymphoid-lineage differentiation was examined. The omission of 2-ME from the W-W system completely eliminated its ability to support the lymphoid-lineage differentiation. Glutathione, which, unlike 2-ME, does not passively permeate through the plasma membrane, did not support the development of a lymphoid lineage. These results indicate that 2-ME, essential for the lymphoid-lineage differentiation in the W-W culture system, is a potent inducer of tenascin-C expression in vitro.     

Root Xylem Influence on the Water Relations and Drought Resistance of Rice

In order to determine the importance of root axial resistanceto water flow for drought resistance of rice (Oryza sativa L.)aseries of glasshouse and growth chamber studies was conductedfrom 1985 to 1986. A preliminary study surveyed root distributionand histological characteristics of six cultivars grown in aerobicsoil (20x20x90cm boxes) under well–watered ormoisturedeficit conditions. Subsequently, four experiments were conductedwith plants grown in culture solution. Our results demonstratethat plant breeders can use root thickness as a selection indexfor xylem size for root diameters up to about 1–2 mm.Usingthe Poiseuille–Hagen Law for water movement in capillaries,rice root axial resistance explained differences in leaf waterpotential and transpiration when only one cultivar was used,but did not explain differences among cultivars. Thus, increasingroot xylem vessel radii probably will not directly increasedrought resistance. Key words: Rice (Oryza sativa), roots, xylem characteristics, drought resistance     

苦皮藤试管苗生根培养研究

探讨了培养因子对诱导苦皮藤(Celastrus angulatus Maxim)试管苗生根的作用,采用正交试验设计法测试了苦皮藤生根关键因素多效唑(MET)、吲哚丁酸(IBA)、暗培养及培养基中盐浓度(简称培养基)的效应.方差分析结果显示,暗培养对苦皮藤生根作用极显著,因子作用大小依次为:暗培养＞培养基＞MET×IBA＞MET＞IBA×培养基＞IBA.诱导苦皮藤组培苗生根的最佳因素配比为:1/2 MS MET 3.0 mg·L-1 IBA 0.8 mg·L-1和1/2 MS MET 3.0 mg·L-1 IBA0.5 mg·L-1,暗培养12 d效果最好.