Proton Efflux from Roots of Intact Spergularia marina Plants

Despite numerous considerations of the importance of protonextrusion to plant mineral nutrition, measurements of net H⁺efflux rates in photo-autotrophic plants growing in completemedium are rare, and the rates of efflux reported are considerablylower than that typical of low-salt seedlings. We present herethe first report of short term net proton efflux from rootsof a halophyte. and the highest rate of net efflux reportedto date for any higher plant, in both low-salt and completenutrient media. We also show responses of that efflux to a varietyof treatments, including NaCl fusicoccin, shoot excision anddarkness. Key words: Halophyte, Sea spurrey, H⁺ efflux, Roots     

Nutrient Uptake by Different Parts of the Intact Roots of Plants

An apparatus is described for studying the uptake of ions byshort segments of intact root systems grown in water culture. When the entire root systems of young cereal plants are suppliedwith o'I ppm, P or Sr the quantities of both ions accumulatedin segments 3–5 mm long, or translocated from them toother tissues, are considerably smaller than those which movelongitudinally in the cortex for short distances. This process,which is under metabolic control, causes ions to be releasedto the external solution from parts of the root a few mm distantfrom the site of entry. The contribution, to the nutrition of barley plants 3–4weeks old, of different parts of the root system has been investigated.Between seminal axes, nodal axes, and laterals total uptakeper unit length of root varies largely, though not entirely,with volume. The ratio in which phosphate and strontium areabsorbed is not constant throughout the root system, the absorptionof phosphate being relatively greater by laterals. Little translocationoccurs from the apical 3 mm of roots and the fraction of theabsorbed ions translocated to shoots from older root segmentsis considerably greater for nodal axes than for seminal axesor laterals. The significance of the distribution of absorbing power throughoutthe root system is considered in relation to the nutrition ofplants grown in soil, especially when the rate of diffusionto the root surface may limit nutrient uptake.     

8种木本植物木质部栓塞变化与生理生态指标关系的研究 I.与植物木质部水势的关系

以自然状况下生长良好的耐旱树种刺槐（Robinia pseudoacacia L.）、元宝枫（Acer truncatum Bge）、沙棘（Hippophae rhamnoides L.）、白榆（Ulmus pumila L.）、油松（Pinus tabulaeformis Carr.）、白皮松（Pinus bungeana Zucc.ex Endl.）及中生树种女贞（Ligustrum lucidum Ait.）、柳树（Salix matsudana Koidz.f.pendula Schneid.）为研究对象,用压力室法测定木质部水势,用冲洗法测定木质部栓塞程度,研究不同生长季节木质部栓塞与水势间的火系。结果表明：针叶树油松、白皮松在各个季节水势均较高,水势变化幅度较小,木质部不易发生栓塞,这与其木质部由管胞构成,对木质部栓塞不敏感,在干旱时采用高水势延迟脱水的耐旱策略有关。阔叶树刺槐、元宝枫、沙棘、白榆、女贞和柳树的木质部栓塞现象是其在每天正常生长过程中不可避免的“平常事件”,是它们适应干旱的一种方式。它们的木质部栓塞程度与水势表现出了相反的变化趋势,即同一树种在同一季节内水势值越低,木质部栓塞程度越大,但在不同树种及同一树种的不同季节不存在这种关系。由此可见,植物木质部栓塞对水势的敏感程度（即木质部栓塞脆弱性）主要由树种的木质部结构决定,同时受到树种特性、树木生长发育时期、外界环境因子的影响,木质部栓塞的脆弱性也具有季节变化特征。     

Cell Membrane Potentials of Higher Plants: Changes Induced by Wounding

Cell membrane potentials of cultured soybean cells, freshlycut soybean cotyledons, and freshly cut Jerusalem artichoketubers ranged from –20 to –45 mV. Readings fromthe cultured soybean cells remained within this range over aperiod of several days after the cells were subcultured. However,the membrane potentials of the soybean cotyledonary chlorenchymaand of the Jerusalem artichoke storage parenchyma exhibiteda striking hyperpolarization over a period of hours after thesetissues were sliced. The soybean cotyledons exhibited a morerapid hypopolarization than the artichoke tubers, developinga maximum average potential of –80 mV within 3 h afterwounding. These readings were obtained with the cells bathedin a complete culture medium known to permit sustained cellproliferation from soybean cotyledons. However, the wound-inducedhyperpolarization was not dependent upon any particular componentof the medium, including auxin or cytokinin. The hyperpolarizationwas observed even when cotyledon slices were incubated in isosmoticKCl.     

植物木质部导管栓塞

植物木质部栓塞直接影响植物体内的水分传输,文章对近年来植物木质部导管栓塞的时空分布规律、栓塞修复的微观过程,以及根压与作物木质部导管栓塞的关系研究进展作了概述。     

Unidirectional Ca2+ Fluxes in Roots of Rye (Secale cereale L). A Comparison of Excised Roots with Roots of Intact Plants

The unidirectional Ca²⁺ fluxes across the plasma membrane andtonoplast were determined in both excised roots and roots ofintact seedlings of rye (Secale cereale L. cv. Rheidol). Theunidirectional Ca²⁺ fluxes across the plasma membrane and tonoplastmeasured in excised roots were of a similar order of magnitudeto those determined in roots of intact plants. Influx and effluxof Ca²⁺ across the root plasma membrane were similar (estimatedto be between 0·7 and 3·4 µmol g     

A Method for Characterizing the Relation between Nutrient Concentration and Flux into Roots of Intact Plants

A method based on the rate of depletion of a nutrient from solution was developed to characterize nutrient flux of plant roots. Nutrient concentration of the solution was measured at a series of time intervals to describe the complete depletion curve. An integrated rate equation, based on a Michaelis-Menten model, was developed and fit to the data of the depletion curve using a least-square procedure. The equation contained values for V_max, the maximum rate of influx; Km, the Michaelis constant; and E, efflux, which were used to describe the relation between solution concentration and net influx rate. Models other than Michaelis-Menten could also be used. The method uses only one plant or group of plants to obtain data over a range of nutrient concentrations, is adapted particularly to the low concentration range, and measures the concentration below which net influx ceases. With this method the plant is in steady state absorption prior to the experiment and continues at this steady state until near the end of the experiment.     

A Comparison of the Boron Requirements of Intact Tomato Plants and Excised Tomato Roots grown in Sterile Culture

A method is described by which boron deficiency in excised tomatoroots was obtained. Lack of boron caused complete inhibitionof growth after three days in sterile culture. The boron concentrationsupporting 50 per cent of the maximum root-growth response issimilar to that giving a 50 per cent growth response with intactplants of the same variety. These results are discussed withregard to the function of boron in plant growth.     

Silicon Compounds in Xylem Exudates of Plants

An account is given of a study of silicon compounds in the xylemexudates of Equisetum hyemale and Zea mays. When fractionatedby gel filtration the compounds behaved as silicic acid andnot as an organo-silicon complex.     

Metabolism of Arginine and Ornithine in Suspension-Cultured Cells and Aseptic Roots of Intact Plants of Atropa belladonna

Suspension-cultured cells and aseptically cultured roots ofintact plants of Atropa belladonna L. removed tropane alkaloidprecursors arginine (Arg) and ornithine (Orn) at nearly an equalrate from the feeding medium. A great part of Arg- and Orn-derived¹⁴C-label was found in ethanol-insoluble compounds, mostly inproteins already after 2 h feeding. Ethanol-soluble label inthe roots was found mainly in amino acids (e.g. glutamine, Gln)after 2 h feeding, and after 20 h also in some intermediatesof the urea cycle (e.g. argininosuccinate). In suspension cultures, subculturing of the initiation callusdecreased both the uptake of the basic amino acids tested andtheir binding on to the apoplastic space. After 20 h feedingwith Arg more label was found in organic acids in stationaryphase suspension cultures with repressed alkaloid synthesisthan in roots producing alkaloids. The growth phase and passagenumber also affected into which amino acids the label was incorporated.When the initiation callus was young (the 3rd passage), theintermediates of the urea cycle were actively labelled, butwhen the initiation callus was older (the 8th passage) and thesuspension formed roots, especially Gln was labelled. Only tracesof -N-methylornithine were detected in feeding experiments withOrn and Arg. Considerable arginase activity with a high pH optimumwas observed in cell suspensions and roots of A. belladonna. Key words: Atropa, arginine, ornithine, roots, suspension culture     

Effect of Phloem-Translocated Malate on NO(3) Uptake by Roots of Intact Soybean Plants

In soybean (Glycine max L. Merr. cv Kingsoy), NO₃⁻ assimilation in leaves resulted in production and transport of malate to roots (B Touraine, N Grignon, C Grignon [1988] Plant Physiol 88: 605-612). This paper examines the significance of this phenomenon for the control of NO₃⁻ uptake by roots. The net NO₃⁻ uptake rate by roots of soybean plants was stimulated by the addition of K-malate to the external solution. It was decreased when phloem translocation was interrupted by hypocotyl girdling, and partially restored by malate addition to the medium, whereas glucose was ineffective. Introduction of K-malate into the transpiration stream using a split root system resulted in an enrichment of the phloem sap translocated back to the roots. This treatment resulted in an increase in both NO₃⁻ uptake and C excretion rates by roots. These results suggest that NO₃⁻ uptake by roots is dependent on the availability of shoot-borne, phloem-translocated malate. Shoot-to-root transport of malate stimulated NO₃⁻ uptake, and excretion of HCO₃⁻ ions was probably released by malate decarboxylation. NO₃⁻ uptake rate increased when the supply of NO₃⁻ to the shoot was increased, and decreased when the activity of nitrate reductase in the shoot was inhibited by WO₄²⁻. We conclude that in situ, NO₃⁻ reduction rate in the shoot may control NO₃⁻ uptake rate in the roots via the translocation rate of malate in the phloem.     

Antitranspirant Activity in Xylem Sap of Maize Plants

Xylem sap from unwatered maize plants was collected and testedfor antitranspirant activity. Two assays were used. These werea transpiration assay with detached wheat leaves and a stomatalbio-assay involving the direct microscopic observation of epidermisof Commelina communis. The reduction in transpiration of detached wheat leaves promotedby xylem sap could be duplicated almost exactly by the applicationof solutions of ABA of equivalent concentration to that foundin the xylem sap. Removal of virtually all the ABA from thexylem sap, using an immunoaffinity column, removed virtuallyall the antitranspirant activity in both assays. These results are discussed in the context of other resultswhich suggest the presence of as-yet unidentified inhibitorsin the xylem sap of unwatered plants. We suggest that with maize plants at least, stomatal responsesto soil drying can be entirely explained by enhanced concentrationof ABA in the xylem stream. Key words: Antitranspirant activity, ABA, ABA bio-assay, xylem sap     

盐胁迫下大麦根系木质部压力的自调节现象

用植物木质部压力探针测定的结果表明,水培大麦幼苗根的木质部压力在环境条件恒定不变时始终保持波动,并且在受到轻度的盐胁迫和当盐胁迫解除时表现出高度的自调节现象.这种波动和自调节现象将对植物水势的测定和根的径向反射系数的测定产生很大的影响,并可能与植物的抗盐性有关.小麦根在同样条件下未表现出上述现象.     

Repression of Proton extrusion from Intact Cucumber Roots and the Proton Transport Rate of Microsomal Membrane Vesicles of the Roots due to Ca2+ Starvation

Proton extrusion from cucumber roots decreased markedly duringCa²⁺ starvation in the presence of KC1. Vesicles with ATP-dependentproton transport activity were prepared from the microsomalmembrane fraction of control and Ca²⁺-starved roots. The protontransport rate of the vesicles from Ca²⁺-starved roots was repressedto less than half of the vesicles prepared from the controlroots. K⁺-Mg²⁺-ATPase activity associated with the vesiclesprepared from Ca²⁺-starved roots was approximately one-thirdof the activity associated with those prepared from controlroots. K_m values of the proton transport rate and K⁺-Mg²⁺-ATPasefor ATP were much higher in vesicles prepared from Ca²⁺-starvedroots. The repression of proton extrusion linked with K⁺ uptake inthe Ca²⁺-starved roots could be largely caused by the reducedproton pumping activity associated with microsomal membranesin the roots. (Received May 25, 1987; Accepted October 14, 1987)     

Water Flow Through Cotton Roots in Relation to Xylem Anatomy

The effect of root anatomy on water flow was studied in 7-d-oldcotton (Gossypium hirsutum L.) seedlings grown in solution culture.The total water flux of the intact root system was measuredusing a pressure chamber. Then successive terminal root sectionswere removed at 2,6,10 and 12 cm behind the root tip and theflux was remeasured after each successive cut was made. Xylemdevelopment at different distances behind the root apex wasstudied with a microscope using sections cut free-hand and stainedwith toluidine blue. Water flux increased with the removal ofsuccessive terminal root sections and this coincided with thedegree of basipetal primary xylem development. The large increasein water flux at 10 to 12 cm was associated with secondary xylemdevelopment and increased xylem vessel number. A comparison of water flow and xylem anatomy between roots withtetrarch (Stoneville 506 and Deltapine 41) and pentarch (T25strain) vascular bundle arrangements showed no significant differencesin the measured values of water flux for the primary root. Waterflux, estimated using Poiseuille's equation and measured xylemdimensions, was greater for the tetrarch roots, primarily becauseof the larger diameter of individual vessel elements. The increasednumber of vessel elements in the pentarch primary root of T25did not result in any apparent decrease in axial resistanceto water flow. Key words: Gossypium hirsutum L., roots, vascular bundle, xylem water flux, xylem     

Membrane Uncoating of Intact Enveloped Viruses

Experiments in the 1960s showed that Sendai virus, a paramyxovirus, fused its membrane with the host plasma membrane. After membrane fusion, the virus spontaneously “uncoated” with diffusion of the viral membrane proteins into the host plasma membrane and a merging of the host and viral membranes. This led to deposit of the viral ribonucleoprotein (RNP) and interior proteins in the cell cytoplasm. Later work showed that the common procedure then used to grow Sendai virus produced damaged, pleomorphic virions. Virions, which were grown under conditions that were not damaging, made a connecting structure between virus and cell at the region where the fusion occurred. The virus did not release its membrane proteins into the host membrane. The viral RNP was seen in the connecting structure in some cases. Uncoating of intact Sendai virus proceeds differently from uncoating described by the current standard model developed long ago with damaged virus. A model of intact paramyxovirus uncoating is presented and compared to what is known about the uncoating of other viruses.Enveloped virus entry at the plasma membrane includes binding of the virion to one or more receptors, changes in the virion components, membrane fusion, and membrane uncoating. The term “membrane uncoating” is being used to describe the separation of internal virion components from the viral membrane so the internal components can enter the cell. The term “uncoating” is sometimes used to mean the release of the viral genome from the capsid or other structures that have also entered the cell, but in this review, the term “membrane uncoating” will be used to represent only the separation of the virion internal contents and the viral envelope.Much of the original model of membrane fusion and uncoating was generally accepted as a result of a 1968 paper by Morgan and Howe (41). That paper provided strong evidence that Sendai virus (a paramyxovirus) entered a cell by fusion of the viral membrane with the cell plasma membrane. After membrane fusion, the virion rapidly lost its structure as the viral membrane merged with the host membrane and its components became part of the host membrane. The viral ribonucleoprotein (RNP) and internal proteins were released into the cytoplasm. This model of membrane uncoating is still generally accepted. For instance, in a 2007 virology text (24), this model was presented and illustrated with a figure from the Morgan and Howe paper. (The same figure is shown here as Fig. 2B.)Later, it was shown that Sendai viruses, which had been grown in fertilized chicken eggs, had different properties depending whether they had been harvested after growth for roughly 1 day (“early harvest”) or for several days (“late harvest”). The early-harvest viruses appear to be intact, but the late-harvest viruses have a different morphology and appear to be damaged (20, 26).This review summarizes data showing that intact early-harvest Sendai viruses uncoat quite differently from the way damaged late-harvest Sendai viruses uncoat. A model of intact paramyxovirus membrane uncoating is presented. The membrane uncoating of some other enveloped viruses that enter at the plasma membrane is compared to that described by this model.