Ion Imbalance in Capsicum annuum, scabrous diminutive, a Wilty Mutant of Pepper I. SODIUM FLUXES

Leaves of the wilty pepper mutant, scabrous diminutive, accumulatemore Na+ than those of the normal genotype, when both grow inmedium containing N⁺. It seems that the regulation of Na⁺ fluxin the mutant root was modified. Net uptake of Na⁺ was muchhigher and efflux of ²²Na⁺ was lower in the mutant roots thanin the normal ones. Two possible explanations for these differencesbetween mutant and normal plants are discussed, namely (a) achange in membrane permeability and (b) a change in the mechanismof Na⁺ extrusion.     

Calcium Movement, Graviresponsiveness and the Structure of Columella Cells and Columella Tissues in Roots of Allium cepa L.

Roots of Allium cepa L. cv. Yellow are differentially responsiveto gravity. Long (e.g. 40 mm) roots are strongly graviresponsive,while short (e.g. 4 mm) roots are minimally responsive to gravity.Although columella cells of graviresponsive roots are largerthan those of nongraviresponsive roots, they partition theirvolumes to cellular organelles similarly. The movement of amyloplastsand nuclei in columella cells of horizontally-oriented rootscorrelates positively with the onset of gravicurvature. Furthermore,there is no significant difference in the rates of organellarredistribution when graviresponsive and nongraviresponsive rootsare oriented horizontally. The more pronounced graviresponsivenessof longer roots correlates positively with (1) their caps being9.6 times more voluminous, (2) their columella tissues being42 times more voluminous, (3) their caps having 15 times morecolumella cells, and (4) their columella tissues having relativevolumes 4·4 times larger than those of shorter, nongraviresponsiveroots. Graviresponsive roots that are oriented horizontallyare characterized by a strongly polar movement of ⁴⁵Ca²⁺ acrossthe root tip from the upper to the lower side, while similarlyoriented nongraviresponsive roots exhibit only a minimal polartransport of ⁴⁵Ca²⁺. These results indicate that the differentialgraviresponsiveness of roots of A. cepa is probably not dueto either (1) ultrastructural differences in their columellacells, or (2) differences in the rates of organellar redistributionwhen roots are oriented horizontally. Rather, these resultsindicate that graviresponsiveness may require an extensive columellatissue, which, in turn, may be necessary for polar movementof ⁴⁵Ca²⁺ across the root tip. Allium cepa, onion, root, columella tissue, columella cell, gravitropism, calcium, ultrastructure     

Growth and swainsonine production of Swainsona galegifolia (Andr.) R. Br. untransformed and transformed root cultures

Untransformed and transformed root cultures of Swainsona galegifollawere established for swainsonine production. Transformed rootsgrew faster and produced higher swainsonine levels (62.3 µgg^–1 DW) than untransformed roots (23.6 ,µg g^–1DW) or roots of intact plants (8.7 µg g^–1 DW). Transformationof a number of plant genotypes using A. rhizogenes strain LBA9402 showed that plant genotype Influences swainsonine levelin transformed roots but that a wide range of swainsonine levelscan be induced by separate transformation events in the samegenotype. Enhancement of swainsonine production was attemptedby treatment with sugars and induction of polyploid roots. Key words: Agrobacterium rhizogenes, root cultures, Swainsona galegifolia, swainsonine     

Ion Imbalance in Capsicum annum scarbrous diminutive a Wilty Mutant of pepper: II.RUBIDIUM FLUX

Root tips of the wilty pepper mutant scarbrous diminutive accumulateless rubidium than those of the normal genotype. This phenomenonwas evident in root tips excised from plants maintained for2 d in CaSO₄ solution (low salt plants), especially in the lowerexternal concentration range (0.1– 1.0 mM) of RbCl. Theefflux rate of Rb⁺ from mutant root tips was twice as high asin normal root tips. These results indicate that the ability of the mutant rootsto absorb and accumulate Rb⁺ and K⁺ is impaired. This defectcould be a consequence of either an impaired Na⁺/K⁺ carriersystem, or increased leakiness of mutant membranes, or both. The fact that the normal roots can accumulate Rb⁺ much fasterthan mutant roots supports the first alternative, i.e. thatthe high affinity carrier system was impaired in the mutantroots. However, the higher efflux rate of Rb⁺ from the mutantroots suggests that membrane leakiness was also affected.     

Water Influx Characteristics and Hydraulic Conductivity for Roots of Agave deserti Engelm.

Various plant and environmental factors influence the hydraulicproperties for roots, which were examined using negative hydrostaticpressures applied to the proximal ends of individual excisedroots of a common succulent perennial from the Sonoran Desert,Agave deserti Engelm. The root hydraulic conductivity, L^p, increasedsubstantially with temperature, the approximately 4-fold increasefrom 0.5°C to 40°C representing a Q¹⁰ of 1.45. Suchvariations in L_p with temperature must be taken into accountwhen modelling water uptake, as soil temperatures in the rootzone of such a shallow-rooted species vary substantially bothdaily and seasonally. At 20°C, L_p was 2.3 x 10^–7 ms^{macron}1MPa^{macron}1for 3-week-old roots, decreasing to abouthalf this value at 10 weeks and then becoming approximatelyhalved again at 6 months. For a given root age, L_p for rainroots that are induced by watering as lateral branches on theestablished roots (which arise from the stem base) was aboutthe same as L_p for established roots. Hence, the conventionalbelief that rain roots have a higher L_p than do establishedroots is more a reflection of root age, as the rain roots tendto be shed following drought and thus on average are much youngerthan are established roots. Unlike previous measurements onroot respiration, lowering the gas-phase oxygen concentrationfrom 21% to 0% or raising the carbon dioxide concentration from0.1% to 2% had no detectable effect on L_p for rain roots andestablished roots. L_p for rain roots and established roots wasdecreased by an average of 11% and 35% by lowering the soilwater potential from wet conditions (_soil=0 kPa) to {macron}40kPa and {macron}80 kPa, respectively. Such decreases in L_p mayreflect reduced water contact between soil particles and theroot surface and should be taken into account when predictingwater uptake by A. deserti. Key words: Gas phase, rain roots, root age, soil, temperature, water potential     

Use of a Disarmed Ri Plasmid Vector in Analysis of Transformed Root Induction

Nicotiana glauca, N. tabacum, Solanian dulcamara and S. nigrumwere transformed by Agrobacteriun rhizogenes strain BN1010 (TL^–TR⁺).The TR-DNA stimulated agropine-positive root induction and wastransformation competent in the absence of the TL-DNA. An unusualpattern of root induction was seen when stem explants were inoculatedwith this strain; occasionally, agropine-positive roots wereinduced at the inoculation sites, but prolific agropine-negativeroots were formed in profusion down the stems. The utility ofBN1010 as an efficient co-integrating vector was demonstratedby the separate transfer of a fragment containing rol ABC (BN1010::pEM15) and of a chimeric nopaline synthase-kanamycin resistancegene (BN1010:: Neo) into plants. Root cultures of S. dulcamaratransformed with BN1010:: Neo had an unusual, positively geotropicphenotype. Strain BN1010:: pEM15 (rol ABC⁺D^–TR⁺) incitedmore roots down stem explants than strain A4T. This indicatesthat rol D may act to suppress agropine-negative root productionin N. glauca and N. tabacum. Key words: Agrobacterium rhizogenes, TL-DNA, TR-DNA, disarmed Ri vector, transformed roots, Nicotiana glauca, N. tabacun, Solatium dulcamara, S. nigrum     

Comparison of the Respiratory Metabolism of Plantago lanceolata L. and Plantago major L.

Bryce, J. H. and ap Rees, T. 1985. Comparison of the respiratorymetabolism of Plantago lanceolata L. and Plantago major L.—J.exp. Bot. 36 1559–1565. The aim of this work was to discover if the respiratory metabolismof the roots of Plantago lanceolata L. differed from that ofthe roots of Plantago major L. Measurements of oxygen uptakeand dry weight of excised root systems during growth of seedlingsprovided evidence that the two species differed in the amountof respiration needed to support a given increase in dry weight.Excised root systems were given a 6-h pulse in [U-¹⁴C]sucrosefollowed by a 16.5-h chase in sucrose. The detailed distributionof ¹⁴C amongst the major components of the roots at the endof the pulse and the chase revealed no significant differencebetween the two species. Patterns of ¹⁴CO₂ production from [1-¹⁴C],[2-¹⁴C], [3,4-¹⁴C], and [6-¹⁴C]glucose of excised root systemsfrom plants of three ages were similar for the two species.It is suggested that there is no conclusive evidence for anysignificant inherent difference in the respiratory metabolismof the roots of the two species. Key words: ¹⁴C sugar metabolism, respiration, roots, Plantago     

Phytochemical studies on tobacco alkaloids XIV. The occurrence and properties of putrescine N-methyltransferase in tobacco roots

Putrescine N-methyltransferase, a new enzyme catalyzing theformation of N-methylputrescine from putrescine and S-adenosyl-L-methioninewas found in roots of tobacco plants. The enzyme was purified30-fold from crude extracts of tobacco roots. NMethylputrescinewas identified as the reaction product by comparison with theauthentic compound. The enzyme had a pH optimum between pH 8and 9, and a molecular weight of about 60,000, as determinedby gel filtration. Km values for putrescine and 5-adenosyl-L-methioninewere 4.0 x 10^–4 M and 1.1 x 10^–4 M, respectively.Enzyme activity was inhibited by N-chloromercuribenzoate andAg⁺. No cofactors were required. Of the various substrates tested,only putrescine served as a methyl acceptor. The enzyme waslocalized exclusively in the roots and its activity was greadyenhanced by decapitation. The presence of putrescine N-methyltransferase in tobacco rootsstrongly suggests that N-methylputrescine participates as anintermediate in nicotine biosynthesis. (Received March 2, 1971; )     

Unusual Branching in the Seedlings of Lotus japonicus--Gibberellins Reveal the Nitrogen-sensitive Cell Divisions within the Pericycle on Roots

We studied the effects of several plant-growth regulators onthe induction of nodule-like structures on roots of Lotus japonicus,which has been proposed as a candidate for a leguminous plantfor molecular genetic analysis. Contrary to our expectations,the addition of gibberellin A₃ (GA₃) at concentrations of 10^-4M to 10^-4 M resulted in the formation of nodule-like structureson roots when seedlings were plated on nitrogen-free Fahraeusagar medium. GA₄ also induced such outgrowths but was less activethan GA₃. Application of an inhibitor of auxin transport, N-(1-naphthyl)-phthalamicacid (NPA) and of kinetin, which have been reported to inducepseudonodules in other legumes, had no effect on L. japonicus.Microscopic observations showed that GA₃-induced nodule-likestructures were caused by cell divisions within the pericycleon the roots. In addition, the outgrowths elicited by GA₃ couldbe completely suppressed by the addition of 15 mM potassiumnitrate or ammonium nitrate. These results show that the pericyclecells of the roots of L. japonicus are specifically sensitiveto gibberellins and that potential for cell division might bemodulated by nitrogen compounds. We also examined the effectsof ancymidol and uniconazole [S-3307; (E)-1-(4-chIorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-penten-3-ol],two synthetic plant-growth retardants. Both compounds at 3 x10^-5 M significantly increased the number of stunted lateralroots. The unusual branching could not be counteracted by theexogenous addition of GA₃ but by 10^-6 M brassinolide. We discussthe physiological role of brassinolide in the initiation oflateral roots. (Received August 4, 1995; Accepted March 11, 1996)     

Uptake and Distribution of Copper in Chrysanthemum morifolium

The effects of various levels of copper on the uptake and distributionof copper in Chrysanthemum morifolium grown in solution cultureand peat-sand have been examined. Whole plants growing in shortdays were sampled at regular intervals, divided into roots,stem, leaves and lateral shoots, and analysed for copper. Thepartitioning of copper between these tissues showed that a relativelylarge proportion (30–40 per cent) of the total plant copperwas accumulated in the roots of normal plants during the harvestingperiod, compared with approximately 10 per cent in the rootsof copper deficient plants. Whilst the copper content (ug g^–1) of leaves and stemfrom normal plants was negatively correlated with the amountof dry matter produced (P < 0·001), the correspondingcopper deficient tissues showed little variation in copper contentwith increases in tissue dry weight. A more detailed investigationof the copper content of leaves from normal plants showed thatgradients existed within the plant with respect to both leafposition and time of harvest which could be described by a singlecubic surface equation (P < 0·001).     

Na+/H+ Antiporter in Tonoplast Vesicles from Rice Roots

The Na⁺/H ⁺ antiporter in vacuolar membranes transports Na⁺from the cytoplasm to vacuoles using a pH gradient generatedby proton pumps; it is considered to be related to salinitytolerance. Rice (Oryza sativa L.) is a salt-sensitive crop whosevacuolar antiporter is unknown. The vacuolar pH of rice roots,determined by ³¹P-nuclear magnetic resonance (NMR), increasedfrom 5.34 to 5.58 in response to 0.1 M NaCl treatment. Transportof protons into the tonoplast vesicles from rice roots was fluorometricallymeasured. Efflux of protons was accelerated by the additionof Na⁺. Furthermore, the influx of ²²Na⁺ into the tonoplastvesicles was accelerated by a pH gradient generated by proton-translocatingadenosine 5'-triphosphatase (H⁺-ATPase) and proton-translocatinginorganic pyro-phosphatase (H⁺-PPase). We concluded that thisNa⁺/H⁺antiporter functioned as a Na⁺ transporter in the vacuolarmembranes. The antiporter had a K_m of 10 mM for Na⁺ and wascompetitively inhibited by amiloride and its analogues. TheKⁱ values for 5-(N-methyl-N-isobutyl)-amiloride (MIA), 5-(N-ethyl-N-isopropyI)-amiloride(EIPA), and 5-(N, N-hexamethylene)-amiloride (HMA) were 2.2,5.9, and 2.9 µ M, respectively. Unlike barley, a salt-tolerantcrop, NaCl treatment did not activate the antiporter in riceroots. The amount of antiporter in the vacuolar membranes maybe one of the most important factors determining salt tolerance. ¹This work was supported by a grant from Bio-Media Project ofthe Japanese Ministry of Agriculture, Forestry and Fisheries(BMP96-III-1).     

Hydraulic and osmotic properties of spruce roots

Hydraulic and osmotic properties of roots of 2-year-old Norwayspruce seedlings (Plcea abiea (L.) Karst) were investigatedusing different techniques (steady flow, pressure probe, andstop flow technique). Root pressures were measured using theroot pressure probe. Compared to roots of herbaceous plantsor deciduous trees, excised root systems of spruce did not developappreciable root pressure (-0.001 to 0.004 MPa or -10 to 40cm of water column). When hydrostatic pressure gradients wereused to drive water flows across the roots, hydraulic conductivities(Lp_r) were determined in two types of experiments: (i) rootpressure relaxations (using the root pressure probe) and (ii)steady flow experiments (pneumatic pressures applied to theroot system or xylem or partial vacuum applied to the xylem).Root Lp_r ranged between 0.2 and 810^–8m s^–1 MPa^–1(on average) depending on the conditions. In steady flow experiments,Lpr depended on the pressure applied (or on the flow acrossthe roots) and equalled (0.190.12) to (1.21.7)10^–8m s^–1 MPa^–1 at pressures between 0.2 and 0.4 MPaand (1.51.3)10^–8 m s^–1 MPa^–1 at appliedpressures between 0.8 and 1.0 MPa. When pressures or vacuumwere applied to the xylem, Lp_r values were similar. The hydraulicconductivity measured during pressure relaxations (transientwater flows) was similar to that obtained at high pressures(and water flows). Although there was a considerable scatterin the data, there was a tendency of the hydraulic conductivityof the roots to decrease with increasing size of the root system.When osmotic gradients were used to drive water flows, Lp_r valuesobtained with the root pressure probe were much smaller thanthose measured in the presence of hydrostatic gradients. Onaverage, a root Lp_r=0.01710^–8 was found for osmotic andLp_r=6.410^–8 m s^–1 MPa^–1 in correspondinghydrostatic experiments, i.e. the two values differed by a factorwhich was as large as 380. The same hydraulic conductivity asthat obtained in osmotic experiments using the pressure probewas obtained by the 'stop flow techniquel. In this technique,the suction created by an osmoticum applied to the root wasbalanced by a vacuum applied to the xylem. Lp_r values of rootsystems did not change significantly when measured for up to5 d. In osmotic experiments with different solutes (Na₂S0₄,K₂S0₄, Ca(NO₃)₂, mannitol), no passive uptake of solutes couldbe detected, i.e. the solute permeability was very low whichwas different from earlier findings on roots of herbs. Reflectioncoefficients of spruce roots (O were low for solutes for whichplant cell membranes exhibit values of virtually unity (     

不同生态型东南景天对土壤中Cd的生长反应及吸收积累的差异性

 采用盆栽方法研究了两种生态型东南景天(Sedum alfredii)对土壤中不同含量Cd(即对照, 12.5, 25, 50, 100, 200, 300, 400 mg&;#8226;kg^－1)的生 长反应、吸收和积累Cd的差异性。结果表明,土壤添加重金属Cd后,矿山生态型东南景天生长正常,地上部和根系Cd含量随着土壤中Cd含量的 增加而增加,在400 mg&;#8226;kg^－1 Cd处理下含量分别高达2 900和500 mg&;#8226;kg^－1,其地上部显著大于根部;然而,土壤添加Cd后,非矿山生态型东 南景天的生长受到抑制,地上部和根部的生物量显著降低。当土壤Cd含量为50～100 mg&;#8226;kg^－1 时,非矿山生态型东南景天的地上部和根系Cd含 量随着土壤中Cd含量的增加而增加,而且根系Cd含量则大于地上部。当土壤Cd≤50 mg&;#8226;kg^－1时,矿山生态型东南景天根系Cd含量比非矿山生态 型高 ,但当土壤Cd≥100 mg&;#8226;kg^－1,两者之间无显著差异;然而,但在同一Cd处理水平下,矿山生态型东南景天地上部Cd含量总是高于非矿山 生态型。这些结果表明,矿山生态型东南景天有很强的忍耐和吸收土壤Cd的能力,再次证明其为一种Cd超积累植物。     

Callus, Organogenesis and Plantlet Formation in Tissue Cultures of Clitoria ternatea

Decoated seeds of Clitoria ternatea L. germinated on Murashigeand Skoog (Physiologia Plantarum 1962, 15, 473–97) basalmedium (BM) and differentiated callus and bipolar embryoids(two-step method) in low frequency. Calluses developed on lateralroots [BM+KN(0.1 mg 1^–1)], on roots and hypocotyls [BM+KN(0.5mg 1^–1)], and on roots [BM+KN+IAA (0.5 mg 1^–1 ofeach)]. On basal medium with KN (0.5 mg 1^–1) and withKN+IAA (0.5 mg1^–1 of each), multiple shoot buds and embryoids(one-step method) were differentiated directly on split hypocotylsand roots. In the former, shoot buds developed even on unsplithypocotyls. Rhizogenesis on isolated shoot buds occurred efficientlyin BM+indole butyric acid (IBA 0.1 mg 1^–1) and BM+IAA(0.1 mg 1^–1 and 0.5 mg 1^–1). Profuse direct embryoidsand shoot buds developing on root systems are interesting morphogeneticphenomena rarely reported. Clitoria ternatea L., callus, embryoids, multiple shoot buds, regeneration     

Ionic Relations of Garden Orache, A triplex hortensis L.: Growth and Ion Distribution at Moderate Salinity and the Function of Bladder Hairs

The growth of garden orache, A triplex hortensis was studiedunder conditions of mild NaCl or Na₂SO₄ salinity. Growth, drymatter production and leaf size were substantially stimulatedat 10 mM and 50 mM Na⁺ salts. Increased growth, however, appearedto be due to a K⁺-sparing effect of Na⁺ rather than to salinityper se. The distribution of K⁺ and Na⁺ in the plant revealeda remarkable preference for K+ in the roots and the hypocotyl.In the shoot the K/Na ratio decreased strongly with leaf age.However, the inverse changes in K⁺ and Na⁺ content with leafage were dependent on the presence of bladder hairs, which removedalmost all of the Na⁺ from the young leaf lamina. Measurementsof net fluxes of K⁺ and Na⁺ into roots and shoots of growingAtriplex plants showed a higher K/Na selectivity of the netion flux to the root compared to the shoot. With increasingsalinity the selectivity ratio S_{K, Na}^* of net ion fluxes tothe roots and to the shoots was increased. The data suggestthat recirculation of K⁺ from leaves to roots is an importantlink in establishing the K/Na selectivity in A. hortensis plants.The importance of K⁺ recirculation and phloem transport forsalt tolerance is discussed. Key words: Atriplex hortensis, Salinity, Potassium, Sodium, K⁺ retranslocation, Bladder hairs, Growth stimulation     

Endogenous Hormones in Seeds, Germination Behaviour and Early Seedling Characteristics in a Normal and ogura Cytoplasmic Male Sterile Line of Rapeseed (Brassica napus L.)

Endogenous hormones, namely cytokinins (CKs), indole-3-aceticacid (IAA) and abscisic acid (ABA) were quantified by specificenzyme-linked immunosorbent assay (ELISA) in the mature seedof normal (cv. Westar) and ogura (ogu) cytoplasmic male sterile(CMS) lines of rapeseed (Brassica napus L.). Dihydrozeatin (DZ)and dihydrozeatin riboside (DZR) were the major CK base andriboside, respectively, in seeds of both the normal and oguCMS lines. The normal seed had more than 4-fold DZ levels incomparison to that of ogu CMS. On the other hand, the ogu CMSseed had higher levels of CK o-glucosides and CK. nucleotidesthan normal seed. Seeds of the normal line contained 5-foldmore IAA but had one-quarter the level of ABA in comparisonto those of the ogu CMS line. The normal line also had greaterseed diameter and weight than the ogu CMS line and the normalseed germinated earlier than the male sterile seed. DZ (10^–6M) promoted the germination of ogu CMS seeds, but it was notcomparable to that of the normal line. ABA (10^–6 M) inhibitedseed germination of ogu CMS but had little effect on the normalline. The normal seedlings had shorter primary roots, more lateralroots, longer hypocotyls, greater cotyledon fresh weight andhigher chlorophyll levels in comparison to ogu CMS seedlings.Exogenously supplied DZ, IAA and ABA affected the various parametersof both the normal and ogu CMS seedlings, but in most casesdid not fully restore the differences in the two lines. The results presented show that in the ogura cytoplasmic malesterile line of B. napus (1) a number of seed and seedling characteristicsare affected, and (2) the altered seed morphology is accompaniedby changes in the levels of various hormones. Key words: Brassica napus, cytoplasmic male sterility, enzyme-linked immunosorbent assay, hormone, seed germination     

Nitrate and Ammonium Assimilation by Roots of Maize (Zea mays L.) Seedlings as Investigated by In Vivo 15N-NMR

¹⁵N-Nuclear Magnetic Resonance (NMR) was used to study nitrogenassimilation in apices of maize roots in vivo, perfused eitherwith ¹⁵NO     

Vacuolar Na/K Exchange, its Occurrence in Root Cells of Hordeum, Atriplex and Zea and its Significance for K/Na Discrimination in Roots

Using excised low-salt roots of barley and Atriplex hortenslsthe transport of endogenous potassium through the xylem vesselswas studied It was enhanced by nitrate and additionally by sodiumions which apparently replaced vacuolar potassium which wasthen available in the symplasm of root cells for transport tothe shoot Vacuolar Na/K exchange also has been investigatedby measurements of longitudinal ion profiles in single rootsof both species. In Atriplex roots a change in the externalsolution from K⁺ to Na⁺ induced an exchange of vacuolar K⁺ forNa⁺, in particular in the subapical root tissues and led toincreased K⁺ transport and loss of K⁺ from the cortex. In inverseexperiments a change from Na⁺ to K⁺ did not induce an exchangeof vacuolar Na⁺; merely in meristematic tissues Na⁺—apparentlyfrom the cytoplasm—was extruded in exchange for K⁺. Inroots of barley seedlings without caryopsis, as in excised roots,a massive exchange of K⁺ for Na⁺ was observed in the continuouspresence of external 1.0 mM Na and 0.2 mM K. This exchange alsowas attributed to the vacuole and was most pronounced in theyoung subapical tissues. It did not occur, however, in the correspondingtissues in roots of fully intact barley seedlings. In these,the young tissues retained a relatively high K/Na ratio alsoin their vacuoles. Similarly, contrasting results were obtainedwith intact and excised roots of Zea mays L. Based on theseresults a scheme of the events that lead to selective cationuptake in intact barley roots is proposed. In this scheme acrucial factor of selectivity is sufficient phloem recirculationof K⁺ by the aid of which K⁺ rich cortical cells are formednear the root tip. When matured these cells are suggested tomaintain a high cytoplasmic K/Na ratio due to K⁺ dependent sodiumextrusion at the plasmalemma and due to recovery of vacuolarK⁺ by Na/K exchange across the tonoplast. Key words: Potassium/Sodium selectivity, Vacuolar exchange, Xylem transport, Hordeum, Zea, Atriplex     

Non-specificity of Salt Effects on Mg2+dependent ATPase from Grass Roots

The effect of tris, choline, and ethanolamine chlorides on theactivity of Mg^2–dependent ATPase in membrane fractions(cell walls, mitochondria, and microsomes) of Zea mays L. (cv.Neve Yaar 22), Avena saliva L. (cv. Mulga), and Hordeum vulgareL. (cv. Omer) was compared with the effect of KC1 and NaCl.Considerable salt effects on apparent Mg²⁺ATPase activity werefound only at relatively high pH values (8.2) at which Mg²⁺.ATPaseactivity was low in the absence of monovalent cation salts.The Mg²⁺-dependent ATP hydrolysis by ATPases from all the membranefractions increased in the presence of at least one of the organiccations to the same extent as in the presence of KCI or NaCl.The monovalent organic cations are only very slowly absorbedby corn roots in comparison with K⁺ and Na⁺. It is concluded that monovalent salt effects on ATPase fromthese plant roots are not cation specific and not related tothe capability of root cells to absorb cations. Present evidencefor the existence of a cation-transport ATPase in plant tissueis critically reviewed.     

Effects of External KCl on Electrical Properties and K$(86Rb) Transport in the Elongating Region of Intact Phaseolus mungo Roots

Two simultaneous measurements, extracellular potential V andK^$(⁸⁶Rb) transport, and the intracellular potential of corticalcell E and potential V, were used to study the effects of externalKCl on two-day-old bean roots. High, external KCl concentrations(>10 mM) markedly enhanced K^$ loss from tissues in the elongatingregion to the external solution and induced depolarization ofthe membrane potential difference (PD=V–E). When Phaseolus roots were returned to a solution with a lowerconcentration of K^$, the K^$ loss and the potential difference,PD, were restored to their previous values. K^$ transport fromother parts of the root to the elongating region, however, didnot recover, and the potential, E, increased. These resultsclearly demonstrate that treatment of Phaseolus roots with ahigh external K^$ concentration inhibits K^$ translocation throughthe stele to the elongating cortical cells and is dependenton depolarization of the intracellular potential. (Received October 14, 1983; Accepted January 20, 1984)