In vivo and in vitro effects of cadmium on H+ ATPase activity of plasma membrane vesicles from oat (Avena sativa L.) roots

The effect of an in vivo and in vitro treatment with cadmium on transport activities of root plasma membrane enriched vesicles was studied in oat (Avena sativa L. cv. Argentina) plants. Addition of 100 mumol/L CdSO4 to nutrient solution decreases both proton transport activity and ATPase activity to the same level. In vitro experiments show that cadmium seems to have a differential inhibiting effect on proton transport activity and ATPase activity, the most pronounced one on ATP-dependent H(+)-accumulation, suggesting that cadmium would interfere with membrane permeability properties. This is indeed the case. The results demonstrate that cadmium decreases passive permeability to protons.     

Association of nickel versus transport of cadmium and calcium in tonoplast vesicles of oat roots

The plant vacuole has long been suspected of being a site for accumulation of Ni in plant roots, but testing this hypothesis directly by vacuole isolation is technically difficult and has not been reported. Here, we have attempted to determine if Ni can be transported into isolated oat (Avena sativa L.) root tonoplast vesicles as an alternative approach toward understanding the importance of the vacuole in Ni accumulation in roots. We found that, in contrast to Ca and Cd, Ni did not affect the proton gradient of vesicles (MgATP energized or artificially created), and further, that Cd/H antiport activity was not affected by the presence of Ni. Nickel was associated with vesicles, but relative rates of accumulation/association of metals with vesicles were Ca > Cd Ni. Protonophores and the potential Ni ligands citrate and histidine, and nucleoside triphosphates or PPi did not stimulate Ni association with vesicles. Comparison of Ni versus Ca and Cd associated with vesicles using various membrane perturbants indicated that while Ca and Cd are rapidly and principally antiported to the vesicle sap, Ni is only slowly associated with the membrane in a not-easily dissociated condition. Our results indicate the absence of an Ni/H antiport or Ni-nucleotide-dependent pump in oat root tonoplasts, and support the contention that the vacuole is not a major compartment for Ni accumulation in oat roots. Received: 2 June 1997 / Accepted: 17 July 1997     

Regeneration of fertile green plants from oat isolated microspore culture

Regeneration of fertile green plants from isolated oat microspores is reported for the first time. Factors critical for microspore growth and regeneration include cold pre-treatment, pH of culture medium and the use of conditioned culture medium. It was found that cold pre-treatment at 4°C in the dark for a minimum of 6 weeks was necessary to consistently achieve microspore growth into multicellular structures (MCS). Longer pre-treatments of up to 9 weeks were tested and found to be positively correlated with the number of MCS produced. Microspore culture medium with pH 8.0 produced significantly more MCS larger than eight cells in size than media with pH 5.8. The use of medium conditioned by actively growing barley microspores significantly increased the numbers of MCS larger than eight cells in size compared to non-conditioned media. Plants were regenerated only from cultures using conditioned medium. A total of 2 green plants and 15 albinos were regenerated. Of the green plants, one had the haploid chromosome complement (n = 3x = 21) and the other had the parental hexaploid chromosome complement (2n = 6x = 42) which may be due to spontaneous chromosome doubling. The hexaploid plant set seed naturally and the haploid plant set seed after its chromosome complement was doubled with colchicine.     

Sucrose transport in tonoplast vesicles of red beet roots is linked to ATP hydrolysis

Sucrose uptake into tonoplast vesicles, which were prepared from red beet (Beta vulgaris L.) vacuoles isolated by two different methods, was stimulated by MgATP. Using the same medium as for osmotic disruption of vacuoles, membrane vesicles were prepared from tissue homogenates of dormant red beet roots and separated by high-speed centrifugation through a discontinuous dextran gradient. A low-density microsomal fraction highly enriched in tonoplast vesicles could be further purified from contaminating ER vesicles by inclusion of 5 mM MgCl₂ in the homogenization medium. These vesicles were able to transport sucrose in an ATP-dependent manner against a concentration gradient, whereas vesicles from regions of other densities lacked this feature, indicating that ATP stimulation of sucrose uptake took place only at the tonoplast membrane. Sucrose uptake was optimal at pH 7 in the presence of MgATP and could be stimulated by superimposed pH gradients (vesicle interior acidic) in the absence of MgATP, which is consistent with the operation of a sucrose/H⁺-antiporter at the tonoplast. Tonoplast vesicles, obtained in high yield from tissue homogenates of red beet roots, exhibited sugar-uptake characteristics comparable to those of intact vacuoles; these characteristics included similarities in K _m (1.7 mM), sensitivity to inhibitors and specificity for sucrose.Many experiments were carried out at the Experiment Station of the HSPA, Aiea, Hawaii and financed by an NSF grant to Dr. Maretzki and Mrs. M. Thom.     

Characterization of developing oat seed mRNA: evidence for many globulin mRNAs

Polyadenylated mRNA from developing oat (Avena sativa L.) seeds was isolated and analyzed. Prominent mRNA species of 18S, 15S and 12S were observed; the 18S mRNA was judged to be esentially free of ribosomal RNA by hybridization analysis. Size fractionation andin vitro translation of this mRNA was performed. SDS, IEF-SDS gel electrophoresis and immunoprecipitation were used to analyze the translation products. It is shown that globulin mRNA (18S) accounts for roughly 30% of the total mRNA in developing seeds, the 12S and 15S mRNAs accounting for the remainder. The 18S mRNA directs the synthesis of a series of distinct but related polypeptides, suggesting that some of the heterogeneity seen in the oat globulins is at the amino acid sequence level.     

The function of tonoplast ATPase in intact vacuoles of red beet is governed by direct and indirect ion effects

The pH gradient and the electric potential across the tonoplast in mechanically isolated beetroot vacuoles has been studied by following the uptake of [¹⁴C]methylamine and [¹⁴C]triphenyl-methylphosphoniumchloride. In response to Mg-ATP, the vacuolar interior is acidified by 0.8 units. This strong acidification is accompanied by a slight hyperpolarization of the membrane potential, which is probably caused by a proton diffusion potential. In preparations where only a small acidification (0.4 units) occurred, the membrane potential was depolarized by the addition of Mg-ATP. Different monovalent cations and anions were tested concerning their effect on the pH gradient and ATPase activity in proton-conducting tonoplasts. Chloride stimulation and NO ₃ ^- inhibition were clearly present. The observed decline of the pH gradient upon the addition of Na⁺ salts is probably caused by an Na⁺/H⁺ antiport system.Abbreviations and symbol CCCP carbonylcyanide-m-chlorophenylhydrazone - Mes 2(N-morpholino)ethanesulfonic acid - TPMP⁺ triphenylmethylphosphoniumchloride - Tris 2-amino-2-(hydroxymethyl)-1,3-propanediol - membrane potential Dedicated to Professor A. Betz on the occasion of his 65th birthday     

Evidence for translational control of storage protein biosynthesis during embryogenesis ofAvena sativa L. (oat endosperm)

Oat polysomes direct the synthesisin vitro of a large number of products, the majority of which are the salt-soluble globulins (1,3,10,11,21). Total RNA or poly A⁺ RNA isolated from these polysomes directs the synthesis of the same number and types of products; however, the amount of globulins synthesized no longer represents the major products; rather, there is a decreased level of globulins and an increased amount of the other products synthesizedin vitro (6, 18). These results imply that the translational control can dictate final product levels. Reconstruction experiments using oat poly A⁺ mRNA and polysomal factors that are made free of endogenous RNA by nuclease digestion demonstrate that these factors do influence the translational specificity of oat globulin mRNA relative to other mRNAs. It is suggested that translational control is partially responsible for the levels of globulin in the mature grain.     

Na+/H+ antiport activity in tonoplast vesicles isolated from sunflower roots induced by NaCl stress

Na⁺ transport across the tonoplast and its accumulation in the vacuoles is of crucial importance for plant adaptation to salinity. Mild and severe salt stress increased both ATP- and PP_i-dependent H⁺ transport in tonoplast vesicles from sunflower seedling roots, suggesting the possibility that a Na⁺/H⁺ antiport system could be operating in such vesicles under salt conditions (E. Ballesteros et al. 1996. Physiol. Plant. 97: 259–268). During a mild salt stress, Na⁺ was mainly accumulated in the roots. Under a more severe salt treatment, Na⁺ was equally distributed in shoots and roots. In contrast to what was observed with Na⁺, all the salt treatments reduced the shoot K⁺ content. Dissipation by Na⁺ of the H⁺ gradient generated by the tonoplast H⁺-ATPase, monitored as fluorescence quenching of acridine orange, was used to measure Na⁺/H⁺ exchange across tonoplast-enriched vesicles isolated by sucrose gradient centrifugation from sunflower (Helianthus annuus L.) roots treated for 3 days with different NaCl regimes. Salt treatments induced a Na⁺/H⁺ exchange activity, which displayed saturation kinetics for Na⁺ added to the assay medium. This activity was partially inhibited by 125 μM amiloride, a competitive inhibitor of Na⁺/H⁺ antiports. No Na⁺/H⁺ exchange was detected in vesicles from control roots. The activity was specific for Na⁺. since K⁺ added to the assay medium slightly dissipated H⁺ gradients and displayed non-saturating kinetics for all salt treatments. Apparent K_m for Na⁺/H⁺ exchange in tonoplast vesicles from 150 mM NaCl-treated roots was lower than that of 75 mM NaCl-treated roots, V_max remaining unchanged. The results suggest that the existence of a specific Na⁺/H⁺ exchange activity in tonoplast-enriched vesicle fractions, induced by salt stress, could represent an adaptative response in sunflower plants, moderately tolerant to salinity.     

Characteristics of MgATP2--dependent electrogenic proton transport in tonoplast vesicles of the facultative crassulacean-acid-metabolism plant Mesembryanthemum crystallinum L.

Membrane vesicles were isolated from mesophyll cells of Mesembryanthemum crystallinum in the C₃ state and in the crassulacean acid metabolism (CAM) state. The distribution of ATP-hydrolysis and H⁺-transport activities, and the activities of hydroxypyruvate reductase and Antimycin-insensitive cytochrome-c-reductase on continuous sucrose gradients was studied. For isolations carried out routinely a discontinuous sucrose gradient (24%/37%/50%) was used. Nitrate-sensitive ATP-hydrolysis and H⁺-transport activities increased several-fold during the transition from C₃ photosynthesis to CAM. Nitrate-sensitive ATPase showed a substrate preference for ATP with an apparent K_m (MgATP^2-) of 0.19–0.37 mM. In both C₃ and CAM states the ATPase showed a concentration-dependent stimulation by the anions chloride and malate. However, the pH optima of the two states were different: the ATPase of C_3- M. crystallinum had an optimum of pH 7.4 and that of CAM-M. crystallinum an optimum of pH 8.4. The optical probe oxonol-VI was used to demonstrate the formation of MgATP^2--dependent electric-potential gradients in tonoplast vesicles.Abbreviations Bistris-Pronane 1,3-bis [tris(hydroxymethyl)-methylaminol propane - CAM Crassulacean acid metabolism - DIDS 4,4-dilsothiocyano-2,2-stilbene disulfonic acid: - DTT dithiothreitol - ER endoplasmic reticulum - Hepes 4-(2-hydroxyethyl)-1-piperazineethane sulfonic acid - HPR hydroxypyruvate reductase - IDPase inosine 5-diphosphatase - OX-VI oxonol VI - Tris 2-amino-2-(hydroxymethyl)-1,3-propanediol     

Some characteristics of anion transport at the tonoplast of oat roots,determined from the effects of anions on pyrophosphatedependent proton transport

The effects of anions on inorganicpyrophosphate-dependent H⁺-transport in isolated tonoplast vesicles from oat (Avena sativa L.) roots were determined. Both fluorescent and radioactive probes were used to measure formation of pH gradients and membrane potential in the vesicles. Pyrophosphate hydrolysis by the H⁺-translocating pyrophosphatase was unaffected by anions. Nonetheless, some anions (Cl^-, Br^- and NO₃-) stimulated H⁺-transport while others (malate, and iminodiacetate) did not. These differential effects were abolished when the membrane potential was clamped at zero mV using potassium and valinomycin. Stimulation of H⁺-transport by Cl^- showed saturation kinetics whereas that by NO₃- consisted of both a saturable component and a linear phase. For Cl^- and NO₃-, the saturable phase had a K _m of about 2 mol·m^-3. The anions that stimulated H⁺-transport also dissipated the membrane potential (.) generated by the pyrophosphatase. It is suggested that the stimulatory anions cross the tonoplast in response to the positive generated by the pyrophosphatase, causing dissipation of and stimulation of pH, as expected by the chemiosmotic hypothesis. The work is discussed in relation to recent studies of the effects of anions on ATP-dependent H⁺-transport at the tonoplast, and its relevance to anion accumulation in the vacuole in vivo is considered.Abbreviations and symools BTP 1,3-bis[tris(hydroxymethyl)-methylamino]-propane - EGTA ethylene glycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid - Hepes 4-(2-hydroxyethyl)-1-piperazine ethanesulphonic acid - IDA iminodiacetate - membrane potential - pH pH gradient - PPase inorganic pyrophosphatase - PPi morganic pyrophosphate     

Mapping of beta-tubulin genomic sequences in hexaploid oat (Arena sativa L.)

Summary The allohexaploid nature of Avena sativa L. (2n=6x=42) and the availability of aneuploid lines was exploited in designing a strategy for mapping beta-tubulin sequences in the oat genome. Evidence for a minimum of eight beta-tubulin genes was obtained by Southern-blot analysis. Three betatubulin sequences were localized to chromosomes using DNA from monosomic and nullisomic lines in the variety Sun II. One sequence was localized to the chromosome missing in nullisome I. Two other sequences were mapped to satellite chromosome 2, the chromosome that is missing in nullisome VIII and to which one ribosomal RNA gene cluster had previously been mapped. Restriction fragments carrying these two beta-tubulin genomic sequences and the cluster of ribosomal RNA sequences were missing in DNA from nullisomics VIII, IX and X, suggesting that all three nullisome classes are deficient for an identical chromosomal segment that includes these three loci. This study demonstrates how molecular analyses can be used to characterize aneuploid stocks and to better define their genetic constitution.Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture or the University of Minnesota and does not imply its approval to the exclusion of other products or vendors that may be suitable     

The use of a chloride-sensitive fluorescent probe to measure chloride transport in isolated tonoplast vesicles

A fluorescence method for the direct measurement of Cl^- transport in isolated tonoplast vesicles is described. This technique utilises the Cl^--sensitive fluorescent compound, 6-methoxy-1-(3-sulfonatopropyl)quinolinium (SPQ). This is a water-soluble compound with excitation and emission wavelengths of 350 and 440 nm, respectively. Its fluorescence is quenched by Cl^-, Br^-, I^-, SCN^-, NO ₂ ^- and tetraphenylborate but not by NO ₃ ^- , SO ₄ ^2- , iminodiacetate or malate. These effects are independent of pH. This compound was loaded into tonoplast vesicles from red beet (Beta vulgaris L.) storage roots or from barley (Hordeum vulgare L.) roots by incubation at 37° C and the external probe was then removed by repeated centrifugation of the vesicles in SPQ-free medium. In this way a large proportion of the observed fluorescence signal was from the interior of the vesicles, and its quenching could be used to monitor, quantitatively, and in real time, the intravesicular Cl^- concentration. In this paper we describe some of the problems encountered in using this probe to measure Cl^- transport in tonoplast vesicles, how these were overcome and some characteristics of Cl^- transport at the tonoplast as measured by the probe.Abbreviations and symbols BTP 1,3-bis[tris(hydroxymethyl)-methylamino-propane - DTT dithiothreitol - membrane potential - pH pH gradient - PPase inorganic pyrophosphatase - PPi inorganic pyrophosphate - SPQ 6-methoxy-1-(3-sulfonatopropyl)quinolinium - Tricine N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]glycine     

Purification and characterization of a 60-kDa protein from oat, formerly known as a TCP1-related chaperone

Recently, Mummertet al. [Nature 363, 644–648 (1993)] isolated a proposed TCP1-related chaperone. Here we report several findings concerning the protein which they sequenced. Two similar N-terminal sequences were obtained from this abundant 60-kDa protein. Internal sequences were also acquired by protease digestion. Initially it was believed the protein was able to completely inhibit citrate synthase aggregation, but later purifications demonstrated that the 60-kDa polypeptide lacked both chaperone activity and the previously reported kinase activity [Grimmet al., Planta 178, 199–206 (1989)]. It is now our belief that this protein is neither a chaperone nor a kinase.     

Effects of light and regulators on senescence-related changes in soluble proteins in detached oat (Avena sativa L.) leaves

The rate of senescence and the two-dimensional pattern of soluble proteins from detached oat leaves senescing in either darkness or light were analyzed, and compared to those of leaves in which senescence was delayed by application of the cytokinin benzyladenine or enhanced through the action of abscisic acid.Senescence of detached leaves in light did not differ significantly from senescence in attached leaves on intact plants. In darkness, protein was lost at a higher rate than in light, but several individual proteins showed relative increases. Notably, proteins previously characterized as high-molecular-weight proteins and senescence-associated proteins (Klerk et al., 1992) increased. Changes observed during incubation in light or darkness appeared to be related to this condition rather than the rate or progress of senescence. Cytokinins delayed and abscisic acid accelerated the changes in protein pattern compared to water. Beside changes previously identified in leaves senescing on the plant, detached leaves show alterations that reflect their condition of incubation rather than their developmental progress.Abbreviations 2D-PAG two-dimensional polyacrylamide gel electrophoresis - ABA abscisic acid - BA N⁶-benzyladenine - BSA bovine serum albumin - EDTA ethylenediamine tetraacetic acid - IEF isoelectric focusing - Rubisco ribulosebisphosphate carboxylase/oxygenase - SDS sodium dodecyl sulfate - Tris tris (hydroxymethyl) aminomethane     

Membrane-potential changes in vacuoles isolated from storage roots of red beet (Beta vulgaris L.)

The membrane potential in vacuoles isolated from storage roots of red beet (Beta vulgaris L.) has been studied by following changes in the fluorescence of the dye 3,3-diethylthiodicarbocyanine iodide, and by determining the uptake of the lipophilic triphenylmethylphosphonium cation. The vacuoles have a membrane potential, internal negative, which is estimated to be around-60 mV. These potentials become less negative by nearly 10 mV on addition of ATP. This ATP-dependent depolarisation is inhibited by the protonophore carbonylcyanide p-trifluoromethoxyphenylhydrazone and by the ATPase inhibitors, N,N-dicyclohexylcarbodiimide and trimethyltin chloride, but it is largely insensitive to sodium orthovanadate. Fusicoccin had no significant effect on the isolated vacuoles, but its addition to excised tissue caused a hyperpolarisation of the cells measured using a microelectrode.Abbreviations DCCD N,N-dicyclohexylcarbodiimide - DiS-C₂-(5) 3,3-diethylthiodicarbocyanine iodide - FCCP carbonylcyanide p-trifluoromethoxyphenylhydrazone - TPMP⁺ triphenylmethylphosphonium ion     

Localization of repetitive DNA in cereals byin situ hybridization: Cross hybridization among wheat,rye, barley,and oat

³H-RNA, complementary to repetitive DNA of wheat, rye, barley, and oat, was hybridizedin situ to root tip or pollen mother cells of the species mentioned. The cRNAs hybridized best with the DNA in cell nuclei of the species from which they were prepared. Cross hybridization with cells of the other related species resulted in a significant but diminished labelling. Wheat, rye, and barley hybridized better to each other than to oat, andvice versa, in agreement with the usual taxonomical classification. Over the interphase nuclei the label was distributed unevenly; not all regions of dense chromatin were labelled, and little label was found over the nucleoli. On chromosomes, the repetitive DNA was located somewhere along the chromosome arms or near the centromers in wheat, barley, and oat. Only in rye, most of the label was located near the telomers, probably over the large heterochromatin areas.     

Electrostatic surface properties of plasmalemma vesicles from oat and wheat roots. Ion binding and screening investigated by 9-aminoacridine fluorescence

Right-side-out and sealed plasmalemma vesicles were isolated from roots of spring wheat (Triticum aestivum L. cv. Drabant) and oat (Avena sativa L. cv. Brighton) by two-phase partition in a medium containing sucrose (0.25 mol l^-1). Oat root plasmalemma vesicles were discovered to contain a strongly fluorescent compound with an emission maximum at 418 nm. The surface potential of the membranes was monitored by 9-aminoacridine fluorescence and the effect of protein concentration, mannitol versus sucrose, absence of osmoticum, concentrations of salt, and titrations with chelators investigated. It is concluded that i) protein concentrations of less than 50 g ml^-1 for oat and 100 g ml^-1 for wheat plasmalemma vesicles should be used to avoid serious problems with non-linearity of response of 9-aminoacridine fluorescence, ii) mannitol can be used instead of sucrose as the osmoticum, iii) the vesicles were ruptured in the absence of osmoticum allowing us to monitor both sides of the membranes, iv) plasmalemma vesicles from oat roots are more negative than vesicles from wheat roots, and v) oat and wheat root plasmalemma vesicles are isolated with about the same amounts of bound Ca²⁺ and Mg²⁺. These bound divalent cations may not, however, reflect the in-vivo conditions since the tissues were homogenised in the presence of ethylenediaminetetraacetic acid.Abbreviations EDTA ethylenediaminetetraacetic acid - EGTA ethylene glycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid - c1/2 value concentration at which half of the maximum effect is observed - Mops 3-(N-morpholino)propanesulfonic acid     

Modification of chemical properties of cell walls by silicon and its role in regulation of the cell wall extensibility in oat leaves

Effects of silicon on the mechanical and chemical properties of cell walls in the second leaf of oat (Avena sativa L.) seedlings were investigated. The cell wall extensibility in the basal region of the second leaf was considerably higher than that in the middle and subapical regions. Externally applied silicon increased the cell wall extensibility in the basal region, but it did not affect the extensibility in the middle and subapical regions. The amounts of cell wall polysaccharides and phenolic compounds, such as diferulic acid (DFA) and ferulic acid (FA), per unit length were lower in the basal region than in the middle and subapical regions of the leaf, and silicon altered these amounts in the basal region. In this region, silicon decreased the amounts of matrix polymers and cellulose per unit length and of DFA and FA, both per unit length and unit matrix polymer content. Silicon treatment also lowered the activity of phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) in the basal region. In contrast, the amount of silicon in cell walls increased in response to silicon treatment in three regions. These results suggest that in the basal region, silicon reduces the net wall mass and the formation of phenolic acid-mediated cross-linkages between wall polysaccharides. Such modifications of wall architecture may be responsible for the silicon-induced increase in the cell wall extensibility in oat leaves.