Interaction between electron transport at the plasma membrane and nitrate uptake by maize (Zea mays L.) roots

Summary In the present study nitrate uptake by maize (Zea mays L.) roots was investigated in the presence or absence of ferricyanide (hexacyanoferrate III) or dicumarol. Nitrate uptake caused an alkalization of the medium. Nitrate uptake of intact maize seedlings was inhibited by ferricyanide while the effect of dicumarol was not very pronounced. Nitrite was not detected in the incubation medium, neither with dicumarol-treated nor with control plants after application of 100 M nitrate to the incubation solution. In a second set of experiments interactions between nitrate and ferricyanide were investigated in vivo and in vitro. Nitrate (1 or 3 mM) did neither influence ferricyanide reductase activity of intact maize roots nor NADH-ferricyanide oxidoreductase activity of isolated plasma membranes. Nitrate reductase activity of plasma-membrane-enriched fractions was slightly stimulated by 25 M dicumarol but was not altered by 100 M dicumarol, while NADH-ferricyanide oxidoreductase activity was inhibited in the presence of dicumarol. These data suggest that plasma-membrane-bound standard-ferricyanide reductase and nitrate reductase activities of maize roots may be different. A possible regulation of nitrate uptake by plasmalemma redox activity, as proposed by other groups, is discussed.Abbreviations ADH alcohol dehydrogenase - HCF III hexacyanoferrate III (ferricyanide) - ME NADP-dependent malic enzyme - NR nitrate reductase - PM plasma membrane - PM NR nitrate reductase copurifying with plasma membranes     

Latent nitrate reductase activity is associated with the plasma membrane of corn roots

Latent nitrate reductase activity (NRA) was detected in corn (Zea mays L., Golden Jubilee) root microsome fractions. Microsome-associated NRA was stimulated up to 20-fold by Triton X-100 (octylphenoxy polyethoxyethanol) whereas soluble NRA was only increased up to 1.2-fold. Microsome-associated NRA represented up to 19% of the total root NRA. Analysis of microsomal fractions by aqueous two-phase partitioning showed that the membrane-associated NRA was localized in the second upper phase (U₂). Analysis with marker enzymes indicated that the U₂ fraction was plasma membrane (PM). The PM-associated NRA was not removed by washing vesicles with up to 1.0 M NACl but was solubilized from the PM with 0.05% Triton X-100. In contrast, vanadate-sensitive ATPase activity was not solubilized from the PM by treatment with 0.1% Triton X-100. The results show that a protein capable of reducing nitrate is embedded in the hydrophobic region of the PM of corn roots.Abbreviations L₁ first lower phase - NR nitrate reductase - NRA nitrate-reductase activity - PM plasma membrane - T:p Triton X-100 (octylphenoxy polyethoxyethanol) to protein ratio - U₂ second upper phase     

Distribution of IAA and ABA in gravistimulated primary roots ofZea mays. L.

The transport of¹⁴C-IAA and¹⁴C-ABA applied exogenously to root cap toward the elongation zone was investigated in gravi- and light-stimulated primary roots ofZea mays L. cv. Golden Cross Bantam 70. No significant difference of either IAA or ABA in radioactivities was observed between upper and lower halves of elongation zones during the latent period (0–60 min after the stimulation) of gravitropic response. When quantitative analysis of endogenous IAA and ABA by an internal standard method was carried out 60 min after gravi- and/or light-stimulation, no asymmetric redistribution of either IAA or ABA was observed between upper and lower halves of elongation zones. Light irradiation increased by 20% the contents of ABA in elongation zones. These results suggest that although both IAA and ABA are basipetally transportable and can transmit their information to the elongation zone during a latent period we cannot explain the gravitropic curvature by their redistributions between the two (upper and lower) halves of primary roots ofZea. On the basis of results from the present work and previous papers, the distribution of IAA and ABA in gravistimulatedZea roots is discussed. A part of this study was reported at the Eighth Annual Meeting of the IUPS Commission on Gravitational Physiology at Tokyo 1986.     

Evidence for electron transport across the plasma membrane of Zea mays root cells

Exogenous ferricyanide is reduced by roots of Z. mays. In contrast to oxidation of exogenous electron donors, ferricyanide reduction occurs mostly at the apical 5 mm of the root. Using just this portion of the root, it is shown that the activity is neither a consequence of uptake of ferricyanide followed by excretion of its reduced form, nor of leakage of a reductant. Addition of ferricyanide for 40 s or 5 min results in an apparent oxidation of NADPH but not of NADH; rates of ferricyanide reduction vary together with levels of NADPH but not of NADH in the presence or absence of oxygen. It is concluded that an enzyme which can oxidize cytoplasmic NADPH and transfer the electrons to an external acceptor exists at the cell surface of maize roots. This finding extends the results of others who showed similar redox activity at the surface of Fe-depleted dicotyledonous roots, and indicates that an energy source other than ATP exists at the cell surface of a variety of plants under unstressed conditions.     

Evidence for a plasma-membrane-bound nitrate reductase involved in nitrate uptake of Chlorella sorokiniana

Anti-nitrate-reductase (NR) immunoglobulin-G (IgG) fragments inhibited nitrate uptake into Chlorella cells but had no affect on nitrite uptake. Intact anti-NR serum and preimmune IgG fragments had no affect on nitrate uptake. Membrane-associated NR was detected in plasma-membrane (PM) fractions isolated by aqueous two-phase partitioning. The PM-associated NR was not removed by sonicating PM vesicles in 500 mM NaCl and 1 mM ethylenediaminetetraacetic acid and represented up to 0.8% of the total Chlorella NR activity. The PM NR was solubilized by Triton X-100 and inactivated by Chlorella NR antiserum. Plasma-membrane NR was present in ammonium-grown Chlorella cells that completely lacked soluble NR activity. The subunit sizes of the PM and soluble NRs were 60 and 95 kDa, respectively, as determined by sodium-dodecyl-sulfate electrophoresis and western blotting.Abbreviations EDTA ethylenediaminetetraacetic acid - FAD flavine-adenine dinucleotide - IgG immunoglobulin G - NR nitrate reductase - PM plasma membrane - TX-100 Triton X-100     

Cytochemical localization of phosphatase activity in vascular bundles and contiguous tissues of the leaf ofZea mays L.

Summary The cytochemical localization of phosphatase activity has been carried out on small and intermediate vascular bundles and contiguous tissues of the leaf ofZea mays L. Similar localization patterns were obtained with the nucleoside triphosphates ATP, CTP, GTP, ITP, and UTP, and with ADP and -GP. Reaction product (lead deposits) was observed on the plasma membrane of all cell types. It was invariably heavier on the plasma membranes of the bundle-sheath cells, vascular-parenchyma cells, and the thin-walled sieve tubes and their associated companion cells than on those of the mesophyll cells. Within the bundles, the heaviest lead deposits frequently were found on the plasma membranes of the thin-walled sieve tubes and the least amount (often lacking) on those of the thick-walled sieve tubes. Formation of reaction product was suppressed by NaF, vanadate, and molybdate but not by PCMBS (p-chloromercuribenzene sulfonic acid). The results of the substrate-specificity and inhibitor-sensitivity studies indicate that a nonspecific acid phosphatase was probably responsible for the deposition of the reaction product and not the plasma membrane H⁺-ATPase. These results, in addition to an evaluation of the pertinent literature, lead us to conclude that H⁺-ATPase activity has yet to be demonstrated unequivocally in association with the plasma membrane of phloem cells with lead precipitation procedures. Nevertheless, the differences in amounts of reaction product generally associated with the plasma membranes of the thick- and thin-walled sieve tubes of the maize leaf indicate that the two types of sieve tube differ from one another physiologically.     

Changes in plasma membrane fluidity of corn (Zea mays L.) roots after Brij 58 treatment

Summary The detergent Brij 58 has been introduced to reverse plasma membrane (PM) vesicles from the right-side-out to the inside-out form. The aim of the present work was to investigate the effect of Brij 58 on the formation of an ATP-dependent proton gradient and on the fluidity of the lipid phase of PM vesicles. PMs of corn (Zea mays L.) roots were isolated by phase-partitioning. The fluidity of PMs was estimated by measurement of fluorescence polarization with 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) and 1,6-diphenyl-1,3,5-hexatriene (DPH). The PMs of corn roots were relatively rigid. The hydrophobic part of the lipid bilayer was more fluid than the hydrophilic part. After intercalation of Brij 58 into the lipid bilayer the membrane fluidity changed in a concentration-dependent manner. Treatment with the detergent Brij 58 increased the degree of fluorescence polarization for TMA-DPH, while it decreased it for DPH. This effect was saturated at a detergent-to-protein ratio of 1 4 for both fluorescence probes. Although the biophysical characteristics of the membrane were changed after Brij 58 treatment, the formation of ATP-dependent proton gradients could still be measured with those vesicles. The generation of an ATP-dependent proton gradient with Brij 58-treated PM vesicles suggests that the detergent treatment indeed turned the originally right-side-out vesicles to sealed inside-out vesicles. The limits of the effect caused by Brij 58 in the context of PM enzyme activities are discussed.Abbreviations Brij 58 polyoxyethylene 20 cetyl ether - DPH 1,6-diphenyl-1,3,5-hexatriene - HCF III hexacyanoferrate (III) - ISO inside-out - PM plasma membrane - RSO right-side-out - TMA-DPH 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene     

Radial transport of water across cortical sleeves of excised roots ofZea mays L.

The stationary radial volume flows across maize (Zea mays L.) root segments without steles (sleeves) were measured under isobaric conditions. The driving force of the volume flow is an osmotic difference between the internal and external compartment of the root preparations. It is generated by differences in the concentrations of sucrose, raffinose or polyethylene glycol. The flows are linear functions of the corresponding osmotic differences ( ) up to osmotic values which cause plasmolysis. The straight lines obtained pass through the origin. No asymmetry of the osmotic barrier could be detected within the range of driving forces applied ( =±0.5 MPa), corresponding to volume-flow densities of j_{v, s}=±7·10^–8 m·s^–1. Using the literature values for the reflection coefficients of sucrose and polyethylene glycol in intact roots (E. Steudle et al. (1987) Plant Physiol.84, 1220–1234), values for the sleeve hydraulic conductivity of about 1·10^–7 m·s^–1 MPa^–1 were calculated. They are of the same order of magnitude as those reported in the literature for the hydraulic conductivity of intact root segments when hydrostatic pressure is applied.Abbreviations and symbols a _s outer surface of sleeve segment - c concentration of osmotically active solute - j _{v, s} radial volume flow density across sleeve segment - Lp_s hydraulic conductivity of sleeves - Lp_r hydraulic conductivity of intact roots - _N thickness of Nernst diffusion layer - reflection coefficient of root for solute - osmotic value of bulk phase - osmotic coefficient     

The carotenoid and abscisic acid content of viviparous kernels and seedlings ofZea mays L.

Carotenoid and abscisic acid (ABA) levels were determined in endosperm, embryos and seedlings of wild-type and viviparous (vp) mutants ofZea mays L. Carotenoid concentrations were determined by absorption spectrometry following purification by high-performance liquid chromatography and ABA concentrations by combined gas chromatography-mass spectrometry. Lutein and zeaxanthin were the terminal carotenoids in wild-type tissue. The carotenoid profiles ofvp-1 andvp-8 tissue were similar to that of the wild type; invp-2, vp-5, vp-7 andvp-9 carotenogenesis was blocked at early stages so that xanthophylls were absent. Except forvp-1, where the ABA content was similar to the wild type, the ABA content ofvp embryos was substantially reduced, to 6–16% of the corresponding wild type. Thus, the absence of xanthophylls was associated with reduced ABA content, which was in turn correlated with vivipary. Kernels ofvp-8 had a reduced ABA content although xanthophylls were present. Seedlings of carotenoid-deficient mutants rescued from viviparous kernels contained less ABA than did wild-type seedlings grown in the same way. Furthermore, the ABA concentration of such seedlings did not increase in response to water deficit. Conversely,vp-1 seedlings contained normal levels of carotenoids and ABA. Carotenoid-deficient seedlings did not contain appreciable amounts of chlorophyll so that chloroplast development was not normal. Thus ABA-deficiency could be associated with abnormal plastid development rather than the absence of carotenoids per se.Abbreviations ABA abscisic acid - DAP days after pollination - i.d. internal diameter - FW fresh weight - GC-MS combined gas chromatography-mass spectrometry - HPLC high-performance liquid chromatography - MS mass spectrometry - vp viviparous     

A multidisciplinary approach to the study of the plasma membrane of Zea mays pollen during controlled dehydration

A multidisciplinary approach (freeze-fracture, nuclear magnetic resonance, differential scanning calorimetry, isoelectric focusing and fluorochromatic reaction test) has been used to follow the behaviour of Zea mays pollen during dehydration - and to estimate its quality. At anthesis, the water content of maize pollen is 57–58% and the vegetative plasma membrane is continous and well structured with a very low density of intramembraneous particles on the extraplasmic fracture face. Maize pollen grains can withstand the drying process until a water content of 28% is reached, at which point 60–80% of the individuals show a negative reaction in the fluorochromatic test. At this water content, there is no more crystallizable water and thus metabolism decreases, leading to oxidative damage and the formation of gelphase microdomains in the plasma membrane. Consequently, the plasma-membrane permeability is modified. At 15–13% water content, all pollen grains show a negative fluorochromatic reaction, and gel-phase microdomains are more numerous but membranes still have a bilayer structure. Relaxation-time experiments indicate the occurrence of water replacement at the membrane level. Thus, sugar may stabilize the membrane structure at water contents as low as 3%. During the dehydration process, pollen walls act as elastic structures and remain closely applied to the protoplast. The combination of wall deformation and water replacement would permit pollen survival until oxidative damage occurs in the dehydrated grain.Abbreviations EF extraplasmic fracture face - FCR fluorochromatic reaction - IMP intramembraneous particle - NMR nuclear magnetic resonance - PF protoplasmic fracture face - T₂ relaxation time     

The action of divalen Zn,Cd, Hg,Cu and Pb ions on the ATPase activity of a plasma membrane fraction isolated from roots ofZea mays

The effects of the divalent metal ions Zn, Cd, Hg, Cu and Pb on the ATPase activity of a plasma membrane fraction isolated from roots ofZea mays have been investigated. When Mg-ions (3 mM), with or without K-ions (50mM) are included in the reaction medium, inhibition of ATPase activity was found in all cases, the relative order of the inhibitors over the concentration range 10 to 100M, being Hg>>CuCd>ZnPb. Below 1.0M only Hg caused substantial inhibition. In the absence of Mg ions, Zn and to a lesser extent Cd, activated the enzyme up to a concentration of 1 mM, activity being further stimulated in the presence of K-ions (50mM). No activation of ATPase activity was found for Hg, Cu or Pb. It was concluded that Zn-ATP and Cd-ATP are both alternative substrates for the enzyme. Further experiments showed that both K_m and V_max for the substrates Zn-ATP and Cd-ATP are very much lower than for the usual substrate Mg-ATP.These present results are discussed in relation to the known actions of these divalent cations on the trans-root potential and H-ion efflux in excised maize roots (Kennedy and Gonsalves, 1987).     

Lateral hydraulic conductivity of early metaxylem vessels in Zea mays L. roots

The hydraulic conductivity of the lateral walls of early metaxylem vessels (Lp_x in m · s^–1 · MPa^–1) was measured in young, excised roots of maize using a root pressure probe. Values for this parameter were determined by comparing the root hydraulic conductivities before and after steam-ringing a short zone on each root. Killing of living tissue virtually canceled its hydraulic resistance. There were no suberin lamellae present in the endodermis of the roots used. The value of Lp_x ranged between 3 · 10^–7 and 35 · 10^–7 m · s^–1 · MPa^–1 and was larger than the hydraulic conductivity of the untreated root (Lp_r = 0.7 · 10^–7 to 4.0 · 10^–7 m · s^–1 · MPa^–1) by factor of 3 to 13. Assuming that all flow through the vessel walls was through the pit membranes, which occupied 14% of the total wall area, an upper limit of the hydraulic conductivity of this structure could be given(Lp_pm=21 · 10^–7 to 250 · 10^–7 m · s^–1 · MPa^–1). The specific hydraulic conductivity (Lp_cw) of the wall material of the pit membranes (again an upper limit) ranged from 0.3 · 10^–12 to 3.8 · 10^–12 m² · s^–1 · MPa^–1 and was lower than estimates given in the literature for plant cell walls. From the data, we conclude that the majority of the radial resistance to water movement in the root is contributed by living tissue. However, although the lateral walls of the vessels do not limit the rate of water flow in the intact system, they constitute 8–31% of the total resistance, a value which should not be ignored in a detailed analysis of water flow through roots.Abbreviatations and Symbols k_wr (T ₁ ^2/W ) rate constant (half-time) of water exchange across root (s^–1 or s, respectively) - Lp_cw specific hydraulic conductivity of wall material (m² · s^–1 · MPa^–1) - Lp_pm hydraulic conductivity of pit membranes (m · s ^–1 · MPa^–1) - Lp_r hydraulic conductivity of root (m · s^–1 · MPa^–1) - Lp_x lateralhydraulic conductivity of walls of root xylem (m · s ^–1 · MPa^–1) This research was supported by a grant from the Bilateral Exchange Program funded jointly by the Natural Sciences and Engineering Research Council of Canada and the Deutsche Forschungsgemeinschaft to C.A.P., and by a grant from the Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 137, to E.S. The expert technical help of Mr. Burkhard Stumpf and the work of Ms. Martina Murrmann and Ms. Hilde Zimmermann in digitizing chart-recorder strips is gratefully acknowledged.     

Expression of genes for cell-wall proteins in dividing and wounded tissues ofZea mays L.

Hydroxyproline-rich glycoproteins (HRGPs) fromZea mays have been immunolocalized in the cell wall of root tip cells using ultrathin sections and antibodies ellicited against the purified protein. The accumulation of mRNA corresponding to this protein was studied using the cDNA probe. Maximum accumulation of the mRNA was found in tissues with a high proportion of dividing cells such as those in the root tip of young maize seedlings and a close relationship with cellular division was also observed in in-vitro cultures. However, the level of the mRNA in elongating tissues was minimal, as shown by studies carried out on the elongation zones of root tips and coleoptiles. The mRNA was induced by stress conditions, particularly by wounding young leaves and coleoptiles. It is concluded that in maize this group of proline-rich cell-wall proteins accumulates during cell division and not during cell elongation or differentiation, and participates in the stress-response mechanisms of the plant.     

Factors affecting the binding between fusicoccin and plasma membranes from maize roots

Plasma membranes have been purified from roots of maize (Zea mays L.) using a two-phase aqueous polymer system, dextran-polyethylene glycol. The plant material was homogenized in the presence of a mixture of natural protease inhibitors from potato (Solanum tuberosum L.); these inhibitors have been shown to be more effective than phenylmethylsulfonyl fluoride in suppressing the endogenous proteases in maize roots. Inhibition of proteolysis in the homogenization medium markedly increased (about tenfold) the number of lowaffinity binding sites for fusicoccin (FC). In addition, storage of plasma membranes at −20° C decreased both the number of the low-affinity sites and their dissociation constant (K_D); this effect was in all probability caused by lipid peroxidation. The presence of EDTA throughout isolation and storage of the plasma membranes stabilized the parameters of FC binding to the membranes. The kinetics of binding of [³H]dihydroFC and the competition between [³H]dihydroFC and FCs A, C, J, and H were determined for the low-affinity sites. It was found that (i) the rate constant of association between FC and the low-affinity binding sites is about two orders of magnitude lower than that for the high-affinity sites; (ii) different FCs can be arranged in the order of decreasing avidity for the low-affinity FCbinding site: FC A>FC C>FC J>FC H. The authors are indebted to Dr. L.M. Krasnopolskaya (Institute of Agricultural Biotechnology, Moscow, Russia) for fusicoccins A, C, J, and H, and to Dr. A.V. Galkin (Institute of Agricultural Biotechnology, Moscow, Russia) for valuable comments and ren dering the paper into English.     

Fucose in the surface deposits of axenic and field grown roots ofZea mays L.

Summary The location of materials containing terminal fucose residues on the surface of axenic and field grown roots of corn has been determined.Binding patterns of FITC-labelled,Lotus purpureus Moench lectin indicate the presence of the fucose residues in the cell walls and mucilage of the peripheral region of the root cap. During development, fucose residues also appear in the outer periclinal walls and overlying mucilage of columnar epidermal cells. Surface material rich in these residues persists between the mature root hairs but is not found on their surface. Fucose-rich mucilage is present on the exposed surface of aerial roots and at the point where they enter the soil. No lectin binding residues are indicated elsewhere in the roots.     

Internode length in Zea mays L.

[¹³C, ³H]Gibberellin A₂₀ (GA₂₀) has been fed to seedlings of normal (tall) and dwarf-5 and dwarf-1 mutants of maize (Zea mays L.). The metabolites from these feeds were identified by combined gas chromatography-mass spectrometry. [¹³C, ³H]Gibberellin A₂₀ was metabolized to [¹³C, ³H]GA₂₉-catabolite and [¹³C, ³H]GA₁ by the normal, and to [¹³C, ³H]GA₂₉ and [¹³C, ³H]GA₁ by the dwarf-5 mutant. In the dwarf-1 mutant, [¹³C, ³H]GA₂₀ was metabolized to [¹³C, ³H]GA₂₉ and [¹³C, ³H]GA₂₉-catabolite; no evidence was found for the metabolism of [¹³C, ³H]GA₂₀ to [¹³C, ³H]GA₁. [¹³C, ³H]Gibberellin A₈ was not found in any of the feeds. In all feeds no dilution of ¹³C in recovered [¹³C, ³H]GA₂₀ was observed. Also in the dwarf-5 mutant, the [¹³C]label in the metabolites was apparently undiluted by endogenous [¹³C]GAs. However, dilution of the [¹³C]label in metabolites from [¹³C, ³H]GA₂₀ was observed in normal and dwarf-1 seedlings. The results from the feeding studies provide evidence that the dwarf-1 mutation of maize blocks the conversion of GA₂₀ to GA₁.Abbreviations GA_n gibberellin A_n - GC-MS combined gas chromatography-mass spectrometry - HPLC high-performance liquid chromatography - RP reverse phase     

Pyridine nucleotide-dependent ferricyanide reduction associated with isolated plasma membranes of maize (Zea mays L.) roots

Summary Plasma membranes (PM) from maize roots (Zea mays L.) were isolated by aqueous two-phase partitioning. The isolated membrane fraction showed a 4.6-fold enrichment in specific activity of the PM marker enzyme vanadate-sensitive, Mg²⁺-ATPase over a microsomal pellet collected at 50,000 × g. Activities of marker enzymes for mitochondria, endoplasmic reticulum, tonoplast, and Golgi apparatus were low or not detectable in the PM fraction. Quantitative morphometric analysis using the PM-specific silicotungstic acid stain showed the fraction to be > 92% PM vesicles. Using detergent stimulation of ATPase activity as a measure of structurally linked latency, greater than 90% of the PM vesicles were oriented with the cytoplasmic surface inside.An electron transport activity was investigated in the PM fraction. The rate of NADH oxidation in the absence of an artificial electron acceptor was < 167pkat·mg protein^–1; however, NADH catalysed the reduction of a variety of artificial electron acceptors including ferricyanide (2.6 nkat·mg protein^–1), cytochromec (0.8 nkat·mg protein^–1), a tetrazolium derivative (0.6 nkat·mg protein^–1) and dichlorophenol indophenol (0.4 nkat·mg protein^–1). While the NADH-dependent ferricyanide and dichlorophenol indophenol reductases were stimulated 6-fold by 0.025% (v/v) Triton X-100, the cytochromec and INT reductases were not greatly stimulated. Washing membranes with high salt significantly decreased the NADH-dependent, and eliminated the NADPH-dependent, ferricyanide reductase activity measured in the absence of detergent. These results suggest that NADH was oxidized on the extracytoplasmic surface of the membrane; however, a significant portion of this activity was extrinsic and may have originated from cytoplasmic contamination during isolation. The greater portion of the PM-associated NAD(P)H oxidation and/or ferricyanide reduction was catalyzed on sites not exposed to the outer surface of the membrane.Abbreviations BTP 1,3-bis[tris(hydroxymethyl)-methylamino]-propane - CHAPS 3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulfonate dihydrate - cytc cytochromec - DCIP 2,6-dichlorophenol indolphenol - INT 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyltetrazolium chloride - kat mole·s^–1 - Mes 2-(N-morpholino)ethanesulfonic acid - MF microsomal fraction - PM plasma membrane - STA silicotungstic acid - Tris 2-amino-2-(hydroxymethyl)-1,3-propanediol The mention of vendor or product does not imply that they are endorsed or recommended by U.S. Department of Agriculture over vendors of similar products not mentioned.     

Graviresponsiveness and abscisic-acid content of roots of carotenoid-deficient mutants of Zea mays L.

The abscisic-acid (ABA) content of roots of the carotenoid-deficient w-3, vp-5, and vp-7 mutants of Z. mays was analyzed using gas chromatography-mass spectrometry with an analysis sensitivity of 6 ng ABA g^–1 fresh weight (FW). Roots of normal seedlings of the same lines were characterized by the following amounts of ABA (as ng ABA g^–1 FW,±standard deviation): w-3, 279±43; vp-5, 237±26; vp-7, 338±61. We did not detect any ABA in roots of any of the mutants. Thus, the lack of carotenoids in these mutants correlated positively with the apparent absence of ABA. Primary roots of normal and mutant seedlings were positively gravitropic, with no significant differences in the curvatures of roots of normal as compared with mutant seedlings. These results indicate that ABA 1) is synthesized in maize roots via the carotenoid pathway, and 2) is not necesary for positive gravitropism by primary roots of Z. mays.Abbreviation ABA abscisic acid     

Characterization of the plasma-membrane-bound nitrate reductase in Chlorella saccharophila (Krüger) Nadson

The plasma membranes of Chlorella saccharophila (Krüger) Nadson cells contained a membrane-bound nitrate reductase. This form of nitrate reductase was purified and characterized. Several differences from the soluble form of nitrate reductase were apparent, the most important being: (i) the greater hydrophobicity, as proven using Triton X-114 phase separation, hydrophobic interaction chromatography and stimulation by phosphilipids; (ii) the differences in the native molecular mass compared with Chlorella sorokiniana (Krüger) Nadson; and (iii) the different polypeptide pattern obtained by two-dimensional polyacrylamide gel electrophoresis. Only the plasma-membrane-bound nitrate reductase could be found in both inside-out and right-side-out plasma-membrane vesicles.Abbreviations HIC hydrophobic interaction chromatography - IEF isoelectric focusing - MV methyl viologen - NR nitrate reductase - PM plasma membrane - PMNR plasma-membrane-bound nitrate reductase - SDS-PAGE sodium dodecyl sulfatepolyacrylamide gel electrophoresis This work is part of the Ph.D. Thesis of Christine Stöohr, University of Göttingen. This work was supported by the Deutsche Forschungsgemeinschaft.