A single dominant gene for Fusarium wilt resistance in protoplast-derived tomato plants

Summary Autotetraploids were established from 8 diploid wild species of section Arachis. In all the autotetraploids the chromosomes paired largely as bivalents even though they possess the ability to pair as multivalents. Pollen and pod fertility in the C₁ generation were not directly associated with chromosome pairing. The C₂ generation autotetraploids showed a gradual increase in bivalent associations and pollen and pod fertility. The identification of two genomes, A and B, in the diploid species and in the tetraploid, A. hypogaea, of the section Arachis, a fairly good crossability, and the type of chromosome associations observed in hybrids between A. hypogaea and the autotetraploids of wild Arachis species indicated good prospects of utilizing autotetraploids as genetic bridges in transferring desired traits from these taxa into groundnut.Submitted as Journal Article No. 516 by International Crops Research Institute for the Semi-Arid Tropics (ICRISAT)     

Consequences of artificial and natural chromosome doubling on DNA,RNA and protein contents inCochlearia (Brassicaceae)

The effects of chromosome doubling on macromolecular composition, i.e. DNA, RNA and protein, were examined in diploidCochlearia pyrenaica DC., its established natural autotetraploidC. officinalis L., and their newly colchicine-induced autotetraploid and autooctoploid derivatives. DNA, RNA and protein contents increase from lower to higher ploidy levels (2x > 4x > 8x). The established natural autotetraploids and newly induced autotetraploids also differ, as DNA, RNA and protein have been reduced during the course of establishment. Net synthesis of RNA and protein per unit DNA does not change significantly neither from lower to higher ploidy levels nor between the autotetraploids of newly induced and established natural origins.     

Obtaining autotetraploids in vitro at a high frequency in Citrus sinensis

Tetraploid plants are essential for interploid hybridization to create triploid seedless citrus. Here we report a simple and efficient in vitro method for generating autotetraploids for sweet orange (Citrus sinensis). Cell-division activity in ‘Anliucheng’ sweet orange callus was analyzed using flow cytometry to determine the peak frequency of cell division at which time callus in a liquid media and solid media was treated with 1000 mg l⁻¹ colchicine. The percentage of the DNA-content-varied cells in the callus increased markedly from 11.0% to 44.4% and to 59.0% for liquid and solid media respectively. A total of 20 tetraploid plantlets were recovered via embryogenesis from 47 plantlets regenerated from the treated callus. All the autotetraploids were derived from different embryoids. Autotetraploids will be useful parents for interploid hybridization to generate commercially valuable seedless triploid citrus cultivars.     

Cloning of a rhodococcal promoter using a transposon for dibenzothiophene biodesulfurization

The expression of biodesulfurization genes (dsz) in Rhodococcus erythropolis strain KA2-5-1 is repressed by sulfate which is the product of biodesulfurization. The application of a sulfate non-repressible promoter could be effective in enhancing biodesulfurization. A promoter-probe transposon was constructed using the promoterless, red-shifted green fluorescence protein gene (rsgfp). A 340 bp putative promoter element, designated kap1, was isolated from a strain KA2-5-1 recombinant that had shown high fluorescence intensity. The activity of kap1 was not affected by 1 mM sulfate. It gave about a 2-fold greater activity than the 16S ribosomal RNA promoter in R. erythropolis strain KA2-5-1 and is therefore useful for expressing desulfurization genes in rhodococcal strains.     

Intracellular localization of serine acetyltransferase in spinach leaves

Intact chloroplasts isolated from spinach leaves by a combination of differential and Percoll density gradient centrifugation and free of mitochondrial and peroxisomal contamination contained about 35% of the total leaf serine acetyltransferase (EC 2.3.1.30) activity. No appreciable activity of the enzyme could be detected in the gradient fractions containing broken chloroplasts, mitochondria, and peroxisomes. L-cysteine added to the incubation mixture at 1 mM almost completely inhibited serine acetyltransferase activity, both of leaf and chloroplast extracts. D-cysteine was much less inhibitory. L-cystine up to 5 mM and O-acetyl-L-serine up to 10 mM had no effect on the enzyme activity. When measured at pH 8.4, the enzyme extracted from the leaves had a K _m for L-serine of 2.4, the enzyme from the chloroplasts a K _m of 2.8 mM.Abbreviations NAS N-acetyl-L-serine - NADP-GPD NADP-dependent glyceraldehyde-3-phosphate dehydrogenase - OAS O-acetyl-L-serine - OASSase O-acetyl-L-serine sulfhydrylase - 3-PGA D-3-phosphoglycerate - SATase serine acetyltransferase     

Selenium requirement for active xanthine dehydrogenase from Clostridium acidiurici and Clostridium cylindrosporum

The xanthine dehydrogenase of Clostridium acidiurici and C. cylindrosporum was assayed with methyl viologen as acceptor. In C. acidiurici the basal activity level was about 0.3 mol/min x mg of protein. Cells grown on uric acid in the presence of 10^-7 M selenite showed a 14-fold increase in xanthine dehydrogenase activity, which decreased with higher selenite concentrations (10^-5 M). The supplementation with 10^-7 M molybdate or tungstate was without effect. High concentrations of tungstate decreased the xanthine dehydrogenase if selenite was also present. In comparison, high concentrations of molybdate affected only a small decrease in activity level at the optimal concentration for selenite and relieved to some degree the inhibitory effect of 10^-5 M selenite. With hypoxanthine and xanthine as substrates for growth again only the addition of selenite was necessary to show a similar increase in xanthine dehydrogenase activity. C. acidiurici could be grown in a mineral medium. Both xanthine dehydrogenase and formate dehydrogenase exhibited the highest level of activity if selenite and tungstate were present in that medium.In C. cylindrosporum the basal activity level of xanthine dehydrogenase was about 0.95 mol/min x mg of protein. The addition of 10^-7 M selenite to the growth medium increased the activity level about 3-fold, but the highest level (3.7 U/mg) was reached if 10^-7 M molybdate was also added. The presence of tungstate resulted in a decreased enzyme activity.     

Enzymic activities of carbohydrate,purine, and pyrimidine metabolism in the Anaeroplasmataceae (class Mollicutes)

Cell-free extracts of two strictly anaerobic mollicutes, Anaeroplasma intermedium 5LA and Asteroleplasma anaerobium 161^T, were tested for enzymic activities of intracellular carbohydrate metabolism. Asteroleplasma anaerobium was also tested for enzymes of purine and pyrimidine metabolism. Both organisms had enzymic activities associated with the nonoxidative portion of the pentose phosphate pathway, and with the Embden-Meyerhoff-Parnas pathway. The 6-phosphofructokinase (PFK) of Asteroleplasma anaerobium was ATP-dependent, whereas the PFK of Anaeroplasma intermedium was PP_i-dependent. The two anaerobic mollicutes also differed with respect to the enzymes that converted phosphoenolpyruvate (PEP) to pyruvate; Anaeroplasma intermedium had pyruvate kinase activity, but Asteroleplasma anaerobium had pyruvate, orthophosphate dikinase activity (PP_i-dependent). Both organisms had lactate dehydrogenase activity which was activated by fructose 1,6-bisphosphate (Fru-1,6-P ₂). Anaeroplasma intermedium had activity for PEP carboxykinase (activated by Fru-1,6-P ₂), but Asteroleplasma anaerobium did not. PEP carboxytransphosphorylase activity was not detected in either organism. Anaeroplasma intermedium had malate dehydrogenase and isocitrate dehydrogenase activities, but it had no activities for the three other tricarboxylic acid cycle enzymes examined; Asteroleplasma anaerobium had malate dehydrogenase activity only. Asteroleplasma anaerobium had enzymic activities for the interconversion of purine nucleobases, (deoxy)ribonucleosides, and (deoxy)ribomononucleotides, including PP_i-dependent nucleoside kinase, reported heretofore only in some other mollicutes. Asteroleplasma anaerobium could synthesize dTDP by the thymine salvage pathway if deoxyribose 1-phosphate was provided, and it had dUTPase, ATPase, and dCMP kinase activities. It lacked (deoxy)cytidine deaminase, dCMP deaminase, and deoxycytidine kinase activities.Abbreviations EMP Embden-Meyerhof-Parnas - ICDH isocitrate dehydrogenase - LDH lactate dehydrogenase - PEP phosphoenolpyruvate - PFK phosphofructokinase - PPDK pyruvate, orthophosphate dikinase - TCA cycle tricarboxylic acid cycle Note: Other abbreviations used are as per the instruction to authors, or the reference cited therein (Eur J Biochem 1:259), or Biochem J 120:449 (which supercedes a portion of the first reference)     

Two Agrobacterium tumefaciens genes for cytokinin biosynthesis: Ti plasmid-coded isopentenyltransferases adapted for function in prokaryotic or eukaryotic cells

Summary Tzs and ipt are two Ti plasmid genes coding for proteins with isopentenyltransferase (IPT) activity in vitro. We cloned both genes for protein expression in Escherichia coli and in Agrobacterium tumefaciens, and we investigated differences between the two genes by analysing the properties of the proteins in vitro and in vivo. In vitro, extracts with tzs or ipt-coded proteins had high IPT activity, and the enzymes were identical in most properties. The most important difference was detected in vivo: the tzs-encoded protein was very active in cytokinin production, while the ipt protein required overexpression in order to obtain measurable activity in bacteria. In both cases, rans-zeatin was the major product of the gene activity. Formation of this cytokinin requires a hydroxylase function in addition to the IPT reaction. No such activity could be ascribed to tzs or ipt-encoded proteins in vitro or in vivo, but cytokinin hydroxylase activity was detected in cells and extracts of E. coli, regardless of the presence or absence of the cytokinin genes. Based on these results it is proposed that both genes code for a single enzyme activity (isopentenyltransferase), that the genes and proteins are adapted for function either in bacteria (tzs) or in transformed plant cells (ipt), and that in both prokaryotic and eukaryotic cells hydroxylation to trans-zeatin is a function contributed by host enzymes.Abbreviations DMAPP dimethylallylpyrophosphate - iP isopentenyladenine - iPA isopentenyladenosine - iPMP isopentenyladenosine 5-monophosphate - IPT isopentenyltransferase - trans-Z trans-zeatin     

Enhanced desulfurization in a transposon-mutant strain of Rhodococcus erythropolis

The dsz desulfurization gene cluster from Rhodococcus erythropolis strain KA2-5-1 was transferred into R. erythropolis strain MC1109, unable to desulfurize light gas oil (LGO), using a transposon-transposase complex. As a result, two recombinant strains, named MC0203 and MC0122, were isolated. Resting cells of strain MC0203 decreased the sulfur concentration of LGO from 120 mg l^–1 to 70 mg l^–1 in 2 h. The LGO-desulfurization activity of strain MC0203 was about twice that of strain MC0122 and KA2-5-1. The 10-methyl fatty acids of strain MC0203 were about 28%–41% that of strain MC1109. It is likely that strain MC0203 had a mutation involving alkylenation or methylation of 9-unsaturated fatty acids caused by the transposon inserted in the chromosome, which increased the fluidity of cell membranes and enhanced the desulfurization activity.     

N2-fixation in Erwinia herbicola

Four from 18 strains of Erwinia herbicola tested had nitrogenase activity and grew with N₂ as sole source of nitrogen under strict anaerobic conditions with a doubling time of 20–24 h. Nitrogenase activity started only 96–120 h after transfer to a special medium maintained under anaerobic conditions. A ten fold increase in protein per culture found after the maximum nitrogenase activity of 80–130 nmol C₂H₄. mg protein^-1·min^-1 was accompanied by a fall in pH of the medium (20 mM phosphate buffer and in 125 mM Tris-buffer) from pH 7.2 to 5.4 or less, but only to 6.8 in 100 mM phosphate buffer. In all cases we found a sharp curtailing of nitrogenase activity 48 h after the maximum. The bacteria utilized only 35–50% of the nitrogen fixed for growth. Erwinia herbicola strains differed from two strains of Enterobacter agglomerans in being unable to fix nitrogen on agar surfaces exposed to air. Specific nitrogenase activity in Erwinia herbicola is compared with data reported for other Enterobacteriaceae and is found to be higher than that reported for Klebsiella pneumoniae, Enterobacter cloacae or Citrobacter freundii.     

Some properties of formate dehydrogenase,accumulation and incorporation of 185W-tungsten into proteins of Clostridium formicoaceticum

Formate dehydrogenase of Clostridium formicoaceticum used only methyl and benzyl viologen, but not NAD as electron acceptor. The S_0.5 values were 0.9×10^-4 M for formate and 5.8×10^-3 M for methyl viologen. Using potassium phosphate buffer a pH-optimum of 7.9 was observed. The initial velocity of the formate dehydrogenase activity reached a maximum at 70°C, whereas the activity was stable only up to 50°C. The level of formate dehydrogenase in C. formicoaceticum was increased to its maximum when 10^-6 M selenite and 10^-7 M tungstate were added to a synthetic medium. Addition of molybdate instead of tungstate did not increase the level of formate dehydrogenase. ¹⁸⁵W-tungsten was concentrated about 100-fold by C. formicoaceticum; molybdate had no major effect on the uptake of tungsten. ¹⁸⁵W-tungsten was found almost exclusively in the soluble fluid and was predominantly recovered after chromatography in a protein of about 88000 molecular weight. Occasionally a labelled protein of low molecular weight was observed. Again molybdate added even in high molar excess did not influence the labelling pattern. No radioactivity peak could be obtained at the elution peak of formate dehydrogenase activity. The extreme instability of formate dehydrogenase prevented further purification.Abbreviations FDH formate dehydrogenase - DTE dithioerythritol - HEPES hydroxyethylpiperazine N-2-ethane sulconic acid - TEA triethylamine - DCPIP 2,6-dichlorophenolindophenol - PMS phenazine methosulfate - TTC triphenyltetrazolium     

Annual changes in body mass in captive Svalbard ptarmigan: role of changes in locomotor activity and food intake

The influence of changes in the amount of locomotor activity on the annual body mass cycle was investigated in captive Svalbard ptarmigan kept indoors at thermoneutrality and exposed to seasonal changes in daylength or continuous light from the summer onwards. In both groups there was a close correlation between locomotor activity and metabolic rate. Only birds exposed to changes in daylength showed an annual cycle in locomotor activity, with low activity in autumn and mid-winter and a peak in spring. The birds permanently exposed to continuous light had a relatively low activity throughout the year with no systematical changes. Body mass began to increase in both groups in early autumn and the food intake was elevated during most of the following fattening period. It is concluded that elevated food intake is the prime factor involved in autumnal fattening in captive Svalbard ptarmigan. Body mass increased significantly faster under decreasing daylength compared with continuous light, associated with a lower activity as well as a higher food intake. The birds exposed to continuous light maintained a high body mass and a relatively low activity level during spring. In birds exposed to changing daylength, body mass fell from late February onwards, which is about 3 months later than in outdoor caged or free-living Svalbard ptarmigan. In the birds exposed to increasing daylength a fourfold increase in the amount of locomotor activity occurred from February to April. This increased activity was correlated with a negative energy balance and may be casually associated with the fall in body mass in these birds. Under outdoor conditions, elevated locomotor activity in spring may be responsible for a continuation of the decline in body mass commencing in November, despite a slight tendency for an increased food intake towards the end of this period.Abbreviations BM body mass - CE _f caloric equivalent of food - EAE energy assimilation efficiency - EE energy expenditure - FI food intake - LA locomotor activity - LL continuous light - LD simulated annual changes in daylength - MEI metabolizable energy intake - MR metabolic rate - RQ respiratory quotient     

Ethanol-resistant mutants of Nicotiana plumbaginifolia are deficient in the expression of pollen and seed alcohol dehydrogenase activity

Summary Six independent mutant lines ofNicotiana plumbaginifolia resistant to ethanol, designated E3, E8, E101, E112, E144 and E251, were isolated as germinating seedlings on selective medium. In all cases, resistance to ethanol was conferred by a single recessive nuclear mutation at the same locus. Mutant seeds and pollen lacked detectable ADH activity, with the exception of E251 where a residual activity was detected. An antiserum directed againstArabidopsis thaliana ADH detected an ADH-related polypeptide of 44 kDa present in wild-type seeds and, to a lesser extent, in the seeds of the leaky mutant E251. No ADH-related polypeptide could be detected in seeds of the other mutants. However, all of them had a nearly normal level of ADH mRNA except one which did not synthesize any mRNA. These results suggest that these ethanol-resistant mutants are impaired in one of the structural genes coding for alcohol dehydrogenase. The corresponding locus has been designatedAdh1.Abbreviations ADH alcohol dehydrogenase - EMS ethyl methane-sulfonate - MTT dimethyl thiazol tetrazolium - NAD nicotinamide adenine dinucleotide - NBT nitro blue tetrazolium - p-cells protoplast-derived cells - PMS phenazine methosulfate - SDS sodium dodecyl sulfate     

Species specific release of sulfate from adenylyl sulfate by ATP sulfurylase or ADP sulfurylase in the green sulfur bacteria Chlorobium limicola and Chlorobium vibrioforme

High activities of ATP sulfurylase were found in the soluble protein fraction of two Chlorobium limicola strains, whereas ADP sulfurylase was absent. ATP sulfurylase was partially purified and characterized. It was a stable soluble enzyme with a molecular weight of 230,000, buffer-dependent pH optima at 8.6 and 7.2 and an isoelectric point at pH 4.8. No physiological inhibitor was found. Inhibition was observed with p-CMB and heavy metals. Sulfur compounds had no effect on enzyme activity. The stoichiometry of the reaction was proven. In contrast, an ADP sulfurylase, but no ATP sulfurylase, was found in Chlorobium vibrioforme. This enzyme was very labile with a molecular weight of about 120,000 and buffer-dependent pH optima at 9.0 and 8.5. Under test conditions the apparent K _m value was determined to be 0.28 mM for adenylyl sulfate and 8.0 mM for phosphate.Abbreviations APS adenylyl sulfate - p-CMB parachloromercuribenzoate - PP_i inorganic pyrophosphate     

Cloning,characterization and expression of the extracellular lipase gene from <Emphasis Type="Italic">Aureobasidium </Emphasis><Emphasis Type="Italic">pullulans</Emphasis> HN2-3 isolated from sea saltern

The extracellular lipase structural gene was isolated from cDNA of Aureobasidium pullulans HN2-3 by using SMART^TM RACE cDNA amplification kit. The gene had an open reading frame of 1245 bp long encoding a lipase. The coding region of the gene was interrupted by only one intron (55 bp). It encodes 414 amino acid residues of a protein with a putative signal peptide of 26 amino acids. The protein sequence deduced from the extracellular lipase structural gene contained the lipase consensus sequence (G-X-S-X-G) and three conserved putative N-glycosylation sites. According to the phylogenetic tree of the lipases, the lipase from A. pullulans was closely related to that from Aspergillus fumigatus (XP_750543) and Neosartorya fischeri (XP_001257768) and the identities were 50% and 52%, respectively. The mature peptide encoding cDNA was subcloned into pET-24a (+) expression vector. The recombinant plasmid was expressed in Escherichia coli BL21(DE3). The expressed fusion protein was analyzed by SDS-PAGE and western blotting and a specific band with molecular mass of about 47 kDa was found. Enzyme activity assay verified the recombinant protein as a lipase. A maximum activity of 0.96 U/mg was obtained from cellular extract of E. coli BL21(DE3) harboring pET-24a(+)LIP1. Optimal pH and temperature of the crude recombinant lipase were 8.0 and 35 °C, respectively and the crude recombinant lipase had the highest hydrolytic activity towards peanut oil.     

A single amino acid substitution in soybean VSPα increases its acid phosphatase activity nearly 20-fold

Soybean [Glycine max (L.) Merr.] contains two proteins called vegetative storage proteins (VSPs) that function as temporary storage reserves, but are also closely related to plant acid phosphatases of the haloacid dehalogenase (HAD) superfamily. This study examined the biochemical basis for the relatively low catalytic activity previously reported for these VSPs. The specific activity of purified recombinant VSP on GMP was about 40-fold lower than for a related soybean root nodule acid phosphatase (APase), which had a specific activity of 845 U mg^–1 protein. Conversion of Ser¹⁰⁶ to Asp increased VSP activity about 20-fold. This Asp residue is present in nodule APase and is a highly conserved nucleophile in the HAD superfamily. Related VSPs from cultivated soybean and from three wild perennial soybeans, as well as a pod storage protein (PSP) from Phaseolus vulgaris L. all lack the catalytic Asp, suggesting they too are catalytically inefficient. Phylogenetic analysis showed the VSPs and PSP are more closely related to each other than to 21 other VSP-like proteins from several plant species, all of which have the nucleophilic Asp. This study suggests that loss of catalytic activity may be a requirement for the VSPs and PSP to function as storage proteins in legumes.Abbreviations APase Acid phosphatase - GST Glutathione S-transferase - HAD Haloacid dehalogenase - pNPP Para-nitrophenol phosphate - PSP Pod storage protein - RIP Ribosome inactivating protein - VSP Vegetative storage protein Accession numbers for the VSP sequences reported in this paper are from G. falcata, AY523602; G. tomentella, AY523603; G. curvata, AY523604     

Phylogenetic relations in section Arachis based on seed protein profile

Summary Seed protein profiles of nine diploid species (2n = 20), ten tetraploid accessions, two synthetic amphidiploids and two autotetraploids (2n = 40) were studied using SDS-polyacrylamide gel electrophoresis. While the general profiles suggested considerable homology among these taxa in spite of speciation and ploidy differences, appreciable genetic differences were present to support the existing genomic divisions and sub-divisions in the section Arachis. A high degree of relationship was indicated between the two diploid species (A. duranensis containing the A genome and A. batizocoi (ICG 8210) containing the B genome) and tetraploids A. monticola/ A. hypogaea (2n = 40) containing AABB genome. Similar relationships were recorded between the AABB synthetic amphidiploid and the profile obtained from the mixture of protein of A. duranensis and A. batizocoi, suggesting that these two diploid species were the donors of the A and B genome, respectively, to tetraploid A. monticola/A. hypogaea.Submitted as Journal Article No. 1114 by International Crops Research Institute for the Semi-Arid Tropics (ICRISAT)     

Metabolism of germinating teliospores of Ustilago nuda

Teliospores of Ustilago nuda are exogenously dormant. Germination and respiration of these thick-walled spores were greatly stimulated by glucose. Cycloheximide, actinomycine D, salicylhydroxamic acid and cyanide inhibited germination completely. Dormant spores in water had a R.Q. of about 0.85. However, during early germination in glucose containing media the R.Q. increased to 1.4. The chemical composition of the spores did not change dramatically during early germination. The main reserve compounds of the spores were glycogen and lipid. Trehalose could not be detected. Radiorespirometric as well as enzymatic evidence suggested that glucose was metabolized along glycolysis and the hexose monophosphate pathway. The increasing activity of phosphofructokinase might allow an increased flow through the Embden-Meyerhof-Parnas pathway during early germination.Abbreviations EMP-pathway Embden-Meyerhof-Parnas pathway - HMP-pathway hexose monophosphate pathway - SHAM salicyl-hydroxamic acid - HEPES 4-(2-hydroxyethyl)-1-piperazineethane-sulfonic acid - MES 2-morpholinoethanesulfonic acid     

β-1,3-glucanase activity in the stigma of healthy petunia flowers

β-1,3-Glucanase activity was detected in extracts of different tissues of healthy mature petunia flowers except the filament. The stigma was studied further as it had the highest enzyme activity and there is a paucity of information on the occurrence of this enzyme in this tissue. Specific activity of the enzyme was found to increase within the stigmatic tissue from early development until just before anthesis. Following non-denaturing polyacrylamide gel electrophoresis at pH 8.8, extracts of dehiscent stigma seem to contain three acidic isoforms of β-1,3-glucanase. Crude extracts of stigma was passed through a pachyman affinity column. A fraction of affinity-purified active β-1,3-glucanase enzyme was found to have no antifungal activity against Trichoderma viride, Phloma clematidina and Cladosporium fulvum.     

Auxin-stimulated ATPase in membrane fractions from pumpkin hypocotyls (Cucurbita maxima L.)

Membrane fractions from Cucurbita maxima hypocotyls were isolated in a medium which inhibits the action of endogenous phospholipases. After removal of soluble phosphatases by Sepharose 2B-CL column chromatography, an auxin-stimulated ATPase activity was found in membrane fractions from linear sucrose gradients. In the presence of 10^-4 M phenylacetic acid (PAA), the stimulation by indol-3-acetic acid (IAA) exhibited a bimodal concentration dependence with maximal stimulation of about 50% at 10^-6 M IAA. Without PAA, only a high concentration of 10^-4 M IAA was stimulatory, whereas 10^-6 M IAA had no apparent effect and 10^-8 M IAA exhibited weak inhibition. PAA alone had only weak or no effects. The effects of IAA must be considered as hormone-specific. The ATPase activity in the presence of 10^-4 M PAA was activated only by 2,4-dichlorophenoxyacetic acid (2,4-D), an active auxin analogue, but not by the inactive stereoisomers, 2,3-D and 3,5-D. Comparison with marker enzyme profiles suggested that part of the auxin-stimulated ATPase was localized on plasma membranes as well as other compartments. Thus, the auxin-stimulated ATPase may become a useful tool in the investigation of the mechanism of action of auxin.Abbrevations 2,4-D 2,4-dichlorophenoxyacetic acid - 2,3-D 2,3-dichlorophenoxyacetic acid - 3,5-D 3,5-dichlorophenoxyacetic acid - IAA indol-3-acetic acid - PAA phenylacetic acid - MES (2-(N-morpholino))-ethanesulfonic acid - EDTA ethylenediamine tetraacetic acid