Etiolated Mung Bean Hypocotyls Research Articles

Differential regulation of Ku gene expression in etiolated mung bean hypocotyls by auxins

Plant Ku genes were identified very recently in Arabidopsis thaliana, and their roles in repair of double-stranded break DNA and maintenance of telomere integrity were scrutinized. In this study, the cDNAs encoding Ku70 ( VrKu70) and Ku80 ( VrKu80) were isolated from mung bean ( Vigna radiata L.) hypocotyls. Both genes were expressed widely among different tissues of mung bean with the highest levels in hypocotyls and leaves. The VrKu gene expression was stimulated by exogenous auxins in a concentration- and time-dependent manner. The stimulation could be abolished by auxin transport inhibitors, N-(1-naphthyl) phthalamic acid and 2,3,5-triiodobenzoic acid implicating that exogenous auxins triggered the effects following their uptake by the cells. Further analysis using specific inhibitors of auxin signaling showed that the stimulation of VrKu expression by 2,4-dichlorophenoxyacetic acid (2,4-D) was suppressed by intracellular Ca 2+ chelators, calmodulin antagonists, and calcium/calmodulin dependent protein kinase inhibitors, suggesting the involvement of calmodulin in the signaling pathway. On the other hand, exogenous indole-3-acetic acid (IAA) and α-naphthalene acetic acid (NAA) stimulated VrKu expression through the mitogen-activated protein kinase/extracellular signal-regulated kinase pathway. Altogether, it is thus proposed that 2,4-D and IAA (or NAA) regulate the expression of VrKu through two distinct pathways.

Ethylene-regulated expression of ACC oxidase and ACC synthase genes in mung bean hypocotyls

Ethylene induces an increase in transcript levels of the ACC oxidase gene (VR- ACO1) but suppresses expression of the ACC synthase gene (VR- ACS1) in etiolated mung bean hypocotyls. Here, treatment with either the transcription inhibitor α-amanitin or the protein synthesis inhibitor cycloheximide (CHI) completely abolished ethylene-induced accumulation ofVR- ACO1 mRNA. This indicated that ethylene-induction ofVR- ACO1 is due to transcriptional activation, which also relies onde novo protein synthesis. In contrast, CHI induced the accumulation ofVR- ACS1 transcripts. ABA also inhibited ethylene-inducedVR- ACO1 expression, but restored ethylene-suppressedVR- ACS1 expression. Results of time-course experiments and an interaction analysis of CHI and ABA suggested that the latter may exert its effect by preventing the synthesis of a factor(s) necessary for ethylene action. Ethylene-signaling was studied in more detail, using two pharmacological inhibitors — EGTA and sodium orthovanadate. Those experiments demonstrated that calcium ions and a Tyr type of protein phosphatase may be involved in regulating ethylene biosynthetic genes.

Light differentially regulates the expression of two members of the auxin-induced 1-aminocyclopropane-1-carboxylate synthase gene family in mung bean (Vigna radiata L.) seedlings.

Auxin induces the expression of the two ethylene-biosynthetic genes VR-ACS6 and VR-ACS7 in etiolated mung bean hypocotyls. However, while it also enhances VR-ACS6 expression in light-grown tissues, it does not up-regulate VR-ACS7 expression in these tissues. Here we show that transfer of 3-day-old etiolated seedlings into light quickly reduced the auxin-induced expression of both genes. However, while auxin-induced VR-ACS6 expression recovered after 24 h of light, VR-ACS7 transcription continued to reduce and was almost completely absent at 36 h. Thus, light differentially modulates the expression of the auxin-inducible VR-ACS genes. In hormone-treated etiolated seedlings, VR-ACS7 was primarily induced in the rapidly elongating zones of hypocotyl and epicotyl tissues, while auxin-induced VR-ACS6 mRNA was evenly distributed throughout the whole seedling. VR-ACS7 promoter-driven beta-glucuronidase (GUS) activity in auxin-treated etiolated transgenic Arabidopsis seedlings was observed in the highly elongating zones of the hypocotyl. During de-etiolation, the GUS activity gradually declined to become confined to the uppermost region of hypocotyls. In situ mRNA localization studies showed that in etiolated mung bean hypocotyls, the auxin-dependent VR-ACS7 transcript was predominantly present in the epidermis, which is the driving site for auxin-mediated elongation. Thus, it appears that the modulation by light of auxin-induced VR-ACS7 expression may correlate closely with the elongation growth response in early seedling development.

Wound-induced expression of ACC synthase genes in etiolated mung bean hypocotyls

After wounding the intact tissues of developing etiolated mung bean hypocotyls, we investigated how the expression of all known members of the ACC synthase gene family was effected. Of the seven members, transcripts of only VR-ACS1, VR-ACS6, and VR-ACS7 were detectable in the control (non-stressed) hypocotyls, and their activities were strongly correlated with growth rate. In addition, expression of both VR-ACS1 and VR-ACS6 was stimulated by wounding, reaching a peak after about 1 h and sustaining that effect for about 6 h. This induced response did not occur with 5-d-old seedlings, in which transcripts were not normally detected at that stage. When auxin activity and transport were blocked by co-treatment with two inhibitors, TIBA and PCIB, the expression of those two genes was significantly reduced. However, when seedlings were co-treated before being injured, the effect of wounding was not substantially altered. Our results suggest that expression of these two ACC genes in non-stressed hypocotyls is regulated by the endogenous level of auxin. Likewise, transcripts of those genes are stimulated both by wounding and by treatment with auxin, although the two signal transduction pathways are partially independent

Differential accumulation of transcripts for ACC synthase homologs in etiolated mung bean hypocotyls in response to Li+

In mung bean(Vigna radiate), 1-aminocyclopropane-1-carboxylate synthase (ACS) is encoded by a mutigene family that comprises at least seven members. Their expression is induced by hormones, developmental signals, inhibition of protein synthesis, or stress. We performed an RT-PCR assay to understand the differential accumulation of transcripts for ACC synthase homologs as a response to Li+ in etiolated mung bean hypocotyls. Treating the seedlings with liCI caused inductions of theACS1, ACS4, ACSS, ACS6, andACS7 genes. The induction level ofACS7 was particularly high. This effect onACS7 expression was specific, lasting more than 8 h after the treatment To understand the relationship of this Li+ action with the phosphoinositide (PI) second messenger system, we examined the effect of Ca2+ treatment on Li+-induction of theACS7 gene. Because Ca2+ did not reverse the Li+ effect, we suggest that regulation of theACS7 gene by Li+ in the mung bean may not involve the PI system.

Differential Accumulation of Transcripts for ACC Synthase and ACC Oxidase Homologs in Etiolated Mung Bean Hypocotyls in Response to Various Stimuli

Differential Accumulation of Transcripts for ACC Synthase and ACC Oxidase Homologs in Etiolated Mung Bean Hypocotyls in Response to Various Stimuli

A soluble auxin‐binding protein from mung bean hypocotyls has indole‐3‐acetaldehyde reductase activity

To clarify the roles of auxin‐binding proteins (ABPs) in the action of auxin, soluble auxin‐binding proteins were isolated from an extract of etiolated mung bean hypocotyls by affinity chromatography on 2,4‐dichlorophenoxyacetic acid (2,4‐D)‐linked Sepharose 4B. A 39‐kDa polypeptide was retained on the affinity column and eluted with a solution containing IAA or 2,4‐D, but not with a solution containing benzoic acid. The protein was then purified by several column‐chromatographic steps. The apparent molecular mass of the protein was estimated to be 77 kDa by gel filtration and 39 kDa by SDS‐PAGE. We designated this protein ABP39. The partial amino acid sequences of ABP39, obtained after chemical cleavage by CNBr, revealed high homology with alcohol dehydrogenase (ADH; EC 1.2.1.1). While the ABP39 was not capable of oxidizing ethanol, it did catalyze the reduction of indole‐3‐acetaldehyde (IAAld) to indole‐3‐ethanol (IEt) with an apparent Km of 22 μM. The IAAld reductase (EC 1.2.3.1) is specific for NADPH as a cofactor. The ABP39 also catalyzed the reduction of other aldehydes, such as acetaldehyde, benzaldehyde, phenylacetaldehyde and propionealdehyde. Indole‐3‐aldehyde was a poor substrate. The enzyme activity was inhibited by both indole‐3‐acetic acid and 2,4‐D in a competitive manner. Therefore, the enzyme is considered to be retained on the affinity column by recognition of auxin structure.

Identification of a soluble auxin-binding protein as a glutathione-dependent formaldehyde dehydrogenase

Antibodies against the putative auxin-binding site of an ER auxin-binding protein from maize coleoptiles were raised by injecting rabbits with a synthetic oligopeptide (Ile-His-Arg-His-Ser-Cys-Glu) conjugated to hemocyanin from the Keyhole limpet. Soluble auxin-binding proteins were isolated from an extract of etiolated mung bean hypocotyls by affinity chromatography on 2,4-dichlorophenoxyacetic acid-linked (2,4-D-linked) Sepharose 4B. The antiserum against the oligopeptide recognized a specific 40 kDa polypeptide among auxin-binding proteins from mung bean hypocotyls. An auxin-binding protein of 40 kDa was then purified by several column-chromatographic steps. The apparent molecular mass of the protein was estimated to be 80 kDa by gel-filtration and 40 kDa by SDS-PAGE. We designated this protein ABP40. The dissociation constant of purified ABP40 for [ 14C]-2,4-D was calculated to be 1 × 10 −5 M. Binding of [ 14C]-2,4-D was completely inhibited by p-chlorophenoxyisobutyric acid (PCIB) and weakly inhibited by indole-3-acetic acid (IAA) and naphthalene-1-acetic acid (NAA). Benzoic acid and tryptophan had no effect on the binding. The partial amino acid sequences of ABP40, obtained after chemical cleavage by CNBr, revealed high homology to glutathione-dependent formaldehyde dehydrogenase (FDH; EC 1. 2. 1. 1). Moreover, the purified ABP40 had FDH activity.

Molecular Cloning and Analysis of the cDNA for an Auxin-Regulated Calmodulin Gene

An auxin-regulated calmodulin cDNA (arCaM) were isolated by differential screening from a mung bean (Vigna radiata) cDNA library. The expression of the arCaM transcript in the etiolated mung bean hypocotyl was examined by RNA gel blot analysis. The arCaM transcript was induced depending on indole-3-acetic acid (IAA) concentrations. An increase in level of the arCaM transcript upon treatment of hypocotyl segments with 10 microM IAA was detected after 1 h and a maximum level was detected at 2 h. Induction of the arCaM transcript occurred upon treatment with 10 microM 2,4-dichlorophenoxyacetic acid (2,4-D) or naphthalene-1-acetic acid (NAA) as well as with IAA, while treatment with 10 microM p-chlorophenoxyisobutyric acid (PCIB) as an anti-auxin, prevented the induction. Ethylene did not have any effect. Other stress conditions, such as exposure to salt stress, heavy metal ions and heat shock, also had no effect on the induction. The levels of the arCaM transcript in leaves of light-grown mung bean plants treated with IAA showed steady but small increases with time.

Amino acid N-malonyltransferases from mung beans. Action on 1-aminocyclopropane-1-carboxylic acid and D-phenylalanine.

1-Aminocyclopropane-1-carboxylate (ACC) N-malonyltransferase from etiolated mung bean hypocotyls was examined for its relationship to D-phenylalanine N-malonyltransferase and other enzymes which transfer malonyl groups from malonyl-CoA to D-amino acids. Throughout a 3600-fold purification the ratio of D-phenylalanine N-malonyltransferase activity to ACC N-malonyltransferase activity was unchanged. Antibodies raised against purified ACC N-malonyltransferase 55-kDa protein were also able to precipitate all D-phenylalanine-directed activity from partially purified mung bean extracts. The irreversible inhibitors phenylglyoxal and tetranitromethane reduced malonyltransferase activity towards D-phenylalanine to the same extent as that for ACC. In addition, several other D-amino acids, particularly D-tryptophan and D-tyrosine, were able to inhibit action towards both ACC and D-phenylalanine. These lines of evidence suggest that a single enzyme is capable of promoting malonylation of both ACC and D-phenylalanine. Km values for D-phenylalanine and malonyl-CoA were found to be 48 and 43 microM, respectively; these values are 10-fold lower than the corresponding values when ACC was substrate. Coenzyme A was a noncompetitive (mixed type) product inhibitor towards malonyl-CoA at both unsaturated and saturated ACC concentrations. The enzyme was also inhibited uncompetitively at high concentrations of malonyl-CoA. We propose that the enzyme follows an Ordered Bi-Bi reaction pathway, with the amino acid substrate being bound initially.

Purification and Characterization of 1-Aminocyclopropane-1-Carboxylate N-Malonyltransferase from Etiolated Mung Bean Hypocotyls

1-Aminocyclopropane-1-carboxylate (ACC) N-malonyltransferase converts ACC, an immediate precursor of ethylene, to the presumably inactive product malonyl-ACC (MACC). This enzyme plays a role in ethylene production by reducing the level of free ACC in plant tissue. In this study, ACC N-malonyltransferase was purified 3660-fold from etiolated mung bean (Vigna radiata) hypocotyls, with a 6% overall recovery. The final specific activity was about 83,000 nmol of MACC formed mg(-1) protein h(-1). The five-step purification protocol consisted of polyethylene glycol fractionation, Cibacron blue 3GA-agarose chromatography using salt gradient elution, Sephadex G-100 gel filtration, MonoQ anion-exchange chromatography, and Cibacron blue 3GA-agarose chromatography using malonyl-CoA plus ACC for elution. The molecular mass of the native enzyme determined by Sephadex G-100 chromatography was 50 +/- 3 kD. Protein from the final purification step showed one major band at 55 kD after sodium dodecyl sulfate polyacrylamide gel electrophoresis, indicating that ACC N-malonyltransferase is a monomer. The mung bean ACC N-malonyltransferase has a pH optimum of 8.0, an apparent K(m) of 0.5 mm for ACC and 0.2 mm for malonyl-coenzyme A, and an Arrhenius activation energy of 70.29 kJ mol(-1) degree(-1).

Identification and characterization of three putative genes for 1-aminocyclopropane-1-carboxylate synthase from etiolated mung bean hypocotyl segments.

The polymerase chain reaction (PCR) was used to produce 3 putative clones for ACC synthase from etiolated mung bean (Vigna radiata Rwilcz cv. Berken) hypocotyls. This was accomplished by utilizing genomic DNA from mung bean and degenerate primers made from information derived from highly conserved regions of ACC synthase from different plant tissues. The total length of pMAC-1, pMAC-2 and pMAC-3 are 308, 321, and 326 bp, respectively, all of which code for 68 amino acids. The introns for pMAC-1, pMAC-2 and pMAC-3 are 92, 105, and 110 bp, respectively. The degrees of homology at the DNA level for each of these clones is ca. 80% in their coding region and ca. 50% in their respective introns. This is the first report providing evidence that there are at least 3 genes for ACC synthase in etiolated mung bean.

The Inhibition of Brassinosteroid-Induced Ethylene Biosynthesis in Etiolated Mung Bean Hypocotyl Segments by 2,3,5-Triiodobenzoic Acid and 2-(p-Chlorophenoxy)-2-methylpropionic Acid

The effect of two auxin antagonists, 2,3,5-triiodobenzoic acid (TIBA) and 2-(p-chlorophenoxy)-2-methyl propionic acid (CMPA) on brassinosteroid (BR)-induced ethylene biosynthesis in etiolated mung bean hypocotyl ( Vigna radiata L. Rwilcz cv. Berken) segments was studied. The maximum inhibition of both ethylene and 1-aminocyclopropane-1-carboxylic acid (ACC) biosynthesis by TIBA and CMPA was achieved at concentrations of 50 μM and 10 μM, respectively. With increasing concentrations of BR, there were significant increases in both ethylene and ACC production. When varying concentrations of BR were used in combination with 50 μM TIBA or 10 μM CMPA, there was a decrease in ethylene and ACC production at all BR concentrations tested, with the exception of the lowest. After 18 h, mung bean hypocotyl segments pre-incubated for 8 h with either 50 μM TIBA or 10 μM CMPA showed a maximum inhibition of BR-induced ethylene and ACC production. The results of treatment sequences showed that both TIBA and CMP A caused the same inhibitory effect whether applied before or after BR-treatment.

Characterization of 1-Aminocyclopropane-1-carboxylate synthase purified from mung bean hypocotyls

Summary Analysis of the properties of the key enzyme for ethylene production, 1-aminocyclopropane-1-carboxylate (ACC) synthase, isolated in pure form from hormonally induced etiolated mung bean hypocotyl segments, has revealed that the optimum pH for catalytic activity under normal assay conditions was pH 8.0 although maximal stability was noted at pH 6 to 7. The purified enzyme has an isoelectric point of 5.1 when analyzed by isoelectric focusing and the enzyme's content of pyridoxal phosphate was determined by two separate procedures to be one per subunit of molecular weight 65,000. Edman degradation provided the sequence of 26 residues from the N-terminal portion of the protein: V-A-H-A-K-D-D-A-Y-L-Q-A-A-I-P-K-R-I-K-L-F-E-T-I-Q-A-. Routine assays conducted for 5 minutes with the hydrogen sulfate salt of S-adenosyl methionine (AdoMet) revealed no apparent inhibition. Longer incubation time with substrate, however, indicated that AdoMet was irreversibly inactivating the enzyme and suggested the possibility that this might have important consequences for enzyme turnover. Aminooxyacetic acid was a potent competitive inhibitor of enzyme activity with a Ki of 2 µM. No inhibition was noted with L-homoserine, methylthioadenosine, 5'-AMP, 5'-ADP, 5'-ATP or fusicoccin. An investigation of the methods required to stabilize ACC synthase from mung beans, tomato and apple found that high concentration (>0.5M) of potassium phosphate buffer were effective. Activity remained unchanged during 48-hour storage at 4 °C, and after 10 days in storage, 50 % of the original activity remained for enzyme extracted from mung bean and tomato, while activity from apple tissue was lost after 7 days. Such findings should facilitate the comparative analyses of these important ACC synhases when all have been purified.

Effects of Indole-3-acetic Acid and Brassinosteroid on Ethylene Biosynthesis in Etiolated Mung Bean Hypocotyl Segments

Summary Brassinosteroid (BR) and indole-3-acetic acid (IAA) alone and in combination were evaluated for their effects on ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC), and ACC-synthase production in etiolated mung bean hypocotyl segments. Eighteen hours following treatment with BR (0.25 to 2.0 μM) or IAA (0.5 to 10.0 μM) alone promoted an increase in ethylene and ACC production. When BR and IAA were used in combination there was a synergistic increase in ethylene and ACC production at all concentrations tested 18 h following treatment. Aminooxyacetic acid (AOA), cycloheximide (CHI), and cobalt chloride (COCl2) treatments after 18 h inhibited BR, IAA, and IAA + BR-induced ethylene and ACC production at 2 mM, 100 μM and 10 mM concentrations respectively. Segments treated with 10 μM IAA showed an increase in ACC and ACC-synthase production 3 h after treatment initiation with little change between 3 to 6 h. This plateau was followed by a sharp decline in both ACC and ACC-synthase from 6 to 12 h following treatment. BR treated segments showed a sharp increase in both ACC and ACC-synthase between 6 to 24 h following treatment. When IAA was used in combination with BR there was a sharp increase in ACC and ACC-synthase for the first 12 h following treatment, followed by a plateau. Cobalt chloride dramatically inhibited BR-induced ACC and ACCsynthase over a 24 h period whereas it had a stimulatory effect on both IAA and BR + IAA-induced ACC and ACC-synthase production shortly following treatment. AOA stimulated IAA-induced ACCsynthase activity but not BR-induced. Both IAA and BR induced ethylene and ACC production were both inhibited by AOA.

Purification and characterization of 1-aminocyclopropane-1-carboxylate synthase from etiolated mung bean hypocotyls

1-Aminocyclopropane-l-carboxylate (ACC) synthase, EC 4.4.1.14, was purified to homogeneity from etiolated mung bean hypocotyl segments. This was made possible by the ability to elevate the enzyme level markedly through hormone treatments and by stabilization of the enzyme with high phosphate concentrations. The four-step procedure resulted in 1050-fold purification with 25% yield, and consisted of stepwise elution from hydroxylapatite, chromatography on phenyl-Sepharose CL-4B, gradient elution from hydroxylapatite, and fast protein liquid chromatography (FPLC) on a MonoQ anion-exchange column. FPLC-purified ACC synthase migrated as a single band of M r 65,000 on denaturing polyacrylamide gel electrophoresis. The molecular weight of native enzyme by Bio-Gel A-0.5 m chromatography was 125,000, indicating that the enzyme probably exists as a dimer of identical 65,000 M r subunits. The mung bean ACC synthase exhibited a pH optimum of 8.0 for activity and a K m for S-adenosylmethionine (AdoMet) of 55 μ m at 30 °C. It exhibited an Arrhenius activation energy of 12 kcal mol −1 degree −1 and was inactivated at temperatures in excess of 40 °C. The specific activity for pure ACC synthase was 21 μmol of ACC formed/mg protein/h when determined under optimal conditions with 400 μ m AdoMet.

Uncoupling properties of three flavonols from plane-tree buds

Three new flavonols from Platanus acerifolia bud secretions were investigated for their uncoupling activity. They were platanetin (3,5,7,8-tetrahydroxy-6-dimethylallylflavone) platanin (3,5,7,8-tetrahydroxy-6-methylflavone) and 3-hydroxywogonin (3,5,7-trihydroxy-8-methoxyflavone). Their activities were studied on mitochondria (potato tubers, etiolated mung bean hypocotyls and rat livers), thylakoids and chloroplasts (spinach leaves) and Acer cells. The uncoupling activity was demonstrated using polarography and spectrophotometry. Platanetin is the most potent uncoupler, inducing a full uncoupling with 5, 10 and 6 μM in potato, mung bean and rat liver mitochondria respectively and 30 μM in spinach thylakoids and in Acer cells. The uncoupling activity of the other two flavonoids was lower. The presence of bovine serum albumin in the reaction medium and the variations in pH (between 6.5 and 8) did not affect the uncoupling efficiency. In contrast with other flavonoids, these compounds were only protonophoric and not ionophoric. The p K a and log P values of the three flavonols studied were near those of reference uncouplers. However, for platanetin and 3-hydroxywogonin in the p K a and log P values were the same, but the biological activities were not: a binding of 3-hydroxywogonin to a protein component of the membrane might explain this difference. In contrast, the lower uncoupling activity of platanin, when compared to platanetin, is probably due to a one-unit lower log P. Uncoupling activity of these lipophilic flavonols can be explained using the simplest scheme of Terada, but taking into account the protein-binding effects which interfere with the direct transmembrane proton transport.

Inhibition of activity of the ethylene-forming enzyme by α(p-chlorophenoxy)isobutyric acid

α(p-Chlorophenoxy)isobutyric acid (PCIB) inhibited indole-3-acetic acid (IAA)-induced ethylene production in etiolated mung bean hypocotyl sections. The endogenous level of 1-aminocyclopropane-1-carboxylic acid (ACC) was not significantly affected by PCIB, indicating that PCIB exerted its effect primarily by inhibiting the activity of the ethylene-forming enzyme (EFE). This conclusion was supported by the observations that PCIB inhibited the conversion of exogenously applied ACC to ethylene. The inhibitory effect of PCIB was already evident with 0.05 mM PCIB, and it increased with time after application of the inhibitor. PCIB also significantly inhibited ethylene production in apple fruit tissues, but it only slightly reduced the level of endogenous ACC. Similar to mung bean, EFE activity in apple tissue was significantly inhibited by PCIB. The possibility that PCIB also inhibits auxin-induced ACC synthase activity is discussed.

Lipid Composition of Plasma Membranes and Tonoplasts Isolated from Etiolated Seedlings of Mung Bean (Vigna radiata L.)

The lipid composition of plasma membranes and tonoplasts from etiolated mung bean hypocotyls was examined in detail. Phospholipids, sterols, and ceramide monohexoside(s) were the major lipid classes in both membranes. The content of phospholipids on a protein basis was higher in the tonoplast, but the content of total sterols was similar in both membranes. Accordingly, the sterol to phospholipid molar ratio in the plasma membrane was higher than that of the tonoplast. Phosphatidylethanolamine and phosphatidylcholine comprised the major phospholipids in both membranes. Phosphatidylinositol, phosphatidylserine, and phosphatidylglycerol were identified as minor phospholipid components. The content of phosphatidylinositol and phosphatidylglycerol was relatively high in the tonoplast, comprising 11 and 5% of the total phospholipids, respectively. Although special care was taken against the degradative action of phospholipase D and phosphatidic acid phosphatase during the isolation of these membranes, by adding EDTA, EGTA, KF, choline, and ethanolamine to the homogenizing medium, significant amounts of phosphatidic acid, about 15% of the total phospholipids, were detected in the plasma membrane. On the other hand, the content of phosphatidic acid in tonoplasts and other membrane fractions was very low. This fact may indicate that high levels of phosphatidic acid occur naturally in plasma membranes. Phosphatidylglycerol in both membranes and phosphatidylinositol in the tonoplast contained high levels of palmitic acid, which comprised more than 50% of the total fatty acids. Significant differences were observed in the sterol compositions of plasma membranes and tonoplasts. More than 90% of the sterols in the plasma membrane were unesterified, while the tonoplast was enriched in glycosylated sterols, especially acylated sterylglycosides. Ceramide monohexoside was found to be specifically located in these membranes, in particular, in the tonoplast, in which it comprised nearly 17% of the total lipids.

Inactivation of 1-Aminocyclopropane-1-carboxylic Acid Synthase of Etiolated Mung Bean Hypocotyl Segments by its Substrate, S-Adenosyl-L-methionine

Inactivation of 1-Aminocyclopropane-1-carboxylic Acid Synthase of Etiolated Mung Bean Hypocotyl Segments by its Substrate, S-Adenosyl-L-methionine