Phytoalexin synthesis in soybean cells: elicitor induction of phenylalanine ammonia-lyase and chalcone synthase mRNAs and correlation with phytoalexin accumulation

Rhizobacterial Bacillus mycoides functions in stimulating the antioxidant defence system and multiple phytohormone signalling pathways to regulate plant growth and stress tolerance

AIMS

To analyse effects and mechanisms of plant growth promotion mediated by Bacillus mycoides strain A3 (BmA3), in Arabidopsis thaliana seedlings.

METHODS AND RESULTS

Bacillus mycoides strain A3 (BmA3) isolated from the bamboo rhizosphere produced phytohormones, including indole-3-acetic acid (IAA) and gibberellic acid (GA), and exhibited phosphate solubilization and radical scavenging activities. A. thaliana seedlings inoculated with BmA3 exhibited an altered root architecture including an increased number of lateral roots and root hairs. Likewise, enhanced photosynthetic efficiency through the accumulation of higher levels of chlorophyll and starch, and increased plant size and fresh weight were observed in the BmA3-treated seedlings. This bacterial inoculation stimulated the antioxidant defence system by increasing the activities of catalase (CAT), guaiacol peroxidase (GPX), ascorbate peroxidase (APX) and phenylalanine ammonia-lyase (PAL). Secondary metabolites, including phenolic compounds, flavonoids and glucosinolates, were induced to higher levels in the BmA3-treated plants. Under drought and heat stresses, lower levels of H₂ O₂ , malondialdehyde (MDA) and electrolyte leakage were noticed in the treated seedlings. Genes involved in the signalling pathway of jasmonic acid (JA) including MYC2 and lipoxygenase 1 (LOX1) and salicylic acid (SA) including SAR DEFICIENT 1 (SARD1) and CAM-BINDING PROTEIN 60-LIKE G (CBP60G), and the antioxidant defence system including Ascorbate peroxidase (AtAPX) and alternative oxidase (AOX) were upregulated in BmA3-treated plants. Moreover, pathogenesis-related protein 1 (PR-1) and PR-2, marker genes for disease resistance, as well as DREB2A and HsFA2, which function in abiotic stress regulation, were also upregulated.

CONCLUSIONS

BmA3 was able to activate JA and SA signalling pathways to induce plant growth and abiotic stress tolerance in A. thaliana seedlings.

SIGNIFICANCE AND IMPACT OF STUDY

The plant growth promotion and increased stress tolerance induced by BmA3 were the result of the combined effects of microbial metabolites and activated host plant responses, including phytohormone signalling pathways and antioxidant defence systems.

Use of Alginate Extracted from Moroccan Brown Algae to Stimulate Natural Defense in Date Palm Roots

Our study aimed to search for seaweed polysaccharides able to stimulate date palm defense mechanisms. Extraction, purification, characterization, and elicitor activity of sodium alginate (FSSA and BBSA) from Moroccan brown seaweeds Fucus spiralis and Bifurcaria bifurcata were investigated. FSSA and BBSA were characterized by proton nuclear magnetic resonance spectroscopy (1H-NMR) and size exclusion chromatography (HPLC-SEC). The mannuronic acid/guluronic acid (M/G) ratio of FSSA was M/G= 0.92 indicating that FSSA contained 48% and 52% of mannuronic and guluronic acids respectively, and the M/G ratio of BBSA was 0.47 indicating that BBSA contained 32% and 68% of mannuronic and guluronic acids respectively. Elicitor activity of FSSA and BBSA was carried out by developing an innovative study model on the date palm. The elicitor capacities were evaluated by investigating phenolic metabolism including phenylalanine ammonia-lyase (PAL) activity and total polyphenol content in seedling roots of date palm maintained in alginates solution (FSSA and BBSA) at different concentrations. The results obtained show that the PAL activity and the phenolic compound content were significantly stimulated with 1 mg.mL-1 of FSSA and BBSA; after 1 day of treatment with FSSA, and after 12 hours of treatment with BBSA. These results show clearly those alginates extracted from Moroccan brown algae induced in date palm roots the stimulation of natural defense mechanisms.

Cooperative functioning between phenylalanine ammonia lyase and isochorismate synthase activities contributes to salicylic acid biosynthesis in soybean

Salicylic acid (SA), an essential regulator of plant defense, is derived from chorismate via either the phenylalanine ammonia lyase (PAL) or the isochorismate synthase (ICS) catalyzed steps. The ICS pathway is thought to be the primary contributor of defense-related SA, at least in Arabidopsis. We investigated the relative contributions of PAL and ICS to defense-related SA accumulation in soybean (Glycine max). Soybean plants silenced for five PAL isoforms or two ICS isoforms were analyzed for SA concentrations and SA-derived defense responses to the hemibiotrophic pathogens Pseudomonas syringae and Phytophthora sojae. We show that, unlike in Arabidopsis, PAL and ICS pathways are equally important for pathogen-induced SA biosynthesis in soybean. Knock-down of either pathway shuts down SA biosynthesis and abrogates pathogen resistance. Moreover, unlike in Arabidopsis, pathogen infection is associated with the suppression of ICS gene expression. Pathogen-induced biosynthesis of SA via the PAL pathway correlates inversely with phenylalanine concentrations. Although infections with either virulent or avirulent strains of the pathogens increase SA concentrations, resistance protein-mediated response to avirulent P. sojae strains may function in an SA-independent manner. These results show that PAL- and ICS-catalyzed reactions function cooperatively in soybean defense and highlight the importance of PAL in pathogen-induced SA biosynthesis.

Inducible versus constitutive PI 227687 soybean resistance to mexican bean beetle,Epilachna varivestis

Contrary to constitutive resistance, inducible resistance to Mexican bean beetle (MBB) (Epilachna varivestis) herbivory in PI 227687 soybean leaves was positively correlated with total phenolic content and temporally unique, increasedL-phenylalanine ammonia-lyase (PAL) andL-tyrosine ammonia-lyase (TAL) activities. Initial expression of the induced resistance was localized at or near the site of herbivory. Systemic parameters of the induced resistance also were observed. Inducible MBB resistance in PI 227687 soybeans apparently involves increased phenylpropanoid metabolism.

Rapid switching of plant gene expression induced by fungal elicitor

The pattern of messenger RNA synthesis in suspension-cultured bean cells (Phaseolus vulgaris L.) was analyzed by blot hybridization and in vitro translation of newly synthesized messenger RNA. The RNA was separated from preexisting RNA by organomercurial affinity chromatography after in vivo labeling with 4-thiouridine. The elicitor induced the synthesis of messenger RNA's encoding phenylalanine ammonia-lyase, chalcone synthase, and chalcone isomerase, three enzymes of phenylpropanoid metabolism involved in the synthesis of isoflavonoidderived phytoalexins. This is part of a rapid and extensive change in the pattern of messenger RNA synthesis directing production of a set of proteins associated with expression of disease resistance.

Accumulation of hydroxyproline-rich glycoprotein mRNAs in response to fungal elicitor and infection

Hydroxyproline-rich glycoproteins (HRGPs) are important structural components of plant cell walls and also accumulate in response to infection as an apparent defense mechanism. Accumulation of HRGP mRNA in biologically stressed bean (Phaseolus vulgaris L.) cells was monitored by blot hybridization with (32)P-labeled tomato genomic HRGP sequences. Elicitor treatment of suspension-cultured cells caused a marked increase in hybridizable HRGP mRNA. The response was less rapid but more prolonged than that observed for mRNAs encoding enzymes of phytoalexin biosynthesis. HRGP mRNA also accumulated during race:cultivar-specific interactions between bean hypocotyls and the partially biotrophic fungus Colletotrichum lindemuthianum, the causal agent of anthracnose. In an incompatible interaction (host resistant) there was an early increase in HRGP mRNA correlated with expression of hypersensitive resistance; whereas, in a compatible interaction (host susceptible), marked accumulation of HRGP mRNA occurred as a delayed response at the onset of lesion formation. In both interactions, mRNA accumulation was observed in uninfected cells distant from the site of fungal inoculation, indicating intercellular transmission of an elicitation signal.

Rapid transient induction of phenylalanine ammonia-lyase mRNA in elicitor-treated bean cells

DNAs complementary to a size-selected fraction of poly(A)(+) RNA present in elicitor-treated cells of bean (Phaseolus vulgaris L.) were inserted into pAT153 and used to transform Escherichia coli strain C600. Five clones were identified by hybrid-selected translation and cross-hybridization that contained sequences complementary to mRNA encoding phenylalanine ammonia-lyase (EC 4.3.1.5), which catalyzes the first reaction of phenylpropanoid biosynthesis. The longest insert contained a single open reading frame of 1520 base pairs together with 223 base pairs of 3' untranslated sequence. RNA blot hybridization showed that elicitor caused a rapid, marked but transient increase in phenylalanine ammonia-lyase mRNA that was closely correlated with changes in translatable mRNA activity in vitro and enzyme synthesis in vivo. Blot hybridization of newly synthesized mRNA purified by organomercurial affinity chromatography following in vivo pulse-labeling with 4-thiouridine indicates that elicitor caused a rapid stimulation of phenylalanine ammonia-lyase mRNA synthesis as an early in the defense response leading to accumulation of phenylpropanoid-derived phytoalexins.

Genomic evidences for the existence of a phenylpropanoid metabolic pathway in Aspergillus oryzae

Plants interact with their environment by producing a diverse array of secondary metabolites. A majority of these compounds are phenylpropanoids and flavonoids which are valued for their medicinal and agricultural properties. The phenylpropanoid biosynthesis pathway proceeds with the basic C6-C3 carbon skeleton of phenylalanine, and involves a wide range of enzymes viz., phenylalanine ammonia lyase, coumarate hydroxylase, coumarate ligase, chalcone synthase, chalcone reductase and chalcone isomerase. Recently, bacteria have also been shown to contain homodimeric polyketide synthases belonging to the plant chalcone synthase superfamily linking the capabilities of plants and bacteria in the biosynthesis of flavonoids. We report here the presence of genes encoding the core enzymes of the phenylpropanoid pathway in an industrially useful fungus, Aspergillus oryzae. Although the assignment of enzyme function must be confirmed by further biochemical evidences, this work has allowed us to anticipate the phenylpropanoid metabolism profile in a filamentous fungus for the first time and paves way for research on identifying novel fungal flavonoid-like metabolites.

Volatile C6-aldehydes and Allo-ocimene activate defense genes and induce resistance against Botrytis cinerea in Arabidopsis thaliana

Green leafy volatiles or isoprenoids are produced after mechanical wounding or pathogen/herbivore attacks in higher plants. We monitored expression profiles of the genes involved in defense responses upon exposing Arabidopsis thaliana to the volatiles. Among the genes investigated, those known to be induced by mechanical wounding and/or jasmonate application, such as chalcone synthase (CHS), caffeic acid-O-methyltransferase (COMT), diacylglycerol kinase1 (DGK1), glutathione-S-transferase1 (GST1) and lipoxygenase2 (LOX2), were shown to be induced with (E)-2-hexenal, (Z)-3-hexenal, (Z)-3-hexenol or allo-ocimene (2,6-dimethyl-2,4,6-octatriene). A salicylic acid-responsive gene, pathogenesis-related protein2 (PR2), was not induced by the volatiles. Detailed analyses of the expression profiles showed that the manner of induction varied depending on either the gene monitored or the volatile used. A chemically inert compound, (Z)-3-hexenol, was also potent, which suggested that chemical reactivity was not the sole requisite for the inducing activity. With a jasmonate-insensitive mutant (jar1), the induction by the volatiles was mostly suppressed, however, that of LOX2 was unaltered. An ethylene-insensitive mutant (etr1) showed responses almost identical to the wild type, with minor exceptions. From these observations, it was suggested that both the jasmonate-dependent and -independent pathways were operative upon perception of the volatiles, while the ETR1-dependent pathway was not directly involved. When Botrytis cinerea was inoculated after the volatile treatment, retardation of disease development could be seen. It appears that volatile treatment could make the plants more resistant against the fungal disease.

The matrix metalloproteinase gene GmMMP2 is activated in response to pathogenic infections in soybean

Matrix metalloproteinases (MMPs) play an important role in host defense responses against pathogens in mammals where their activities lead to the production of antimicrobial peptides. We have identified a novel soybean (Glycine max) metalloproteinase gene, GmMMP2, that is transcriptionally up-regulated in infected tissues. The deduced amino acid sequence indicates that this gene belongs to the MMP family. It is a preproprotein containing an N-terminal signal peptide, a cysteine switch, a zinc-binding catalytic motif, and a C-terminal transmembrane domain. The GmMMP2 expressed in and purified from Escherichia coli exhibited an in vitro enzymatic activity in digesting myelin basic protein. All plant metalloproteinases reported so far have no known functions. However, they have been suggested to be involved in extracellular cell matrix degradation during development or senescence. Our investigations demonstrate that the GmMMP2 transcript levels were rapidly increased in compatible and incompatible interactions of soybean tissues with the oomycete pathogen Phytophthora sojae or the bacterial pathogen Pseudomonas syringae pv. glycinea. In agreement with the GmMMP2 activation, a metalloproteinase activity was gradually increased in suspension-cultured cells following the bacterial infection. GmMMP2 was also activated in response to wounding and dehydration. However, GmMMP2 activation did not correlate with the oxidative burst leading to the hypersensitive response cell death or the tissue senescence progress that involves programmed cell death. Our investigations suggest that GmMMP2 may be involved in a novel defense response of soybean against pathogenic infections.

The octadecanoid pathway is required for pathogen-induced multi-functional acetyl-CoA carboxylase accumulation in common bean (Phaseolus vulgaris L.)

A partial cDNA clone corresponding to the multi-functional acetyl-CoA carboxylase (ACCase, EC 6.4.1.2) was isolated using RNA extracted from methyl jasmonate (MeJA)-induced common bean cell cultures. Most of this clone corresponds to the 3' untranslated region and it showed high identity to alfalfa and soybean ACCase sequences. Southern hybridization revealed one copy of this gene in the common bean genome. In addition to being induced by MeJA in cell cultures and leaves, ACCase mRNA accumulated after yeast elicitor or Pseudomonas syringae pv tabaci treatment. Inhibitors of the octadecanoid pathway severely reduced ACCase mRNA and protein accumulation induced by yeast elicitor or P. syringae pv tabaci, indicating that jasmonates or a precursor mediate ACCase induction after pathogen infection. These results provide a role for the eukaryotic ACCase during the defense response to pathogens in common bean.

A multisubunit acetyl coenzyme A carboxylase from soybean

A multisubunit form of acetyl coenzyme A (CoA) carboxylase (ACCase) from soybean (Glycine max) was characterized. The enzyme catalyzes the formation of malonyl CoA from acetyl CoA, a rate-limiting step in fatty acid biosynthesis. The four known components that constitute plastid ACCase are biotin carboxylase (BC), biotin carboxyl carrier protein (BCCP), and the alpha- and beta-subunits of carboxyltransferase (alpha- and beta-CT). At least three different cDNAs were isolated from germinating soybean seeds that encode BC, two that encode BCCP, and four that encode alpha-CT. Whereas BC, BCCP, and alpha-CT are products of nuclear genes, the DNA that encodes soybean beta-CT is located in chloroplasts. Translation products from cDNAs for BC, BCCP, and alpha-CT were imported into isolated pea (Pisum sativum) chloroplasts and became integrated into ACCase. Edman microsequence analysis of the subunits after import permitted the identification of the amino-terminal sequence of the mature protein after removal of the transit sequences. Antibodies specific for each of the chloroplast ACCase subunits were generated against products from the cDNAs expressed in bacteria. The antibodies permitted components of ACCase to be followed during fractionation of the chloroplast stroma. Even in the presence of 0.5 M KCl, a complex that contained BC plus BCCP emerged from Sephacryl 400 with an apparent molecular mass greater than about 800 kD. A second complex, which contained alpha- and beta-CT, was also recovered from the column, and it had an apparent molecular mass of greater than about 600 kD. By mixing the two complexes together at appropriate ratios, ACCase enzymatic activity was restored. Even higher ACCase activities were recovered by mixing complexes from pea and soybean. The results demonstrate that the active form of ACCase can be reassembled and that it could form a high-molecular-mass complex.

Effects of UV-B radiation on growth, photosynthesis, UV-B-absorbing compounds and NADP-malic enzyme in bean (Phaseolus vulgaris L.) grown under different nitrogen conditions

The effects of UV-B radiation on growth, photosynthesis, UV-B-absorbing compounds and NADP-malic enzyme have been examined in different cultivars of Phaseolous vulgaris L. grown under 1 and 12 mM nitrogen. Low nitrogen nutrition reduces chlorophyll and soluble protein contents in the leaves and thus the photosynthesis rate and dry-matter accumulation. Chlorophyll, soluble protein and Rubisco contents and photosynthesis rate are not significantly altered by ambient levels of UV-B radiation (17 microW m-2, 290-320 nm, 4 h/day for one week). Comparative studies show that under high nitrogen, UV-B radiation slightly enhances leaf expansion and dry-matter accumulation in cultivar Pinto, but inhibits these parameters in Vilmorin. These results suggest that the UV-B effect on growth is mediated through leaf expansion, which is particularly sensitive to UV-B, and that Pinto is more tolerant than Vilmorin. The effect of UV-B radiation on UV-B-absorbing compounds and on NADP-malic enzyme (NADP-ME) activity is also examined. Both UV-B radiation and low-nitrogen nutrition enhance the content of UV-B-absorbing compounds, and among the three cultivars used, Pinto exhibits the highest increases and Arroz the lowest. The same trend is observed for the specific activity and content of NADP-ME. On a leaf-area basis, the amount of UV-B-absorbing compounds is highly correlated with the enzyme activity (r2 = 0.83), suggesting that NADP-ME plays a key role in biosynthesis of these compounds. Furthermore, the higher sensitivity of Vilmorin than Pinto to UV-B radiation appears to be related to the activity of NADP-ME and the capacity of the plants to accumulate UV-B-absorbing compounds.

Co-purification, co-imniunoprecipitation, and coordinate expression of acetyl-coenzyme A carboxylase activity, biotin carboxylase, and biotin carboxyl carrier protein of higher plants

Acetyl-CoA carboxylase (ACCase; EC 6.4.1.2) is a regulatory enzyme of fatty acid synthesis, and in some higher-plant plastids is a multi-subunit complex consisting of biotin carboxylase (BC), biotin-carboxyl carrier protein (BCCP), and carboxyl transferase (CT). We recently described a Nicotiana tabacum L. (tobacco) cDNA with a deduced amino acid sequence similar to that of prokaryotic BC. We here provide further biochemical and immunological evidence that this higher-plant polypeptide is an authentic BC component of ACCase. The BC protein co-purified with ACCase activity and with BCCP during gel permeation chromatography of Pisum sativum L. (pea) chloroplast proteins. Antibodies to the Ricinus communis L. (castor) BC co-precipitated ACCase activity and BCCP. During castor seed development, ACCase activity and the levels of BC and BCCP increased and subsequently decreased in parallel, indicating their coordinate regulation. The BC protein comprised about 0.8% of the soluble protein in developing castor seed, and less than 0.05% of the protein in young leaf or root. Polypeptides cross-reacting with antibodies to castor BC were detected in several dicotyledons and in the monocotyledons Hemerocallis fulva L. (day lily), Iris L., and Allium cepa L. (onion), but not in the Gramineae species Hordeum vulgare L. (barley) and Panicum virgatum L. (switchgrass). The castor endosperm and pea chloroplast ACCases were not significantly inhibited by long-chain acyl-acyl carrier protein, free fatty acids or acyl carrier protein. The BC polypeptide was detected throughout Brassica napus L. (rapeseed) embryo development, in contrast to the multi-functional ACCase isoenzyme which was only detected early in development. These results firmly establish the identity of the BC polypeptide in plants and provide insight into the structure, regulation and roles of higherplant ACCases.

Molecular cloning, characterization, and elicitation of acetyl-CoA carboxylase from alfalfa

Acetyl-CoA carboxylase [ACCase; acetyl-CoA:carbon-dioxide ligase (ADP-forming), EC 6.4.1.2] catalyzes the ATP-dependent carboxylation of acetyl CoA to produce malonyl CoA. In plants, malonyl CoA is needed for plastid localized fatty acid biosynthesis and for a variety of pathways in the cytoplasm including flavonoid biosynthesis. We have determined the full nucleotide sequence of an ACCase from alfalfa, which appears to represent a cytoplasmic isozyme. Partial cDNAs were isolated from a cDNA library of suspension culture cells that had been elicited for isoflavonoid phytoalexin synthesis. The full-length sequence was obtained by primer extension and amplification of the cDNA with synthetic primers. The sequence codes for a protein of 2257 amino acids with a calculated M(r) of 252,039. The biotin carboxylase, biotin carboxyl carrier protein, and carboxyltransferase domains, respectively, show approximately 72%, 50%, and 65% sequence similarity to those of animal, diatom, and yeast ACCase sequences. ACCase enzyme activity and transcripts are induced severalfold upon addition of yeast or fungal elicitors to alfalfa cell cultures.

Detection and time-course analysis of phospholipid hydroperoxide in soybean seedlings after treatment with fungal elicitor, by chemiluminescence-HPLC assay

Direct evidence for the existence of phosphatidylcholine hydroperoxide (PCOOH) and the determination of the changes in PCOOH after treatment of soybean seedlings with fungal elicitor, were examined using chemiluminescence-HPLC of hydroperoxide specific assay. PCOOH was transiently accumulated within 6 h after elicitor treatment but such an event was not observed in control plants, thus suggesting that accumulation of PCOOH was a response to fungal elicitor in the host plant. The result suggested that singlet oxygen had participated in the lipid hydroperoxidation, since non-conjugated fatty acid hydroperoxide isomers due to the singlet oxygen oxidation were detected in the phospholipid fraction. The reaction of lipid hydroperoxidation, preceding the induction of a defense compound, may be involved in the triggering of a plant defense mechanism against fungal invasion.

Elicitor-induced metabolic changes in cell cultures of chickpea (Cicer arietinum L.) cultivars resistant and susceptible to Ascochyta rabiei : II. Differential induction of chalcone-synthase-mRNA activity and analysis of in-vitro-translated protein patterns

Cell-suspension cultures of two chickpea (Cicer arietinum L.) cultivars, resistant (ILC 3279) and susceptible (ILC 1929) to the fungus Ascochyta rabiei (Pass.) Lab., showed differential accumulation of the phytoalexins medicarpin and maackiain, and transient induction of related enzyme activities after application of an A. rabiei-derived elicitor. The chalcone-synthase (CHS) activity (EC 2.3.1.74) which is involved in the first part of phytoalexin biosynthesis exhibited a maximum 8-12 h after elicitation in the cells of both cultivars. Concomitant with the fivefold-higher phytoalexin accumulation, CHS activity increased twofold in the cells of the resistant cultivar. The maximum of the elicitor-induced CHS-mRNA activity was determined 4 h after onset of induction in the cultures of both cultivars, although in cells of cultivar ILC 3279 this mRNA activity was induced at a level twofold higher than that in cells of the susceptible race ILC 1929. Investigations of CHS isoenzymes by two-dimensional gel electrophoresis of immunoprecipitated in-vitro-translated protein indicated the presence of five proteins. In the cells of both cultivars only two of the isoenzymes were induced after elicitor treatment. Analysis of the total in-vitro-translated proteins by two-dimensional gel electrophoresis showed that the constitutively expressed patterns of mRNA activities in the cell cultures of the two cultivars were identical. After elicitation, considerably more translatable mRNAs were induced in the cells of cultivar ILC 3279. The few induced proteins, and their respective mRNA activities, which could be detected in the cells of the susceptible cultivar, all existed in the cells of the resistant cultivar, too. One highly induced protein (Mr 18 kDa) found in the cells of cultivar ILC 3279 reached its maximum mRNA activity 6 h after elicitor application. The amount of this protein was hardly increased in the cells of the susceptible cultivar. This protein appears to be excreted from the cells into the growth medium.

Elicitor-induced metabolic changes in cell cultures of chickpea (Cicer arietinum L.) cultivars resistant and susceptible to Ascochyta rabiei : I. Investigations of enzyme activities involved in isoflavone and pterocarpan phytoalexin biosynthesis

Cell-suspension cultures of Ascochyta rabiei-resistant (ILC 3279) and -susceptible (ILC 1929) chickpea (Cicer arietinum L.) cultivars were compared with regard to their elicitor-induced accumulation of pterocarpan phytoalexins and increases in the activities of biosynthetic enzymes. The growth performances and protein patterns of the two cell-culture lines were essentially identical. Treatment of cell cultures with a polysaccharide elicitor from A. rabiei induced fivefold-higher amounts of the phytoalexins medicarpin and maackiain in the cells of the resistant than in the susceptible cultivar. Glucose 6-phosphate dehydrogenase and eight enzymes representing the general phenylpropanoid pathway, the flavonoid-forming steps and the pterocarpanspecific branch of phytoalexin biosynthesis were found to be elicitor-induced. Phenylalanine ammonia-lyase and chalcone synthase reached sharp, transient optima some 8 h after elicitor application in the cells of both cultivars. The activities of isoflavone 2'- and 3'-hydroxylases were only induced in cells of the resistant cultivar with a maximum after 8 h. Cinnamic acid 4-hydroxylase, chalcone isomerase, 2'-hydroxyisoflavone reductase and pterocarpan synthase showed a later or no sharp optimum. The isoflavone-specific 7-O-glucosyltransferase was not induced in either cell-culture line. Cells of the susceptible cultivar failed to induce significant activities of isoflavone 2'-hydroxylase and these cells produced only very low amounts of phytoalexins. Isoflavone 2'-hydroxylase is postulated to be the main limiting enzyme for pterocarpan biosynthesis in cells of the susceptible cultivar. The pterocarpan biosynthetic pathway in chickpea cells represents a suitable model for investigations of differential gene activation in connection with the expression of antimicrobial defence reactions.

Defense gene expression in elicitor-treated cell suspension cultures of french bean cv. Imuna

Cell suspension cultures of bean (Phaseolus vulgaris) cv. Imuna accumulated isoflavonoid phytoalexins on exposure to elicitor from the phytopathogenic fungus Colletotrichum lindemuthianum (CL). This was preceeded by rapid increases in the activities of phenylalanine ammonia-lyase (PAL) and chalcone synthase (CHS). However, the patterns of expression of PAL and CHS genes differed from those observed in cultures of a previously studied bean cultivar. The relative levels of transcripts from individual members of the CHS multigene family differed significantly at 1.5 h compared to 22.5 h after elicitation. More strikingly, three PAL genes were expressed in cultivar Imuna in response to fungal elicitor, whereas two are expressed in elicitor-treated cell cultures of cultivar Canadian Wonder.

An endogenous factor from soybean (Glycine max L.) cell cultures activates phosphorylation of a protein which is dephosphorylated in vivo in elicitor-challenged cells

The existence of specific binding sites for a β-glucan elicitor of phytoalexin synthesis derived from the fungus Phytophthora megasperma f.sp. glycinea at the plasma membrane of soybean (Glycine max L.) tissues (W.E. Schmidt, J. Ebel (1987) Proc. Natl. Acad. Sci. USA 84, 4117-4121) might imply that stimulation of phytoalexin formation by the elicitor is a membrane-mediated process. Addition of the β-glucan elicitor to soybean cellsuspension cultures, which has previously been shown to induce phytoalexin accumulation, also results in rapid changes in the phosphate turnover of several phosphoproteins. The effect of the elicitor on protein phosphorylation was tested after labeling of the cells with [(32)P]orthophosphate. As shown by analysis using one-and two-dimensional gel electrophoresis, decreases as well as increases in the labeling of several phosphoroteins occurred rapidly, being detectable within 5 min after elicitor application, and persisted for at least 15 min. As judged by their relative molecular masses (Mr) and isoelectric points (pI), a number of proteins which were radioactively labeled in vivo were also phosphorylated in vitro by endogenous protein-kinase activity in the presence of Ca(2+). The most pronounced effect was observed with a protein substrate with Mr=69000 and pI=5.7 (pp69) whose phosphate labeling markedly decreased in response to elicitor treatment in vivo. Phosphorylation of pp69 in vitro in the presence of γ-[(32)P]ATP was strongly enhanced by a phosphorylation-stimulating factor (effector) derived from soybean cell cultures and occurred predominantly at serine residues. The effector possessed a low apparent Mr (≤1000), was negatively charged at pH 7.3, and was relatively heat stable. The effector was inactivated by treatment with alkaline phosphatase from calf intestine. Phosphorylation of pp69 was only slightly stimulated by Ca(2+), and was insensitive to cAMP, cGMP, calmodulin, a lipid mixture, a ganglioside mixture, or spermine under the assay conditions used. A 10 mM concentration of 3-phosphoglycerate increased pp69 phosphorylation to the extent of about 50% of that induced by the soybean effector. There was no evidence, however, that such concentrations of 3-phosphoglycerate occurred in effector preparations. The results are discussed in relation to hypothetical signal transduction during elicitor action on soybean cells.

Phytoalexin synthesis in soybean cells: elicitor induction of reductase involved in biosynthesis of 6'-deoxychalcone

Chromatofocusing on Mono P proved to be an efficient purification procedure for the NADPH-dependent reductase from soybean (Glycine max L.) cell cultures which acts together with chalcone synthase in the biosynthesis of 2',4',4-trihydroxychalcone (6'-deoxychalcone). By isoelectric focusing the pI of reductase was determined to be 6.3. Addition of pure soybean reductase to cell-free extracts from stimulated cell cultures of parsley and bean (Phaseolus vulgaris) and from young flowers of Dahlia variabilis caused in each case synthesis of 6'-deoxychalcone. When 4-coumaroyl-CoA was replaced by caffeoyl-CoA in the reductase assay, formation of 2',4',3,4-tetrahydrochalcone (butein) was observed. A polyclonal antireductase antiserum was raised in rabbits and proved to be specific in Ouchterlony diffusion experiments, Western blots and immunotitration. The reductase antiserum showed no cross-reactivity with soybean chalcone synthase (CHS). A biotin/[125I]streptavidin system provided a quantitative Western blot for the reductase. Changes in the activities, amounts of protein, and mRNA activities of reductase and CHS were determined after challenge of soybean cell cultures by elicitor (from Phytophthora megasperma f.sp. glycinea or yeast). For both enzymes a pronounced and parallel increase in activity and amounts of protein was observed after elicitor addition with a maximum at about 16 h after challenge. Parallel increases in mRNA activities occurred earlier. The results indicate a parallel induction of de novo synthesis of reductase and CHS which coact in synthesis of 6'-deoxychalcone.

Formation of trans-caffeoyl-CoA from trans-4-coumaroyl-CoA by Zn2+-dependent enzymes in cultured plant cells and its activation by an elicitor-induced pH shift

A novel hydroxylase activity catalyzing the formation of trans-caffeoyl-CoA from trans-4-coumaroyl-CoA was identified in crude extracts from cultured parsley cells. The extracts were less active (Vmax/Km) in converting trans-4-coumaric to trans-caffeic acid. Optimal hydroxylase activity was found at pH 6.5 with a steep decline toward both pH 7.4 and pH 5.0. The enzyme activity requires ascorbate and Zn2+ at optimal concentrations of 50 and 0.5 mM, respectively. No other reductant could replace ascorbate, whereas high concentrations of Ca2+ partially substituted for Zn2+. The enzyme is soluble and appears to be located in the cytoplasm. The unusual pH optimum suggests that the hydroxylase is inactive at the normal cytoplasmic pH. Upon treatment of parsley cells with an elicitor derived from Phytophthora megasperma f. sp. glycinea, the cytoplasmic pH dropped by approximately 0.25 pH unit within 55 min as determined by 31P NMR spectroscopy. Our results suggest that this shift in the cytoplasmic pH is sufficient for the activation of the hydroxylase, eventually leading to the formation of caffeoyl and feruloyl esters. Such esters may be a part of a very rapid resistance response of the plant cells, which would leave no time for de novo enzyme synthesis.

The chalcone synthase multigene family of Petunia hybrida (V30): differential, light-regulated expression during flower development and UV light induction

We have analysed the expression of the 8-10 members of the gene family encoding the flavonoid biosynthetic enzyme chalcone synthase (CHS) from Petunia hybrida. During normal plant development only two members of the gene family (CHS-A and CHS-J) are expressed. Their expression is restricted to floral tissues mainly. About 90% of the total CHS mRNA pool is transcribed from CHS-A, wheares CHS-J delivers about 10% in flower corolla, tube and anthers. Expression of CHS-A and CHS-J during flower development is coordinated and (red) light-dependent. In young seedlings and cell suspension cultures expression of CHS-A and CHS-J can be induced with UV light. In addition to CHS-A and CHS-J, expression of another two CHS genes (CHS-B and CHS-G) is induced in young seedlings by UV light, albeit at a low level. In contrast to CHS genes from Leguminoseae, Petunia CHS genes are not inducible by phytopathogen-derived elicitors. Expression of CHS-A and CHS-J is reduced to a similar extent in a regulatory CHS mutant, Petunia hybrida Red Star, suggesting that both genes are regulated by the same trans-acting factors. Comparison of the promoter sequences of CHS-A and CHS-J reveals some striking homologies, which might represent cis-acting regulatory sequences.

Rapid induction of phenylalanine ammonia-lyase and chalcone synthase mRNAs during fungus infection of soybean (Glycine max L.) roots or elicitor treatment of soybean cell cultures at the onset of phytoalexin synthesis

The differential regulation of the activities and amounts of mRNAs for two enzymes involved in isoflavonoid phytoalexin biosynthesis in soybean was studied during the early stages after inoculation of primary roots with zoospores from either race 1 (incompatible, host resistant) or race 3 (compatible, host susceptible) of Phytophthora megasperma f.sp. glycinea, the causal fungus of root rot disease. In the incompatible interaction, cloned cDNAs were used to demonstrate that the amounts of phenylalanine ammonia-lyase and chalcone synthase mRNAs increased rapidly at the time of penetration of fungal germ tubes into epidermal cell layers (1-2 h after inoculation) concomitant with the onset of phytoalxxin accumulation; highest levels were reached after about 7 h. In the compatible interaction, only a slight early enhancement of mRNA levels was found and no further increase occurred until about 9 h after inoculation. The time course for changes in the activity of chalcone synthase mRNA also showed major differences between the incompatible and compatible interaction. The observed kinetics for the stimulation of mRNA expression related to phytoalexin synthesis in soybean roots lends further support to the hypothesis that phytoalexin production is an early defense response in the incompatible plant-fungus interaction. The kinetics for the enhancement of mRNA expression after treatment of soybean cell suspension cultures with a glucan elicitor derived from P. megasperma cell walls was similar to that measured during the early stages of the resistant response of soybean roots.

Different cell-wall components from Phytophthora megasperma f. sp. glycinea elicit phytoalexin production in soybean and parsley

Different components of a crude cell-wall preparation from the phytopathogenic fungus, Phytophthora megasperma f. sp. glycinea, act as elicitors of phytoalexin accumulation in parsley (Petroselinum crispum) and soybean (Glycine max). Treatments of cultured parsley cells and protoplasts or soybean cells and cotyledons with proteinase-digested or deglycosylated elicitor preparations identify proteinaceous constituents as active eliciting compounds in parsley, which are inactive in soybean. The proteinase-treated elicitor as well as a defined heptaglucan are active in soybean but do not stimulate phytoalexin synthesis in parsley. Soybean and parsley cells therefore not only perceive different signals from cell walls of Phytophthora megasperma f. sp. glycinea, but are unable to respond to the fungal compounds primarily recognized by the other plant.

NAD(P)H-dependent 6'-deoxychalcone synthase activity in Glycyrrhiza echinata cells induced by yeast extract

The crude extract prepared from Glycyrrhiza echinata cells treated with yeast extract catalyzed the formation of liquiritigenin (5-deoxyflavanone) and isoliquiritigenin (6'-deoxychalcone) in addition to naringenin (5-hydroxyflavanone) when incubated with 4-coumaroyl-CoA and malonyl-CoA in the presence of high concentrations (0.1 mM or higher) of NADPH. Incubation without NADPH, or with low concentrations (0.01 mM or lower), gave only naringenin as a reaction product. With NADH (1 mM), the major product was naringenin accompanied by a small quantity of liquiritigenin. The initial product of the assay with 1 mM NADPH was isoliquiritigenin, indicating a reaction catalyzed by 6'-deoxychalcone synthase (DOCS). Subsequent formation of liquiritigenin was attributed to the presence of chalcone isomerase in the crude extract. The results constitute the first demonstration in vitro of DOCS activity which, in G. echinata cells and other leguminous plants, is involved in the biosynthesis of retrochalcone and 5-deoxyisoflavonoid-derived phytoalexins.

Molecular analysis of resveratrol synthase. cDNA, genomic clones and relationship with chalcone synthase

Resveratrol synthase (RS), a key enzyme in biosynthesis of stilbene-type phytoalexins, catalyzes the formation of resveratrol from coumaroyl-CoA and malonyl-CoA. Two cDNA clones, pGSC1 and pGSC2, have been isolated from cDNA libraries established with poly(A)-rich RNA from peanut (Arachis hypogaea) cell cultures specifically induced for RS. These cDNAs were used to identify two genomic clones (pGSG10 and pGSG11). Sequence analysis shows that the two clones overlap in a large stretch of nearly identical sequences, and that pGSG10 contains the 5' and pGSG11 the 3' end of RS genes. The sequences reveal a single intron, and the size of the predicted protein is 42.7 kDa, in close agreement with that observed in polyacrylamide gels (43 kDa). Chalcone synthase (CHS), a key enzyme of flavonoid biosynthesis, utilizes the same substrates as RS, but the product is different (naringenin chalcone). Comparison of RS with CHS consensus sequences shows that the two genes are related. Homology extends throughout the coding region, and the intron in RS is at the same position as a conserved intron in CHS. However, RS reveals a substantial number of amino acid differences to CHS in positions highly conserved in all CHS enzymes. It is proposed that the two proteins possess a common scaffold necessary for binding of the substrates and the type of enzyme reaction, and that the differences are responsible for the formation of different products.

Elicitor-induced tyrosine decarboxylase in berberine-synthesizing suspension cultures of Thalictrum rugosum

Tyrosine decarboxylase (EC 4.1.1.25) was induced in suspension cultures of Thalictrum rugosum by treatment with a yeast glucan elicitor. Maximum induction was observed at a carbohydrate concentration of 0.4 mg/g fresh weight of cells and maximum enzyme activity was reached 20 h after addition of elicitor. The enzyme was inducible in late exponential and early stationary growth phases. A good correlation between induced tyrosine decarboxylase activity and berberine biosynthesis has been established. It is suggested that tyrosine decarboxylase may be a key enzyme between primary and secondary metabolisms in the biosynthesis of norlaudanosoline-derived alkaloids.

Stimulation of chalcone synthase activity by yeast extract in cultured Glycyrrhiza echinata cells and 5-deoxyflavanone formation by isolated protoplasts

Chalcone synthase activity catalyzing the formation of naringenin (5-hydroxyflavanone) was detected in cell suspension cultures of Glycyrrhiza echinata. This activity rapidly increased by treatment of the cells with yeast extract, while non-treated cells showed a constant low activity. Isolated G. echinata protoplasts accumulated retrochalcone (echinatin) and its biosynthetic intermediate (licodione) during 24 h of culture. When the protoplasts were incubated with [(14)C(U)]phenylalanine, liquiritigenin (5-deoxyflavanone) was transiently labeled, indicating the induction of 6'-deoxychalcone synthase. The formation of liquiritigenin, in addition to naringenin, was observed when the crude extracts from the protoplasts were assaved for CHS activity.

Common responses of cultured soybean cells to 2,4-D starvation and fungal elicitor treatment

The patterns of in vivo protein synthesis in soybean cell suspensions were compared by polyacrylamide gel electrophoresis after the cells had been submitted to different stress conditions : treatment with Phytophthora megasperma (Pmg) cell wall elicitors, 2,4-D starvation and heat shock (HS) temperatures. Changes in protein synthesis patterns induced after elicitation of cell suspensions or after infection of soybean hypocotyls by Pmg were found to be similar to changes brought about by auxin starvation of the cells. Changes common to both stress situations involve a prominent 17 kDa peptide family and 27, 29, 35 and about 45 kDa peptides. Moreover, "defense" reactions, i.e. glyceollin accumulation and synthesis of chalcone synthase (CHS) were also strongly stimulated in auxin-starved cells. On the contrary, although characteristic sets of low molecular weight heat shock (HS) proteins were synthesized by cells grown at 37°C, no clear similarity was observed with peptides characteristic of auxin-starved cells.

Effects of Ca2+ on phytoalexin induction by fungal elicitor in soybean cells

A glucan elicitor from the cell walls of the fungus Phytophthora megasperma f.sp. glycinea caused increases in the activities of the phytoalexin biosynthetic enzymes, phenylalanine ammonia-lyase and chalcone synthase, and induced the production of the phytoalexin, glyceollin, in soybean (Glycine max) cell suspension cultures when tested in culture medium containing 1.2 mmol/liter Ca2+. Removal of extracellular Ca2+ by treatment with ethylene glycol bis(beta-aminoethyl ether)-N, N'-tetraacetic acid followed by washing the cells with Ca2+-free culture medium abolished the elicitor-mediated phytoalexin response. This suppression was largely reversed on readdition of Ca2+. Elicitor-mediated enhancement of biosynthetic enzyme activities and accumulation of glyceollin was strongly inhibited by La3+; effective concentrations for 50% inhibition were (mumol/liter) 40 for phenylalanine ammonia-lyase, 100 for chalcone synthase, and 30 for glyceollin. Verapamil caused similar effects only at concentrations higher than 0.1 mmol/liter, whereas trifluoperazine and 8-(diethylamino)-octyl-3,4,5-trimethoxybenzoate did not affect enzyme induction by the elicitor in the concentration range tested. Uptake of alpha-amino isobutyric acid into soybean cells, which was rapidly inhibited in the presence of the glucan elicitor, was not affected by La3+ nor was uptake inhibition by the elicitor relieved by La3+. The Ca2+ ionophore, A23187, enhanced phytoalexin biosynthetic enzyme activities and glyceollin accumulation in a dose-dependent manner, with 50% stimulation (relative to the elicitor) occurring at about 5 mumol/liter. The results suggest that the glucan elicitor causes changes in metabolite fluxes across the plasma membrane of soybean cells, among which changes in Ca2+ fluxes appear to be important for the stimulation of the phytoalexin response.

Differential induction of enzyme in soybean cell cultures by elicitor or osmotic stress

Soybean cell cultures were challenged either by glucan elicitor from Phytophthora megasperma f.sp. glycinea or by osmotic stress (0.4 M glucose). Osmotic stress induced production of a microsomal NADPH-dependent flavone synthase (flavone synthase II) which catalyses conversion of (2S)-naringenin to apigenin. In one of our cell-lines this enzyme activity was not detected either in unchallenged cells or in cells treated with glucan elicitor. Inducibility of flavone synthase II by 0.4 M glucose was highest at the end of the linear growth phase. Changes in the activities of a number of other enzymes were determined after treatment of the cells with elicitor or 0.4 M glucose. The activities of phenylalanine ammonialyase, cinnamate 4-hydroxylase, chalcone synthase and dihydroxypterocarpan 6a-hydroxylase all increased with elicitor and with osmoticum, albeit to a different degree. The rise in enzyme activity occurred later with osmoticum than with elicitor. The prenyltransferase involved in glyceollin synthesis was induced strongly by elicitor but only very weakly by osmoticum, whereas isoflavone synthase and NADPH: cytochrome-c reductase were only induced by elicitor. The activity of glucose-6-phosphate dehydrogenase did not change with elicitor or with osmoticum. Different product patterns were also obtained: whereas with elicitor, glyceollin I was the major product, intermediates of the glyceollin pathway (7,4'-dihydroxyflavanone, trihydroxypterocarpan) accumulated with osmoticum.

L-Phenylalanine ammonia-lyase fromPhaseolus vulgaris: Modulation of the levels of active enzyme bytrans-cinnamic acid

The extractable activity ofL-phenylalanine ammonia-lyase (PAL; EC 4.3.1.5) in cell suspension cultures of bean (Phaseolus vulgaris) is greatly induced following exposure to an elicitor preparation from the cell walls of the phytopathogenic fungusColletotrichum lindemuthianum. Following exogenous application oftrans-cinnamic acid (the product of the PAL reaction) to elicitor-induced cells, the activity of the enzyme rapidly declines. Loss of enzyme activity is accompanied by inhibition of the rate of synthesis of PAL subunits, as determined by [(35)S]methionine pulse-labelling followed by specific immunoprecipitation; this is insufficient to account for the rapid loss of PAL enzyme activity. Pulse-chase and immune blotting experiments indicate that cinnamic acid does not affect the rate of degradation of enzyme subunits, but rather mediates inactivation of the enzyme. A non-dialysable factor from cinnamicacid-treated bean cells stimulates removal of PAL activity from enzyme extracts in vitro; this effect is dependent on the presence of cinnamic acid. Such loss of enzyme activity in vitro is accompanied by an apparent loss or reduction of the dehydroalanine residue of the enzyme's active site, as detected by active-site-specific tritiation, although levels of immunoprecipitable enzyme subunits do not decrease. Furthermore, cinnamic-acid-mediated loss of enzyme activity in vivo is accompanied, in pulse-chase experiments, by a greater relative loss of(35)S-labelled enzyme subunits precipitated by an immobilised active-site affinity ligand than of subunits precipitated with anti-immunoglobulin G. It is therefore suggested that a possible mechanism for cinnamic-acid-mediated removal of PAL activity may involve modification of the dehydroalanine residue of the enzyme's active site.

Several biotic and abiotic elicitors act synergistically in the induction of phytoalexin accumulation in soybean

Plants often respond to microbial infection by producing antimicrobial compounds called phytoalexins. Plants also produce phytoalexins in response to in vitro treatment with molecules called elicitors. Specific elicitors, including a hexa-β-glucosyl glucitol derived from fungal cell walls, the pectin-degrading enzyme endopolygalacturonic acid lyase, and oligogalacturonides obtained by either partial acid hydrolysis or enzymatic degradation of plant cell walls or citrus polygalacturonic acid, induce soybean (Glycine max. L.) cytoledons to accumulate phytoalexins. The experiments reported here demonstrate that the elicitor-active hexa-β-glucosyl glucitol acts synergistically with several biotic and abiotic elicitors in the induction of phytoalexins in soybean cotyledons. At concentrations below 50 ng/ml, the hexa-β-glucosyl glucitol does not induce significant phytoalexin accumulation. When assayed in combination with either endopolygalacturonic acid lyase or with a decagalacturonide released from citrus polygalacturonic acid by this lyase, however, the observed elicitor activity of the hexa-β-glucosyl glucitol is as much as 35-fold higher than the sum of the responses of these elicitors assayed separately. A similar synergism was also demonstrated for the combination of the hexa-β-glucosyl glucitol with dilute solutions of sodium acetate, sodium formate, or sodium propionate buffers. These buffers are thought to damage or kill plant cells, which may cause the release of oligogalacturonides from the plant cell wall. The results suggest that oligogalacturonides act as signals of tissue damage and, as such, can enhance the response of plant tissues to other elicitor-active molecules during the initiation of phytoalexin accumulation.

Elicitor-induced phytoalexin synthesis in soybean cells: changes in the activity of chalcone synthase mRNA and the total population of translatable mRNA

Rapid changes in the mRNA activity encoding chalcone synthase, a central enzyme involved in isoflavonoid phytoalexin synthesis, were induced in cultured cells of soybean (Glycine max) after treatment with a glucan elicitor from the cell walls of the fungus, Phytophthora megasperma f. sp. glycinea, a soybean pathogen. Two-dimensional gel electrophoresis of the in vitro- and in vivo-synthesized chalcone synthase showed that it consisted of a group of proteins of similar molecular weights of about 41,000, but with differing isoelectric points between pH 6.1 and pH 7.1. Total activity of chalcone synthase mRNA increased as early as 40 to 60 min after the onset of elicitor induction, and reached a peak at about 4 h. Treatment with the fungal elicitor caused major changes in the population of total translatable RNA as indicated by two-dimensional electrophoresis of the translation products. The mRNA activities for at least 16 proteins were increased and for at least 4 proteins were decreased. The elicitor-induced changes in the population of translatable mRNA occurred at a rate similar to that observed for chalcone synthase mRNA activity. Our results suggest that soybean cells respond to the glucan elicitor by major metabolic changes at the RNA level including the enhanced capacity for phytoalexin synthesis.

L-Phenylalanine ammonia-lyase from Phaseolus vulgaris. Characterisation and differential induction of multiple forms from elicitor-treated cell suspension cultures

L-Phenylalanine ammonia-lyase (EC 4.3.1.5) has been purified over 200-fold from cell cultures of bean (phaseolus vulgaris L.) exposed to elicitor heat-released from the cell walls of the phytopathogenic fungus Colletotrichum lindemuthianum. Four forms of the enzyme, with identical Mr but differing apparent pI values of 5.4, 5.2, 5.05 and 4.85, were observed following the final chromatofocussing stage of the purification. A preparation (purified 43-fold by ammonium sulphate precipitation, gel-filtration and ion-exchange chromatography) containing all four forms exhibited apparent negative rate cooperativity with respect to substrates. However, the individual forms displayed normal Michaelis-Menten kinetics, with Km values of 0.077 mM, 0.122 mM, 0.256 mM and 0.302 mM in order of decreasing apparent pI value. A preparation purified 200-fold and containing all four forms was used to immunise rabbits for the production of anti-(phenylalanine ammonia-lyase) serum. The antiserum was characterised by: immunotitration experiments; solid phase enzyme-linked immunosorbent assays; comparison of immunoprecipitates of 35S-labelled phenylalanine ammonia-lyase subunits (synthesized both in vivo and in vitro) on both one-dimensional and two-dimensional polyacrylamide gels after immunoprecipitation with the bean antiserum or antisera raised against pea and parsley phenylalanine ammonia-lyase preparations and immune blotting. SDS/polyacrylamide gels and SDS/polyacrylamide gel electrophoresis followed by immune blotting, indicated that the Mr of newly synthesized (in vivo and in vitro) bean phenylalanine ammonia-lyase subunits is 77000; a 70000-Mr form is readily generated as a partial degradation product during purification. Immunoprecipitates of bean phenylalanine ammonia-lyase synthesized both in vivo and in vitro showed the presence of multiple subunit types of identical Mr but differing in pI. Furthermore, treatment of bean cultures with Colletotrichum elicitor resulted in a 10-fold increase in phenylalanine ammonia-lyase extractable activity within 8 h, and chromatofocussing analysis indicated that this was associated with differential increased appearance of the high-pI, low-Km forms as compared to the two higher Km forms. This differential induction was further confirmed by immune blotting of crude extracts subjected to isoelectric focussing.