Induction of phenylalanine ammonia-lyase and 4-coumarate:CoA ligase mRNAs in cultured plant cells by UV light or fungal elicitor

Functional Food Based on Potato

Potato (Solanum tuberosum L.) has gradually become a stable food worldwide since it can be a practical nutritional supplement and antioxidant as well as an energy provider for human beings. Financially and nutritionally, the cultivation and utility of potatoes is worthy of attention from the world. Exploring the functionality and maximizing the utilization of its component parts as well as developing new products based on the potato is still an ongoing issue. To maximize the benefits of potato and induce new high-value products while avoiding unfavorable properties of the crop has been a growing trend in food and medical areas. This review intends to summarize the factors that influence changes in the key functional components of potatoes and to discuss the focus of referenced literature which may require further research efforts. Next, it summarizes the application of the latest commercial products and potential value of components existing in potato. In particular, there are several main tasks for future potato research: preparing starchy foods for special groups of people and developing fiber-rich products to supply dietary fiber intake, manufacturing bio-friendly and specific design films/coatings in the packaging industry, extracting bioactive proteins and potato protease inhibitors with high biological activity, and continuing to build and examine the health benefits of new commercial products based on potato protein. Notably, preservation methods play a key role in the phytochemical content left in foods, and potato performs superiorly to many common vegetables when meeting the demands of daily mineral intake and alleviating mineral deficiencies.

Comparison between the Chemical Composition of Essential Oil from Commercial Products and Biocultivated Lavandula angustifolia Mill

The main aim of this study was to assess the differences in the chemical composition of essential oil from biocultivated Lavandula angustifolia in the Thracian Lowland floristic region, Bulgaria, and commercially available products from Bulgarian markets. Following the analytical results conducted with gas chromatography-mass spectrometry, we have established some differences in the chemical composition of the tested samples. The essential oil of biocultivated lavender contained 35 compounds, which represent 94.13% of the total oil. Samples from commercial products contained 28-42 compounds that represent 93.03-98.69% of the total oil. All the examined samples were rich in monoterpene hydrocarbons (1.68-12.77%), oxygenated monoterpenes (70.42-87.96%), sesquiterpene hydrocarbons (4.03-13.78%), and oxygenated sesquiterpenes (0.14-0.76%). The dominant components in all examined samples were linalool (20.0-45.0%) and linalyl acetate (20.79-39.91%). All the examined commercial samples contained linalool and linalyl acetate as was described in the European Pharmacopoeia, but in one of the samples, the quality of linalyl acetate is lower than that recommended in the European Pharmacopoeia.

Phenotypic, Phytochemical, and Transcriptomic Analysis of Black Sorghum (Sorghum bicolor L.) Pericarp in Response to Light Quality

Black sorghum [Sorghum bicolor (L.) Moench] is characterized by the black appearance of the pericarp and production of 3-deoxyanthocyanidins (3-DOA), which are valued for their cytotoxicity to cancer cells and as natural food colorants and antioxidant additives. The black pericarp phenotype is not fully penetrant in all environments, which implicates the light spectrum and/or photoperiod as the critical factor for trait expression. In this study, black- or red-pericarp genotypes were grown under regimes of visible light, visible light supplemented with UVA or supplemented with UVA plus UVB (or dark control). Pericarp 3-DOAs and pericarp pigmentation were maximized in the black genotype exposed to a light regime supplemented with UVB. Changes in gene expression during black pericarp development revealed that ultraviolet light activates genes related to plant defense, reactive oxygen species, and secondary metabolism, suggesting that 3-DOA accumulation is associated with activation of flavonoid biosynthesis and several overlapping defense and stress signaling pathways.

Disruption of a C69-Family Cysteine Dipeptidase Gene Enhances Heat Shock and UV-B Tolerances in Metarhizium acridum

In fungi, peptidases play a crucial role in adaptability. At present, the roles of peptidases in ultraviolet (UV) and thermal tolerance are still unclear. In this study, a C69-family cysteine dipeptidase of the entomopathogenic fungus Metarhizium acridum, MaPepDA, was expressed in Escherichia coli. The purified enzyme had a molecular mass of 56-kDa, and displayed a high activity to dipeptide substrate with an optimal Ala-Gln hydrolytic activity at about pH 6.0 and 55°C. It was demonstrated that MaPepDA is an intracellular dipeptidase localized in the cytosol, and that it is expressed during the whole fungal growth. Disruption of the MaPepDA gene increased conidial germination, growth rate, and significantly improved the tolerance to UV-B and heat stress in M. acridum. However, virulence and conidia production was largely unaffected in the ΔMaPepDA mutant. Digital gene expression data revealed that the ΔMaPepDA mutant had a higher UV-B and heat-shock tolerance compared to wild type by regulating transcription of sets of genes involved in cell surface component, cell growth, DNA repair, amino acid metabolism, sugar metabolism and some important signaling pathways of stimulation. Our results suggested that disruption of the MaPepDA could potentially improve the performance of fungal pesticides in the field application with no adverse effect on virulence and conidiation.

Characterization of VvPAL-like promoter from grapevine using transgenic tobacco plants

A 2000-bp 5'-flanking region of VvPAL-like was isolated from 'Summer Black' grapevine by PCR amplification, named pVvPAL-like. To gain a better understanding of the expression and regulatory mechanism of VvPAL-like, a chimeric expression unit consisting of the β-glucuronidase (GUS) reporter gene under the control of a 2000-bp fragment of the VvPAL-like promoter was transformed into tobacco via Agrobacterium tumefaciens. Histochemical staining showed that the full-length promoter directs efficient expression of the reporter gene in cotyledons and hypocotyls, stigma, style, anthers, pollen, ovary, trichomes, and vascular bundles of transgenic plants. A series of 5' progressive deletions of the promoter revealed the presence of a negative regulatory region (-424 to -292) in the VvPAL-like promoter. Exposure of the transgenic tobacco plants to various abiotic stresses demonstrated that the full-length construct could be induced by light, copper (Cu), abscisic acid (ABA), indole-3-acetic (IAA), methyl jasmonate (MeJA) (N-1-naphthylphthalamic acid), ethylene, and drought. Furthermore, the ethylene-responsive region was found to be located in the -1461/-930 fragment, while the element(s) for the MeJA-responsive expression may be present in the -424/-292 region in the VvPAL-like promoter. These findings will help us to better understand the molecular mechanisms by which VvPAL-like participates in biosynthesis of flavonoids and stress responses.

Multiple phytohormones and phytoalexins are involved in disease resistance to Magnaporthe oryzae invaded from roots in rice

Blast, caused by the fungus Magnaporthe oryzae, is one of the most devastating diseases of rice worldwide. Phenylalanine ammonia lyase (PAL) is a key enzyme in the phenylpropanoid pathway, which leads to the biosynthesis of defense-related phytohormone salicylic acid (SA) and flavonoid-type phytoalexins sakuranetin and naringenin. However, the roles and biochemical features of individual rice PALs in defense responses to pathogens remain unclear. Here, we report that rice OsPAL06, which can catalyze the formation of trans-cinnamate using l-phenylalanine, is involved in rice root-M. oryzae interaction. OsPAL06-knockout mutant showed increased susceptibility to M. oryzae invaded from roots and developed typical leaf blast symptoms, accompanied by nearly complete disappearance of sakuranetin and naringenin and a two-third reduction of the SA level in roots. This mutant also showed compensatively induced expression of chalcone synthase, which is involved in flavonoid biosynthesis, isochorismate synthase 1, which is putatively involved in SA synthesis via another pathway, reduced jasmonate content and increased ethylene content. These results suggest that OsPAL06 is a positive regulator in preventing M. oryzae infection from roots. It may regulate defense by promoting both phytoalexin accumulation and SA signaling that synergistically and antagonistically interacts with jasmonate- and ethylene-dependent signaling, respectively.

Effects of latitude and weather conditions on phenolic compounds in currant (Ribes spp.) cultivars

Effects of growth latitude and weather conditions on phenolic compounds of currants (Ribes spp.) were investigated. The berries of red currant cultivar 'Red Dutch', white currant 'White Dutch', and green currant 'Vertti' were collected in seven consecutive years from two growth sites (south and north) with a latitudinal distance of 690 km. The contents of hydroxycinnamic acid conjugates and flavonol glycosides in 'Vertti' were higher than those in 'White Dutch' by 8 and 5 times, respectively, and by 50 and 3 times than those in 'Red Dutch', respectively. The total content of phenolic compounds was 10-19% higher in the north than in the south (p < 0.05). In 'Red Dutch', anthocyanins were 12% richer in berries from the north compared with those from the south (p < 0.05). The total content of hydroxycinnamic acid conjugates in 'Vertti' and 'White Dutch' from the north was 30% higher than those from the south (p < 0.05). High radiation and temperature were associated with low contents of the major phenolic compounds in all the cultivars studied. High humidity correlated with low levels of hydroxycinnamic acid conjugates in green and white currants.

Changes in potato phenylpropanoid metabolism during tuber development

Phenylpropanoid metabolite and transcript expression during different developmental stages were examined in field grown potatoes. Carbohydrate and shikimic acid metabolism was assessed to determine how tuber primary metabolism influences phenylpropanoid metabolism. Phenylpropanoid concentrations were highest in immature tubers, as were some transcript levels and enzyme activities including phenylalanine ammonia lyase (PAL). Phenylpropanoid concentration differences between mature and immature tubers varied by genotype, but in some cases were approximately three-fold. The most abundant phenylpropanoid was chlorogenic acid (5CGA), which decreased during tuber maturation. Hydroxycinnamoyl-CoA:quinate hydroxycinnamoyl transferase (HQT) transcripts were highly expressed relative to other phenylpropanoid genes, but were not well correlated with 5CGA concentrations (r = -0.16), whereas HQT enzyme activity was. In contrast to 5CGA, less abundant chlorogenic isomers increased during development. Concentrations of hydroxycinnamic acid amides were higher in immature tubers, as was expression of arginine- and ornithine decarboxylases. Expression of several genes involved in carbohydrate or shikimate metabolism, including sucrose synthase and DAHP, showed similar developmental patterns to phenylpropanoid pools, as did shikimate dehydrogenase enzyme activity. Sucrose, glucose and fructose concentrations were highest in immature tubers. Exogenous treatment of potatoes with sugars stimulated phenylpropanoid biosynthesis, suggesting sugars contribute to the higher phenylpropanoid concentrations in immature tubers. These changes in phenylpropanoid expression suggest the nutritional value of potatoes varies during development.

QTL involved in the modification of cyanidin compounds in black and red raspberry fruit

Fruit from Rubus species are highly valued for their flavor and nutritive qualities. Anthocyanin content contributes to these qualities, and although many studies have been conducted to identify and quantify the major anthocyanin compounds from various Rubus species, the genetic control of the accumulation of these complex traits in Rubus is not yet well understood. The identification of the regions of the genome involved in the production of anthocyanins is an important first step in identifying the genes underlying their expression. In this study, ultra and high-performance liquid chromatography (UHPLC and HPLC) and two newly developed Rubus linkage maps were used to conduct QTL analyses to explore the presence of associations between concentrations of five anthocyanins in fruit and genotype. In total, 27 QTL were identified on the Rubus linkage maps, four of which are associated with molecular markers designed from transcription factors and three of which are associated with molecular markers designed from anthocyanin biosynthetic pathway candidate genes. The results of this study suggest that, while QTL for anthocyanin accumulation have been identified on six of seven Rubus linkage groups (RLG), the QTL on RLG2 and RLG7 may be very important for genetic control of cyanidin modification in Rubus.

Plant aging and excess light enhance flavan-3-ol content in Cistus clusii

Physiological studies on aging in perennials are mainly focused either on the primary metabolism or the hormonal regulation of the process. However, to our knowledge, the involvement of the secondary metabolism in this process has not yet been explored. Cistus clusii, a Mediterranean sclerophyllous evergreen bush, shows considerable amounts of flavan-3-ols in leaves. In the present study, we aimed at determining the impact of environmental conditions and plant aging in the flavan-3-ol content in C. clusii plants grown in field conditions, which included summer drought and recovery periods. Six-year-old plants suffered more from photo-oxidative stress, especially during excess light periods, and showed lower maximum photosynthetic rates than 1-year-old plants. C. clusii leaves accumulated (-)-epigallocatechin gallate in early summer, in a strong positive correlation with both the photon flux density and the photoperiod, but not with the plant water status. Moreover, C. clusii plants accumulated proanthocyanidins (polymeric flavan-3-ols) in leaves during summer. Older plants showed higher levels of proanthocyanidins and (-)-epicatechin, but only during late spring and summer. From the result of the present study, we conclude that excess light enhances flavan-3-ol content in C. clusii, a process enhanced as plants age due to increased excess light stress.

Plant defense genes are regulated by ethylene

One of the earliest detectable events during plant-pathogen interaction is a rapid increase in ethylene biosynthesis. This gaseous plant stress hormone may be a signal for plants to activate defense mechanisms against invading pathogens such as bacteria, fungi, and viruses. The effect of ethylene on four plant genes involved in three separate plant defense response pathways was examined; these included (i and ii) genes that encode L-phenylalanine ammonia-lyase (EC 4.3.1.5) and 4-coumarate:CoA ligase [4-coumarate:CoA ligase (AMP-forming), EC 6.2.1.12], enzymes of the phenylpropanoid pathway, (iii) the gene encoding chalcone synthase, an enzyme of the flavonoid glycoside pathway, and (iv) the genes encoding hydroxyproline-rich glycoprotein, a major protein component(s) of plant cell walls. Blot hybridization analysis of mRNA from ethylene-treated carrot roots reveals marked increases in the levels of phenylalanine ammonia-lyase mRNA, 4-coumarate CoA ligase mRNA, chalcone synthase mRNA, and certain hydroxyproline-rich glycoprotein transcripts. The effect of ethylene on hydroxyproline-rich glycoprotein mRNA accumulation was different from that of wounding. Ethylene induces two hydroxyproline-rich glycoprotein mRNAs (1.8 and 4.0 kilobases), whereas wounding of carrot root leads to accumulation of an additional hydroxyproline-rich mRNA (1.5 kilobases). These results indicate that at least two distinct signals, ethylene and a wound signal, can affect the expression of plant defense-response genes.

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.

Elicitor rapidly induces chalcone synthase mRNA in Phaseolus vulgaris cells at the onset of the phytoalexin defense response

DNAs complementary to poly(A)(+) RNA present in elicitor-treated cells of Phaseolus vulgaris L. were inserted into pBR325 and used to transform Escherichia coli strain JA221. A clone was identified that contained sequences complementary to mRNA encoding chalcone synthase, a regulatory enzyme of phenylpropanoid biosynthesis, which catalyzes the first reaction of a branch pathway specific to flavonoid and isoflavonoid biosynthesis. Rapid, marked but transient increases in chalcone synthase mRNA in response to elicitor treatment were observed by RNA blot hybridization with (32)P-labeled chalcone synthase cDNA sequences. Induction of chalcone synthase mRNA governs the rate of enzyme synthesis throughout the phase of rapid increase in enzyme activity at the onset of accumulation of isoflavonoid-derived phytoalexins. The data are consistent with the hypothesis that elicitor causes a rapid transient stimulation of transcription of chalcone synthase gene(s) as an early event in the expression of the phytoalexin defense response.

Rapid activation by fungal elicitor of genes encoding "pathogenesis-related" proteins in cultured parsley cells

Administration of a cell-wall preparation from the fungus Phytophthora megasperma f. sp. glycinea, which acts as an elicitor of phytoalexin production in cell suspension cultures of parsley (Petroselinum crispum), also results in a rapid and dramatic increase in the relative amounts of mRNAs coding for a number of small proteins having low isoelectric points. According to various operational criteria, the translation products are classified as "pathogenesis-related" (PR) proteins. Here we report that the cDNA inserts of two pBR322-derived plasmids, pcPR1 and pcPR2, are homologous to mRNAs coding for one (PR1) and three (PR2) of these proteins in hybrid-selected in vitro translation experiments. Nuclear run-off transcription studies show that activation of the corresponding genes is extremely rapid; we observed a 4-fold increase in the transcription rate of the PR1 gene within 5 min and a 3-fold increase for the PR2 gene within 20 min following elicitation. Subsequent increases in the amounts of PR1 and PR2 mRNAs indicate that regulation of PR protein synthesis occurs at the transcriptional level.

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.

Quantitative iTRAQ proteome and comparative transcriptome analysis of elicitor-induced Norway spruce (Picea abies) cells reveals elements of calcium signaling in the early conifer defense response

Long-lived conifer trees depend on both constitutive and induced defenses for resistance against a myriad of potential pathogens and herbivores. In species of spruce (Picea spp.), several of the late events of pathogen-, insect-, or elicitor-induced defense responses have previously been characterized at the anatomical, biochemical, transcriptome, and proteome levels in stems and needles. However, accurately measuring the early events of induced cellular responses in a conifer is technically challenging due to limitations in the precise timing of induction and tissue sampling from intact trees following insect or fungal treatment. In the present study, we used the advantages of Norway spruce (Picea abies) cell suspensions combined with chitosan elicitation to investigate the early proteome response in a conifer. A combination of iTRAQ labeling and a new design of iterative sample analysis employing data-dependent exclusion lists were used for proteome analysis. This approach improved the coverage of the spruce proteome beyond that achieved in any prior study in a conifer system. Comparison of elicitor-induced proteome and transcriptome responses in Norway spruce cells consistently identified features associated with calcium-mediated signaling and response to oxidative stress that have not previously been observed in the response of intact trees to fungal attack.

Factors Affecting Chemical Variability of Essential Oils: A Review of Recent Developments

This review, covering mainly papers of the last decade, focuses on recent findings on the different factors affecting the chemical composition of essential oils, such as exogenous and endogenous factors. The endogenous factors are related to anatomical and physiological characteristics of the plants and to the biosynthetic pathways of the volatiles, which might change in either the different tissues of the plants or in different seasons, but also could be influenced by DNA adaptation. The exogenous factors, over a long period, might affect some of the genes responsible for volatiles formation. Those factors lead to ecotypes or chemotypes in the same plant species. In the last few years chemotaxonomy has been widely used to classify plants with essential oils characterized by intra-specific chemical polymorphism. It could be evidenced that chemotypes are frequently genotypes and recently the application of the Random Amplified Polymorphic DNA (RAPD) markers, coupled with powerful statistical methods, appeared to be useful in discriminating the different genotypes. The data presented led to the suggestion that further chemotaxonomic studies should be the result of the analysis of morphological traits combined both with chemical and molecular markers.

Cyclic GMP acts as a common regulator for the transcriptional activation of the flavonoid biosynthetic pathway in soybean

Cyclic GMP (cGMP) is an important signaling molecule that controls a range of cellular functions. So far, however, only a few genes have been found to be regulated by cGMP in higher plants. We investigated the cGMP-responsiveness of several genes encoding flavonoid-biosynthetic enzymes in soybean (Glycine max L.) involved in legume-specific isoflavone, phytoalexin and anthocyanin biosynthesis, such as phenylalanine ammonia-lyase, cinnamate 4-hydroxylase, 4-coumarate:CoA ligase, chalcone synthase, chalcone reductase, chalcone isomerase, 2-hydroxyisoflavanone synthase, 2-hydroxyisoflavanone dehydratase, anthocyanidin synthase, UDP-glucose:isoflavone 7-O-glucosyltransferase, and isoflavone reductase, and found that the majority of these genes were induced by cGMP but not by cAMP. All cGMP-induced genes were also stimulated by sodium nitroprusside (SNP), a nitric oxide (NO) donor, and illumination of cultured cells with white light. The NO-dependent induction of these genes was blocked by 6-anilino-5,8-quinolinedione, an inhibitor of guanylyl cyclase. Moreover, cGMP levels in cultured cells were transiently increased by SNP. Consistent with the increases of these transcripts, the accumulation of anthocyanin in response to cGMP, NO, and white light was observed. The treatment of soybean cotyledons with SNP resulted in a high accumulation of isoflavones such as daidzein and genistein. Loss- and gain-of-function experiments with the promoter of chalcone reductase gene indicated the Unit I-independent activation of gene expression by cGMP. Together, these results suggest that cGMP acts as a second messenger to activate the expression of genes for enzymes involved in the flavonoid biosynthetic pathway in soybean.

Molecular cloning, expression and characterization of a phenylalanine ammonia-lyase gene (SmPAL1) from Salvia miltiorrhiza

Phenylalanine ammonia-lyase (PAL) is one of the branch point enzymes between primary and secondary metabolism. It plays an important role during plant development and defense. A PAL gene designated as SmPAL1 was cloned from Salvia miltiorrhiza using genome walking technology. The full-length SmPAL1 was 2,827 bp in size and consisted of an intron and two extrons encoding a 711-amino-acid polypeptide. Sequence alignment revealed that SmPAL1 shared more than 80% identity with the PAL sequences reported in Arabidopsis thaliana and other plants. The 5' flanking sequence of SmPAL1 was also cloned, and a group of putative cis-acting elements such as TATA box, CAAT box, G box and TC-rich repeats were identified. Transcription pattern analysis indicated that SmPAL1 expressed in all tissues examined, but more highly in leaf. Besides, expression of SmPAL1 was found to be induced by various treatments including ABA, wounding, and dehydration. To further confirm its function, SmPAL1 was expressed in Escherichia coli strain M15 with pQE-30 vector. The recombinant protein exhibited high PAL activity and could catalyze the conversion of L: -Phe to trans-cinnamic acid. This study will enable us to further understand the role SmPAL1 plays in the synthesis of active pharmaceutical compounds in S. miltiorrhiza at molecular level.

Histopathology comparison and phenylalanine ammonia lyase (PAL) gene expressions in Fusarium wilt infected watermelons

Fusarium wilt disease of watermelon (Citrullus lanatus (Thunb.) Matsum & Nakai), caused by Fusarium oxysporum f. sp. niveum (FON), is one of the limiting factors of worldwide watermelon production. In this study, a Fusarium wilt resistant watermelon JSB, which was derived from a spontaneous mutation of the susceptible Sugar Baby (SB), was used to investigate histopathology. The number and diameter of xylem vessels in the root (10 mm below the shoot base) of resistant JSB plants were significantly higher than those in susceptible SB plants. At 9 days post inoculation (dpi), using the plate assay on Nash-PCNB media, FON could be recovered from 86% of the roots in the symptomless plants of both watermelon lines, and from 55% and 64% of the stem segments (5 mm above the shoot base) in resistant and susceptible plants, respectively. In paraffin and free-hand tissue sections, at 8, 13, and 35 dpi, the xylem of roots and stems close to the soil surface in resistant watermelon JSB plants was also colonised by FON, but to a much lower percentage than the susceptible SB ones. No colonisation below the middle of stems was observed in the resistant JSB plants. The susceptible plants grown in infested soil were all dead by 35 dpi, while the resistant plants remained healthy. These observations suggest that reducing FON colonisation in the vascular systems of the host may contribute to the resistance in JSB. Furthermore, the higher expression of the phenylalanine ammonia lyase (PAL) gene in JSB induced by FON and the effects of PAL inhibitor on the resistance of JSB suggested that PAL is involved in resistance of watermelon to Fusarium wilt pathogen.

The lipopolysaccharide of Sinorhizobium meliloti suppresses defense-associated gene expression in cell cultures of the host plant Medicago truncatula

In the establishment of symbiosis between Medicago truncatula and the nitrogen-fixing bacterium Sinorhizobium meliloti, the lipopolysaccharide (LPS) of the microsymbiont plays an important role as a signal molecule. It has been shown in cell cultures that the LPS is able to suppress an elicitor-induced oxidative burst. To investigate the effect of S. meliloti LPS on defense-associated gene expression, a microarray experiment was performed. For evaluation of the M. truncatula microarray datasets, the software tool MapMan, which was initially developed for the visualization of Arabidopsis (Arabidopsis thaliana) datasets, was adapted by assigning Medicago genes to the ontology originally created for Arabidopsis. This allowed functional visualization of gene expression of M. truncatula suspension-cultured cells treated with invertase as an elicitor. A gene expression pattern characteristic of a defense response was observed. Concomitant treatment of M. truncatula suspension-cultured cells with invertase and S. meliloti LPS leads to a lower level of induction of defense-associated genes compared to induction rates in cells treated with invertase alone. This suppression of defense-associated transcriptional rearrangement affects genes induced as well as repressed by elicitation and acts on transcripts connected to virtually all kinds of cellular processes. This indicates that LPS of the symbiont not only suppresses fast defense responses as the oxidative burst, but also exerts long-term influences, including transcriptional adjustment to pathogen attack. These data indicate a role for LPS during infection of the plant by its symbiotic partner.

Spectral quality and UV-B stress stimulate glycyrrhizin concentration of Glycyrrhiza uralensis in hydroponic and pot system

Glycyrrhizin, the major bioactive component of Glycyrrhiza uralensis, is widely used as a natural sweetener. Recently glycyrrhizin has been shown to have anti-tumor activity, highly active in inhibiting replication of HIV-1 and SARS-associated virus and exhibits a number of pharmacological effects. The principle objective of the current study was to evaluate the effects of different spectral quality including red, blue, white and UV-B radiation on the production of glycyrrhizin, in a controlled environment. Plants were grown under artificial lights with elevated CO(2) concentration and both the pot and hydroponic plants were assigned to red and blue light treatments and those grown under white fluorescent lamps were used as control. In a separate experiment, pot plants were exposed to ultraviolet (UV)-B radiation (wavelength: 280-315 nm). The net photosynthetic rates (NPR) of the leaves reduced significantly immediately after exposure to the high intensity UV-B radiation (3 days at 1.13 W m(-2)). In case of the low intensity UV-B radiation (15 days at 0.43 W m(-2)), NPR was also reduced, but the rate of reduction was significantly slower than that of the high intensity treatment. The concentrations of glycyrrhizin quantified in the root tissues were highest in the plants grown under red light in both hydroponic and pot systems and the concentration increased linearly from 1- to 3-month-old pot plants. Both the low and high intensity of UV-B exposure increased the concentration of glycyrrhizin in the root tissues of 3-month-old pot plants, the values being nearly X1.5 those of the control. The results also indicate that the glycyrrhizin concentrations of 3-6 months old pot plants were similar or even higher than the previously reported values for 3-4 years old field-grown plants and confirm that high concentration of glycyrrhizin production is possible within a very short production period under controlled environments.

Enhancement of lignan biosynthesis in suspension cultures of Linum nodiflorum by coronalon, indanoyl-isoleucine and methyl jasmonate

The effect of the two synthetic elicitors coronalon and indanoyl-isoleucine and of methyl jasmonate (MeJA) on the accumulation and biosynthesis of lignans by cell suspension cultures of Linum nodiflorum (Linaceae) was investigated. The production of 6-methoxypodophyllotoxin (MPTOX) could be increased more than tenfold, the maximal content reaching up to over 2.5% of the cell dry weight. The highest yield was achieved by administering 50 microM of the synthetic elicitors on the fourth day and extracting the products on the tenth day of the culture period. An additional lignan accumulated in elicitor-treated cultures. Its structure was elucidated by extensive 1D and 2D NMR measurements, revealing its identity as 5'-demethoxy-MPTOX (5'-dMPTOX). Its average content amounted up to over 5% of the cell dry weight. Growth was only slightly affected by the addition of the elicitors. Methyl jasmonate exerted a moderate stimulating effect on the L. nodiflorum cells with MPTOX and 5'-dMPTOX contents going up to 1.4 and 2.1% of the cell dry weight, respectively. The activities of deoxypodophyllotoxin 6-hydroxylase and beta-peltatin 6-O-methyltransferase, two enzymes involved in MPTOX biosynthesis, were increased up to 21.9-fold and 14.6-fold, respectively, in the treated cultures.

Effects of conditioned medium on activities of PAL, CHS, DAHP synthase (DS-Co and DS-Mn) and anthocyanin production in suspension cultures of Fragaria ananassa

A conditioned medium (CM) prepared from cell suspension cultures of strawberry stimulated anthocyanin synthesis. The effect was significantly (P<0.05) greater than that of synthetic medium (SM), with macronutrient concentrations, carbohydrate concentrations and pH adjusted to those of CM. The activity of 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP) synthase (EC 4.1.2.15) (DS-Mn, DS-Co), phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) and chalcone synthase (CHS, EC 2.3.1.74) were monitored in the CM- and SM-cultured cells. PAL and CHS activities were found to increase significantly (P<0.05) in the CM-cultured cells. CHS transcript levels were higher in the CM-cultured cells compared to transcript abundance in SM-cultured cells. There was no significant difference in the DS-Mn and DS-Co activities of cells grown in conditioned or synthetic media.

The influence of alpha-amanitin on the NaCl-induced up-regulation of antioxidant enzyme activity in cotton callus tissue

Liquid suspensions of cotton callus tissue from a NaCl-sensitive cell line and a NaCl-tolerant cell line were subjected to the following treatments: (a) 0 and 150 mM NaCl, respectively (controls); (b) 75 and 250 mM NaCl, respectively; (c) 100 ng ml(-1) alpha-amanitin; or (d) pretreatment for 2 h with 100 ng ml(-1) alpha-amanitin followed by the respective NaCl treatments. The callus tissue was harvested at 0, 0.5, 1, 2, 4, and 8h and analyzed for antioxidant enzyme activity. In the NaCl-tolerant callus, the 250 mM NaCl treatment resulted in transient 2- to 4-fold increases above the control levels in the activities of ascorbate peroxidase, catalase, glutathione reductase, and peroxidase within 1 h after treatment, while superoxide dismutase activity increased 4-fold within 4 h. This rapid increase suggests that the up-regulation of antioxidant capacity is an early response to NaCl stress and perhaps provides protection against oxidative damage until other acclimating mechanisms can be invoked. In the control callus, peroxidase activity remained unchanged, and significant increases in the other enzymes were not observed until 8 h after treatment with 75mM NaCl. Pre-treatment with alpha-amanitin prior to the NaCl treatment completely inhibited the NaCl-induced increase in the activities of all five enzymes in both cell lines. This data supports the conclusion that the NaCl-induced up-regulation of antioxidant enzyme activity in cotton callus tissue is transcriptionally regulated, proceeding via a de novo synthesis of poly(A)+RNA and is not due to the translation of existing transcripts or the mobilization of existing enzyme pools. In addition, the results suggest that it is not only the up-regulation of antioxidant activity that bestows a degree of tolerance to environmental stress, but also the speed with which this response occurs.

Use of plant cell cultures in biotechnology

Plant cell cultures are being widely used in scientific studies on the physiology, biochemistry and molecular biology of primary and secondary metabolism, developmental regulation and cellular responses to pathogens and stress. In this chapter the significance of plant cell cultures in biotechnology is discussed with special emphasis on commercial production of secondary metabolites and pharmaceuticals, the potential of genetically transformed cell cultures, photosynthetically active cell cultures, production of somatic embryos, and novel assay systems based on the use of plant cells. Future aspects of biotechnical applications with respect to the potentials and limitations of these approaches are assessed, particularly in comparison with the productivity of lower eucaryotes.

The expression of a grapefruit gene encoding an isoflavone reductase-like protein is induced in response to UV irradiation

Exposure of harvested grapefruit to UV-C (254 nm) irradiation was previously found to induce resistance against the green mold decay caused by Penicillium digitatum. In order to gain insight into the mechanism of this UV-induced resistance we initiated a study for isolation of genes induced during this process. Using the differential display method we cloned cDNA representing an mRNA which is accumulated in grapefruit peel upon UV irradiation. Sequence analysis revealed that this cDNA represents a gene encoding for an isoflavone reductase-like protein and was termed IRL (isoflavone reductase-like). The grapefruit IRL protein sequence has high homology also to a novel family of other isoflavone reductase-like proteins present in few non-legume plants and whose function is not clear yet. The UV dose, and time following it, which lead to maximal accumulation of the IRL transcript were found to be similar to those leading to maximal induced resistance. The expression of the IRL gene was demonstrated to be induced also by wounding and pathogen infection.

Differential transcript induction of parsley pathogenesis-related proteins and of a small heat shock protein by ozone and heat shock

Parsley (Petroselinum (crispum L.) is known to respond to pathogen attack by the synthesis of furanocoumarins and to UV irradiation by the synthesis of flavone glycosides whereas ozone treatment results in the induction of both pathways. A cDNA library from parsley plants was differentially screened using labelled reverse-transcribed poly(A)+ RNA isolated from ozone-treated parsley plants. This resulted in the isolation of 13 independent cDNA clones representing ozone-induced genes and of 11 cDNA clones representing ozone-repressed genes. DNA sequencing of several clones resulted in the identification of pathogenesis-related protein 1-3 (PR1-3), of a new member of PR1 cDNAs (PRI-4) and of a small heat shock protein (sHSP). Northern blot analyses showed a transient induction of the three mRNA species after ozone fumigation. In contrast, heat shock treatment of parsley plants resulted in an increase of sHSP mRNA whereas no increase for transcripts of PR1-3 and PR1-4 could be observed. This is the first characterized sHSP cDNA clone for plants induced by heat shock, as well as by oxidative stress caused by ozone.

The relationship between yield and the antioxidant defense system in tomatoes grown under heat stress

Four putative heat-tolerant tomato (Lycopersicum esculentum) cultivars (Tamasabro, Heat Wave, LHT-24, and Solar Set) and one putative heat-sensitive tomato cultivar (Floradade) were grown in the field under non-stress (average daily temperature of 26 degrees C) and heat-stress (average daily temperature of 34 degrees C) conditions. At anthesis, approximately five weeks after being transplanted to the field, leaf samples were collected for antioxidant analyses. Yield was determined by harvesting ripe fruit seven weeks after the collection of leaf samples. Heat stress resulted in a 79.1% decrease in yield for the heat-sensitive Floradade, while the fruit yield in the heat-tolerant cultivars Heat Wave, LHT-24, Solar Set, and Tamasabro was reduced 51.5%, 22.1%, 43.8%, and 34.8% respectively. When grown under heat stress, antioxidant activities were also greater in the heat-tolerant cultivars. Superoxide dismutase (SOD) activity increased up to 9-fold in the heat-tolerant cultivars but decreased 83.1% in the heat-sensitive Floradade. Catalase, peroxidase, and ascorbate peroxidase activity increased significantly in all cultivars. Only Heat Wave showed a significant increase in glutathione reductase in response to heat stress but all heat-tolerant cultivars exhibited significantly lower oxidized ascorbate/reduced ascorbate ratios, greater reduced glutathione/oxidized glutathione rations, and greater alpha-tocopherol concentrations compared to the heat-sensitive cultivar Floridade. These data indicate that the more heat-tolerant cultivars had an enhanced capacity for scavenging active oxygen species and a more active ascorbate-glutathione cycle and suggest a strong correlation between the ability to up-regulate the antioxidant defense system and the ability of tomatoes to produce greater yields when grown under heat stress.

Antioxidant Response to NaCl Stress in a Control and an NaCl-Tolerant Cotton Cell Line Grown in the Presence of Paraquat, Buthionine Sulfoximine, and Exogenous Glutathione

A cotton (Gossypium hirsutum L.) control and NaCl-tolerant cell line (cv Coker 312) were grown on media with or without NaCl in the presence or absence of paraquat, buthionine sulfoximine, and oxidized glutathione. On medium with 150 mM NaCl the NaCl-tolerant cell line exhibited no reduction in growth, whereas a 96% reduction was observed in the control line. The NaCl-tolerant cell line that was grown on 150 mM NaCl exhibited significantly greater catalase (341%), peroxidase (319%), glutathione reductase (287%), ascorbate peroxidase (450%), [gamma]-glutamylcysteine synthetase (224%), and glutathione S-transferase (500%) activities than the intolerant control. The NaCl-tolerant cell line had a significantly lower dehydroascorbic acid/ascorbic acid ratio. Paraquat reduced growth by 20 and 53.7%, respectively, in the NaCl-tolerant and control cell line. The NaCl-tolerant cell line also showed a slight tolerance to buthionine sulfoximine. In the buthionine sulfoximine experiments reduced glutathione restored growth in both cell lines, whereas oxidized glutathione restored growth only in the NaCl-tolerant cell line. These data indicate that the NaCl-tolerant cell line exhibited a cross-tolerance to a variety of stress variables and had a more active ascorbate-glutathione cycle.

Immunocytochemical localization of phenylalanine ammonia-lyase in tissues of Populus kitakamiensis

The polypeptide encoded by the partial fragment of cDNA of phenylalanine ammonia-lyase (PAL; EC 4.3.1.5), PALcDNA1 (Osakabe et al., 1995, Plant Sci. 105: 217-226), isolated from Populus kitakamiensis (P. sieboldii x P. grandidentata), was expressed in Escherichia coli cells. The polypeptide was purified and an antiserum raised against it. The antiserum recognized a protein of 77 kDa on nitrocellulose blots after sodium dodecyl sulfate-polyacrylamide gel electrophoresis of total protein and the partially purified PAL protein from P. kitakamiensis. Moreover, the antiserum recognized a protein on the blot after non-denaturing polyacrylamide gel electrophoresis of P. kitakamiensis proteins and this protein had PAL activity. Furthermore, the antibody inhibited PAL activity of extracts from stem tissues. These results showed that the antiserum against the partial PAL peptide recognized only the PAL subunits in extracts of P. kitakamiensis. Immunolocalization studies of P. kitakamiensis tissues revealed that the PAL protein was specifically localized in the xylem and the phloem fibers and no immunogold signal was found in the epidermis, the cortex, the pith, or the cambium of either stems or leaves.

Infection-induced rapid cell death in plants: a means of efficient pathogen defense

The hypersensitive reaction represents one of the major means by which plants actively defend themselves against infection by pathogenic bacteria, fungi, viruses, and nematodes. This complex defense reaction, often associated with the synthesis of phytoalexins (antimicrobial secondary metabolites), involves at the cellular level highly dynamic cytoplasmic rearrangements, rapid metabolic changes, and finally cell death. It also correlates with the rapid and transient activation of various defense-related genes in a region of tissue surrounding infection sites and later, with the systemic increase in expression of a number of other genes. Examination of the reactions of individual living cells of potato leaves infected with Phytophthora infestans enabled the comprehensive description of the dynamic aspects of all stages of the defense response. Cytochemical investigations, employing cultured cells of parsley infected with P. infestans as a versatile model system, have contributed to a better understanding of cytoplasmic and metabolic processes occurring during the defense response, and suggest that hypersensitive cell death requires the preceding activation of respiration and specific metabolic pathways. Key words: defense responses, defense-related genes, hypersensitive reaction, programmed cell death.

The phenylalanine ammonia-lyase gene family in Arabidopsis thaliana

Phenylpropanoid derivatives are a complex class of secondary metabolites that have many important roles in plants during normal growth and in responses to environmental stress. Phenylalanine ammonialyase (PAL) catalyzes the first step in the biosynthesis of phenylpropanoids, and is usually encoded by a multi-gene family. Genomic clones for three Arabidopsis thaliana PAL genes containing the entire protein-coding region and upstream and downstream sequences have been obtained and completely sequenced. Two A. thaliana PAL genes (PAL1 and PAL2) are structurally similar to PAL genes that have been cloned from other plant species, with a single intron at a conserved position, and a long highly conserved second exon. Previously identified promoter motifs plus several additional sequence motifs were found in the promoter regions of PAL1 and PAL2. Expression of PAL1 and PAL2 is both qualitatively and quantitatively similar in different plant organs and under various inductive conditions. A third A. thaliana PAL gene, PAL3, differs significantly from PAL1 and PAL2 and other sequenced plant PAL genes. PAL3 contains an additional intron, and its deduced amino acid sequence is less homologous to other PAL proteins. The PAL3 promoter region lacks several sequence motifs conserved between A. thaliana PAL1 and PAL2, as well as motifs described in other genes involved in phenylpropanoid metabolism. A. thaliana PAL3 was expressed at very low levels under the conditions examined.

Immediate Activation of Respiration in Petroselinum crispum L. in Response to the Phytophthora megasperma f. sp. Glycinea Elicitor

Treatment of parsley (Petroselinum crispum L.) cell cultures with the Phytophthora megasperma elicitor isolated from the fungus Phytophthora megasperma f. sp. Glycinea caused an immediate increase in the rate of respiratory CO2 evolution in the dark. The respiratory response was biphasic, showing a rapid enhancement in the first 20 min and then a slower increase until a steady rate was attained 60 min posttreatment. The enhanced rate of CO2 evolution corresponded to the activation of phosphofructokinase and glucose-6-phosphate dehydrogenase, key enzymes in the regulation of carbohydrate flow to glycolysis and the oxidative pentose phosphate (OPP) pathway, respectively. The increased rate of CO2 evolution and the activation of phosphofructokinase and glucose-6-phosphate dehydrogenase were maintained for the duration of the experiments, indicating long-term stimulation of respiration through both glycolysis and the OPP pathway. A 23% decrease in the C6:C1 ratio of 14CO2 evolution from labeled glucose 60 min after the addition of Phytophthora megasperma elicitor is consistent with an increased contribution of the OPP pathway to cellular respiration. Long-term activation of the OPP pathway following elicitation could serve to maintain the pools of substrates necessary during activation of the shikimic acid pathway, leading to the production of defensive compounds.

Cloning and regulation of flavonol 3-sulfotransferase in cell-suspension cultures of Flaveria bidentis

Flaveria spp. accumulate flavonol sulfate esters whose biosynthesis is catalyzed by a number of position-specific flavonol sulfotransferases. Although the accumulation of sulfated flavonols appears to be tissue specific and developmentally regulated and to vary among related species, little is known about the mechanism of regulation controlling the synthesis of these metabolites. In the present work, we report the isolation of a cDNA clone from Flaveria bidentis (pBFST3) encoding flavonol 3-sulfotransferase (F3-ST), which catalyzes the first step in the biosynthesis of flavonol polysulfates. This clone (pBFST3) was expressed in Escherichia coli and produced an F3-ST with high affinity for the flavonol aglycones, quercetin, and its 7-methyl derivative, rhamnetin. In addition, the synthetic auxin 2,4-dichlorophenoxyacetic acid was shown to induce F3-ST enzyme activity and F3-ST mRNA transcript levels in cell cultures of F. bidentis. The F3-ST mRNA levels increased within the first 3 h, reaching a maximum after 24 h of treatment, and remained elevated for up to 48 h. Treatments with either quercetin 3-sulfate or quercetin 3,7,4'-trisulfate reduced F3-ST enzyme activity in cell cultures but had no effect on the transcript levels. These results are discussed in relation to the putative role of flavonoid conjugates in the regulation of auxin transport.

UV-B damage and protection at the molecular level in plants

Influx of solar UV-B radiation (280-320 nm) will probably increase in the future due to depletion of stratospheric ozone. In plants, there are several targets for the deleterious UV-B radiation, especially the chloroplast. This review summarizes the early effects and responses of low doses of UV-B at the molecular level. The DNA molecules of the plant cells are damaged by UV due to the formation of different photoproducts, such as pyrimidine dimers, which in turn can be combatted by specialized photoreactivating enzyme systems. In the chloroplast, the integrity of the thylakoid membrane seems to be much more sensitive than the activities of the photosynthetic components bound within. However, the decrease of mRNA transcripts for the photosynthetic complexes and other chloroplast proteins are among very early events of UV-B damage, as well as protein synthesis. Other genes, encoding defence-related enzymes, e.g., of the flavonoid biosynthetic pathway, are rapidly up-regulated after commencement of UV-B exposure. Some of the cis-acting nucleotide elements and trans-acting protein factors needed to regulate the UV-induced expression of the parsley chalcone synthase gene are known.

Biochemical Plant Responses to Ozone (IV. Cross-Induction of Defensive Pathways in Parsley (Petroselinum crispum L.) Plants)

Parsley (Petroselinum crispum L.) is known to respond to ultraviolet irradiation by the synthesis of flavone glycosides, whereas fungal or elicitor stress leads to the synthesis of furanocoumarin phytoalexins. We tested how these defensive pathways are affected by a single ozone treatment (200 nL L-1; 10 h). Assays were performed at the levels of transcripts, for enzyme activities, and for secondary products. The most rapid transcript accumulation was maximal at 3 h, whereas flavone glycosides and furanocoumarins were maximally induced at 12 and 24 h, respectively, after the start of ozone treatment. Ozone acted as a cross-inducer because the two distinct pathways were simultaneously induced. These results are consistent with the previously observed ozone induction of fungal and viral defense reactions in tobacco, spruce, and pine.