Accumulation Of Polyphenolic Compounds Research Articles

Features of Growth and Accumulation of Polyphenolic Compounds in Callus Cultures of Lavandula angustifolia Mill.

Features of Growth and Accumulation of Polyphenolic Compounds in Callus Cultures of Lavandula angustifolia Mill.

The content of polyphenolic compounds in buckwheat grass depending on agrotechnical and abiotic factors and the assessment of the possibility of its use in food technologies

Relevance. Buckwheat is a source of many biologically active substances. Especially there are a lot of them in leaves and inflorescences from which it is possible to get tea beverages for specialized and functional nutrition. These plant parts are rich in polyphenolic compounds (PC), the main one being rutin. Their content in the plant depends on many factors.The aim of this study is to estimate the effect of sowing dates, ultraviolet (UV) radiation and temperature on PC accumulation in buckwheat plants.Methods. Buckwheat seeds were sown four times in June-July. The PC content of buckwheat water-ethanol extracts and water infusions was determined by Folin-Ciocalteu, method antioxidant activity — by DPPH radical scavenging method.Results. The sowing dates influence the PC content. At the earlier sowing dates of seeds the accumulation of PC in the extracts was higher (8.42–9.33%) in comparison with the later ones (6.10%). The PC content in the infusions varied from 2.10 to 2.83%. There are indications of a direct relationship between the accumulation of PC and the level of UV radiation during the growing season requiring further verification. A significant effect of temperature was not revealed. The AOA of all samples was high. The content of PC in aqueous infusions allows us to recommend buckwheat grass as a raw material for tea beverages.

Histone Deacetylase Inhibitor, Sodium Butyrate-Induced Metabolic Modulation in Platycodon grandiflorus Roots Enhances Anti-Melanogenic Properties.

While the status of histone acetylation is a critical regulator of chromatin's structure with a significant impact on plant physiology, our understanding of epigenetic regulation in the biosynthesis of active compounds in plants is limited. In this study, Platycodon grandiflorus was treated with sodium butyrate (NaB), a histone deacetylase inhibitor, to investigate the influence of histone acetylation on secondary metabolism. Its treatment with NaB increased the acetylation of histone H3 at lysine 9, 14, and 27 and enhanced the anti-melanogenic properties of P. grandiflorus roots. Through transcriptome and differentially expressed gene analyses, we found that NaB influenced the expression of genes that were involved in both primary and secondary metabolic pathways. In addition, NaB treatment caused the accumulation of polyphenolic compounds, including dihydroquercetin, gallic acid, and 2,4-dihydroxybenzoic acid. The NaB-induced transcriptional activation of genes in the phenylpropanoid biosynthetic pathway influenced the anti-melanogenic properties of P. grandiflorus roots. Overall, these findings suggest the potential of an epigenomic approach to enhance the medicinal qualities of medicinal plants.

Influence of flower bud removal on the growth and anti-inflammatory properties of Platycodon grandiflorus roots

Platycodon grandiflorus roots have been used as a popular food additive and traditional medicinal product because of their therapeutic effects. During cultivation of this crop, flower bud removal has been used to increase root yield. However, the underlying mechanisms by which flower bud removal increases the yield of P. grandiflorus roots are still unknown. In this study, to investigate the effect of flower bud removal, we analyzed the level of gibberellic acid 3 (GA3) production, anti-inflammatory properties, and polyphenolic compounds in P. grandiflorus roots. Flower bud removal led to reduced GA3 content, resulting in increased root yield. In addition, we found that the accumulation of polyphenolic compounds through induction of the phenylpropanoid pathway is presumably a positive effect of flower bud removal that improves the anti-inflammatory properties of P. grandiflorus roots. Our results revealed that flower bud removal is a promising strategy for improving yield and quality of storage roots by rebalancing the assimilate exchange between sink organs.

Bioactive polyphenolic compounds, water-soluble vitamins, in vitro anti-inflammatory, anti-diabetic and free radical scavenging properties of underutilized alternate crop Amaranthus spinosus L. from Gangetic plain of West Bengal

Studies associated with validation of folklore and ethnomedicinal claim of utilization of different plant parts of ‘spiny amaranth’ (Amaranthus spinosus L.) against degenerative diseases with chemical data, particularly the bioactive polyphenolic compounds and associated anti-degenerative properties are scanty and is the purpose of the present investigations. RP-HPLC coupled photodiode assay was employed for the quantification of twenty-one health promoting bioactive polyphenolic antioxidants derived from phenylpropanoid pathway from different plant parts of Amaranthus spinosus L. for validating organoleptic traditional claims as well as current trends in practice of this underutilized medicinal herb. Further, important water-soluble vitamins [vitamin B1, B2, B3, B6, B9] present in different plant parts were extracted and estimated through RP-HPLC for validating the claim of their functional food properties. The antioxidant-based functional food property of different plant parts of Amaranthus spinosus were corroborated from the data of in vitro free radical scavenging, metal-chelating, reducing, superoxide radical scavenging, hydroxyl radical scavenging, anti-protein coagulation, anti-lipid peroxidation and antidiabetic properties. When compared, a positive correlation in accumulation of polyphenolic compounds and water-soluble vitamins tested with antioxidant attributes were noticed for different plant parts, strongly substantiating their phytonutrient properties. Taken as a whole, the present work provides data on organ-specific bioavailability of bioactive polyphenolic antioxidant compounds, water soluble B- vitamins and their functional attributes for validating traditional claims as well as existing trends in consumption of this underutilized medicinal vegetable as low-cost natural antioxidant supplement and functional food, which may encourage their effective exploration and utilization.

Plant Response to Cold Stress: Cold Stress Changes Antioxidant Metabolism in Heading Type Kimchi Cabbage (Brassica rapa L. ssp. Pekinensis).

Cold stress is known as the important yield-limiting factor of heading type Kimchi cabbage (HtKc, Brassica rapa L. ssp. pekinensis), which is an economically important crop worldwide. However, the biochemical and molecular responses to cold stress in HtKc are largely unknown. In this study, we conducted transcriptome analyses on HtKc grown under normal versus cold conditions to investigate the molecular mechanism underlying HtKc responses to cold stress. A total of 2131 genes (936 up-regulated and 1195 down-regulated) were identified as differentially expressed genes and were significantly annotated in the category of “response to stimulus”. In addition, cold stress caused the accumulation of polyphenolic compounds, including p-coumaric, ferulic, and sinapic acids, in HtKc by inducing the phenylpropanoid pathway. The results of the chemical-based antioxidant assay indicated that the cold-induced polyphenolic compounds improved the free-radical scavenging activity and antioxidant capacity, suggesting that the phenylpropanoid pathway induced by cold stress contributes to resistance to cold-induced reactive oxygen species in HtKc. Taken together, our results will serve as an important base to improve the cold tolerance in plants via enhancing the antioxidant machinery.

Diagnostic significance of the synthesis of phenolic compounds and proline in the leaves of Schisandra chinensis and Actinidia arguta for the indication of the stress levels of plants under conditions of mixed plantings

The peculiarities of the accumulation of polyphenolic compounds and free proline were investigated in the leaves of Actinidia arguta and Shisandra chinensis during their cultivation in vegetation containers with different ratios of the number of plants, namely 1 : 1, 2 : 1, 1 : 2. Monocultural (single-species) planting was used as a control. The content of free proline in plant leaves was carried out according to the method, which is based on the interaction of proline with a ninhydrin reagent, forming a pink-red color. The amount of polyphenolic compounds was determined by the Folin-Ciocalteu method. It was found that the ratio of plants grown together significantly affects the accumulation of primary and secondary metabolites in their leaves. Under conditions of mixed planting, more proline and phenolic substances are accumulated in plant leaves compared to monoculture. The maximum proline content, 19.44 ± 0.91 mg/g of dry weight (DW), was observed in the leaves of A. arguta in the experiment combination with a prevailing number of schisandra plants at a ratio of S. chinensis and A. arguta plants of 2:1. In the same combination, the leaves of actinidia contained the highest amount of phenolic compounds (36.87 ± 2.22 mg/g DW). The studied root exudates of the experimental plants had an allelopathic inhibitory effect on the test culture. The exudates caused 12.0 % average decrease in root growth of A. arguta test objects, and 30.0 % average decrease in root growth of S. chinensis test objects compared with the control. This allows us to conclude about the high activity of schisandra’s allelochemicals, which negatively affect the development of actinidia plants. The optimal ratio of plants A. arguta and S. chinensis when grown together is 2 : 1, since a higher concentration of schisandra plants in a container more stress in actinidia plants, expressed as an increased accumulation of phenols and prolines in its leaves. The result of a comparative analysis of the amount of proline and phenolic compounds can be used to assess the mutual influence of plants in mixed plantings to optimize their growing conditions, which confirms the diagnostic significance of these metabolites for indicating the stress state of the studied plants.

Oligosaccharins as Elicitors of Defense Responses in Wheat.

Wheat is a highly relevant crop worldwide, and like other massive crops, it is susceptible to foliar diseases, which can cause devastating losses. The current strategies to counteract wheat diseases include global monitoring of pathogens, developing resistant genetic varieties, and agrochemical applications upon diseases’ appearance. However, the suitability of these strategies is far from permanent, so other alternatives based on the stimulation of the plants’ systemic responses are being explored. Plants’ defense mechanisms can be elicited in response to the perception of molecules mimicking the signals triggered upon the attack of phytopathogens, such as the release of plant and fungal cell wall-derived oligomers, including pectin and chitin derivatives, respectively. Among the most studied cell wall-derived bioelicitors, oligogalacturonides and oligochitosans have received considerable attention in recent years due to their ability to trigger defense responses and enhance the synthesis of antipathogenic compounds in plants. Particularly, in wheat, the application of bioelicitors induces lignification and accumulation of polyphenolic compounds and increases the gene expression of pathogenesis-related proteins, which together reduce the severity of fungal infections. Therefore, exploring the use of cell wall-derived elicitors, known as oligosaccharins, stands as an attractive option for the management of crop diseases by improving plant readiness for responding promptly to potential infections. This review explores the potential of plant- and fungal-derived oligosaccharins as a practical means to be implemented in wheat crops.

Accumulation of Polyphenolic Compounds and Osmolytes under Dehydration Stress and Their Implication in Redox Regulation in Four Indigenous Aromatic Rice Cultivars

Present work was undertaken to screen some drought tolerant indigenous aromatic rice cultivars (IARCs), commonly cultivated in West Bengal, India, based on their capacity to produce osmolytes, redox-sensitive phenolic acids and flavonoids, as contrivances for redox-regulation under drought stress. Polyethylene glycol induced post imbibitional dehydration stress mediated changes in redox regulatory properties of the germinating seeds of the four IARCs (Jamainadu, Tulaipanji, Sitabhog, Badshabhog), which were assessed in terms of changes in prooxidant accumulation (in-situ localization of reactive oxygen species (ROS) by confocal microscopy, DCFDA (2′,7′-dichlorofluorescin diacetate) oxidation, O2− and H2O2 accumulation), cumulative antioxidative defense (radical scavenging property and total thiol content), ROS scavenging phenolic acids (gallic acid, protocatechuic acid, gentisic acid, para-hydroxy benzoic acid, chlorogenic acid, caffeic acid, syringic acid, salicylic acid, sinapic acid and p-coumaric acid) and flavonoids (catechin, naringin, rutin, quercetin, kaempferol, myricetin and apigenin). The capability of germinating seeds to accumulate osmolytes (like glycinebetaine, proline, soluble carbohydrates and K+ ion) and polyphenolic compounds was also correlated with their corresponding redox status and redox biomarkers (conjugated diene, hydroperoxide, thiobarbituric acid reactive substances and free carbonyl content) produced under the same conditions. The results in general showed that accumulation of osmolytes along with the redox-sensitive phenolics and flavonoids conferred the ability to maintain the redox homeostasis under drought stress for the tolerant IARCs (Badshabhog and Tulaipanji).

Effect of seed sowing period on polyphenolic compounds content in basil (Ocimum basilicum L.) under greenhouse conditions

The object of the research is the process of formation of the polyphenolic complex by basil plants. The complexity in evaluating the process of polyphenols accumulation lies in the fact that the formation of these compounds occurs under the influence of a number of biotic and abiotic factors, leading to variation in the level of polyphenols in a very wide range even for plants of the same cultivar.The influence of different seed sowing periods of five cultivars of basil on the accumulation of polyphenolic compounds in each cutting of green mass was investigated. The obtained data were mathematically computed using AgrostatNew and MicrosoftExcel software. It was found that cultivars with purple coloration of leaves accumulate by 51.2–66.6 % more polyphenols than green cultivars. It was observed that in the green cultivars Bad’oryi, Rutan and Siaivo, the level of polyphenols increases with each subsequent cutting of green mass during the February and April seed sowing periods. The cultivars with purple coloration of leaves have shown the highest level of accumulated polyphenols in the first cutting for the February seed sowing period and in the fourth and fifth cutting in April. The level of polyphenols in all the cultivars, which were sown in March, did not significantly change during cutting, indicating the optimal cultivation conditions.

Regulation of the Phenylpropanoid Pathway: A Mechanism of Selenium Tolerance in Peanut (Arachis hypogaea L.) Seedlings.

To clarify the mechanisms of selenium (Se) tolerance in peanut seedlings, we grew peanut seedlings with sodium selenite (0, 3, and 6 mg/L), and investigated the phenylpropanoids metabolism in seedling roots. The results showed that selenite up-regulated the expression of genes and related enzyme activities involving in the phenylpropanoids biosynthesis cascade, such as phenylalanine ammonia-lyase, trans-cinnamate-4-hydroxylase, chalcone synthase, chalcone isomerase, and cinnamyl-alcohol dehydrogenase. Selenite significantly increased phenolic acids and flavonoids, which contributed to the alleviation of selenite-induced stress. Moreover, selenite enhanced the formation of endodermis in roots, which may be attributed to the up-regulation of lignin biosynthesis mediated by the selenite-induced changes of H2O2 and NO, which probably regulated the selenite uptake from an external medium. Accumulation of polyphenolic compounds via the phenylpropanoid pathway may be one of the mechanisms of the increasing selenite tolerance in plants, by which peanut seedlings survived in seleniferous soil, accompanied by accumulation of Se.

Phosphorus supply, arbuscular mycorrhizal fungal species, and plant genotype impact on the protective efficacy of mycorrhizal inoculation against wheat powdery mildew.

A potential alternative strategy to chemical control of plant diseases could be the stimulation of plant defense by arbuscular mycorrhizal fungi (AMF). In the present study, the influence of three parameters (phosphorus supply, mycorrhizal inoculation, and wheat cultivar) on AMF protective efficiency against Blumeria graminis f. sp. tritici, responsible for powdery mildew, was investigated under controlled conditions. A 5-fold reduction (P/5) in the level of phosphorus supply commonly recommended for wheat in France improved Funneliformis mosseae colonization and promoted protection against B. graminis f. sp. tritici in a more susceptible wheat cultivar. However, a further decrease in P affected plant growth, even under mycorrhizal conditions. Two commercially available AMF inocula (F. mosseae, Solrize®) and one laboratory inoculum (Rhizophagus irregularis) were tested for mycorrhizal development and protection against B. graminis f. sp. tritici of two moderately susceptible and resistant wheat cultivars at P/5. Mycorrhizal levels were the highest with F. mosseae (38%), followed by R. irregularis (19%) and Solrize® (SZE, 8%). On the other hand, the highest protection level against B. graminis f. sp. tritici was obtained with F. mosseae (74%), followed bySZE (58%)and R. irregularis (34%), suggesting that inoculum type rather than mycorrhizal levels determines the protection level of wheat against B. graminis f. sp. tritici. The mycorrhizal protective effect was associated with a reduction in the number of conidia with haustorium and with an accumulation of polyphenolic compounds at B. graminis f. sp. tritici infection sites. Both the moderately susceptible and the most resistant wheat cultivar were protected against B. graminis f. sp. tritici infection by F. mosseae inoculation at P/5, although the underlying mechanisms appear rather different between the two cultivars. This study emphasizes the importance of taking into account the considered parameters when considering the use of AMF as biocontrol agents.

СКРИНИНГ СОДЕРЖАНИЯ И ДИНАМИКА НАКОПЛЕНИЯ ПОЛИФЕНОЛЬНЫХ ВЕЩЕСТВ НЕКОТОРЫХ ВИДОВ БАЗИДИОМИЦЕТОВ

<p>The <strong><em>aim </em></strong>of the study was to investigate the total content of polyphenolic substances in Basidiomycetes carpophores from 50 species, of which 27 belong to the order <em>Polyporales</em> and 23 to the order <em>Agaricales</em>. Introduced 23 strains of 8 species of Basidiomycetes. <strong><em>Methods.</em></strong> Gathered wild carpophores dried and crushed to a particle size of 0,1 till 0,01 mm and searching strains were cultured in Erlenmeyyers flasks by surface method on standard glucose-peptone culture medium. Determination of total content of polyphenolic compounds was carried out in ethanol extracts of mycological material by a modified method of Folin-Chokalteu. Completely dry biomass of carpophores and mycelium was determined gravimetrically. <strong><em>Results.</em></strong> There was identified the species of polyporal fungi <em>Ganoderma applanatum</em>, <em>Ganoderma lucidum</em>, <em>Laetiporus sulphureus</em> and <em>Fomes fomentarius</em> and types of agarical mushrooms <em>Stropharia rugosoannulata</em>, <em>Agrocybe cylindracea</em>, <em>Tricholoma flavovirens</em>, <em>Flammulina velutipes</em>, <em>Pleurotus ostreatus</em> and <em>Fistulina hepatica</em> high in polyphenolic compounds. It was determined the content of polyphenols ranging from more than 60 mg / g completely dry biomass. For introduced strains established dynamics of growth and accumulation of polyphenolic compounds in the mycelium and culture filtrate during fermentation on glucose-peptone medium. All cultures reach a maximum accumulation of biomass on the 12th day of growth. <em>Shizophyllum commune</em> Sc-1101 and 10 and <em>F. velutipes </em>F-202 have been identified as the most productive strains. The lowest accumulation of absolutely dry biomass was recorded for strain <em>P. ostreatus</em> P-192 and strain <em>F. fomentarius</em> Ff-09. Cultures have investigated individual value growth such as biomass accumulation in the applied cultivation conditions, which probably reflects the suitability of the medium for their growth and genotypic characteristics. Strains are overwhelmingly able to accumulate polyphenolic compounds in both mycelium and culture fluid during the whole period of cultivation. Maximum content of polyphenols in the mycelium to 96%, and in the culture fluid - for 91% of strains coincided with the end of their term cultivation. Calculated correlation coefficient between the content of polyphenols in the mycelium and culture fluid showed that there is a very high positive correlation of 73.2%, a positive high at 17.4% and the average 4.5% of experiment data. <strong><em>Conclusion.</em></strong> The strains of species <em>Shizophyllum</em> <em>commune</em>, <em>Pleurotus ostreatus</em>, <em>Fistulina hepatica</em> and <em>Laetiporus sulphureus</em> were selected for further research in order to obtain polyphenols mycelial and extracellular origin.<em></em></p> <p><em>Key words:</em> <em>polyphenols, Basidiomycetes, carpophores, mycelium, cultural filtrate</em></p>

Effects of shading on synthesis and accumulation of polyphenolic compounds in ginger (Zingiber officinale Roscoe) varieties

Extracts of leaves and rhizomes of two varieties (Halia Bara and Halia Bentong) of Malaysian young ginger (Zingiber officinale) grown under different shade net (0 and 60%) were examined as potential sources of phenolics and flavonoids compounds for antioxidant activities. High performance liquid chromatography (HPLC) with UV detection was employed for the identification and quantification of the polyphenolic compounds (flavonoids and phenolic acids). Flavonoid compounds (quercetin, apigenin, luteolin, and myricetin) and phenolic acids (gallic acid, vanillic acid, ferulic acid, tannic acid and caffeic acid) were identified with different concentration in leaves and rhizomes of ginger varieties. The most abundant phenolic acid in ginger was gallic acid, and flavonoids were quercetin and apigenin. Accordingly, accumulations of flavonoids in the leaves were high under 60% shade, while most phenolic acids were observed in the rhizomes under 0% shade. Furthermore, caffeic acid was only detected from ginger grown under 0% shade, while tannic acid only accumulated in the leaves of ginger grown under 60% shade level. The results indicated phenolic acids and flavonoids absolutely light dependent and them biosynthetic rate is related to light intensity. Additionally, this study also validated Halia Bara and Halia Bentong medicinal potential based on polyphenolics compound. Key words: High performance liquid chromatography, shade, flavonoids, phenolic acids, Halia Bentong, Halia Bara.

Continuous UV-B Irradiation Induces Endoreduplication and Peroxidase Activity in Epidermal Cells Surrounding Trichomes on Cucumber Cotyledons

Most trichomes on the surface of cucumber (Cucumis sativus L.) cotyledons consist of three cells. We previously showed that continuous UV-B (290-320 nm) irradiation induces rapid cellular expansion and the accumulation of polyphenolic compounds, possibly stress lignin, in epidermal cells around these trichomes.(1)) To examine the mechanism of the UV-B-induced cellular expansion and to determine which step is stimulated by UV-B irradiation in the lignin synthesis pathway, we investigated relative DNA contents in epidermal cells, including trichomes, and enzyme activity and gene expression in the phenylpropanoid pathway. UV-B irradiation increased the ploidy level over 15 days, specifically in the epidermal cells surrounding trichomes, but not in the other epidermal cells or trichomes. In epidermal cells surrounding trichomes, UV-B irradiation induced peroxidase (POX) activity from days 7 to 15. In cotyledons, UV-B exposure induced CS-POX1 and CS-POX3 gene expression within 2 days, and it also induced two other enzymes in the phenylpropanoid pathway, sinapyl alcohol dehydrogenase and coniferyl alcohol dehydrogenase, from days 9 to 11. Thus, exposure to UV-B induces expansion, endoreduplication, POX activity, and the accumulation of polyphenolic compounds in epidermal cells surrounding the trichomes of cucumber cotyledons. Because polyphenolic compounds such as lignin absorb UV-B, our data indicate a physiological protective mechanism against UV-B irradiation in cucumber.

Effect of photoperiod on flavonoid pathway activity in sweet potato (Ipomoea batatas (L.) Lam.) leaves

Compared with those of major commercial leafy vegetables, leaves of sweet potato have higher contents of flavonoids and phenolic acids, which provide significant health benefits and may be used as natural colourants. We have analysed the expression of key flavonoid biosynthesis genes using RT-PCR and the accumulation of polyphenolic compounds using high-performance liquid chromatography coupled to a photodiode-array detector, during the development of leaves of sweet potato plants growing under either long day or short day photoperiods. A massive induction of flavonoid pathway gene expression, correlating with a dramatic increase in the content of an anthocyanin, catechins, flavonols, hydroxycinnamic acids and hydroxybenzoic acids, was observed during sweet potato leaf exposure to a long day photoperiod. These results provide further support for the protective role of flavonoids and phenolic acids against enhanced light exposure in plants.

The Sinorhizobium meliloti MsbA2 protein is essential for the legume symbiosis

Sinorhizobium meliloti is a beneficial legume symbiont, closely related to Brucella species, which are chronic mammalian pathogens. We discovered that the S. meliloti MsbA2 protein is essential to ensure the symbiotic interaction with the host plant, alfalfa. S. meliloti invades plant cells via plant-derived structures known as infection threads. However, in the absence of MsbA2, S. meliloti remains trapped within abnormally thickened infection threads and induces a heightened plant defence response, characterized by a substantial thickening of the nodule endodermis layer and the accumulation of polyphenolic compounds. The S. meliloti MsbA2 protein is homologous to the Escherichia coli lipopolysaccharide/phospholipid trafficking protein MsbA. However, MsbA2 was not essential for the membrane transport of either lipopolysaccharide or phospholipids in S. meliloti. We determined that the msbA2 gene is transcribed in free-living S. meliloti and that in the absence of MsbA2 the polysaccharide content of S. meliloti is altered. Consequently, we propose a model whereby the altered polysaccharide content of the S. meliloti msbA2 mutant could be responsible for its symbiotic defect by inducing an inappropriate host response.

Continuous UV-B Irradiation Induces Morphological Changes and the Accumulation of Polyphenolic Compounds on the Surface of Cucumber Cotyledons

Sharp-headed and globular-headed trichomes are found on the surface of cucumber (Cucumis sativus L.) cotyledons. Most sharp-headed trichomes consist of three cells. Toluidine blue O stains sharp-headed but not globular-headed trichomes. The effect of continuous ultraviolet-B (UV-B; 290-320 nm) irradiation on the surface of cucumber cotyledons was examined with respect to the two trichome types. Continuous UV-B irradiation induced cell division at or under the basal part of sharp-headed trichomes, resulting in an increase in the number of cell layers from three to six. In parallel, the area stained by toluidine blue O expanded to include epidermal cells surrounding sharp-headed trichomes. Regions of alkali-induced fluorescence due to the presence of polyphenolic compounds coincided with areas stained by toluidine blue O. In contrast, continuous UV-B irradiation did not cause morphological changes in globular-headed trichomes. Thus, continuous UV-B irradiation causes the accumulation of polyphenolic compounds in cucumber cotyledons and induces specific morphological changes in or around sharp-headed trichomes. UV-B exposure also increases lignin content in this tissue. Therefore, continuous UV-B irradiation may induce the specific accumulation of polyphenolic compounds, especially stress lignins, in and near sharp-headed trichomes.

Identification of Compatible and Incompatible Interactions BetweenArabidopsis thalianaandXanthomonas campestrispv.campestrisand Characterization of the Hypersensitive Response

Both compatible and incompatible interactions between Arabidopsis thaliana and Xanthomonas campestris have been identified and, for the first time, a strong hypersensitive response has been characterized. A highly reproducible mass spray inoculation protocol has been established and was used together with the more commonly used infiltration inoculation procedure to study the defense responses occurring in mature A. thaliana plants. A series of bacterial strains have been tested on A. thaliana ecotype Columbia (Col-O). X. c. pv. campestris was the most effective pathogen in these tests and was used for further detailed analysis. Several X. c. pv. campestris isolates were tested on A. thaliana Col-O, and one particular X. c. pv. campestris strain (147) was tested on 27 Arabidopsis ecotypes. Symptom development of compatible and incompatible interactions, including the hypersensitive response, was extensively characterized in A. thaliana Col-O. Lesion structure, bacterial distribution, accumulation of polyphenolic compounds, and the deposit of callose in inoculated leaves were documented by microscopic analysis. Activation of the defense-associated genes coding for phenylalanine ammonia lyase (PAL), beta-1, 3-glucanases, chitinases, and peroxidases was evaluated by Northern blot analysis.