Increase In Phenylalanine Ammonia-lyase Activity Research Articles

Interaction of Gibberellic Acid and Glyphosate on Growth and Phenolic Metabolism in Soybean Seedlings

The plant growth regulator gibberellic acid (GA) and the herbicide glyphosate were examined for their possible interactions with growth and phenolic metabolism in soybean [Glycine max (L.) Merr. Cv. Hill] seedlings. GA caused increases in phenylalanine ammonia-lyase activity (PAL) (per axis basis) above those of the control seedling levels 48 h after treatment in light-grown seedlings. This effect increased to two-fold greater than control levels by 72 and 96 h after treatment. In dark-grown plants, GA had no effect on PAL levels at 24 h, reduced levels at 48 and 72 h, and increased PAL at 96 h. Early studies in our lab reported that glyphosate increased PAL levels, and also reduced hydroxyphenolic compound accumulation in both light- and dark-grown soybean seedlings. Treatments of GA plus glyphosate caused additive increases in PAL activity in light-grown seedlings, but GA lowered glyphosate’s increase in PAL levels at 48–96 h after treatment in dark-grown seedlings. GA had little effect on hydroxyphenolic compound levels in either light- or dark-grown seedlings. GA treatment alone did not significantly affect root elongation, but stimulated hypocotyl and epicotyl elongation and caused marginal reversal of glyphosate inhibition of elongation in roots, hypocotyls, and epicotyls in light-grown plants. These results show some differential effects of GA and glyphosate on growth and phenolic metabolism, and their interactions that are dependent on plants grown in light or darkness.

Adding value to strawberry agro-industrial by-products through ultraviolet A-induced biofortification of antioxidant and anti-inflammatory phenolic compounds.

The revalorization of agro-industrial by-products by applying ultraviolet A (UVA) radiation to biofortify with phenolic compounds has been studied in recent times, showing improvements in the individual and total phenolic content and their bioactivity. Therefore, the main aim of this work was to optimize the biofortification process of phenolic compounds by UVA radiation to strawberry agro-industrial by-products (RF). Moreover, the effect of UVA radiation on the potential biological activity of the phenolics accumulated in RF due to the treatment was also determined. The assays followed a factorial design with three variables at three levels: UVA dose (LOW, MEDIUM, and HIGH), storage temperature (5, 10, and 15°C), and storage time (0, 24, 48, and 72 h). At each experimental condition, phenylalanine ammonia-lyase (PAL) and polyphenol oxidase (PPO) enzymatic activities, total phenolic compound content (TPC), phenolics profile (TPCHPLC), and agrimoniin content (AGN) were evaluated; and the optimal UVA dose, storage time, and temperature were determined. In vitro bioaccessibility of the accumulated phenolic compound was studied on RF tissue treated with UVA at optimal process conditions. The digested extracts were tested for antiproliferative activity in colorectal cancer cells, cellular antioxidant capacity, and anti-inflammatory activity. The results showed that applying UVA-HIGH (86.4 KJ/m2) treatment and storing the tissue for 46 h at 15°C increased PAL activity (260%), phenolic content (240%), and AGN (300%). The biofortification process improves the bioaccessibility of the main phenolic compound of RF by 9.8 to 25%. The digested optimum extract showed an IC50 for HT29 and Caco-2 cells of 2.73 and 5.43 μg/mL, respectively, and presented 60% cellular antioxidant capacity and 30% inhibition of NOX production. The RF treated with UVA is an excellent source of phenolic compounds; specifically, ellagitannins and the UVA radiation proved to be efficient in biofortify RF, significantly improving the phenolic compounds content and their bioactive properties with adequate bioaccessibility, adding value to the strawberry agro-industrial by-products.

Gene expression pattern and taxane biosynthesis in a cell suspension culture of Taxus baccata L. subjected to light and a phenylalanine ammonia lyase (PAL) inhibitor.

Taxus baccata L. cell culture is a promising commercial method for the production of taxanes with anti-cancer activities. In the present study, a T. baccata cell suspension culture was exposed to white light and 2-aminoindan-2-phosphonic acid (AIP), a phenylalanine ammonia lyase (PAL) inhibitor, and the effects of this treatment on cell growth, PAL activity, total phenol content (TPC), total flavonoid content (TFC), taxane production and the expression of some key taxane biosynthetic genes (DXS, GGPPS, T13OH, BAPT, DBTNBT) as well as the PAL were studied. Light reduced cell growth, whereas AIP slightly improved it. Light increased PAL activity up to 2.7-fold relative to darkness. The highest TPC (24.89mg GAE/g DW) and TFC (66.94mg RUE/g DW) were observed in cultures treated with light and AIP. Light treatment also resulted in the maximum content of total taxanes (154.78μg/g DW), increasing extracellular paclitaxel and cephalomannin (3.3-fold) and intracellular 10-deacetyl paclitaxel (2.5-fold). Light significantly increased the expression level of PAL, DBTNBT, BAPT, and T13αOH genes, whereas it had no effect on the expression of DXS, a gene active at the beginning of the taxane biosynthetic pathway. AIP had no significant effect on the expression of the target genes. In conclusion, the light-induced activation of PAL transcription and altered expression of relevant biosynthetic genes reduced cell growth and increased the content of total phenolic compounds and taxanes. These findings can be applied to improve taxane production in controlled cultures and bioreactors.

Melatonin mediates isoflavone accumulation in germinated soybeans (Glycine max L.) under ultraviolet-B stress

Soybean germination under ultraviolet-B (UV–B) radiation stress is a common and effective way to enrich the isoflavone content of sprouts. However, the growth and biomass of germinated soybeans are significantly suppressed using this method. Melatonin (MT), a novel plant biostimulant, not only plays a vital protective role in responses to various abiotic stresses but also regulates the accumulation of secondary metabolites. In the present study, the effects of exogenous MT on the growth and isoflavone metabolism of germinating soybeans exposed to UV-B stress were investigated. Compared to UV-B stress, the application of exogenous MT (25 μM) significantly increased sprout length, fresh weight, Ca2+ influx, and peroxidase activity; markedly decreased the content of malondialdehyde and H2O2 and the fluorescence intensity of H2O2 and O2•-; but had no noticeable effect on the activity of superoxide dismutase and catalase during germination. Moreover, the content of total flavonoids and isoflavone monomers (including daidzein, genistein, daidzin, glycitin and genistin) in 4-day-old germinated soybeans was significantly enhanced by MT application under UV-B stress and was not only companied by dramatically increased phenylalanine ammonia lyase activity, but also by markedly increased relative expression levels of phenylalanine ammonia lyase1, chalcone synthase, isoflavone reductase and flavanone 3-hydroxylase that are involved in the isoflavone biosynthesis pathway. The inhibitory effects of UV-B stress on the growth and biomass of germinated soybeans were alleviated with exogenous MT. MT enhanced the content of total flavonoids and isoflavone monomers under UV-B stress by increasing the activity and relative gene expression level of critical isoflavone biosynthesis-related enzymes.

Improving the Berry Quality and Antioxidant Potential of Flame Seedless Grapes by Foliar Application of Chitosan-Phenylalanine Nanocomposites (CS-Phe NCs).

The production and sustainability of grape berries with high quality and health-promoting properties is a major goal. In this regard, nano-engineered materials are being used for improving the quality and marketability of berries. In this study, we investigated the potential role of chitosan–phenylalanine nanocomposites (CS–Phe NCs) in improving the quality of Flame Seedless (Vitis vinifera L.) grape berries, such as titratable acidity (TA), pH, total soluble solids (TSS), ascorbic acid, total phenolics, total flavonoids, anthocyanin, 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) radical scavenging activity, and phenylalanine ammonia-lyase (PAL) activity. In this context, grape berries collected in two growing seasons (2018–2019) were screened. Regarding the experimental design, the treatments included chitosan at a 0.5% concentration (CS 0.5%), phenylalanine at 5 mM and 10 mM concentrations (Phe 5 mM and Phe 10 mM), and chitosan–phenylalanine nanocomposites (CS–Phe NCs) at 5 mM and 10 mM concentrations. The lowest TA was recorded in grape berries treated with CS–Phe NCs with a 10 mM concentration. However, treatments enhanced with TSS, which reached the highest value with 10 mM of CS–Phe NCs, were reflected as the highest ratio of TSS/TA with 10 mM of CS–Phe NC treatment. Nanocomposites (NCs) also increased pH values in both study years compared to the control. Similarly, the ascorbic acid and total phenolic content increased in response to NP treatment, reaching the highest value with 5 mM and 10 mM of CS–Phe NCs in 2018 and 2019, respectively. The highest flavonoid content was observed with 5 mM of CS–Phe NCs in both study years. In addition, the anthocyanin content increased with 5 and 10 mM of CS–Phe NCs. PAL activity was found to be the highest with 5 mM of CS–Phe NCs in both study years. In addition, in accordance with the increase in PAL activity, increased total phenolics and anthocyanin, and higher DPPH radical scavenging activity of the grapes were recorded with the treatments compared to the control. As deduced from the findings, the coating substantially influenced the metabolic pathway, and the subsequent alterations induced by the treatments were notably appreciated due to there being no adverse impacts perceived.

Effect of Phytochrome Deficit on Activity of Ascorbate Peroxidase and Phenylalanine Ammonia-Lyase and Expression of Genes APX1, tAPX, sAPX, and PAL in the Leaves of Arabidopsis thaliana Plants Exposed to UV-A and Red Light

Effect of UV-A radiation (10 W/m2, 2 h) and modifying effect of brief exposure to red light (RL) (1.8 W/m2, 20 min) on photochemical activity of photosystem II (PSII) (Fv/Fm), as well as on activity of ascorbate peroxidase (AsP) and phenylalanine ammonia-lyase (PAL), were investigated in the leaves of 26–28-day-old Аrabidopsis thaliana (L.) Heynh. plants of wild type (WT) and mutants: hy3 deficient in phytochrome B (phyB) and hy2 defective in phytochromobilin synthesis. UV-A reduced photochemical activity of PSII and activities of AsP and PAL. Exposure to RL increased PAL activity in only WT plants and in mutant hy3. Elevation of expression of genes APX1, sAPX, tAPX, and PAL encoding enzymes AsP and PAL was detected upon the exposure to RL and UV-A. For instance, expression of gene APX1 in WT plants and in mutant hy3 rose upon exposure to RL and UV-A; in mutant hy2, it increased only upon UV-A treatment. Expression of gene tAPX in WT plants rose only under the effect of RL, whereas expression of gene sAPX did not rise in any type of treatment. In mutant hy2, expression of the above-named genes decreased upon the effect of RL. Upon joint action of RL and UV-A (RL followed by UV), the negative effect of UV-A on the activity of the total pool of AsP was nullified by RL in only WT plants and in mutant hy3. Partial removal of the negative effect of UV-A on activity of PSII as a result of pretreatment of plants with RL is probably related to a rise in the activity of antioxidant enzymes. This is evident in WT plants whose PSII is more sensitive to RL radiation than in mutants deficient in phytochromes. We believe that PSII resistance to UV-A radiation depends on the potential of the plant antioxidant system, which rises when the share of the active form of phytochrome in its total pool increases as a result of plants’ pretreatment with RL and is partially realized by way of induction of transcriptional activity of antioxidant genes.

Chemical composition and deterioration mechanism of Pleurotus tuoliensis during postharvest storage

Pleurotus tuoliensis is a popular edible and medical mushroom, but it is highly perishable during postharvest storage. The quality parameters, chemical composition, malondialdehyde (MDA) concentration, and activity of metabolic enzymes were studied during 12 days of storage at 4 °C and 6 days of storage at 25 °C. Degradation was well described by changes in quality parameters, losses in nutritional value, increased metabolic enzyme activity, the accumulation of MDA concentrations, and the increase of total phenolic (TP) content. The phenylalanine ammonia lyase (PAL) significantly positively correlated with TP, which suggested an underlying mechanism of browning that the increased PAL activity stimulates the biosynthesis of phenols through the phenylalanine pathway. These results suggest that increased activity of laccase, lipoxygenase, PAL, TP and MDA accumulation, together with polysaccharide degradation, are the main factors involved in the deterioration of P. tuoliensis during storage.

Induction of resistance to Meloidogyne graminicola in rice

Root-knot nematodes are responsible for substantial losses in rice production. These parasites are difficult to control, particularly in flooded fields, which require carefully designed strategies to avoid contamination of water bodies. This study investigated whether biotic and abiotic elicitors can induce resistance to the root-knot nematode Meloidogyne graminicola in rice plants. An initial screening test was performed to determine the elicitors with the greatest potential to control nematodes. Then, a second experiment was conducted under net house conditions to assess the effects of a mannanoligosaccharide-based fertilizer (MOS), acibenzolar-S-methyl (ASM), and silicate clay on nematode reproduction, penetration, and activation of plant defence-related enzymes. Elicitor treatment reduced nematode reproduction by 57.4 to 75.6% at 60 days after inoculation (DAI). Two factors that may have contributed to this result include reduced nematode penetration and delayed development, as observed in the screening test. All elicitors increased phenylalanine ammonia-lyase activity at 10 DAI. MOS and silicate clay also increased catalase, peroxidase, and glucanase activity at 8 DAI. Elicitor treatment activates defence responses in rice plants and may be an environmentally friendly strategy for controlling M. graminicola in an integrated management system.

Wounding and UVB Light Synergistically Induce the Biosynthesis of Phenolic Compounds and Ascorbic Acid in Red Prickly Pears (Opuntia ficus-indica cv. Rojo Vigor).

The present study evaluated the effects of ultraviolet B (UVB) radiation and wounding stress, applied alone or combined, on the biosynthesis of phenolic compounds and ascorbic acid in the peel and pulp of red prickly pear (Opuntia ficus-indica cv. Rojo Vigor). Whole and wounded-fruit samples were treated with UVB radiation (6.4 W·m−2) for 0 and 15 min, and stored for 24 h at 16 °C. Phytochemical analyses were performed separately in the peel and pulp. The highest phenolic accumulation occurred after storage of the whole tissue treated with UVB, where the main phenolic compounds accumulated in the peel and pulp were quercetin, sinapic acid, kaempferol, rosmarinic acid, and sinapoyl malate, showing increases of 709.8%, 570.2%, 442.8%, 439.9%, and 186.2%, respectively, as compared with the control before storage. Phenylalanine ammonia-lyase (PAL) activity was increased after storage of the whole and wounded tissue treated with UVB light, and this increase in PAL activity was associated to phenolic accumulation. On the other hand, l-galactono-γ-lactone dehydrogenase (GalLDH) activity and ascorbic acid biosynthesis was enhanced due to UVB radiation, and the effect was increased when UVB was applied in the wounded tissue showing 125.1% and 94.1% higher vitamin C content after storage when compared with the control. Respiration rate was increased due to wounding stress, whereas ethylene production was increased by wounding and UVB radiation in prickly pears. Results allowed the generation of a physiological model explaining the UVB and wound-induced accumulation of phenolic compounds and ascorbic acid in prickly pears, where wounding facilitates UVB to access the underlying tissue and enhances an apparent synergistic response.

The Associations between Leaf Morphology, Phenylalanine Ammonia Lyase Activity, Reactive Oxygen Species, and Fusarium Resistance in Selected Species of Wheat with Different Ploidy Levels.

In wheat, resistance to Fusarium is conditioned by anatomical, morphological, and physiological traits. The aim of this study was to evaluate selected elements of constitutive barriers in common wheat, spelt, Polish wheat, emmer, and einkorn. The activity of the phenylalanine ammonia-lyase (PAL) enzyme and rate of reactive oxygen species (ROS) production were evaluated in the tissues of common wheat and spelt inoculated with Fusarium culmorum. Most of the relict wheat species were more abundant in morphological barriers than common wheat. F. culmorum penetrated constitutive barriers, which increased PAL activity and intensified ROS production 24 h after inoculation in wheat tissues. The lowest increase in PAL activity after inoculation was observed in cv. Sumai3, which resistance is based on limiting the spread of F. culmorum within the spike. Spelt line Tas 581 glumes were characterized by the highest concentration of ROS 24 h after inoculation. The ROS content remained high for five days. The results of this study indicate that high trichome density plays a key role in resistance to pathogens. In the resistant spelt line with effective constitutive barriers, PAL activity and ROS content were higher than those observed in susceptible wheats after inoculation with F. culmorum.

Preharvest multiple sprays with sodium nitroprusside promote wound healing of harvested muskmelons by activation of phenylpropanoid metabolism

Muskmelons are susceptible to mechanical damage at harvest and subsequent postharvest handling before storage. The wounds provide an easy pathway for fungi to infect, leading to postharvest decay of fruit during storage. Wound healing is considered as a positive defense process, which can restrict the invasion of pathogens. In this study, muskmelon fruit (Cucumis melo cv. Manao) during growth were repeatedly sprayed with 0.5 mM sodium nitroprusside (SNP, a exogenous donor of nitric oxide (NO)) or 0.1 mM 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO, a scavenger of NO), to test the effect of these preharvest treatments on wound healing of harvested muskmelon fruit. The results showed that SNP sprays reduced decay incidence and disease severity of harvested muskmelons inoculated with Trichothecium roseum. SNP also promoted the accumulation of suberin and lignin at wound sites through increasing phenylalanine ammonia lyase (PAL) activity and stimulating the accumulation in total phenolics, flavonoids and lignin. On the contrary, c-PTIO sprays enhanced decay incidence and disease severity of wounded inoculated fruit, while decreasing PAL activity, the content of total phenolics, flavonoids and lignin and reduced the accumulation of suberin and lignin at wound sites. The present results suggest that NO released by SNP sprays promote the wound healing and prevent disease development in harvested muskmelons by inducing increase in PAL activity, the contents of phenolics, flavonoids, suberin and lignin accumulation at wound sites.

Induction of postharvest resistance in melon using pulsed light as abiotic stressor

The aim of this study was use the pulsed light (PL) as tool to booster the postharvest resistance in melons. Cantaloupe melons at mature stage were submitted to the treatments as follows: control, pulsed light (PL; 9 J cm−2), 1-methylcyclopropene (1-MCP; 600 nL L-1) and 1-MCP + PL (600 nL L-1 + 9 J cm−2). Postharvest resistance measurements according survival analysis developed at 4 °C, included: ethylene production, 1-aminocyclopropane-l-carboxylic acid (ACC) oxidase activity, ACC synthase activity, firmness, pH, soluble solids, titratable acidity, SS/AT ratio, soluble sugars, vitamin C, total polyphenols, phenylalanine ammonia lyase (PAL) activity, colour epicarp, free polyamines (putrescine-Put, spermine-Spe and spermidine-Spd) and total polyamines (TPo). Combined effect of the PL+1-MCP promoted an additional of 12 days in the shelf life of melons. PL limited the ethylene biosynthesis leading to an immediate upregulation of polyamines (Put + Spe + Spd), hence, associated with high amounts of TPo (56%). PL treatment promoted an increase of PAL activity (67%) that synthesized high content of phenolic compounds (55%). The results suggest that PL with a fluence of 9 J cm−2 stimulate the postharvest defense mechanisms in melon, due to the ethylene production limitation, which was influenced by the increased polyamines, maintaining the quality attributes.

Postharvest light-emitting diode irradiation of sweet cherries (Prunus avium L.) promotes accumulation of anthocyanins

Light influences postharvest formation of bioactive compounds in fruit and vegetables. The objectives of this study were to determine the physicochemical changes and phenylalanine ammonia lyase and flavonoid 3′-hydroxylase activities in sweet cherries (Prunus avium L.) irradiated with light-emitting diodes. Cherries were stored under light-emitting diodes for 10 days, exposed to UV-B and blue light, and to the combination of white, blue and green light. Irradiation with blue light significantly increased the anthocyanin content (cyanidin 3-O-glucoside, cyanidin 3-O-rutinoside) and significantly influenced the CIE color parameters hue, C* and ΔE. Combined white-blue-green light provoked similar but less pronounced effects, while UV-B light was similar to control (in the dark). Blue and white-blue-green light increased phenylalanine ammonia lyase activity. Light irradiation had no significant effects on ascorbic acid and the phenolic profile. Highly significant correlations were found between anthocyanins and phenylalanine ammonia lyase on the one side, and the color parameters hue, C* and ΔE on the other.

EFFICIENCY OF GLYPHOSATE COMPLEXED WITH COPPER COMPARED TO THE COMMERCIAL PRODUCT IN Brachiaria decumbens Stapf

<p><span style="font-size: medium;">Glyphosate, a non-selective herbicide with systemic action, is one of the most widely used substances in modern agriculture. With the objective of comparing the efficiency of glyphosate previously complexed with copper (Cu421) with that of the commercial product (Roundup WG®) and the purified substance (purified glyphosate) in controlling <em>Brachiaria decumbens </em>Stapf (signal grass), tests were conducted of the <em>in vitro </em>and <em>in vivo </em>activity of the enzymes 5-enolpyruvylshikimate-3-phosphate synthase (EPSPs) and phenylalanine ammonia lyase (PAL). The Cu421 complex significantly inhibited the EPSPs activity, as did the commercial product. <em>In vivo </em>test showed that treatments increased PAL activity more than double. The Cu421 complexed caused a substantial decline in the Falker chlorophyll index, as well as, the greatest reduction in the fresh mass yield and total protein concentration. In addition, the Cu 421 complexed application resulted in an increase in N-NO3- content in <em>B. decumbens</em>. The Cu421 complex had similar action as Roundup WG® and the purified glyphosate, indicating the possibility of using this complex to control weeds.</span></p>

Exogenous Brassinosteroid Enhances Plant Defense Against Colletotrichum gloeosporioides by Activating Phenylpropanoid Pathway in Camellia sinensis L.

The phytohormones brassinosteroids (BRs) regulate multiple aspects of plant growth, development, and responses to stress. However, the role of BRs in the defense response of tea (Camellia sinensis L.), one of the most important beverage crops, remains largely unknown. Previously, we reported that BRs improve tea quality both under normal and unfavorable temperature conditions. Here, we showed that 24-epibrassinolide (EBR, a bioactive BR) enhanced defense against Colletotrichum gloeosporioides in tea plants, which was associated with EBR-induced reduction in H2O2 accumulation in tea leaves. C. gloeosporioides-caused necrotic lesions and its actin gene expression increased over the postinoculation period, but exogenous EBR remarkably suppressed C. gloeosporioides spread. Time-course analysis of a key enzyme, phenylalanine ammonia-lyase (PAL), involved in phenylpropanoid biosynthesis, revealed that PAL activity gradually increased from 6 to 24 h postinoculation with C. gloeosporioides following an initial decline. Meanwhile, exogenous EBR sharply increased PAL activity of inoculated leaves compared with that of only C. gloeosporioides inoculation. Expression analysis of genes involved in phenylpropanoid pathway showed that both exogenous EBR and C. gloeosporioides inoculation increased transcript levels of CsPAL, CsC4H, and Cs4CL; however, combined treatment with EBR and C. gloeosporioides resulted in a greater increase. Furthermore, CsPR1 and CsLOX1 expression analyses revealed that EBR potentially activates systemic induced tolerance, but not the lipoxygenase pathway to enhance tea plant resistance to C. gloeosporioides. These findings indicate a positive role of BR in strengthening disease resistance and thus may have potential implications in the control of C. gloeosporioides-caused disease in tea plants.

Effect of preharvest application of tea tree oil on strawberry fruit quality parameters and possible disease resistance mechanisms

Abstract Strawberries were sprayed with 1.4 mL L−1 of tea tree oil (TTO) 6, 3, and 0 d before harvest to investigate the effects of preharvest TTO treatment on fruit quality parameters. The results showed that TTO treatment reduces the incidence of natural decay and delays the loss of firmness during storage at 20 °C for 5 d. TTO treatment has no effect on total soluble solids content or titratable acidity. Preharvest treatment with TTO reduces the number of microorganisms on the surface of fruit at harvest, reduces H2O2 accumulation by increasing the activities of catalase and ascorbate peroxidase, and increases β-1,3-glucanase activity by the first day postharvest. Treated fruits also accumulate more phenolics as a result of increased phenylalanine ammonia-lyase activity. A total of 188 differentially expressed proteins were identified by comparing untreated and TTO-treated fruit using isobaric tags for relative and absolute quantification (iTRAQ). Of these, 29 were more abundant and 159 were less abundant in TTO-treated fruit. Three proteins related to cell wall metabolism were down-regulated by TTO treatment, while 4 proteins involved in stress response were up-regulated. Therefore, TTO treatment prior to harvest effectively controls postharvest decay in strawberries by reducing microorganisms at harvest, delaying fruit senescence, and inducing defense responses.

Wheat leaf resistance to Pyrenophora tritici‐repentis induced by silicon activation of phenylpropanoid metabolism

Tan spot caused by Pyrenophora tritici‐repentis is a disease present in all wheat‐producing countries and silicon (Si) treatment of wheat plants has been shown to increase plant resistance to tan spot. In this study, the effect of phenylpropanoid metabolism on resistance to tan spot was evaluated and some phenolic compounds that accumulated in response to P. tritici‐repentis attack were identified. Furthermore, the effect of Si on phenylalanine ammonia‐lyase (PAL) activity and phenolic compound accumulation were determined in situ. Antifungal activity of differentially accumulated phenolic compounds was also evaluated in in vitro tests. Results showed that the increase in concentration of phenolic compounds was greatest at the onset of infection, and that some compounds showed fungitoxic effects including fungal tip swelling, granulation of germ tube and hyphae, and hyphal hyperbranching. Silicon‐induced reduction in both lesion size and tan spot disease progression were associated with activation of phenylpropanoid metabolism. PAL activity and accumulation of antifungal phenolic compounds were greater in pathogen‐inoculated plants supplied with Si. In these plants, fluorescence indicative of accumulation of phenolic compounds occurred early in epidermal cells and its intensity increased during the evaluation period, showing higher numbers of fluorescent cells around infected cells. Thus, the combined responses of cell fluorescence at sites of infection, increased PAL activity and accumulation of phenols indicate that Si strengthened wheat defence responses to infection by P. tritici‐repentis, reducing the severity of tan spot.

Red Walnut: Characterization of the Phenolic Profiles, Activities and Gene Expression of Selected Enzymes Related to the Phenylpropanoid Pathway in Pellicle during Walnut Development.

A rare walnut variant with a red seed coat (pellicle) was examined for alterations in its phenolic profile during development. The red-walnut (RW) pellicle was compared with two commonly colored walnut varieties: 'Lara' (brown) and 'Fernor' (light brown). Furthermore, the activities of selected enzymes of the phenylpropanoid- and flavonoid-related pathways and the relative expressions of the structural genes phenylalanine ammonia lyase ( PAL) and anthocyanidin synthase ( ANS) were examined in the pellicles of the three varieties. In the pellicles of the RWs, phenylalanine ammonia lyase (PAL) activity and related PAL expression was most pronounced in August, about one month before commercial maturity, suggesting a high synthesis rate of phenolic compounds at this development stage. The most pronounced differences between the red and light- and dark-brown varieties were the increased PAL activity, PAL expression, and ANS expression in RWs in August. The vibrant color of the RW pellicle is based on the presence of four derivatives of cyanidin- and delphinidin-hexosides.

INDUCED TEMPORAL AND SPATIAL VARIATION IN HOST DEFENCE ENZYMES IN RESPONSE TO FUSARIUM WILT IN CHICKPEA

The present study evaluated the defense response of Chickpea wilt resistant and susceptible cultivars inoculated with pathogen Fusarium oxyporum f.sp. ciceri (Foc). Evaluation of pre-induced and pathogen-induced defense at 7 (S1), 15 (S2) and 30 (S3) days showed that the enzymatic activities differed not only within the root, stem and leaves but also between susceptible and resistant cultivars of chickpea and increased after inoculation with Foc. Peroxidase (PO) activity increased in all the tissues from S1 to S2 and declined thereafter. Conspicuous changes occurred at the rate of increase in activity of the enzyme between resistant and susceptible cultivars upon Foc inoculation over their corresponding control at the S2. Polyphenol oxidase (PPO) activity in resistant cultivars increased by 30% with over uninoculated control and induction was up to S3. The level of enzyme activity diminished from S2 to S3 and even fell below control levels in susceptible cultivars. Catalase (CAT) activity followed peroxidase trend however it was induced at S1 in Foc inoculated and at S2 in un-inoculated plants. Increase in CAT induction was significant in leaf tissues of infected plants and continued up to S3. Phenylalanine ammonia lyase (PAL) activity increased from S1 to S2 and thereafter it either slightly decreased or remained unchanged at S3. Foc inoculation elicited a sharp increase in PAL activity in the leaf and stem tissue of resistant cultivars. Foc inoculated induced β-1,3-glucanase and chitinase activity in the test cultivars. Maximum induction of chitinase was observed at S2 in roots of resistant cultivars whereas un-inoculated plants showed much less conspicuous changes. β-1,3-glucanase activity was high in stem tissues. Both control and challenged plants had higher levels of β-1,3-glucanase activity at S2 and S3, but the proportionate increase was much higher in resistant cultivars. The expression pattern of these defense enzymes reveals their use as established resistance markers and provides scope for manipulating their expression and development of wilt-resistant transgenic chickpea.

Physiological and biochemical modifications by postharvest treatment with sodium nitroprusside extend vase life of cut flowers of two gerbera cultivars

Senescence is a major problem of gerbera (Gerbera jamesonii) cut flowers limiting their long-distance transportation and subsequent marketing. This study was designed to evaluate whether external application of nitric oxide (NO), provided through 150μM sodium nitroprusside (SNP), could extend the vase life of gerbera cut flowers, as well as the potential physiological and biochemical mechanisms involved. We used two gerbera cultivars ‘Bayadère’ and ‘Sunway’; watered ‘Bayadère’ cut flowers have a better performance than watered ‘Sunway’ cut flowers. NO extended the vase life of cut flowers of both cultivars as compared with their respective control treated with water alone, with ‘Sunway’ showing better postharvest performance than ‘Bayadère’. Application of SNP in vase solution resulted in a decrease in proline content in the stems of cut flowers of both cultivars, providing evidence for alleviation of water deficit in SNP-supplied cut flowers. Improved postharvest performance of SNP-treated gerbera cultivars could be attributed to increases in total phenol and flavonoid contents, which resulted from decreased polyphenol oxidase activity and increased phenylalanine ammonia-lyase activity. A decline in malondialdehyde accumulation in the stems of SNP-treated cut flowers was greater in ‘Sunway’ flowers than in ‘Bayadère’ flowers, which was ascribed to the better performance of antioxidant systems in SNP-treated ‘Sunway’ flowers to reduce the adverse effect of oxidative stress. Taken together, exogenous NO might be promising approaches to improve postharvest performance of flowers.