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The gene fusion system was used to study UV light-control of PS PAL1 and PS PAL2 genes encoding phenylalanine ammonia-lyase of pea. The induction of pea PAL promoters was analysed in transgenic tobacco plants. Binary plasmids (derivatives of pBI101.2 vector) containing 5’ regulatory fragments of PS pAl1 and PS PAL2 linked to reporter genes (GUS, LUC) were constructed. The analyses were performed with the use of single constructs (containing one variant of PS PAL promoter and one reporter gene) and dual constructs (containing both PS PAL1 and PS PAL2 promoters connected with different reporter genes). The use of dual constructs enabled the evaluation of both PS PAL promoters activity in the same plant. The analyses of in vitro grown plants have shown that both PAL promoters are strongly induced in leaves subjected to UV radiation. In some cases, the UV-stimulated expression exceeded the exposed areas. This phenomenon was observed more often in the leaves of plants containing the PS PAL1:: GUS than PS PAL2::GUS construct. Removal ofboxes 2, 4, 5 from PS PAL1 promoter and deletion of its 5’end region (-339 to -1394) decreases the level of gene expression but does not eliminate its responsiveness to UV.
Activation of the phenolic pathway is known to be part of a defense response against cell wall-derived elicitors from pathogens. Many examples of a defense re­sponse by increasing the synthesis of phenolic compound against the elicitor were demonstrated in the past, but the elicitor structure has so far been poorly character­ized. Our results indicate that a disaccharide fraction containing the following structure: a-D-mannopyranosyl (1=>2)a/ß-D-glucopyranosyl and a-D-mannopyranosyl (1=>x) ino­sitol, isolated from Fusarium oxysporum L., promotes rapid and transient phenylalanine ammonia lyase activity in Rubus fructicosus cells at nanomolar con­centration. The disaccharides were isolated by size-exclusion chromatography di­rectly from extracts obtained by alkaline treatment of F. oxysporum mycelium. Their structure was determined by 500-MHz-1H-NMR spectroscopy combined with methylation analysis and fast atom bombardment mass spectrometry.
Increased UV-B radiation due to depletion of stratospheric ozone has potentially harmful effects on plant growth and development. The present study uses a field experiment to examine the effect of long-term supplemental UVB radiation at two intensities (+1.8 and +3.6 kJ m-2 d-1 above ambient) on the growth and physiology of the medicinal plant Acorus calamus L. (sweet flag). Plant height and leaf area were inhibited in a dose-dependent manner, with greater inhibition at the higher dose. At the lower dose the net photosynthetic rate increased, with an increase in stomatal conductance and water use efficiency. Stimulation of physiological functions in plants under the lower dose resulted in increased biomass production. At the higher dose, total chlorophyll content showed no marked variation, whereas carotenoids and UV-B-screening pigment flavonoids increased significantly after treatment. Increased flavonoid content under lower exposure correlates well with higher activity of phenylalanine ammonia lyase, a key enzyme of flavonoid biosynthesis. This study clearly showed that the lower dose of supplemental UV-B promoted rhizome growth in A. calamus, perhaps due to improved photosynthesis. Plant defense was stronger under the lower dose
Phenylalanine ammonia lyase (PAL) is a specific branch point enzyme of primary and secondary metabolism. It plays a key role in plant development and defense mechanisms. Phenylalanine ammonia lyase from Hevea brasiliensis (HbPAL) presented a complete open reading frame (ORF) of 2,145 bp with 721 encoded amino acids. The sequence alignment indicated that the amino acid sequence of HbPAL shared a high identity with PAL genes found in other plants. Phylogenetic tree analysis indicated that HbPAL was more closely related to PALs in Manihot esculenta and Jatropha curcas than to those from other plants. Transcription pattern analysis indicated that HbPAL was constitutively expressed in all tissues examined, most highly in young leaves. The HbPAL gene was evaluated by quantitative real-time PCR (qRT-PCR) after infection with Rigidoporus microporus at 0, 12, 24, 48, 72 and 96 hours post inoculation. The expression patterns of the PAL gene differed among the three rubber clones used in the study. The transcription level of the white root rot disease tolerant clone, PB5/51 increased sharply during the latter stages of infection, while it was relatively subdued in the white root rot disease susceptible clones, RRIM600 and BPM24. These results suggest that the HbPAL gene may play a role in the molecular defense response of H. brasiliensis to pathogen attack and could be used as a selection criterion for disease tolerance.
Seven-day-old seedlings of cucumber (Cucumis sativus L.) cv. Wisconsin were treated with 0.1 mM solutions of cinnamic acid (ferulic and p-coumaric acids) and benzoic acid (p-hydroxybenzoic and vanillic acids) derivatives as stressors. The content of free and glucosylated soluble phenols and the activity of phenylalanine ammonia-lyase (E.C.4.3.1.5), phenol-β-glucosyltransferase (E.C.2.4.1.35.), and β-glucosidase (E.C.3.2.1.21.) in seedling roots as well as their length and fresh weight were examined. Changes in glucosylated phenolic content and phenol-β-glucosyltranspherase activity were observed under the influence of all phenolics applied. Treatment with ferulic and p-coumaric acids stimulated the increase of phenylalanine ammonia-lyase and β-glucosidase activity and slightly inhibited cucumber root growth.
The ability of fluorescent pseudomonads of cotton rhizosphere of induction of systemic resistance (ISR) against bacterial blight of cotton was investigated. Of the 21 isolates tested, 19 were observed to increase the resistance of plants. This was demonstrated by a lower percentage of infected leaf area. On the basis of growth promotion and ISR induction ability, isolates 148, 35Q, 16Q and 113 were selected for further investigations. All isolates increased the resistance of plants, and per cent of infected area on leaves of these treatments were lower than those control of plants. Levels of peroxidase (PO) and phenylalanine ammonia lyase (PAL) activity in the leaves of bacterized plants with selected isolates were similar to that in control plants, but after inoculation of leaves with the pathogen, the amount of these enzymes increased in bacterized plants to high levels. The increase of enzyme activity in control plants was low after inoculation.
So far only little data have been available concerning the eliciting capacity of well de­fined glycan molecules isolated from plant pathogens. This study brings new informa­tion about changes in plant cells caused by fungal pathogens. Sugar fractions derived from glycoproteins isolated from the fungus Fusarium sp. M7-1 have been tested here as signaling molecules. The ability of three O-glycan fractions (named in this work in- ducer I, II, III) to trigger responses in Rubus protoplasts has been examined. It was found that inducer III was the most efficient as it elicited changes in the levels of phenylpropanoid pathway intermediates in relation to phenylalanine-ammonia lyase (PAL) activation.
The effect of chitosan coating in fresh-cut mushroom preservation, including microbiological, enzyme activities, colour characteristics and chemical quality attributes, was examined. However, application of chitosan coating to enzyme activity control and quality maintenance of fresh-cut mushroom was investigated. Fresh-cut mushroom were treated with aqueous solution containing 5, 10 and 20 g of chitosan/1 L, placed in polyethylene bags, and then stored at 4°C. Changes in total phenolic content, and cellulase (CEL), total amylase, α and β amylase, laccase (LAC), phenylalanine ammonia lyase (PAL), peroxidase (POD), catalase (CAT) and polyphenoloxidase (PPO) enzymes activities were measured. Applications of chitosan coating delayed discoloration associated with reduced enzyme activities of LAC, PAL, POD, CAT and PPO as well as lowered total phenolic content. Also, it slowed down texture changes associated with reduced enzyme activities of CEL, total amylase and α-amylase. Results showed that increasing the concentration of chitosan coating resulted in higher contents of total soluble solids (TSS), total acidity and TSS/T acid ratio of fresh-cut mushroom. In mushroom, during storage at 4°C for 15 days, 20 g/kg chitosan coating inhibited the growth of total bacteria, yeasts and moulds counts. Chitosan also had a good effect on the evolution of the colour characteristics and parameters (C* and BI) of fresh-cut mushroom during storage at 4°C. The results showed that increasing the concentration of chitosan coating enhanced the beneficial effects of chitosan on extended shelf-life and maintained quality of fresh-cut mushroom.
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