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The activation of plant defensive genes in leaves of tomato plants in response to herbivore damage or mechanical wounding is mediated by a mobile 18-amino acid polypeptide signal called systemin. Systemin is derived from a larger, 200-amino acid precursor called prosystemin, similar to polypeptide hormones and soluble growth factors in animals. Systemin activates a lipid-based signaling cascade, also analogous to signaling systems found in animals. In plants, linolenic acid is released from membranes and is converted to the oxylipins phytodienoic acid and jasmonic acid through the octadecanoid pathway. Plant oxylipins are structural analogs of animal prostaglandins which are derived from arachidonic acid in response to various signals, including polypeptide factors. Constitutive overexpression of the prosystemin gene in transgenic tomato plants resulted in the overproduction of prosystemin and the abnormal release of systemin, conferring a constitutive overproduction of several systemic wound-response proteins (SWRPs). The data indicate that systemin is a master signal for defense against attacking herbivores. The same defensive proteins induced by wounding are synthesized in response to oligosaccharide elicitors that are generated in leaf cells in response to pathogen attacks. Inhibitors of the octadecanoid pathway, and a mutation that interrupts this pathway, block the induction of SWRPs by wounding, systemin, and oligosaccharide elicitors, indicating that the octadecanoid pathway is essential for the activation of defense genes by all of these signals. The tomato mutant line that is functionally deficient in the octadecanoid pathway is highly susceptible to attacks by Manduca sexta larvae. The similarities between the defense signaling pathway in tomato leaves and those of the defense signaling pathways of macrophages and mast cells of animals suggests that both the plant and animal pathways may have evolved from a common ancestral origin.

Introduction. Pomegranate fruits (Punica granatum L.) are chilling-sensitive crops. Materials and methods. Pomegranate fruits were treated with calcium chloride and spermidine, alone or in combination, by normal dip and vacuum infiltration methods. The treated fruits were stored at 2 °C for 4 months. At the end of the storage period, samples were held for 3 days at 20 °C, then the qualitative constituents were evaluated. Results and discussion. Treated fruits exhibited less weight loss and higher juice content than control fruits. Non-treated fruits developed chilling injury manifested as an increase in K+ leakage and polyphenol oxidase activity. Calcium chloride and spermidine treatments resulted in lower soluble solid content, but some fruits showed higher titratable acidity. All treatments significantly increased ascorbic acid content. The pH of aril juice in treated fruits was lower than that of non-treated fruits, probably due to higher titratable acidity. Total antioxidant activity and total phenolic content increased in treated fruits. In our study, a correlation was observed between total phenolic content and total antioxidant activity. Conclusion. The treatments applied in our experiments maintained overall quality of pomegranate fruits during long-term storage. Postharvest application of calcium and spermidine either alone or in combination could ameliorate adverse effects of low temperature on pomegranate fruit quality during cold storage. Vacuum infiltration was as effective as the normal dip method. However, normal dip is a simpler and faster treatment method. Introduction. Les fruits du grenadier (Punica granatum L.) sont sensibles au froid. Matériel et méthodes. Des grenades ont été traitées avec du chlorure de calcium et de la spermidine, seuls ou en combinaison, par simple immersion et par une méthode d'infiltration sous vide. Les fruits traités ont été stockés à 2 °C pendant 4 mois. À la fin de la période de stockage, les échantillons ont été maintenus pendant 3 jours à 20 °C, puis certains caractères qualitatifs ont été évalués. Résultats et discussion. Les fruits traités ont perdu moins de poids et ont présenté une meilleure teneur en jus que les fruits témoins. Les fruits non traités ont présenté des dommages dus au froid qui se sont manifestés par une augmentation de la perte de K+ et de l'activité de la polyphénol oxydase. Les traitements de chlorure de calcium et de spermidine ont entrainé de plus faibles teneurs en solides solubles, mais certains fruits ont montré une augmentation de l'acidité titrable. Tous les traitements ont significativement augmenté la teneur en acide ascorbique des fruits. Le pH du jus de l’arille dans les fruits traités a été plus faible que celui des fruits non traités, probablement à cause de l'augmentation de l’acidité titrable. L’activité antioxydante totale et la teneur totale en phénol ont augmenté dans les fruits traités. Dans notre étude, une corrélation a été observée entre la teneur totale en phénol et l'activité antioxydante totale. Conclusion. Les traitements appliqués dans nos expérimentations ont maintenu la qualité globale des fruits du grenadier tout au long de l'entreposage à long terme. L’application après récolte de calcium et de spermidine, seuls ou en combinaison, pourrait atténuer les effets néfastes des basses températures sur la qualité des grenades au cours de leur stockage au froid. La méthode d'infiltration sous vide a été aussi efficace que la simple immersion. Toutefois, l’immersion est une méthode de traitement plus simple et plus rapide. Introducción. Los frutos del granadero (Punica granatum L.) son sensibles al frío. Material y métodos. Se trataron granadas con cloruro de calcio y con espermidina, individual o combinadamente, mediante simple inmersión y mediante un método de infiltración al vacío. Los frutos tratados se almacenaron a 2 °C durante 4 meses. Al finalizar el periodo de almacenaje, las muestras se mantuvieron durante 3 días a 20 °C, a continuación se evaluaron ciertos rasgos cualitativos. Resultados y discusión. Los frutos tratados perdieron menos peso y presentaron un mejor contenido en jugo que los frutos testigo. Los frutos no tratados presentaron daños causados por el frío manifestados por un aumento de la pérdida de K+ y de la actividad de la polifenol oxidasa. Los tratamientos de cloruro de calcio y de espermidina conllevaron unos contenidos más bajos en sólidos solubles, pero ciertos frutos mostraron un aumento de la acidez valorable. Todos los tratamientos aumentaron significantemente el contenido de ácido ascórbico de los frutos. El pH del jugo del arilo en los frutos tratados fue más flojo que aquél de los frutos no tratados, probablemente a causa del aumento de la acidez valorable. La actividad antioxidante total así como el contenido total de fenol, aumentaron en los frutos tratados. En nuestro estudio, se observó una correlación entre el contenido total de fenol y la actividad antioxidante total. Conclusión. Los tratamientos aplicados en nuestros experimentos mantuvieron la calidad general de los frutos del granadero en el trascurso del almacenamiento a largo plazo. La aplicación post cosecha de calcio y de esperdimidina, individual o combinadamente, podría atenuar los efectos nefastos de las bajas temperaturas en la calidad de las granadas durante su almacenamiento en frío. El método de infiltración al vacío fue tan eficaz como la simple inmersión. No obstante, la inmersión es un método de tratamiento más simple y más rápido.

The inhibitory capacity of the globulin fraction of wheat bran against the diphenolase activity of mushroom tyrosinase, using l-tyrosine as substrate, was evaluated. Enzyme kinetics was monitored in the presence of globulin solutions by measuring the absorbance at 475nm. Lineweaver-Burk plots were drawn in order to determine Vmax, Km, and type of inhibition. Results showed that globulins from wheat bran competitively inhibited, the activity of mushroom tyrosinase with a KI of 0.79%(w/v). The degree of inhibition was 24% at 2 mM of the substrate L-tyrosine.

Tomato plants overexpressing a prosystemin gene that encodes the precursor of a mobile wound signal called systemin have been shown previously to constitutively synthesize extraordinarily high levels of two defensive proteinase inhibitor proteins in leaves in the absence of wounding. We herein report that leaves of these transgenic plants possess enhanced levels of another defensive protein, polyphenol oxidase (PPO) at levels that are up to 70-fold higher than levels found in leaves of wild-type plants. Supplying young wild-type tomato plants with systemin through cut stems induced PPO activity in leaves, and wounding lower leaves of young tomato plants induced PPO activity in both wounded and unwounded leaves to levels equal to those induced by systemin. Exposing young tomato plants to methyl jasmonate vapor caused an increase in PPO activity equivalent to levels found in plants overexpressing the prosystemin gene. The data indicate that PPO and proteinase inhibitor genes are coactivated systemically by wounding via the octadecanoid signal transduction pathway and that systemin has a much broader role in signaling plant defensive genes than was previously known.

Tomato (Lycopersicon esculentum Mill.) polyphenol oxidases (PPOs) are encoded by a seven-member gene family that exhibits complex patterns of differential expression during growth and differentiation. Antisense down-regulation of constitutive and induced PPO expression results in hypersusceptibility to pathogens, suggesting a critical role for PPO-mediated phenolic oxidation in plant defense. However, the nature and extent of PPO induction and its contribution to resistance are unclear. In this study we examined the inducibility of the tomato PPO gene family. In mature plants PPO transcript levels systemically increased in young leaves (nodes 1-3) when mature leaflets (node 5) were injured. Transcripts hybridizing to PPO E/F-specific probes were the predominant wound-induced PPO mRNAs in young leaves. Analysis of PPO promoter: GUS fusion constructs shows that mechanical wounding and infection by fungal and bacterial pathogens induced transcription of PPO F. Different injuries, salicylic acid, ethylene, and jasmonates elicited distinct, cell-specific and developmental stage-specific patterns of PPO F expression. Whereas jasmonates and mechanical wounding significantly induced PPO F only in young leaves (nodes 1-3), and ethylene induced PPO F only in older leaves (node 7), salicylic acid induced PPO F in stems and foliage at all developmental stages. These results demonstrate that cis-element(s) sufficient for PPO F inducibility reside in the 5' flanking region, and these elements are responsive to a broad range of signals

The effect of chitosan on the growth and morphology of Fusarium oxysporum f. sp. albedinis (Foa), the causal agent of Bayoud disease, and its ability to elicit a defence reaction against this fungus in date palm roots were investigated. Chitosan at 1 mg mlE-1 reduced the growth of Foa on potato dextrose agar medium by an average of 75%, while mycelial growth was totally inhibited in a liquid medium. When added to a solid medium, chitosan caused morphological changes in Foa mycelium. In addition, when injected into roots at three concentrations (0.1, 0.5 and 1 mg mlE-1), chitosan elicited peroxidase (PO) and polyphenoloxidase (PPO) activity and, particularly at the concentration of 1 mg mlE-1, increased the level of phenolic compounds. Concerning phenolics, chitosan led to an accumulation of non-constitutive hydroxycinnamic acid derivatives, known to be of great importance in date palm resistance to Bayoud. The accumulation of hydroxycinnamic acid derivatives was greater in cv BSTN than in cv JHL. Chitosan could be used to protect date palm against this vascular disease [Sono stati studiati l´effetto del chitosano sulla crescita e la morfologia di Fusarium oxysporum f. sp. albedinis (Foa), agente causale della malattia del Bayoud, e la sua capacità di provocare una reazione di difesa contro questo fungo nella palma da datteri. Il chitosano a 1 mg mlE-1 ha ridotto la crescita di Foa su un substrato agar-patata-destrosio del 75% in media, mentre in substrato liquido la crescita del micelio era inibita completamente. Aggiunto a un substrato solido, il chitosano ha determinato cambiamenti morfologici nel micelio di Foa. Inoltre, quando veniva iniettato nelle radici a tre concentrazioni (0,1, 0,5 e 1 mg mlE-1), il chitosano stimolava l´attività della perossidasi (PO) e della polifenolossidasi (PPO) e, in particolare alla concentrazione di 1 mg mlE-1, determinava un aumento del livello di composti fenolici. Riguardo ai composti fenolici, il chitosano portava a un accumulo di derivati non costitutivi dell´acido idrossicinnamico, noti per la loro importanza notevole nella resistenza della palma da datteri al Bayoud. L´accumulo di derivati dell´acido idrossicinnamico è risultato maggiore nella cv BSTN rispetto alla cv JHL. Il chitosano potrebbe essere utilizzato nella difesa della palma da datteri da questa malattia vascolare.]

Polyphenol oxidases (PPOs) are encoded by a highly conserved, seven-member gene family clustered within a 165-kb locus on chromosome 8 of tomato (Lycopersicon esculentum). Using gene-specific probes capable of differentiating between PPO A/C, PPO B, PPO D, and PPO E/F, we examined the spatial and temporal expression of this gene family during vegetative and reproductive development. RNA blots and in situ hybridization using these probes showed that although PPO expression is primarily confined to early stages of development, the steady-state mRNA levels of these genes are sublect to complex patterns of spatial and temporal regulation in vegetative and reproductive organs. Young tomato leaves and flowers possess the most abundant PPO transcripts. PPO B is the most abundant in young leaves, whereas in the inflorescence PPO B and E/F transcripts are dominant. Differential expression of PPOs is also observed in various trichome types. PPO A/C are specifically expressed in type I and type IV trichomes. In contrast, PPO D is only expressed in type VI trichomes. Type I, IV, and VI trichomes possess PPO E/F transcripts. Immunolocalization verified the translational activity of PPOs identified by in situ hybridization and suggested cell-type-specific, developmentally programmed PPO turnover. In addition, immunolocalization demonstrated the accumulation of PPO in specific idioblast cells of stems, leaves, and fruits

Polyphenol oxidase (PPO) activity in potato (Solanum tuberosum) plants was high in stolons, tubers, roots, and flowers but low in leaves and stems. PPO activity per tuber continued to increase throughout tuber development but was highest on a fresh weight basis in developing tubers. PPO activity was greatest at the tuber exterior, including the skin and cortex tissue 1 to 2 mm beneath the skin. Flowers had high PPO activity throughout development, particularly in the anthers and ovary. Five distinct cDNA clones encoding PPO were isolated from developing tuber RNA. POT32 was the major form expressed in tubers and was found in all parts of the tuber and at all stages of tuber development. It was also expressed in roots but not in photosynthetic tissues. POT33 was expressed in tubers but mainly in the tissue near the skin. POT72 was detected in roots and at low levels in developing tubers. NOR333 was identical with the P2 PPO clone previously isolated from potato leaves (M.D. Hunt, N.T. Eannetta, Y. Haifeng, S.M. Newman, I.C. Steffens [1993] Plant Mol Biol 21: 59-68) and was detected in young leaves and in tissue near the tuber skin but was highly expressed in flowers. The results indicate that PPO is present as a small multigene family in potato and that each gene has a specific temporal and spatial pattern of expression.

Tobacco hydroxyproline-rich glycopeptide systemin precursor A (TobpreproHypSys-A), from which TobHypSys Ⅰ and Ⅱ are released, plays a crucial role in defense responses. Here, we investigated the expression of TobpreproHypSys-A and the activity of defense proteins in tobacco organs during wounding. Expression was induced more rapidly in upper, non-wounded leaves than in lower, wounded leaves. At 24 h after mechanical wounding, expression was low in the roots, but increased in the stems and flowers, although to a lesser extent than in the leaves. At 3 or 10 d after insect-wounding, expression did not differ among organs, suggesting that TobpreproHypSys-A could be induced globally and continuously throughout such stress. During that period, the activity of two defense proteins -- PPO and PI -- was consistent with the expression of TobpreproHypSys-A in various organs. This indicates that those proteins also could be regulated by TobHypSys, both globally and continuously.

Tobacco (Nicotiana tabacum) plants transformed with a chimeric tobacco anionic peroxidase gene have previously been shown to synthesize high levels of peroxidase in all tissues throughout the plant. One of several distinguishable phenotypes of transformed plants is the rapid browning of pith tissue upon wounding. Pith tissue from plants expressing high levels of peroxidase browned within 24 hours of wounding, while tissue from control plants did not brown as late as 7 days after wounding. A correlation between peroxidase activity and wound-induced browning was observed, whereas no relationship between polyphenol oxidase activity and browning was found. The purified tobacco anionic peroxidase was subjected to kinetic analysis with substrates which resemble the precursors of lignin or polyphenolic acid. The purified enzyme was found to readily polymerize phenolic acids in the presence of H2O2 via a modified ping-pong mechanism. The percentage of lignin and lignin-related polymers in cell walls was nearly twofold greater in pith tissue isolated from peroxidase-overproducer plants compared to control plants. Lignin deposition in wounded pith tissue from control plants closely followed the induction of peroxidase activity. However, wound-induced lignification occurred 24 to 48 hours sooner in plants overexpressing the anionic peroxidase. This suggests that the availability of peroxidase rather than substrate may delay polyphenol deposition in wounded tissue