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1. Salicylic acid mediated by the oxidative burst is a key molecule in local and systemic responses of cotton challenged by an avirulent race of Xanthomonas campestris pv malvacearum.

Author

Martinez, C, Baccou, J C, Bresson, E, Baissac, Y, Daniel, J F, Jalloul, A, Montillet, J L, Geiger, J P, Assigbetsé, K, and Nicole, M

Abstract

We analyzed the production of reactive oxygen species, the accumulation of salicylic acid (SA), and peroxidase activity during the incompatible interaction between cotyledons of the cotton (Gossypium hirsutum) cv Reba B50/Xanthomonas campestris pv malvacearum (Xcm) race 18. SA was detected in petioles of cotyledons 6 h after infection and 24 h post inoculation in cotyledons and untreated leaves. The first peak of SA occurred 3 h after generation of superoxide (O(2)(.-)), and was inhibited by infiltration of catalase. Peroxidase activity and accumulation of SA increased in petioles of cotyledons and leaves following H(2)O(2) infiltration of cotyledons from 0.85 to 1 mM. Infiltration of 2 mM SA increased peroxidase activity in treated cotyledons and in the first leaves, but most of the infiltrated SA was rapidly conjugated within the cotyledons. When increasing concentrations of SA were infiltrated 2. 5 h post inoculation at the beginning of the oxidative burst, the activity of the apoplastic cationic O(2)(.-)-generating peroxidase decreased in a dose-dependent manner. We have shown that during the cotton hypersensitive response to Xcm, H(2)O(2) is required for local and systemic accumulation of SA, which may locally control the generation of O(2)(.-). Detaching cotyledons at intervals after inoculation demonstrated that the signal leading to systemic accumulation of SA was emitted around 3 h post inoculation, and was associated with the oxidative burst. SA produced 6 h post infection at HR sites was not the primary mobile signal diffusing systemically from infected cotyledons.

Published
2000
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2. Resistance of olive tree to Spilocaea oleagina is mediated by the synthesis of phenolic compounds

Author

Aabidine, A. Z. E., Baissac, Y., Abdelmajid Moukhli, Jay-Allemand, C., Khadari, B., Modafar, C. E., Université Cadi Ayyad [Marrakech] (UCA), Université Montpellier 2 - Sciences et Techniques (UM2), Institut national de la recherche agronomique [Maroc] (INRA Maroc), Développement et amélioration des plantes (UMR DAP), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut National de la Recherche Agronomique (INRA)-Université Montpellier 2 - Sciences et Techniques (UM2)-Centre National de la Recherche Scientifique (CNRS), and Centre National de la Recherche Scientifique (CNRS)-Université Montpellier 2 - Sciences et Techniques (UM2)-Institut National de la Recherche Agronomique (INRA)-Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)

Subjects
résistance aux maladies, OLIVE TREE, SPILOCAEA OLEAGINA, RESISTANCE, MULTIFACTORIAL PHENOLICS, MOROCCO, OLIVIER, OLEA EUROPEA, TAVELURE DE L'OLIVIER, MALADIE EN OEIL DE PAON, afrique, composé phénolique, food and beverages, pays méditerranéen, croisement, enzyme, maroc, [SDV.IDA]Life Sciences [q-bio]/Food engineering, [SPI.GPROC]Engineering Sciences [physics]/Chemical and Process Engineering, génotype
Abstract

E-mail Addresses: elmodafar@fstg-marrakech.ac.ma Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; International audience; To understand the resistance of the olive tree to the leaf-spot disease caused by Spilocaea oleagina, the constitutive and postinfectional synthesis phenolic compounds of the leaves were analyzed by HPLC in 110 genotypes F1 (susceptible cultivar “Picholine marocaine” x resistant cultivar “Picholine du Languedoc”) presenting of the differential behaviours to this disease (highly resistant, resistant, intermediate, susceptible & highly susceptible genotypes). The HPLC analysis distinguished 15 majors phenolic compounds according to their chromatographic and spectral characteristics into five phenolic families (hydroxycinnamic derivatives, flavonoids, verbascoside derivatives, tyrosol derivatives, oleuropein derivatives). No qualitative difference was observed between cultivars. Principal components analysis (PCA) highlighted three multifactorial components distinguishing the various genotypes according to their behaviour to the disease. These components were determined by the postinfectional contents of oleuropein and rutin and by the constitutive contents of tyrosol and its derivatives. The tyrosol and its derivatives were associated with constitutive resistance, whereas the oleuropein and rutin were associated with induced resistance. These results suggest that the activity ratio of the enzymes implied in various biosynthesis ways of these phenolic compounds and/or the expression rate of the corresponding genes would be at the origin of the resistance degree of olive tree to S. oleagina.

3. The velamen protects photosynthetic orchid roots against UV-B damage, and a large dated phylogeny implies multiple gains and losses of this function during the Cenozoic.

Author

Chomicki G, Bidel LPR, Ming F, Coiro M, Zhang X, Wang Y, Baissac Y, Jay-Allemand C, and Renner SS

Subjects
Acyltransferases genetics, Acyltransferases metabolism, Apigenin metabolism, Crosses, Genetic, Flavonoids metabolism, Gene Duplication, Gene Expression Regulation, Plant radiation effects, Glucosides metabolism, Orchidaceae genetics, Stress, Physiological radiation effects, Time Factors, Orchidaceae physiology, Orchidaceae radiation effects, Photosynthesis, Phylogeny, Plant Roots anatomy & histology, Plant Roots radiation effects, Ultraviolet Rays
Abstract

UV-B radiation damage in leaves is prevented by epidermal UV-screening compounds that can be modulated throughout ontogeny. In epiphytic orchids, roots need to be protected against UV-B because they photosynthesize, sometimes even replacing the leaves. How orchid roots, which are covered by a dead tissue called velamen, avoid UV-B radiation is currently unknown. We tested for a UV-B protective function of the velamen using gene expression analyses, mass spectrometry, histochemistry, and chlorophyll fluorescence in Phalaenopsis × hybrida roots. We also investigated its evolution using comparative phylogenetic methods. Our data show that two paralogues of the chalcone synthase (CHS) gene family are UV-B-induced in orchid root tips, triggering the accumulation of two UV-B-absorbing flavonoids and resulting in effective protection of the photosynthetic root cortex. Phylogenetic and dating analyses imply that the two CHS lineages duplicated c. 100 million yr before the rise of epiphytic orchids. These findings indicate an additional role for the epiphytic orchid velamen previously thought to function solely in absorbing water and nutrients. This new function, which fundamentally differs from the mechanism of UV-B avoidance in leaves, arose following an ancient duplication of CHS, and has probably contributed to the family's expansion into the canopy during the Cenozoic., (© 2014 The Authors. New Phytologist © 2014 New Phytologist Trust.)

Published
2015
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