Although different mechanisms have been proposed in the recent years, plant pathogen partial resistance is still poorly understood. Components of the chemical warfare, including the production of ...plant defense compounds and plant resistance to pathogen-produced toxins, are likely to play a role. Toxins are indeed recognized as important determinants of pathogenicity in necrotrophic fungi. Partial resistance based on quantitative resistance loci and linked to a pathogen-produced toxin has never been fully described. We tested this hypothesis using the Alternaria dauci - carrot pathosystem. Alternaria dauci, causing carrot leaf blight, is a necrotrophic fungus known to produce zinniol, a compound described as a non-host selective toxin. Embryogenic cellular cultures from carrot genotypes varying in resistance against A. dauci were confronted with zinniol at different concentrations or to fungal exudates (raw, organic or aqueous extracts). The plant response was analyzed through the measurement of cytoplasmic esterase activity, as a marker of cell viability, and the differentiation of somatic embryos in cellular cultures. A differential response to toxicity was demonstrated between susceptible and partially resistant genotypes, with a good correlation noted between the resistance to the fungus at the whole plant level and resistance at the cellular level to fungal exudates from raw and organic extracts. No toxic reaction of embryogenic cultures was observed after treatment with the aqueous extract or zinniol used at physiological concentration. Moreover, we did not detect zinniol in toxic fungal extracts by UHPLC analysis. These results suggest that strong phytotoxic compounds are present in the organic extract and remain to be characterized. Our results clearly show that carrot tolerance to A. dauci toxins is one component of its partial resistance.
Although different mechanisms have been proposed in the recent years, plant pathogen partial resistance is still poorly understood. Components of the chemical warfare, including the production of ...plant defense compounds and plant resistance to pathogen-produced toxins, are likely to play a role. Toxins are indeed recognized as important determinants of pathogenicity in necrotrophic fungi. Partial resistance based on quantitative resistance loci and linked to a pathogen-produced toxin has never been fully described. We tested this hypothesis using the Alternaria dauci - carrot pathosystem. Alternaria dauci, causing carrot leaf blight, is a necrotrophic fungus known to produce zinniol, a compound described as a non-host selective toxin. Embryogenic cellular cultures from carrot genotypes varying in resistance against A. dauci were confronted with zinniol at different concentrations or to fungal exudates (raw, organic or aqueous extracts). The plant response was analyzed through the measurement of cytoplasmic esterase activity, as a marker of cell viability, and the differentiation of somatic embryos in cellular cultures. A differential response to toxicity was demonstrated between susceptible and partially resistant genotypes, with a good correlation noted between the resistance to the fungus at the whole plant level and resistance at the cellular level to fungal exudates from raw and organic extracts. No toxic reaction of embryogenic cultures was observed after treatment with the aqueous extract or zinniol used at physiological concentration. Moreover, we did not detect zinniol in toxic fungal extracts by UHPLC analysis. These results suggest that strong phytotoxic compounds are present in the organic extract and remain to be characterized. Our results clearly show that carrot tolerance to A. dauci toxins is one component of its partial resistance.
In this study, the physiological functions of fungal mannitol metabolism in the pathogenicity and protection against environmental stresses were investigated in the necrotrophic fungus Alternada ...brassicicola. Mannitol metabolism was examined during infection of Brass/ca oleracea leaves by sequential HPLC quantification of the major soluble carbohydrates and expression analysis of genes encoding two proteins of mannitol metabolism, i.e., a mannitol dehydrogenase (AbMdh), and a mannito1-1-phosphate dehydrogenase (AbMpd). Knockout mutants deficient for AbMdf7 or AbMpd and a double mutant lacking both enzyme activities were constructed. Their capacity to cope with various oxidative and drought stresses and their pathogenic behavior were evaluated. Metabolic and gene expression profiling indicated an increase in mannitol production during plant infection. Depending on the mutants, distinct pathogenic processes, such as leaf and silique colonization, sporulation, survival on seeds, were impaired by comparison to the wild-type. This pathogenic alteration could be partly explained by the differential susceptibilities of mutants to oxidative and drought stresses. These results highlight the importance of mannitol metabolism with respect to the ability of A. brassicrcola to efficiently accomplish key steps of its pathogenic life cycle.
In this study, the physiological functions of fungal mannitol metabolism in the pathogenicity and protection against environmental stresses were investigated in the necrotrophic fungus Alternada ...brassicicola. Mannitol metabolism was examined during infection of Brass/ca oleracea leaves by sequential HPLC quantification of the major soluble carbohydrates and expression analysis of genes encoding two proteins of mannitol metabolism, i.e., a mannitol dehydrogenase (AbMdh), and a mannito1-1-phosphate dehydrogenase (AbMpd). Knockout mutants deficient for AbMdf7 or AbMpd and a double mutant lacking both enzyme activities were constructed. Their capacity to cope with various oxidative and drought stresses and their pathogenic behavior were evaluated. Metabolic and gene expression profiling indicated an increase in mannitol production during plant infection. Depending on the mutants, distinct pathogenic processes, such as leaf and silique colonization, sporulation, survival on seeds, were impaired by comparison to the wild-type. This pathogenic alteration could be partly explained by the differential susceptibilities of mutants to oxidative and drought stresses. These results highlight the importance of mannitol metabolism with respect to the ability of A. brassicrcola to efficiently accomplish key steps of its pathogenic life cycle.
Five new 2-aryl and 2-alkyl quinoline alkaloids were obtained from Galipeallongiflora Krause (Rutaceae). These are 2-phenylquinoline 1, 2-(3′,4′-methylenedioxyphenethyl)quinoline 2, ...2-(3′,4′-dimethoxyphenethyl)quinoline 3, 2-(3′,4′-methylenedioxystyryl)-4-methoxyquinoline 4, and 2-(1′,2′-pentenyl)-4-methoxyquinoline 6. They are accompanied by three known 2-substituted quinolines, 2-n-amyl-4-methoxyquinoline 5, 2-(3′4′-methylenedioxyphenethyl)-4-methoxyquinoline 7, and 2-phenyl-4-methoxyquinoline 8, and by two known furo2,3bquinoline alkaloids: evolitrine and skimmianine. Keywords: Galipealongiflora, Rutaceae, new quinolines.
Eleven benzyltetrahydroisoquinoline alkaloids, with an original substitution pattern, were isolated from the stem bark of Aniba canelilla H.B.K. (Lauraceae). Structural studies of these compounds ...including
1
H,
13
C, nOe difference, COSY H-H and C-H, and COLOC nuclear magnetic resonance spectroscopy led to the identification of four benzylisoquinolines, monosubstituted on ring C with an hydroxyl at C-11, (−)-norcanelilline
2
, (+)-canelilline
3
, anicanine
4
, and canelillinoxine
5
; two tetrahydroprotoberberines monosubstituted on ring D at C-9, (−)-anibacanine
6
and (+)-manibacanine
8
; two tetrahydroprotoberberines monosubstituted on ring D at C-11, (−)-pseudoanibacanine
7
and (+)-pseudomanibacanine
9
; and three protoberberines with the same substitution pattern on rings A and D with a methyl substituent at the 8α or 8β position, (−)-α-8-methylpseudoanibacanine
10
, (−)-β-8-methylpseudoanibacanine
11
, and (−)-α-8-methylanibacanine
12
. An examination of all isolated alkaloids suggests the existence of two enzymatic systems in A. canelilla. In the first enzymatic system, reticuline- and coclaurine-type alkaloids are involved in the bioconversion of classical proaporphine and aporphine alkaloids. In the second system, canelilline-type alkaloids are intermediate in biosynthesis of anibacanine and pseudoanibacanine protoberberine alkaloids.
