A comprehensive study of the complex polyphenol biosynthesis in developing leaves of apple (Malus... more A comprehensive study of the complex polyphenol biosynthesis in developing leaves of apple (Malus domestica) was performed comprising gene expression, enzyme activities and polyphenol composition. During leaf development, an early increase in gene expression was observed for phenylalanine ammonia lyase (PAL, EC 4.3.1.5), chalcone synthase (CHS, EC 2.3.1.74), flavanone 3-hydroxylase (FHT, EC 1.14.11.9) and dihydroflavonol 4-reductase/flavanone 4-reductase (DFR/FNR, EC 1.1.1.219). Their enzyme activities showed a corresponding trend during the time course. A parallel set of experiments was carried out with leaves treated with prohexadione-Ca (ProCa), which is an enzyme inhibitor of 2-oxoglutarate dependent dioxygenases (2-ODDs). ProCa is known to induce changes in polyphenol biosynthesis, which are accompanied by a reduced incidence of fire blight and scab, the two major pome fruit diseases. The application of ProCa led to an increase in activities of PAL, CHS, FHT and DFR/FNR, which was based on an enhanced gene expression. In contrast, an inhibition of gene expression was detected for anthocyanidin synthase (EC 1.14.11.19). These effects are interpreted as a feedback regulation by changed polyphenol levels. Because of the inhibition of the 2-ODDs FHT and flavonol synthase (EC 1.14.11.23), some pronounced changes in polyphenol composition were observed. Eriodictyol, the substrate of FHT, accumulated as eriodictyol-7-O-glucoside and 6″-O-trans-p-coumaroyleriodictyol 3′-O-glucoside. In addition, the 3-deoxycatechin luteoliflavan was formed which is not present in untreated apple leaves. Hence, beyond the redirection of polyphenol biosynthesis by the enzyme inhibitor, changed polyphenol levels obviously cause a distinct induction of gene expression by feedback regulation.
The morphology of apple and pear stigma was investigated with confocal laser scanning microscopy ... more The morphology of apple and pear stigma was investigated with confocal laser scanning microscopy and scanning electron microscopy. The floral colonization process by Erwinia amylovora was studied with gfp-labelled bacteria and confocal laser scanning microscopy to allow the in vivo observation of the pathogen colonization on intact, viable plant tissues without any kind of staining of the specimens. The interaction on the stigma between Erwinia amylovora and Pantoea agglomerans, both labelled with genes encoding for fluorescent proteins (DsRed-GFP), was also investigated. A stylar groove, covered by papillae and dwelling from the stigma along the style, was visualized. In laboratory conditions, this groove was shown to be an important way for E. amylovora migration towards the nectarthodes. Due to its anatomical structure the groove can sustain bacterial multiplication and thus may play an important role on the interactions between the pathogen and the bacterial antagonist P. agglomerans.
Growth-regulating acylcyclohexanediones such as prohexadione-calcium and trinexapac-ethyl have be... more Growth-regulating acylcyclohexanediones such as prohexadione-calcium and trinexapac-ethyl have been shown to be effective in controlling fire blight infections on shoots. Since blossoms represent the primary site of infection for the fire blight pathogen, Erwinia amylovora, trinexapac-ethyl and prohexadione-calcium were evaluated for their ability to reduce fire blight infection on apple and pear flowers. Field experiments and experiments under controlled conditions were conducted on apple flowers for 4 years. A reduction of up to 50% of blossom blight was observed in treated plants. In addition, treatment with trinexapac-ethyl reduced up to the 77% the percentage of fireblight-affected flowers from which disease progressed into shoots. On pear, numbers of flower infections were reduced by a quarter and flower infections leading to diseased shoots was reduced by up to 50%. Mechanisms underlying diseased reduction following treatment with the two acylcyclohexanediones was studied using a confocal laser scanning microscope combined with a gpf-labelled strain of E. amylovora. These non-invasive techniques demonstrated bacterial migration was reduced by up to 60 and 66% in apple and pear xylem, respectively.
Treatments with prohexadione-calcium led to lowered incidence of fire blight, scab and other dise... more Treatments with prohexadione-calcium led to lowered incidence of fire blight, scab and other diseases in pome fruit trees and other crop plants. In addition to acting as a growth regulator, prohexadione-calcium interferes with flavonoid metabolism and induces the accumulation of the 3-deoxycatechin luteoliflavan in shoots of pome fruit trees. Luteoliflavan does not possess any remarkable antimicrobial activity. Therefore luteoforol, its unstable and highly reactive precursor, has been tested in vitro for its bactericidal and fungicidal activities. Luteoforol was found to be highly active against different strains of Erwinia amylovora, the causal agent of fire blight, and all other bacterial and fungal organisms tested. Phytotoxic effects were also observed in pear plantlets. The results obtained indicate that prohexadione-calcium induces luteoforol as an active principle with non-specific biocidal properties. It is proposed that luteoforol is released upon pathogen attack from its cellular compartment and inhibits further disease development by destroying pathogen cells as well as by inducing a hypersensitive-like reaction in the host plant tissue. This mechanism would be closely analogous to the one known for structurally related phytoalexins in sorghum.
A comprehensive study of the complex polyphenol biosynthesis in developing leaves of apple (Malus... more A comprehensive study of the complex polyphenol biosynthesis in developing leaves of apple (Malus domestica) was performed comprising gene expression, enzyme activities and polyphenol composition. During leaf development, an early increase in gene expression was observed for phenylalanine ammonia lyase (PAL, EC 4.3.1.5), chalcone synthase (CHS, EC 2.3.1.74), flavanone 3-hydroxylase (FHT, EC 1.14.11.9) and dihydroflavonol 4-reductase/flavanone 4-reductase (DFR/FNR, EC 1.1.1.219). Their enzyme activities showed a corresponding trend during the time course. A parallel set of experiments was carried out with leaves treated with prohexadione-Ca (ProCa), which is an enzyme inhibitor of 2-oxoglutarate dependent dioxygenases (2-ODDs). ProCa is known to induce changes in polyphenol biosynthesis, which are accompanied by a reduced incidence of fire blight and scab, the two major pome fruit diseases. The application of ProCa led to an increase in activities of PAL, CHS, FHT and DFR/FNR, which was based on an enhanced gene expression. In contrast, an inhibition of gene expression was detected for anthocyanidin synthase (EC 1.14.11.19). These effects are interpreted as a feedback regulation by changed polyphenol levels. Because of the inhibition of the 2-ODDs FHT and flavonol synthase (EC 1.14.11.23), some pronounced changes in polyphenol composition were observed. Eriodictyol, the substrate of FHT, accumulated as eriodictyol-7-O-glucoside and 6″-O-trans-p-coumaroyleriodictyol 3′-O-glucoside. In addition, the 3-deoxycatechin luteoliflavan was formed which is not present in untreated apple leaves. Hence, beyond the redirection of polyphenol biosynthesis by the enzyme inhibitor, changed polyphenol levels obviously cause a distinct induction of gene expression by feedback regulation.
The morphology of apple and pear stigma was investigated with confocal laser scanning microscopy ... more The morphology of apple and pear stigma was investigated with confocal laser scanning microscopy and scanning electron microscopy. The floral colonization process by Erwinia amylovora was studied with gfp-labelled bacteria and confocal laser scanning microscopy to allow the in vivo observation of the pathogen colonization on intact, viable plant tissues without any kind of staining of the specimens. The interaction on the stigma between Erwinia amylovora and Pantoea agglomerans, both labelled with genes encoding for fluorescent proteins (DsRed-GFP), was also investigated. A stylar groove, covered by papillae and dwelling from the stigma along the style, was visualized. In laboratory conditions, this groove was shown to be an important way for E. amylovora migration towards the nectarthodes. Due to its anatomical structure the groove can sustain bacterial multiplication and thus may play an important role on the interactions between the pathogen and the bacterial antagonist P. agglomerans.
Growth-regulating acylcyclohexanediones such as prohexadione-calcium and trinexapac-ethyl have be... more Growth-regulating acylcyclohexanediones such as prohexadione-calcium and trinexapac-ethyl have been shown to be effective in controlling fire blight infections on shoots. Since blossoms represent the primary site of infection for the fire blight pathogen, Erwinia amylovora, trinexapac-ethyl and prohexadione-calcium were evaluated for their ability to reduce fire blight infection on apple and pear flowers. Field experiments and experiments under controlled conditions were conducted on apple flowers for 4 years. A reduction of up to 50% of blossom blight was observed in treated plants. In addition, treatment with trinexapac-ethyl reduced up to the 77% the percentage of fireblight-affected flowers from which disease progressed into shoots. On pear, numbers of flower infections were reduced by a quarter and flower infections leading to diseased shoots was reduced by up to 50%. Mechanisms underlying diseased reduction following treatment with the two acylcyclohexanediones was studied using a confocal laser scanning microscope combined with a gpf-labelled strain of E. amylovora. These non-invasive techniques demonstrated bacterial migration was reduced by up to 60 and 66% in apple and pear xylem, respectively.
Treatments with prohexadione-calcium led to lowered incidence of fire blight, scab and other dise... more Treatments with prohexadione-calcium led to lowered incidence of fire blight, scab and other diseases in pome fruit trees and other crop plants. In addition to acting as a growth regulator, prohexadione-calcium interferes with flavonoid metabolism and induces the accumulation of the 3-deoxycatechin luteoliflavan in shoots of pome fruit trees. Luteoliflavan does not possess any remarkable antimicrobial activity. Therefore luteoforol, its unstable and highly reactive precursor, has been tested in vitro for its bactericidal and fungicidal activities. Luteoforol was found to be highly active against different strains of Erwinia amylovora, the causal agent of fire blight, and all other bacterial and fungal organisms tested. Phytotoxic effects were also observed in pear plantlets. The results obtained indicate that prohexadione-calcium induces luteoforol as an active principle with non-specific biocidal properties. It is proposed that luteoforol is released upon pathogen attack from its cellular compartment and inhibits further disease development by destroying pathogen cells as well as by inducing a hypersensitive-like reaction in the host plant tissue. This mechanism would be closely analogous to the one known for structurally related phytoalexins in sorghum.
Uploads
Papers