Differing from most animals, plants have an indeterminate body plan, allowing them to add new bod... more Differing from most animals, plants have an indeterminate body plan, allowing them to add new body parts throughout their lifetime. The realized modular construction of a plant is the result of endogenous processes and exogenous constraints. Plant architectural analysis provides a holistic approach to whole-plant development by disentangling endogenous processes from exogenous constraints. Such analyses have focused more on trees than herbs. We here report a rare growth form discovered in the tropical herb Centella asiatica (Apiaceae) using micro-computed X-ray tomography to understand organogenesis in the meristem. Seeds of C. asiatica germinate to give rise to an orthotropic monochasium (sympodium) with terminal inflorescences. A stolon subsequently emerges from the oldest leaf axils of the sympodium. The primary growth of stolons is indeterminate (monopodial), and they only bear scale leaves. The stolon not only produces new leafy sympodial shoots at each node but also an axillary inflorescence. To place this growth form in context, we illustrate all architectural models so far reported from herbs. Our study highlights the complexity of herb architectures and illustrates the use of a novel methodology to decipher plant branching modes.
Chapter 6 Biological Activity of Phenolics in Plant Cells Luc PR Bidel, Marc Coumans, Yves Baissa... more Chapter 6 Biological Activity of Phenolics in Plant Cells Luc PR Bidel, Marc Coumans, Yves Baissac, Patrick Doumas, and Christian Jay-Allemand 6.1 Introduction Phenolics are secondary metabolites of great interest for plants, animals, and humans. Many of their functions in ...
A cumulative effect of UV-B doses on epidermal flavonol accumulation was observed during the firs... more A cumulative effect of UV-B doses on epidermal flavonol accumulation was observed during the first week of a time course study in Centella asiatica (Apiaceae). However, once flavonol levels had peaked, additional accumulation was possible only if higher daily UV-B irradiances were applied. We aimed to understand the dynamics of flavonol accumulation in leaf tissues using non-destructive spectroscopy and HPLC-mass spectrometry. When leaves that had grown without UV-B were given brief daily exposures to low-irradiance UV-B, they accumulated flavonols, predominantly kaempferol-3-O-β-D-glucuronopyranoside and quercetin-3-O-β-D-glucuronopyranoside, in their exposed epidermis, reaching a plateau after 7 days. More prolonged UV-B exposures or higher doses eventually augmented flavonol concentrations even in non-exposed tissues. If UV-B irradiance was subsequently reduced, leaves appeared to lose their ability to accumulate further flavonols in their epidermis even if the duration of daily ...
Phenolic compounds contribute to food quality and have potential health benefits. Consequently, t... more Phenolic compounds contribute to food quality and have potential health benefits. Consequently, they are an important target of selection for Citrus species. Numerous studies on this subject have revealed new molecules, potential biosynthetic pathways and linkage between species. Although polyphenol profiles are correlated with gene expression, which is responsive to developmental and environmental cues, these factors are not monitored in most studies. A better understanding of the biosynthetic pathway and its regulation requires more information about environmental conditions, tissue specificity and connections between competing sub-pathways. This study proposes a rapid method, from sampling to analysis, that allows the quantitation of multiclass phenolic compounds across contrasting tissues and cultivars. Leaves and fruits of 11 cultivated citrus of commercial interest were collected from adult trees grown in an experimental orchard. Sixty-four phenolic compounds were simultaneous...
Extreme climatic events, including drought, are predicted to increase in intensity, frequency, an... more Extreme climatic events, including drought, are predicted to increase in intensity, frequency, and geographic extent as a consequence of global climate change. In general, to grow crops successfully in the future, growers will need to adapt to less available water and to take better advantage of the positive effects of drought. Fortunately, there are positive effects associated with drought. Drought stimulates the secondary metabolism, thereby potentially increasing plant defences and the concentrations of compounds involved in plant quality, particularly taste and health benefits. The role of drought on the production of secondary metabolites is of paramount importance for fruit crops. However, to manage crops effectively under conditions of limited water supply, for example by applying deficit irrigation, growers must consider not only the impact of drought on productivity but also on how plants manage the primary and secondary metabolisms. This question is obviously complex becau...
UV-B radiation damage in leaves is prevented by epidermal UV-screening compounds that can be modu... more 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 ...
In the present study, we obtained a dried burdock root extract (DBRE) rich in caffeoylquinic acid... more In the present study, we obtained a dried burdock root extract (DBRE) rich in caffeoylquinic acids derivatives. We performed the chemical characterization of DBRE and explored its antihyperglycemic potential in both in vitro and in vivo experiments. Chemical analysis of DBRE using LC-MS and GC-MS revealed the presence of a great majority of dicaffeoylquinic acid derivatives (75.4%) of which 1,5-di-O-caffeoyl-4-O-maloylquinic acid represents 44% of the extract. In the in vitro experiments, DBRE is able to increase glucose uptake in cultured L6 myocytes and to decrease glucagon-induced glucose output from rat isolated hepatocytes together with a reduction of hepatic glucose 6-phosphatase activity. DBRE did not increase insulin secretion in the INS-1 pancreatic β-cell line. In vivo, DBRE improves glucose tolerance both after intraperitoneal and oral subchronic administration. In conclusion, our data demonstrate that DBRE constitutes an original set of caffeoylquinic acid derivatives displaying antihyperglycemic properties.
Carotenoids play an important role in plant adaptation to fluctuating environments as well as in ... more Carotenoids play an important role in plant adaptation to fluctuating environments as well as in the human diet by contributing to the prevention of chronic diseases. Insights have been gained recently into the way individual factors, genetic, environmental or developmental, control the carotenoid biosynthetic pathway at the molecular level. The identification of the rate-limiting steps of carotenogenesis has paved the way for programmes of breeding, and metabolic engineering, aimed at increasing the concentration of carotenoids in different crop species. However, the complexity that arises from the interactions between the different factors as well as from the coordination between organs remains poorly understood. This review focuses on recent advances in carotenoid responses to environmental stimuli and discusses how the interactions between the modulation factors and between organs affect carotenoid build-up. We develop the idea that reactive oxygen species/redox status and sugars/carbon status can be considered as integrated factors that account for most effects of the major environmental factors influencing carotenoid biosynthesis. The discussion highlights the concept of carotenoids or carotenoid-derivatives as stress signals that may be involved in feedback controls. We propose a conceptual model of the effects of environmental and developmental factors on carotenoid build-up in fruits.
Chlorophyll (Chl) and epidermal polyphenol (EPhen) contents were estimated in vivo using two opti... more Chlorophyll (Chl) and epidermal polyphenol (EPhen) contents were estimated in vivo using two optical leaf-clips, SPAD-502 and Dualex, respectively. The area-based measurements were transformed into mass-based data by taking into account the leaf dry mass per area (LMA). Measurements were performed on forest trees and on saplings grown under controlled conditions. While LMA increased with irradiance along a vertical transect in a beech canopy or in saplings grown under different and increasing irradiance levels, mass-based EPhen (EPhen(m)) increased, whereas mass-based Chl (Chl(m)) decreased. This was a signature of a gradual switch of investment from protein into polyphenol production. A similar signature was obtained in saplings grown on nitrogen-deficient soil with respect to fertilized controls. However, nitrogen effects remained moderate compared to irradiance-induced effects. EPhen(m) and Chl(m) both declined with plant ageing-induced increases in LMA, under all tested growth conditions. This was a signature of an accumulation of dry matter that diluted Chl and EPhen. The described competition between Chl and EPhen in leaves fits well with the predictions of the Protein Competition Model (PCM), that is, that the total leaf mass-based polyphenols content (Phen(t)) is controlled by the competition between protein and polyphenol biosynthetic pathways and its metabolic regulation.
Root system architecture partially results from meristem activities, which themselves depend on e... more Root system architecture partially results from meristem activities, which themselves depend on endogenous and environmental factors, such as O2 depletion. In this study, meristem respiration and growth was measured in the root systems of three Prunus persica (L.) Batsch seedlings. The spatial distribution of meristem respiration within the root system was described, and the relationship between the respiration rates and meristem radii was analysed, using a model of radial O2 diffusion and consumption within the root. Histological observations were also used to help interpret the results. Respiration rates were linearly correlated to the root growth rates (rho 2 = 0.9). Respiration reached values greater than 3.5 x 10(-13) mol O2 s-1 for active meristems. The taproot meristem consumed more O2 than the rest of the entire root system meristems. Similarly, the first order lateral meristems used more O2 than the second order ones. A near hyperbolic relationship between respiration rates and meristem radii was observed. This can be explained by a model of radial O2 diffusion and consumption within the root. Therefore, only one maximum potential respiration rate and one O2 diffusion coefficient was estimated for all the meristems.
ABSTRACT To the best of our knowledge, this is the first soft X-ray radiographic study of the dev... more ABSTRACT To the best of our knowledge, this is the first soft X-ray radiographic study of the development of an entire young root system of western red cedar (Thuja plicata D. Don). The experimental device was adapted to radiographic constraints and allowed the plant to grow for several months. Successive radiographs revealed primary growth and differentiation, secondary growth, and primordium development. The younger (8-day-old) part of the root system appeared fully opaque. Afterwards, the stele and the cortex could be distinguished from each other progressively in a second zone where most of the primary differentiation had already occurred. Measuring early cambial growth was made possible by spacing the radiographs at 10-day intervals. Time-course developments of primordia and their histolysis cavities were traced for 8-15 days, depending on the sample. The acropetal sequences of primordia along the same adventitious root were shown. Primordia had different growth curves, most of which were nearly logistic. These meristems were produced by unequal primordia, which generated axes of unequal diameters. Our techniques provide new opportunities for understanding the differentiation of axes and defining potential root growth during primordium development.Key words: soft X-ray radiography, root development, primordia, root differentiation, radial growth, morphogenesis.
Differing from most animals, plants have an indeterminate body plan, allowing them to add new bod... more Differing from most animals, plants have an indeterminate body plan, allowing them to add new body parts throughout their lifetime. The realized modular construction of a plant is the result of endogenous processes and exogenous constraints. Plant architectural analysis provides a holistic approach to whole-plant development by disentangling endogenous processes from exogenous constraints. Such analyses have focused more on trees than herbs. We here report a rare growth form discovered in the tropical herb Centella asiatica (Apiaceae) using micro-computed X-ray tomography to understand organogenesis in the meristem. Seeds of C. asiatica germinate to give rise to an orthotropic monochasium (sympodium) with terminal inflorescences. A stolon subsequently emerges from the oldest leaf axils of the sympodium. The primary growth of stolons is indeterminate (monopodial), and they only bear scale leaves. The stolon not only produces new leafy sympodial shoots at each node but also an axillary inflorescence. To place this growth form in context, we illustrate all architectural models so far reported from herbs. Our study highlights the complexity of herb architectures and illustrates the use of a novel methodology to decipher plant branching modes.
Chapter 6 Biological Activity of Phenolics in Plant Cells Luc PR Bidel, Marc Coumans, Yves Baissa... more Chapter 6 Biological Activity of Phenolics in Plant Cells Luc PR Bidel, Marc Coumans, Yves Baissac, Patrick Doumas, and Christian Jay-Allemand 6.1 Introduction Phenolics are secondary metabolites of great interest for plants, animals, and humans. Many of their functions in ...
A cumulative effect of UV-B doses on epidermal flavonol accumulation was observed during the firs... more A cumulative effect of UV-B doses on epidermal flavonol accumulation was observed during the first week of a time course study in Centella asiatica (Apiaceae). However, once flavonol levels had peaked, additional accumulation was possible only if higher daily UV-B irradiances were applied. We aimed to understand the dynamics of flavonol accumulation in leaf tissues using non-destructive spectroscopy and HPLC-mass spectrometry. When leaves that had grown without UV-B were given brief daily exposures to low-irradiance UV-B, they accumulated flavonols, predominantly kaempferol-3-O-β-D-glucuronopyranoside and quercetin-3-O-β-D-glucuronopyranoside, in their exposed epidermis, reaching a plateau after 7 days. More prolonged UV-B exposures or higher doses eventually augmented flavonol concentrations even in non-exposed tissues. If UV-B irradiance was subsequently reduced, leaves appeared to lose their ability to accumulate further flavonols in their epidermis even if the duration of daily ...
Phenolic compounds contribute to food quality and have potential health benefits. Consequently, t... more Phenolic compounds contribute to food quality and have potential health benefits. Consequently, they are an important target of selection for Citrus species. Numerous studies on this subject have revealed new molecules, potential biosynthetic pathways and linkage between species. Although polyphenol profiles are correlated with gene expression, which is responsive to developmental and environmental cues, these factors are not monitored in most studies. A better understanding of the biosynthetic pathway and its regulation requires more information about environmental conditions, tissue specificity and connections between competing sub-pathways. This study proposes a rapid method, from sampling to analysis, that allows the quantitation of multiclass phenolic compounds across contrasting tissues and cultivars. Leaves and fruits of 11 cultivated citrus of commercial interest were collected from adult trees grown in an experimental orchard. Sixty-four phenolic compounds were simultaneous...
Extreme climatic events, including drought, are predicted to increase in intensity, frequency, an... more Extreme climatic events, including drought, are predicted to increase in intensity, frequency, and geographic extent as a consequence of global climate change. In general, to grow crops successfully in the future, growers will need to adapt to less available water and to take better advantage of the positive effects of drought. Fortunately, there are positive effects associated with drought. Drought stimulates the secondary metabolism, thereby potentially increasing plant defences and the concentrations of compounds involved in plant quality, particularly taste and health benefits. The role of drought on the production of secondary metabolites is of paramount importance for fruit crops. However, to manage crops effectively under conditions of limited water supply, for example by applying deficit irrigation, growers must consider not only the impact of drought on productivity but also on how plants manage the primary and secondary metabolisms. This question is obviously complex becau...
UV-B radiation damage in leaves is prevented by epidermal UV-screening compounds that can be modu... more 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 ...
In the present study, we obtained a dried burdock root extract (DBRE) rich in caffeoylquinic acid... more In the present study, we obtained a dried burdock root extract (DBRE) rich in caffeoylquinic acids derivatives. We performed the chemical characterization of DBRE and explored its antihyperglycemic potential in both in vitro and in vivo experiments. Chemical analysis of DBRE using LC-MS and GC-MS revealed the presence of a great majority of dicaffeoylquinic acid derivatives (75.4%) of which 1,5-di-O-caffeoyl-4-O-maloylquinic acid represents 44% of the extract. In the in vitro experiments, DBRE is able to increase glucose uptake in cultured L6 myocytes and to decrease glucagon-induced glucose output from rat isolated hepatocytes together with a reduction of hepatic glucose 6-phosphatase activity. DBRE did not increase insulin secretion in the INS-1 pancreatic β-cell line. In vivo, DBRE improves glucose tolerance both after intraperitoneal and oral subchronic administration. In conclusion, our data demonstrate that DBRE constitutes an original set of caffeoylquinic acid derivatives displaying antihyperglycemic properties.
Carotenoids play an important role in plant adaptation to fluctuating environments as well as in ... more Carotenoids play an important role in plant adaptation to fluctuating environments as well as in the human diet by contributing to the prevention of chronic diseases. Insights have been gained recently into the way individual factors, genetic, environmental or developmental, control the carotenoid biosynthetic pathway at the molecular level. The identification of the rate-limiting steps of carotenogenesis has paved the way for programmes of breeding, and metabolic engineering, aimed at increasing the concentration of carotenoids in different crop species. However, the complexity that arises from the interactions between the different factors as well as from the coordination between organs remains poorly understood. This review focuses on recent advances in carotenoid responses to environmental stimuli and discusses how the interactions between the modulation factors and between organs affect carotenoid build-up. We develop the idea that reactive oxygen species/redox status and sugars/carbon status can be considered as integrated factors that account for most effects of the major environmental factors influencing carotenoid biosynthesis. The discussion highlights the concept of carotenoids or carotenoid-derivatives as stress signals that may be involved in feedback controls. We propose a conceptual model of the effects of environmental and developmental factors on carotenoid build-up in fruits.
Chlorophyll (Chl) and epidermal polyphenol (EPhen) contents were estimated in vivo using two opti... more Chlorophyll (Chl) and epidermal polyphenol (EPhen) contents were estimated in vivo using two optical leaf-clips, SPAD-502 and Dualex, respectively. The area-based measurements were transformed into mass-based data by taking into account the leaf dry mass per area (LMA). Measurements were performed on forest trees and on saplings grown under controlled conditions. While LMA increased with irradiance along a vertical transect in a beech canopy or in saplings grown under different and increasing irradiance levels, mass-based EPhen (EPhen(m)) increased, whereas mass-based Chl (Chl(m)) decreased. This was a signature of a gradual switch of investment from protein into polyphenol production. A similar signature was obtained in saplings grown on nitrogen-deficient soil with respect to fertilized controls. However, nitrogen effects remained moderate compared to irradiance-induced effects. EPhen(m) and Chl(m) both declined with plant ageing-induced increases in LMA, under all tested growth conditions. This was a signature of an accumulation of dry matter that diluted Chl and EPhen. The described competition between Chl and EPhen in leaves fits well with the predictions of the Protein Competition Model (PCM), that is, that the total leaf mass-based polyphenols content (Phen(t)) is controlled by the competition between protein and polyphenol biosynthetic pathways and its metabolic regulation.
Root system architecture partially results from meristem activities, which themselves depend on e... more Root system architecture partially results from meristem activities, which themselves depend on endogenous and environmental factors, such as O2 depletion. In this study, meristem respiration and growth was measured in the root systems of three Prunus persica (L.) Batsch seedlings. The spatial distribution of meristem respiration within the root system was described, and the relationship between the respiration rates and meristem radii was analysed, using a model of radial O2 diffusion and consumption within the root. Histological observations were also used to help interpret the results. Respiration rates were linearly correlated to the root growth rates (rho 2 = 0.9). Respiration reached values greater than 3.5 x 10(-13) mol O2 s-1 for active meristems. The taproot meristem consumed more O2 than the rest of the entire root system meristems. Similarly, the first order lateral meristems used more O2 than the second order ones. A near hyperbolic relationship between respiration rates and meristem radii was observed. This can be explained by a model of radial O2 diffusion and consumption within the root. Therefore, only one maximum potential respiration rate and one O2 diffusion coefficient was estimated for all the meristems.
ABSTRACT To the best of our knowledge, this is the first soft X-ray radiographic study of the dev... more ABSTRACT To the best of our knowledge, this is the first soft X-ray radiographic study of the development of an entire young root system of western red cedar (Thuja plicata D. Don). The experimental device was adapted to radiographic constraints and allowed the plant to grow for several months. Successive radiographs revealed primary growth and differentiation, secondary growth, and primordium development. The younger (8-day-old) part of the root system appeared fully opaque. Afterwards, the stele and the cortex could be distinguished from each other progressively in a second zone where most of the primary differentiation had already occurred. Measuring early cambial growth was made possible by spacing the radiographs at 10-day intervals. Time-course developments of primordia and their histolysis cavities were traced for 8-15 days, depending on the sample. The acropetal sequences of primordia along the same adventitious root were shown. Primordia had different growth curves, most of which were nearly logistic. These meristems were produced by unequal primordia, which generated axes of unequal diameters. Our techniques provide new opportunities for understanding the differentiation of axes and defining potential root growth during primordium development.Key words: soft X-ray radiography, root development, primordia, root differentiation, radial growth, morphogenesis.
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Papers by Luc Bidel