Amidon

Résumé

L'amidon (du latin amulum ou amylum, non moulu) est un glucide (sucre) complexe (polysaccharide ou polyoside) composé d'unités D-glucose (sucre simple). Il s'agit d'une molécule de réserve pour les végétaux supérieurs et un élément courant de l'alimentation humaine. Chez les animaux et les champignons, l'équivalent de l'amidon est le glycogène : molécule de stockage de glucides et donc d'énergie. Origine botanique L'amidon se trouve dans les organes de réserves de nombreuses plantes :

les graines (en particulier la châtaigne, les céréales (blé, maïs, froment, etc.) et les légumineuses) ;
les racines ;
les tubercules et rhizomes (pomme de terre, patate douce, manioc, etc.) ; dans ce cas, il est appelé fécule et peut être extrait dans une féculerie ;
les fruits (bananes, arbre à pain) où l'amidon a pour fonction de stimuler la dispersion des graines (quand il y en a).

On trouve aussi de l'amidon dans les organes photosynthétiques de plantes, notamment au niveau de

Source officielle

https://fr.wikipedia.org/wiki/Amidon

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Les glucoses sont des sucres de formule brute . Le mot « glucose » provient du grec ancien τὸ γλεῦκος / gleukos qui désignait les vins doux ou liquoreux, voire le moût. Le suffixe -ose est un classi

vignette|150px|Par exemple, le glucose est un glucide à six carbones, cinq groupes hydroxyle et un groupe aldéhyde. vignette|Les grains et céréales contiennent une grande quantité de glucides. Les gl

vignette|Usine sucrière transformant la canne à sucre en sucre de canne à La Réunion. vignette|Cristaux de sucre raffiné (macrophotographie). Le sucre est une substance de saveur douce extraite princi

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The role of carbon (C) and nutrient uptake, allocation, storage and especially their interactions in survival and recovery of trees under increased frequencies and intensities of drought events is not well understood. A full factorial experiment with four soil water content regimes ranging from extreme drought to well-watered conditions and two fertilization levels was carried out. We aimed to investigate whether nutrient addition mitigates drought effects on downy oak (Quercus pubescens Willd.) and whether storage pools of non-structural carbohydrates (NSC) are modified to enhance survival after 2.5 years of drought and recovery after drought relief. Physiological traits, such as photosynthesis, predawn leaf water potential as well as tissue biomass together with pools and dynamics of NSC and nutrients at the whole-tree level were investigated. Our results showed that fertilization played a minor role in saplings’ physiological processes to cope with drought and drought relief, but reduced sapling mortality during extreme drought. Irrespective of nutrient supply, Q. pubescens showed increased soluble sugar concentration in all tissues with increasing drought intensity, mostly because of starch degradation. After 28 days of drought relief, tissue sugar concentrations decreased, reaching comparable values to those of well-watered plants. Only during the recovery process from extreme drought, root NSC concentration strongly declined, leading to an almost complete NSC depletion after 28 days of rewetting, simultaneously with new leaves flushing. These findings suggest that extreme drought can lead to root carbon exhaustion. After drought relief, the repair and regrowth of organs can even exacerbate the root carbon depletion. We concluded that under future climate conditions with repeated drought events, the insufficient and lagged carbon replenishment in roots might eventually lead to carbon starvation and further mortality.

2021

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The ability of endosymbiotic Symbiodinium to fix inorganic nutrients and their translocation to the coral host is considered a key element for the growth of coral reefs in tropical coastal waters and has been a fundamental research topic for over 50 years. With pulse-chase experiments using stable isotopes and combined TEM and NanoSIMS ultrastructural and isotopic analyses it is now possible to visualize and quantify the fixation, translocation, and turnover of essential elements such as carbon and nitrogen with unprecedented subcellular resolution. With these techniques we have monitored the assimilation of 15N nitrate, 15N ammonium, and 13C bicarbonate in the coral Pocillopora damicornis. These studies have revealed dynamic intra-symbiont storage of assimilated nitrate and ammonium in the form of uric acid crystals, and the formation of lipid droplets and starch granules in the symbiont and their subsequent remobilization. Carbon translocation toward the coral gastrodermal lipid droplets was detected within 15 min. Moreover, glycogen granules in the coral tissue were found to be an important sink for translocated carbon. This work has now been extended to the related pocilloporid species, Stylophora pistillata, with the important addition of heterotrophy (feeding the coral with dual-labelled brine shrimps) to contrast the fate and timeframes of heterotrophic vs. autotrophic (15N nitrate/13C bicarbonate) nutrient uptake under natural conditions and environmental stress due to elevated water temperatures. The in situ spatial data provided by NanoSIMS allow us for the first time to address questions that cannot be answered by traditional bulk measurements, such as 1) the influence of local symbiont densities on individual Symbiodinium assimilation rates, 2) metabolic capabilities of different symbiont ITS2 types in hospite, and (3) the effect of changes in intracellular host and symbiosome pH on individual symbiont productivity.

2015

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UNLABELLED: Reef-building corals form essential, mutualistic endosymbiotic associations with photosynthetic Symbiodinium dinoflagellates, providing their animal host partner with photosynthetically derived nutrients that allow the coral to thrive in oligotrophic waters. However, little is known about the dynamics of these nutritional interactions at the (sub)cellular level. Here, we visualize with submicrometer spatial resolution the carbon and nitrogen fluxes in the intact coral-dinoflagellate association from the reef coral Pocillopora damicornis by combining nanoscale secondary ion mass spectrometry (NanoSIMS) and transmission electron microscopy with pulse-chase isotopic labeling using [(13)C]bicarbonate and [(15)N]nitrate. This allows us to observe that (i) through light-driven photosynthesis, dinoflagellates rapidly assimilate inorganic bicarbonate and nitrate, temporarily storing carbon within lipid droplets and starch granules for remobilization in nighttime, along with carbon and nitrogen incorporation into other subcellular compartments for dinoflagellate growth and maintenance, (ii) carbon-containing photosynthates are translocated to all four coral tissue layers, where they accumulate after only 15 min in coral lipid droplets from the oral gastroderm and within 6 h in glycogen granules from the oral epiderm, and (iii) the translocation of nitrogen-containing photosynthates is delayed by 3 h.IMPORTANCE: Our results provide detailed in situ subcellular visualization of the fate of photosynthesis-derived carbon and nitrogen in the coral-dinoflagellate endosymbiosis. We directly demonstrate that lipid droplets and glycogen granules in the coral tissue are sinks for translocated carbon photosynthates by dinoflagellates and confirm their key role in the trophic interactions within the coral-dinoflagellate association.

American Society for Microbiology2015

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