%0 Journal Article %1 Ameglioetal_04 %A Ameglio, T. %A Decourteix, M. %A Alves, G. %A Valentin, V. %A Sakr, S. %A Julien, J. %A Petel, G. %A Guilliot, A. %A Lacointe, A. %D 2004 %J Tree Physiology %K bibtex-import, citeulikeExport embolism, freezebolism, refilling, snowgumpapermaybe %P 785--793 %T Temperature effects on xylem sap osmolarity in walnut trees: evidence for a vitalistic model of winter embolism repair %V 24 %X We studied the effect of temperature on the carbohydrate status of parenchyma cells during winter in relation to the efflux and influx of sugars between parenchyma cells and xylem vessels in 1-year-old twigs of walnut (Juglans regia L.). The mechanism of sugar transfer between contact cells and vessels was also investigated. We obtained new insights into the possible osmotic role of sugars, particularly sucrose, in stem pressure formation and winter embolism repair. Accumulation of sucrose in the xylem sap during winter was mainly influenced by: (1) abundant conversion of starch to sucrose in the symplast at low temperatures; (2) sucrose efflux into the apoplast at low temperatures (1 C); and (3) inefficient sugar uptake at lowtemperatures, although efficient sugar uptake occurred at 15 C. We hypothesize that a diethyl pyrocarbonate (DEPC)-sensitive protein mediates facilitated diffusion of sucrose from parenchyma cells to xylem vessels (efflux) in walnut. We discuss the possible occurrence of active H+-sucrose symports and the coexistence of both influx and efflux processes inwalnut in winter and the modulation of the relative importance of these flows by temperature.

@article{Ameglioetal_04, abstract = {{We studied the effect of temperature on the carbohydrate status of parenchyma cells during winter in relation to the efflux and influx of sugars between parenchyma cells and xylem vessels in 1-year-old twigs of walnut (Juglans regia L.). The mechanism of sugar transfer between contact cells and vessels was also investigated. We obtained new insights into the possible osmotic role of sugars, particularly sucrose, in stem pressure formation and winter embolism repair. Accumulation of sucrose in the xylem sap during winter was mainly influenced by: (1) abundant conversion of starch to sucrose in the symplast at low temperatures; (2) sucrose efflux into the apoplast at low temperatures (1 C); and (3) inefficient sugar uptake at lowtemperatures, although efficient sugar uptake occurred at 15 C. We hypothesize that a diethyl pyrocarbonate (DEPC)-sensitive protein mediates facilitated diffusion of sucrose from parenchyma cells to xylem vessels (efflux) in walnut. We discuss the possible occurrence of active H+-sucrose symports and the coexistence of both influx and efflux processes inwalnut in winter and the modulation of the relative importance of these flows by temperature.}}, added-at = {2019-03-31T01:14:40.000+0100}, author = {Ameglio, T. and Decourteix, M. and Alves, G. and Valentin, V. and Sakr, S. and Julien, J. and Petel, G. and Guilliot, A. and Lacointe, A.}, biburl = {https://www.bibsonomy.org/bibtex/2f2e2ec1c18b3d1d0e48215b81241027e/dianella}, citeulike-article-id = {1523592}, comment = {(private-note)"physical" vs "vitalistic" models. a good terminology It is also known from studies with Acer that, at non-freezing low temperatures, starch in stem parenchyma cells is hydrolyzed to sugars, especially sucrose, which are unloaded, in part, into xylem vessels, resulting in increased xylem sap osmotic potential (Marvin et al 1967, Sauter et al. 1973). Sucrose, glucose and fructose contents were determined spectrophotometrically at 340 nm after enzymatic assays (Boehringer 1984). Starch content was determined by a hexokinase, glucose-6-phosphate linked assays (Kunst et al. 1984) after hydrolysis of the sample with amyloglucosidase (Boehringer 1984). We found significant starch hydrolysis in walnut, resulting in minimum starch concentrations in deep winter, followed by a period of starch resynthesis in late winter, prior to final mobilization of carbohydrates for bud break in spring. I COULDN'T GET INTERESTED IN THIS PAPER.}, interhash = {0433ae4961818076420ce97def571609}, intrahash = {f2e2ec1c18b3d1d0e48215b81241027e}, journal = {Tree Physiology}, keywords = {bibtex-import, citeulikeExport embolism, freezebolism, refilling, snowgumpapermaybe}, pages = {785--793}, pdf = {\\biostore\desktop\$\u2531135\Desktop\references ideas and theory\papers\Ameglioetal\_04\_walnut\_Xy\_solutes\_repair.pdf}, posted-at = {2007-07-31 06:00:54}, priority = {2}, timestamp = {2019-03-31T01:16:26.000+0100}, title = {{Temperature effects on xylem sap osmolarity in walnut trees: evidence for a vitalistic model of winter embolism repair}}, volume = 24, year = 2004 }