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Résumé :
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A method was devised for collecting phloem sap from the CAM species Opuntia ficus-indica using severed stylets of a scale insect (Dactylopius opuntiae), for which exudation could continue for up to 5 d. For both basal (planted) cladodes and first-order daughter cladodes, the concentrations of sucrose and total amino acids in the phloem exudate were virtually constant over 24-h periods whereas the chlorenchyma osmolality had sizeable increases during the night under both current and doubled atmospheric CO2 concentrations. Sucrose, total amino acids, and potassium accounted for 56, 21, and 9%, respectively, of the osmolality of the phloem exudate, which was about 350 m Osm at the two CO2 concentrations; valine, isoleucine, leucine, tyrosine, glutamine, and lysine accounted for about 70% of the total amino acids. Doubling the CO2 concentration led to approx. 5% more sucrose, 560% more mannose and 17% less amino acids in the phloem exudate and also significantly increased mannose, starch and glucomannan in the chlorenchyma. Atmospheric CO2 concentrations thus affected various solute properties in the phloem and the chlorenchyma of O. ficus-indica.
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