Phloem Exudate Collected via Scale Insect Stylets for the CAM Species Opuntia ficus-indica under Current and Doubled CO2 Concentrations

A method was devised for collecting phloem sap from the CAMspecies Opuntia ficus-indica using severed stylets of a scaleinsect (Dactylopius opuntiae), for which exudation could continuefor up to 5 d. For both basal (planted) cladodes and first-orderdaughter cladodes, the concentrations of sucrose and total aminoacids in the phloem exudate were virtually constant over 24-hperiods whereas the chlorenchyma osmolality had sizeable increasesduring the night under both current and doubled atmosphericCO₂ concentrations. Sucrose, total amino acids, and potassiumaccounted for 56, 21, and 9%, respectively, of the osmolalityof the phloem exudate, which was about 350 mOsm at the two CO₂concentrations; 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 exudateand also significantly increased mannose, starch and glucomannanin the chlorenchyma. Atmospheric CO₂ concentrations thus affectedvarious solute properties in the phloem and the chlorenchymaof O. ficus-indica.Copyright 1995, 1999 Academic Press Dactylopius opuntiae, Opuntia ficus-indica, cladode, CO₂ concentrations, Crassulacean acid metabolism, phloem exudate