Selective Diffusion of Basic and Acidic Products of CO2 Fixation into the Transpiration Stream in Grapevine

When ¹⁴CO₂ was supplied to the leaf of a grape-vine shoot, radioactivitywas found in the wood of the shoot and in the fluid extractedby suction from the wood adjacent to the fed leaf. Some radioactivematerial was transported upwards in the transpiration streambut the labelled compounds were not representative of the labelledcompounds either in the wood or in the vacuum-extracted sap.The results suggest that labelled glutamine aaand malic acidare selectively released into the transpiration stream and partlyreabsorbed by the surrounding tissues higher up the shoot, wherethey are converted to glutamic, aspartic, -amono butyric, andcitric acids. Any labelled sugars entering the transpirationstream are preferentially reabsorbed from it.