Characterization of phloem exudation from castor-bean cotyledons.
Exudate was collected fromRicinus communis L. cotyledons after cutting the hypocotyl. It contained high levels of sucrose and potassium, a low level of calcium, and a pH of approx. 7.5. After application of [(14)C] sucrose to the cotyledons, radioactivity could be recovered from the exudate, indicating that the exudate was derived from the phloem. Using data from a number of individual seedlings, correlations between loading rates of sucrose, translocation rates, and sucrose and potassium contents were analyzed. A positive correlation was found between the rate of sucrose loading and the rate of sucrose exudation, whereas a negative correlation existed between the contents of sucrose and potassium in the phloem.
Department of Plant Physiology, Wageningen Agricultural University, Arboretumlaan 4, 6703 BD, Wageningen, The Netherlands.
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Vreugdenhil
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Koot-Gronsveld