, Volume 197, Issue 1, pp 76-83

Study of sucrose and mannitol transport in plasma-membrane vesicles from phloem and non-phloem tissues of celery (Apium graveolens L.) petioles

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The mature petiole of celery is an organ with versatile sink/source capacities where sucrose and mannitol are unloaded from and reloaded into the phloem cells. Plasma-membrane vesicles were purified by twophase partitioning either from phloem strands isolated from mature petioles of celery (Apium graveolens L.) or from mature petioles devoid of vascular bundles. Both types of vesicle were comparable in purity (more than 86% of plasma-membrane origin), size (135 nm diameter) and orientation (72% right-side-out). Plasma-membrane vesicles from phloem tissues had a higher vanadate-sensitive ATPase activity than plasma-membrane vesicles from petioles. Plasma-membrane vesicles from phloem tissues accumulated mannitol and sucrose in response to an artificial proton-motive force, in agreement with the existence of proton/substrate carriers. Plasma-membrane vesicles from petioles devoid of vascular bundles accumulated only mannitol following application of an artificial proton-motive force. The data suggest the volvement of apoplasmic transport events. The pathway for sucrose uptake in storage parenchyma cells is discussed in the light of the available physiological data.
This work was supported by the Centre National de la Recherche Scientifique (URA CNRS 574). The authors wish to thank all the people who helped in preparing phloem strands and also J.M. Perault for the pictures. We thank Professor S. Delrot for critical reading of the manuscript.