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Résumé :
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In celery (Apium graveolens L.), long-distance transport of reduced carbon occurs both in the form of sucrose (Suc) and mannitol. The presence of mannitol has been related to the resistance of celery to salt stress. To investigate the transport events occurring during salt stress, we have cloned the H+/Suc transporter of celery Ag SUT1 (A. graveolens Suc uptake transport 1) from a mature leaf c DNA library. The function of the encoded protein was confirmed by expression in yeast. Ag SUT1 is a H+/Suc transporter with a high affinity for Suc (K-m of 139 mu M). Another closely related c DNA (Ag SUT2) was also identified. Ag SUT1 is mainly expressed in mature leaves and phloem of petioles, but also in sink organs such as roots. When celery plants were subjected to salt stress conditions (30 d watering with 300 m M Na Cl) favoring mannitol accumulation (J.D. Everard, R. Gucci, S.C. Kann, J.A. Flore, W.H. Loescher [1994] Plant Physiol 106: 281-292), Ag SUT1 expression was decreased in all organs, but markedly in roots. The results are discussed in relation to the physiology of celery.
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