, Volume 171, Issue 4, pp 474–482

Sucrose uptake in isolated phloem of celery is a single saturable transport system

  • Jaleh Daie

DOI: 10.1007/BF00392294

Cite this article as:
Daie, J. Planta (1987) 171: 474. doi:10.1007/BF00392294


The uptake of different sugars was studied in segments of isolated phloem from petioles of celery (Apium graveolens L.) in order to determine the kinetics and specificity of phloem loading in this highly uniform conductive tissue. The uptake kinetics of sucrose and the sugar alcohol, mannitol, which are both phloem-translocated, indicated presence of a single saturable system, while uptake of non-phloem sugars (glucose and 3-O-methylglucose) exhibited biphasic kinetics with lower uptake rates than those for sucrose and mannitol. The presence of unlabeled mannitol, 3-O-methylglucose and maltose in the incubation solution did not cause inhibition of labeled-sucrose uptake, indicating high carrier specificity and lack of sucrose hydrolysis in vivo. The pH optimum for sucrose uptake was 5–6. Furthermore, a rapid and transient alkalinization of the external media by sucrose indicated a sugar/H+-cotransport mechanism. Dual-labeling experiments showed that sucrose influx continued at a constant rate (Vmax=15 μmol·h-1·(g FW)-1), whereas sucrose efflux was low and insensitive to external concentration. Therefore, the saturable uptake kinetics for sucrose did not appear to be the result of an equilibrium between rates of sucrose influx and efflux.

Key words

ApiumPhloem loadingSugar uptake and transportTransport, sucrose





p-chloromercuribenzene sulfonate


sieve element-companion cell


vascular bundle

Copyright information

© Springer-Verlag 1987

Authors and Affiliations

  • Jaleh Daie
    • 1
  1. 1.Department of Soils and Crops, Cook CollegeRutgers UniversityNew BrunswickUSA