Plant and Cell Physiology, 2003, Vol. 44, No. 2 163-172
© 2003 Oxford University Press
Sugar Retrieval by Coats of Developing Seeds of Phaseolus vulgaris L. and Vicia faba L.
1 School of Biological Sciences A-08, University of Sydney, NSW 2006, Australia
2 Discipline of Medical Biochemistry, School of Biomedical Sciences, The University of Newcastle, NSW 2308, Australia
3 School of Environmental and Life Sciences, The University of Newcastle, NSW 2308, Australia.
Influxes of glucose, fructose and sucrose were characterised for coat cells of developing seeds of Phaseolus vulgaris L. and Vicia faba L. by monitoring uptake of [14C]sugars into excised seed-coat halves and two different protoplast populations derived from seed coats. Sugar influxes by the two populations of protoplasts were similar for each sugar species [sucrose > (fructose 
glucose)] and hexoses competed with sucrose. Concentration-dependent influxes of all three sugars by excised seed coats could be described by a simple directly proportional relationship between concentration ([S]) and uptake rate (v) in the physiological range of sugar concentrations (v A.[S]). Alternatively, with the exception of fructose influx by Vicia, all could be fitted to a Michaelis-Menten relationship, as could sucrose uptake by Vicia protoplasts. Apparent Km values were high ( 100–500 mM) compared with those reported for other systems. Sucrose transport was distinct from glucose and fructose transport in both species. Sugar influx was decreased by p-chloromercuribenzenesulfonic acid, carbonylcyanide m-chlorophenylhydrazone and erythrosin B. These responses are consistent with sugar/H+ symport acting to retrieve photoassimilates leaked to the apoplasm during post-sieve element transport within seed coats.
4 Corresponding author: E-mail, bijwp{at}alinga.newcastle.edu.au; Fax, +61-2-49-21-6923.