The transport of sugars in developing fruits of satsuma mandarin

Abstract

Transport of sugars to the juice sacs of developing satsuma mandarin (Citrus unshui Marc) has been studied in attached fruits and in isolated fruit pieces. 14CO2 fed to the leaves resulted in [14C]sugar accumulation in the juice sacs, mainly as [14C]sucrose. Uptake of sucrose and glucose by the excised fruit pieces proceeded linearly with time. Sucrose uptake was linearly related to sucrose concentration over the range 25-300 mM, with no indication of saturation. This uptake was insensitive to pH (5, 7 or 9), Ca2+(3 mM), PCMBS (2.5 mM), DNP (1 mM) or vanadate (0.1 mM) but was slightly reduced by erythrosin (21 % by 0-1 mM; 27 % by 1 mM). No competitive effect of glucose (up to 100 mM) was detectable on sucrose uptake from 100 mM solution. Most of the [14C]sucrose uptake observed was reversible, although considerable hydrolysis and metabolic conversion were evidenced. A vanadate-sensitive ATPase was demonstrated by EM localization on the plasma membrane of the juice sac cells. These results are interpreted in relation to the accumulation of assimilates by the developing fruit. © 1991 Annals of Botany Company.