The Transport of Sugars in Developing Fruits of Satsuma Mandarin

Transport of sugars to the juice sacs of developing satsumamandarin (Citrus unshui Marc) has been studied in attached fruitsand in isolated fruit pieces. ¹⁴CO₂ fed to the leaves resultedin ¹⁴C]sugar accumulation in the juice sacs, mainly as ¹⁴C]sucrose.Uptake of sucrose and glucose by the excised fruit pieces proceededlinearly with time. Sucrose uptake was linearly related to sucroseconcentration over the range 25–300 mM, with no indicationof 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. Mostof the ¹⁴C]sucrose uptake observed was reversible, althoughconsiderable hydrolysis and metabolic conversion were evidenced.A vanadate-sensitive ATPase was demonstrated by EM localizationon the plasma membrane of the juice sac cells. These resultsare interpreted in relation to the accumulation of assimilatesby the developing fruit. Transport: sugar, satsuma mandarin, juice sacs