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     

Localization of ATPase in Sink Tissues of Ricinus

Histochemical localization of ATPase was carried out on phloemtissues from vegetative and reproductive sinks of Ricinus communis,using lead precipitation procedures. Reaction products werelocalized mainly at the plasma membrane of the sieve elements,companion cells and phloem parenchyma cells. Activity was alsopresent in plasmodesmata, the tonoplast of companion cells anddispersed P-protein within the sieve element lumen. The resultsare discussed in relation to the possible involvement of a plasmamembrane ATPase in apoplastic and symplastic unloading fromthe phloem conducting tissues. ATPase, sink tissues, unloading, Ricinus communis     

The Effect of Cycloheximide on Absorption of Ions by Bean (Phaseolus vulgaris L) Roots

10^–7 M cycloheximide inhibited bean (Phaseolus vulgaris)root elongation by about 20 per cent but it inhibited absorptionof rubidium, sodium, and phosphate ions to a much greater extent(34–71 per cent). Tips of intact plant roots grown inthe inhibitor showed more inhibition in ion uptake than adjacentproximal portions of the same roots and this is taken to indicatethat 10^–7 M cycloheximide does not exert its effect onion uptake by any uncoupling action. Sodium uptake from 0.5 or 10 mM NaCl solutions by root tipswas inhibited by 10^–7 M cycloheximide to twice the extentthat it was in the elongating region of the root. Assuming thatthe inhibitor affects the plasmalemma more than the tonoplast,Epstein's model of parallel operation of system 1 and system2 at the plasmalemma is supported.