Transnodal Transport of 14C in Nitella flexilis: III. FURTHER STUDIES ON DISSOLVED INORGANIC CARBON MOVEMENTS IN TANDEM CELLS

Using NaH ¹⁴CO₃ (0.1 to 3.0 mol m ^–3) fed to 5.0 mm ofan internodal cell of Nitella flexilis in artificial pond waterat pH 6.8 and 19–25 °C, we have found that the carbohydrates(lactose, xylose, mannose, galactoseand sucrose) are formedby photo-assimilation from ¹⁴C-DIC (dissolved organic carbon)in 1 h and are carried in the cytoplasm with amino acids (glutamineand alanine in particular) to the node attached to a tandeminternodal cell. These small sacchandes and some amino acidspassed, apparently unchanged, across the node into the sinkcell. Influx of DIC was highly sensitive to inhibitors of photosystemsI and II (at concentrations around 1.0 mol m^–3) and touncouplers of phosphorylation. Most influx inhibitors, exceptfor NaN₃, also reduced % transnodal transport. NH₄⁺ (1.0 to5.0 mol m^–3) appeared to reduce % transport in light (butnot in dark) with much less effect on influx. Dinitrophenoland Na citrate (at pH 8.2) also strongly reduced apparent %transport without altering cytoplasmic streaming rates. Someof the apparent reduction of transport could be due to an alterationof metabolism or of sequestering in the feed cell, but withNH₄⁺ the latter was not detectable. Our findings support thehypothesis that transnodal transport, including that via theplasmodesmata, is at least partly ‘active’ and requiresmetabolic energy to sustain it. Key words: Inhibitors, influx, plasmodesmata, nodal transport, ¹⁴C, ³⁶Cl