The Uptake and Transport of 14C in Cells of Conocephalum conicum L. in Light

Dissolved inorganic ¹⁴carbon, fed to a small portion of thetissue of Conocephalun conicum, travelled along the tissuesfrom cell to cell at rates of about 2.0 to 1.7 µm 5^–1,which is of the same order of magnitude as streaming rates inthese cells. Trans-cellular transport can take place againsta pressure gradient, but pressure gradients of 200 kPa or morein either direction reduced the trans-cellular transport significantlywithout reducing streaming rate and are, therefore, thoughtto have induced ‘valving’ effects at the plasmodesmata.Ammonium ion reduced or inhibited transport without reducingstreaming rates and is, therefore, thought to have inhibitedan active component in the plasmodesmata. Thus the results obtainedfrom tandem cells of Nitella can be transferred to tissues. Key words: Conocephalum, transport, plasmodesmata     

Temperature-dependent changes of electric potential differences on opposite sides of the tepals of Eranthis in relation to thermonastic responses

Electric potential differences (PDs) across the plasma membrane in cells of tepals of Eranthis hyemalis (L.) Salisb. were recorded under a regime in which the temperature was changed rapidly between two levels of approximately 8 and 19°C. The warming of an intact tepal resulted in a transient small increase in the magnitude of PD followed by a substantial long-lasting depolarization. Upon cooling the reverse response occurred: a small transient depolarization was followed by a substantial hyperpolarization. These responses were more pronounced in the epidermis on the abaxial side of the tepal than in that on the adaxial side, indicating an electrophysiological dorsiventrality of the tepals which may be related to thermonastic movements through differential proton secretion on the two sides.     

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