科研之友
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摘要
In this work, for the first time the activity of nitrate-permeable channels in the tonoplast of the moss Physcomitrella patens was recorded. The channels allowed nitrate flow in one direction-from the cytoplasm to the vacuole. Selectivity of nitrate over chloride of the channels was proved. The activity of the channels was dependent on cytoplasmic calcium, magnesium, and pH. A patch-clamp study carried out on the vacuolar membrane of the moss Physcomitrella patens has revealed that inhibition of cation-selective channels leads to disclosure of channels permeable to NO3 (-). These channels were inwardly rectifying and allowed anions to flow from the cytoplasm to the vacuole. After a decrease in the cytoplasmic NO3 (-) concentration, the current density recorded in the whole-vacuole configuration and amplitude of the currents flowing through single channels were reduced. Application of the NO3 (-) gradient caused a shift in the reversal potential (E-rev) towards ENO3-, indicating NO3 (-) permeability. Research of the selectivity of the channels to Cl- and NO3 (-) was also done; it indicated that Cl- is less permeable than NO3 (-) (P-NO3/P-Cl = 3.08). Measurements with different concentrations of cytoplasmic Ca2+ and Mg2+ revealed that the channel was activated by different concentrations of these ions-100 A mu M Ca2+ and 10 mM Mg2+. Calcium dependence of the channels was also modulated by a redox agent-DTT (dithiothreitol), which added on the cytoplasmic side, caused a reduction in the threshold of channel activation with cytoplasmic Ca2+. The NO3 (-) permeable channel was also pH dependent. A decrease in the cytoplasmic pH reduced the open probability of the channel; in turn, an increase in the vacuolar pH did not decrease ion channel activity but lowered its conductance.
- 出版日期2015-5
