Nanocellulose enhances the dispersion and toxicity of ZnO NPs to green algae Eremosphaera viridis

The widespread cellulose nanomaterials from industrial production and natural plant degradation inevitably lead to the accumulation of nanocellulose in aquatic environment. However, the effect of nanocellulose on the fate, transport...

Light-triggered action potentials in plants

Special attention is paid in this paper to the criteria of the light-triggered action potential, namely the all-or-none law, propagation, the occurrence of refractory periods. Such action potentials have been recorded in <em>Acetabularia mediterranea, Asplenium trichomanes, Bryum pseudotriquetrum, Eremosphaera viridis </em>and <em>Concephalum conicum. </em>In <em>Acetabularia, </em>action potentials are generated after sudden cessation of light stimuli of sufficient intensity. The depolarization phase of the action potential develops as a result of a transient reversal of the action of the electrogenic Cl- pump. This is a principle of the "metabolic" action potential hypothesis proposed by Gradmann. In the gametophytes of <em>Aspleniam trichoma­nes </em>and <em>Bryum pseudo triquetrum, </em>action potentials are triggered on illumination. Gutation starts 1.5-2 seconds after the passage of an action potential. The active water secretion facilitates fertilization. In the unicellular fresh water alga, <em>Eremosphaera viridis, </em>action potential-like responses are evoked after light termination. The process responsible for its appearance is the opening of potassium channels in the plasmalemma. The liverwort, <em>Conocephalum conicum, </em>generates action potentials in response to light, electrical, chemical and mechanical stimuli. Calcium and potassium channels as well as proton pumps are involved in electrogenesis of action impulses in the species. Excitation causes a significant increase in the respiration rate. The role of action impluses as mediators in a system of a metabolism control is discussed.

Evidence for active CO2 uptake by a CO2-ATPase in the acidophilic green alga Eremosphaera viridis

We examined the mechanism(s) responsible for active uptake of dissolved inorganic carbon (DIC) during photosynthesis in the green alga Eremosphaera viridis De Bary. O2 electrode measurements of algal oxygen evolution and CO2 fluxes as a function of DIC availability indicate that E. viridis actively imports only CO2 during photosynthesis, and does not possess external carbonic anhydrase (CA). The K0.5[CO2] was 14.2 and 10.1 µM at pH 5.0 and 8.0, respectively. Both membrane potential and cellular resistance were measured under controlled conditions of [CO2] at either 2 or 15 µM. Active CO2 uptake was electrically silent, suggesting that CO2 uptake might be mediated by a CO2-ATPase. Comparison of ATPase activity in microsomal preparations at low (0 µM) and high (15 µM) [CO2] indicated a 1.25-fold increase in ATP hydrolysis in high [CO2]. The CO2-ATPase activity was inhibited by the broad-acting inhibitors diethylstilbestrol (DES) and N',N'-dicyclohexylcarbodiimide (DCCD) but unaffected by vanadate, fluoride, and nitrate. The K0.5[CO2] of the ATPase activity was 22.5 µM, a value very similar to the K0.5[CO2] for CO2 uptake by whole algal cells. These results suggest the existence of a CO2-ATPase as the major importer of DIC for photosynthesis in the microalga E. viridis.Key words: chlorophyte, CO2 transport, CO2-ATPase, photosynthesis, electrical potential, mass spectrometry.

CO2 uptake mechanism in Eremosphaera viridis

Electrophysiological measurements of the acidophilic alga Eremosphaera viridis De Bary explored the effects of low CO2 levels on both membrane potential and resistance. This procedure incorporates a double-barreled microelectrode and suction pipette system, coupled with an approximately CO2-free environment. A key requirement is an artificial pond water perfusion media that has been purged of dissolved inorganic carbon by being boiled and bubbled with nitrogen gas. Both membrane potential and resistance were measured at pH5 in both low-CO2 conditions (2µM) and high-CO2 conditions (14µM) in both light, where CO2 transport is known to be active, and dark, where CO2 transport is not active. To avoid dissolved inorganic carbon contamination of the perfusion media, a special chamber was constructed, featuring a laminar flow of nitrogen gas over the solution, which allowed for the manipulation of cells while preventing any contamination by CO2 from the air. Results indicate that the uptake of CO2 by the alga is electrically silent and, therefore, not the result of a symport or antiport cotransport system that would "drive" CO2 uptake by coupling it to the electrochemical gradient of ions such as protons or sodium. The uptake is most likely facilitated by a transporter directly coupled with ATP hydrolysis.Key words: Eremosphaera viridis, dissolved inorganic carbon, CO2-ATPase, electrophysiology.