Electrode insertion generates slow propagating electric potentials in Myriophyllum aquaticum plants.

The insertion of microelectrodes into plants to record electric potentials can generate electric potential responses due to disturbance of plant tissues. Here, the electric potential triggered by Ag/AgCl glass microelectrode insertion into the stele of Myriophyllum aquaticum (parrot feather) plants was recorded. A system potential was triggered upon the electrode insertion and was propagated along the stele of the stem. The microelectrode detected this electric potential that was triggered by its own insertion and the electric potential was identical among the plants assessed. The temporal variation in electric potential registered two prominent peaks at 31.9 ± 1.8 and 17.1 ± 4.3 mV. The electric potential was repolarized after approximately 50-70 min and the stabilized electric potential was 6.5 ± 2.5 mV higher than the initial electric potential of plants. Control experiments conducted using a non-biological spongy rod wetted with distilled water or 1 M KCl confirmed that the peaks were solely due to the electric potential in the stem. These signals can be recognized as system potentials. The systematic EP could develop stimuli responses in distant locations, which is to be tested in further studies.

Oxidative Stress and Antioxidant Responses of Phormidium ambiguum and Microcystis aeruginosa Under Diurnally Varying Light Conditions.

Two harmful cyanobacteria species (Phormidium ambiguum and Microcystis aeruginosa) were exposed to diurnal light-intensity variation to investigate their favorable and stressed phases during a single day. The photosynthetically active radiation (PAR) started at 0 µmol·m-2·s-1 (06:00 h), increased by ~25 µmol·m-2·s-1 or ~50 µmol·m-2·s-1 every 30 min, peaking at 300 µmol·m-2·s-1 or 600 µmol·m-2·s-1 (12:00 h), and then decreased to 0 µmol·m-2·s-1 (by 18:00 h). The H2O2 and antioxidant activities were paralleled to light intensity. Higher H2O2 and antioxidant levels (guaiacol peroxidase, catalase (CAT), and superoxidase dismutase) were observed at 600 µmol·m-2·s-1 rather than at 300 µmol·m-2·s-1. Changes in antioxidant levels under each light condition differed between the species. Significant correlations were observed between antioxidant activities and H2O2 contents for both species, except for the CAT activity of P. ambiguum at 300 µmol·m-2·s-1. Under each of the conditions, both species responded proportionately to oxidative stress. Even under maximum light intensities (300 µmol·m-2·s-1 or 600 µmol·m-2·s-1 PAR intensity), neither species was stressed. Studies using extended exposure durations are warranted to better understand the growth performance and long-term physiological responses of both species.