Asparagine alters action potential parameters in single plant cell

Effect of amino acid L-asparagine on electrical signalling of single Nitellopsis obtusa (Characeaen) cell was investigated using glass-microelectrode technique in current-clamp and voltage-clamp modes. Cell exposure for 30 min to 0.1 mM and 1 mM of asparagine resulted in changes of electrically stimulated action potential (AP) parameters in comparison to standard conditions. Results indicate that asparagine acts in dose-dependent manner: increases AP amplitude by hyperpolarizing AP threshold potential (E_th), prolongs action potential repolarization, increases maximum Cl^- efflux amplitude along with the increase of activation and inactivation durations. Presented findings provide new aspects of exogenous amino acids' effect on plants' electrical signalling with emphasis on separate single plant cell excitability and AP characteristics.

Action potential in charophytes

The plant action potential (AP) has been studied for more than half a century. The experimental system was provided mainly by the large charophyte cells, which allowed insertion of early large electrodes, manipulation of cell compartments, and inside and outside media. These early experiments were inspired by the Hodgkin and Huxley (HH) work on the squid axon and its voltage clamp techniques. Later, the patch clamping technique provided information about the ion transporters underlying the excitation transient. The initial models were also influenced by the HH picture of the animal AP. At the turn of the century, the paradigm of the charophyte AP shifted to include several chemical reactions, second messenger-activated channel, and calcium ion liberation from internal stores. Many aspects of this new model await further clarification. The role of the AP in plant movements, wound signaling, and turgor regulation is now well documented. Involvement in invasion by pathogens, chilling injury, light, and gravity sensing are under investigation.

The characteristics of Ca -activated Cl- channels of the salt-tolerant charophyte Lamprothamnium

The dependence of the Ca++-activated Cl- channels on potential difference (PD) was extracted from current-voltage (I/V) profiles recorded at the time of hypotonic regulation while the large conductance (G) K+ channels were blocked by tetraethylammonium (TEA). The total clamp current (I) was dominated by the Cl- I, i(Cl), with small contribution from the background I (i(background)). The i(Cl) was fitted by the Goldman-Hodgkin-Katz (GHK) model with enhanced PD dependence simulated by Boltzmann probability distributions. The i(background) was modelled by an empirical equation. The i(Cl) responded to PD changes within tens of milliseconds. The G maxima were located between -20 and -150 mV. The Cl- channel number and channel permeability parameter, N(Cl)P(Cl), decreased as a function of time in a hypotonic medium (from 0.45 x 10(-7) to 0.17 x 10(-7) ms(-1) in 19 min), with the positive half activation PD, V50+, shifting from +35 to -65 mV, and the negative half activation PD, V50-, shifting from -134 to -310 mV. The fitted Cl- concentration [Cl-]cyt at the time of hypotonic regulation indicated rapid equalization of vacuolar and cytoplasmic concentrations. Excellent data obtained under similar experimental conditions in a previous study enabled us to infer [Ca++]cyt influences on the Cl- channel characteristics. Thick sulphated polysaccharide mucilage, found on Lamprothamnium cells acclimated to more saline media, eliminated the activation of the i(Cl) at the time of the hypotonic regulation. This effect was reversed by the application of the enzyme heparinase. The characteristics of the i(Cl) were found to be consistent with a component of the excitation Is at the time of the action potential (AP). The short duration of the excitation transients was contrasted with that of the hypotonic regulation. The mechanisms for Cl- channel activation (and hence the Ca++ channel activation) were considered.

The excitability of plant cells: with a special emphasis on characean internodal cells

This review describes the basic principles of electrophysiology using the generation of an action potential in characean internodal cells as a pedagogical tool. Electrophysiology has proven to be a powerful tool in understanding animal physiology and development, yet it has been virtually neglected in the study of plant physiology and development. This review is, in essence, a written account of my personal journey over the past five years to understand the basic principles of electrophysiology so that I can apply them to the study of plant physiology and development. My formal background is in classical botany and cell biology. I have learned electrophysiology by reading many books on physics written for the lay person and by talking informally with many patient biophysicists. I have written this review for the botanist who is unfamiliar with the basics of membrane biology but would like to know that she or he can become familiar with the latest information without much effort. I also wrote it for the neurophysiologist who is proficient in membrane biology but knows little about plant biology (but may want to teach one lecture on "plant action potentials"). And lastly, I wrote this for people interested in the history of science and how the studies of electrical and chemical communication in physiology and development progressed in the botanical and zoological disciplines.