Salinity-Induced Noise in Membrane Potential of Characeae Chara australis: Effect of Exogenous Melatonin

Abstract

Salt sensitive Characeae Chara australis responds to 50 mM NaCl by a prompt appearance of noise in the trans-membrane potential difference (PD). The noise diminishes with time in saline and PD depolarization, leading to altered current-voltage characteristics that could be modeled with H(+)/OH(-) channels. Beilby and Al Khazaaly (JMB 230:21-34, 2009) suggested that the noise might arise from cooperative transient opening of H(+)/OH(-) channels. Presoaking cells in 10 μM melatonin over 24 h abolished the noise in some cells, postponed its appearance in others or changed its characteristics. As melatonin is a very effective antioxidant, we postulated opening of H(+)/OH(-) channels by reactive oxygen species (ROS). Measurement of ROS using dihydrodichlorofluorescein diacetate confirmed substantial reduction in ROS production in melatonin-treated cells in saline and sorbitol media. However, ROS concentration decreased as a function of time in saline medium. Possible schemes for activation of H(+)/OH(-) channels under salinity stress are considered.

A new balancing act: The many roles of melatonin and serotonin in plant growth and development

“…To date ROS have been implicated in a multitude of physiological responses such as pathogen attack, herbivory and wounding, and UV exposure as well as playing a role in seed dormancy, and plant growth and development [147][148][149][150][151][152] . In these responses, ROS interact with phytohormone networks and other signaling cascades including calcium, protein phosphorylation and nitric oxide cascades, as well as modifying transcriptional regulation 147,148,153,154 Additionally, work in an ancestral relative of land plant, Chara australis, has found a direct interaction between MEL application and reduced production of ROS species at the cellular level by using fluorescent probes and examining trans-membrane potential differences; these findings have suggested that the natural circadian rhythms of these compounds produced in Chara species may help to regulate ROS levels 124,155 .…”

Salt tolerance at single cell level in giant-celled Characeae

“…(A) Transition from Sorbitol APW (red) to 50 mM NaCl saline APW (blue) resulted in depolarization and noisy membrane PD. There was no AP, but the resting PD measurement was disrupted by medium change and exhibited spikes between 6800 and 6900 s. (B) Using the same trace on expanded time scale, the higher frequency noise was isolated by subtracting the running average (fitted with n = 100): noise in sorbitol APW (red) and saline-induced noise (blue) that started promptly after ∼50 s of the medium change (data from Beilby et al, 2014). (C) Spontaneous and repetitive APs after ∼80 min of Saline APW (Shepherd et al, 2008).…”

“…In the animal kingdom, the voltage-gated H + channels in the brain microglia are activated by H 2 O 2 (Wu, 2014). Beilby et al (2014) were able to inhibit or postpone the saline-induced noise by presoaking the Chara cells in strong antioxidant melatonin prior to saline stress. Therefore, H + /OH - channels may be activated by an oxidative burst upon exposure to saline.…”

“…With longer exposure to high salinity, the membrane PD of Chara cells continues to depolarize toward zero, while the noise diminishes (suggesting that progressively larger numbers of H + /OH - channels were activated – Beilby et al, 2014). The shape of the I/V characteristics changes and could be simulated by H + /OH - channels and increased background current (see Figure 8 and Beilby and Al Khazaaly, 2009).…”

Rhythms in Plants

“…While there is always some noise in the membrane PD, the degree of "noisiness" was quantified by fitting a running average (n set between 50 and 200), which was then subtracted (Fig. 13.5b, Beilby et al 2014). The classical Fourier analysis identified this increased noise as "red" noise.…”