Salinity-Induced Noise in Membrane Potential of Characeae
Chara australis: Effect of Exogenous Melatonin
Mary J. Beilby
Sabah Al Khazaaly
Mary A. Bisson
Received: 10 July 2014 / Accepted: 23 October 2014 / Published online: 7 November 2014
Ó Springer Science+Business Media New York 2014
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
channels. Beilby and Al
Khazaaly (JMB 230:21–34, 2009) suggested that the noise
might arise from cooperative transient opening of H
channels. Presoaking cells in 10 lM 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
channels by reactive oxygen species (ROS). Mea-
surement of ROS using dihydrodichloroﬂuorescein diace-
tate 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
channels under salinity stress are considered.
Keywords Chara Á Saline-induced noise Á Salinity stress Á
channels Á Reactive oxygen species
Melatonin is a powerful antioxidant of ancient origin,
probably introduced into plant and animal kingdoms by
cyanobacteria (that became chloroplasts) and purple non-
sulfur bacteria (that became mitochondria—Tan et al.
2013). Since 1950s melatonin became generally known for
its role in circadian rhythms in animals including humans
(Brzezinski 1997). Dubbels et al. (1995) and Hattori et al.
(1995) focused attention on plant endogenous melatonin by
surveying its content in common fruits and vegetables.
Murch et al. (1997) measured melatonin in growing plants
and Murch et al. (2000) described a putative pathway for
melatonin synthesis in plants. Melatonin and the related
metabolite serotonin are derived from tryptophan and
indole-3-acetic acid (IAA). The structural similarities of
melatonin and serotonin molecules to that of IAA suggest a
role for these substances in growth and development
(Murch et al. 2001; Murch and Saxena 2002; Murch et al.
2009, 2010; Pelagio-Flores et al. 2012; Tan et al. 2012).
The possible involvement of melatonin in plant circadian
rhythms is also under investigation (Poggeler et al. 2001;
Van Tassel et al. 2001; Wolf et al. 2001; Tan et al. 2007a;
Boccalandro et al. 2011).
Our experimental organisms, the Characeae, are closely
related to ancestors of all land plants (McCourt et al. 2004;
Wodniok et al. 2011; Timme et al. 2012) and have already
been used to establish the fundamentals of plant cell electro-
physiology (Hope and Walker 1975; Beilby and Casanova
2013) and cytoplasmic streaming (Shimmen 2007). The large
cells of the Characeae allow experiments at single cell level,
with minimal disturbance to the cell structure. Salt sensitive
Characeae Chara australis produces endogenous melatonin in
similar amounts to leaf and shoot portions of higher plants,
such as medicinal herb St. John’s wort (Murch et al. 2000).
M. J. Beilby (&) Á S. Al Khazaaly
School of Physics, University of NSW, Kensington 2052,
Sydney, NSW, Australia
M. A. Bisson
Department of Biological Sciences, University at Buffalo,
Buffalo, NY 14260, USA
J Membrane Biol (2015) 248:93–102