UV-B affects photosynthesis, ROS production and motility of the freshwater flagellate, Euglena agilis Carter

Abstract

The effects of ultraviolet B (UV-B; 295-320 nm) radiation on certain vital physiological (photosynthesis), biochemical (production of reactive oxygen species - ROS) and behavioral (motility and orientation) characteristics were investigated in the unicellular photoautotroph, Euglena agilis Carter. The photosynthetic performance of E. agilis was recorded after exposure of between 15 and 60 min followed by a period of recovery lasting 6-24h under dim light (5-10 μmol photons m(-2) s(-1)). The maximum quantum yield of PS II (F(v)/F(m)) was reduced to 65% and 14% of initial values immediately following 15 and 30 min UV-B exposure, but recovered to 100 and 86% of the initials, respectively. Values of rETR(max) in E. agilis exposed to 15 min UV-B were similar to those of the initials, but a 30 min UV exposure resulted in 75% reduction of rETR(max) with only a 43% recovery as compared with the initial after 24h recovery. After a 60 min UV-B exposure, there were no Chl a fluorescence signals, and hence no F(v)/F(m) or rETR(max). A UV dose-dependent increase in DCFH-DA fluorescence was found in E. agilis cells, reflecting an increase in ROS production. After exposures to UV-B for between 15 and 60 min, the percentages of motile cells in the population decreased to 76, 39 and 15%, respectively. Following 24h in dim light, the percentage of motile cells increased to between 66% and 95% of the initial value. The velocity of non-irradiated cells was 60 μm s(-1), which decreased to 16-35 μm s(-1) immediately following exposure for 15-60 min. After periods of time in dim light (6, 12 and 24h) velocities had recovered to between 44 and 81% of the initial value. In untreated controls, the r-value was 0.23, indicating random movement of E. agilis, but it increased to 0.35 and 0.72 after exposure to UV-B for 30 and 60 min, respectively. There was a tendency towards vertical downward movement of cells proportional to the duration of exposure. The compactness of E. agilis decreased from 2.9 in controls to 1.8-2.3 in cells treated with UV-B although significant recovery followed. UV-B dose-dependent interaction between photosynthetic activity, ROS production and movement is discussed in terms of a UV-protective mechanism in E. agilis.

A novel Omega-class glutathione S-transferase gene in Apis cerana cerana: molecular characterisation of GSTO2 and its protective effects in oxidative stress

“…In this study, several antioxidant response elements, such as HSF and AP-1, were predicted in the 5′-flanking region of AccGSTO2. Furthermore, the qPCR analysis revealed that AccGSTO2 was induced by all abiotic stressors examined, such as temperature, H 2 O 2 , insecticides and UV radiation can induce oxidative stress (Lushchak 2011;Kottuparambil et al 2012). Consistent with these results, GSTO from Bombyx mori is activated by a variety of environmental stimuli, including bacteria, ultraviolet-B (UV-B) and three commonly used chemical insecticides (Yamamoto et al 2011).…”

Effects of salinity on the physiology of the red macroalga, Acanthophora spicifera (Rhodophyta, Ceramiales)

“…Carotenoids, phenols and flavonoids are part of the secondary metabolism of red algae and serve as antioxidants (Zeng et al 2001;Apel & Hirt 2004;Ganesan et al 2008;Kottuparambil et al 2012). All three metabolites were in higher concentrations in the samples treated with 50 psu, but lower concentrations in those treated with 30 psu, the latter repeating the pattern and motif found with phycobiliproteins.…”

Identification, genomic organization, and oxidative stress response of a sigma class glutathione S-transferase gene (AccGSTS1) in the honey bee, Apis cerana cerana

“…In D. melanogaster, the sole sigma class GST plays a dominant protective role against oxidative damage (Singh et al 2001; Alias and Induction of AccGSTS1 after exposure to various environmental stresses GSTs are known to be an important component of the oxidative stress response. Previous studies have indicated that environmental conditions such as temperature, heavy metals, salinity, pesticides, and UV radiation can induce oxidative stress (Lushchak 2011;Kottuparambila et al 2012). To elucidate the potential involvement of AccGSTS1 in antioxidant defense, transcripts of AccGSTS1 under cold (4°C), heat (43°C), H 2 O 2 , HgCl 2 , and insecticide (phoxim, cyhalothrin, and acaricide) exposure were examined by qPCR (Fig.…”