Biology Reference
In-Depth Information
Different efficiencies of buffering oxidative stress-induced by copper excess
(20-100 g L
1
) might play a crucial role for the absence of the copper-sensitive
L. nigrescens
and the presence of the copper-tolerant
S. lomentaria
in copper-
enriched coastal areas in Chile (Contreras et al.
2009
). H
2
O
2
formed right after
copper stress was completely scavenged in both species but much slower in
L. nigrescens
than in
S. lomentaria
. Additionally, lipoperoxide production detected
in both species over a 96 h period might be a result from the activation of a
lipoxygenase (LOX) that only uses arachidonic acid as substrate. Both species
show different responses to copper excess. A stable lipoperoxide production in
S.
lomentaria
which was reached early after exposure to copper excess could be
ascribed to the constant LOX activity as well as to an efficient ROS scavenging
by increased activities of APX and GPX. These enzymatic responses seem to be
crucial for macroalgal survival since potentially toxic peroxides are converted into
nontoxic compounds. In contrast, continuously increasing accumulation of
lipoperoxides in
L. nigrescens
over the entire period might be a consequence of
the biphasic boosts in LOX activity. Additionally, inactivation of GPX and APX
possibly due to direct inhibition by copper might be a reason for a further accumu-
lation of fatty acid hydroperoxides and H
2
O
2
at high copper concentrations.
Impaired detoxification may trigger the production of the highly reactive, short-
chain aldehydes such as 4-hydroxy-2(E)-nonenal (HNE) which are cytotoxic,
genotoxic, and mutagenic due to its electrophilic properties (Gu
ยด
raud et al.
2010
).
Dysfunctions of proteins and destruction/changes in the fine structures of
mitochondria and chloroplasts in
L. nigrescens
are a consequence of the accumula-
tion of lipoperoxides. Thus, an efficient detoxifying mechanism seems to be crucial
for survival of macroalgae in copper-impacted habitats.
6.2.2 A Peculiar Antioxidant System in Kelp
An unusual antioxidant system that is based on the enzymatic oxidation of
accumulated iodide (I
-
) has been recently described to be present in the sporophytes
of the kelp
L. digitata
(Kupper et al.
2008
). Two types of vanadium-dependent
haloperoxidases (vHPOs) can be found in this life stage to mediate the oxidation of
halides (X
-
) under consumption of H
2
O
2
to hypohalous acids (HXO), which may
subsequently react to form iodocarbons such as polyhalomethans (CH
2
I
2
):
Bromoperoxidases
Br
-
+H
2
O
2
!
HBrO + OH
and
I
-
+H
2
O
2
!
HIO + OH
Iodoperoxidase
HIO + OH
I
-
+H
2
O
2
!
Although multimeric aggregates of several bromoperoxidases (vBrPOs) oxidize
both iodide (I
-
) and bromide (Br
-
) ions, these enzymes are not involved in the
