Biology Reference
In-Depth Information
into the medium after elicitation (K
upper et al.
2008
). The simultaneous repression
of the
vBPO1 gene
coding for a vanadium-dependent bromoperoxidase indicates a
tightly coordinated regulation of these two distinct haloperoxidase gene families
(Cosse et al.
2009
). This antagonistic response on transcription level might lead to
the conclusion that oligoguluronate-induced oxidative burst switches the iodine
metabolism on to achieve a more efficient and effective pathogen defence (Cosse
et al.
2009
).
Stress- and defence-related signals might be responsible for communication
between marine macroalgae, e.g., to transmit warning messages to their neighbor-
ing conspecifics, as recently demonstrated for
L. digitata
(Thomas et al.
2011
). It
was shown that elicited sporophytes have a great impact on defence responses to
oligoguluronate in un-elicited neighboring conspecifics. It seems that elicited
sporophytes release signaling agents (of unknown nature so far) into the
surrounding water which are integrated by their neighboring conspecifics. As a
consequence of the perception of the putative waterborne signal,
L. digitata'
s
capacity to detoxify ROS has potentiated: the pattern of oxidative burst and
emission of volatile organic compounds (VOCs) changed as well as genes regulated
in response to oligoguluronate become faster induced. This effect resembles the
priming
in terrestrial plants where species that had been in contact with signals
borne off infested neighbors show earlier and stronger effects in defence response
(Thomas et al.
2011
). The less intense oxidative burst in primed sporophytes
represented by a significantly earlier decrease in H
2
O
2
release after oligoguluronate
elicitation may be attributed to a faster triggering of ROS detoxification processes.
Lower emission of VOCs might also reflect an enhanced ROS detoxification
mechanism. Moreover, the higher and faster elicitation-dependent upregulation of
genes involved in ROS management (
prx
, peroxiredoxin, and
msr
, methionine
sulfoxide reductase) also represents a more efficient antioxidative response early
after elicitation. These responses prepare the primed sporophyte to a better response
to subsequent challenges without directly triggering defence responses (Thomas
et al.
2011
).
In this way, the generation and scavenging of ROS does also play a central role
in biotic interactions, which certainly needs to be explored in much more detail.
€
6.5 Summary
Overall, the formation and effective detoxification of ROS represents a crucial
feature in seaweed responses to the abiotic and biotic environment, and it still
requires more intense research activities. Hitherto, the mechanisms of ROS-
mediated signal transduction pathways in seaweeds are just basically studied. It
should also be emphasized that based on the multitude of chemically mediated
biotic interactions of seaweeds with their environment, the significance of ROS for
grazing and pathogen defences is a challenging but extremely exciting field of
future research. With respect to the importance of the oxygen radical metabolism to
