Biology Reference
In-Depth Information
products of alginate (a major cell wall component of
L. digitata
and other brown
algae). K
upper et al. (
2001
) also reported that H
2
O
2
concentrations in the range
released by the algae were toxic to pathogenic, alginate-degrading bacteria and,
using histological techniques, demonstrated that the response was primarily con-
fined to the meristoderm. These authors also began to dissect the underlying
physiological mechanisms and showed that at least some of the mechanisms are
likely conserved within the oxidative burst responses of algae, terrestrial plants, and
animals. Kupper et al
.
(
2002
) surveyed 45 species of brown algae from 11 Orders for
constitutive vs. induced production of H
2
O
2
. They reported that oxidative bursts in
response to alginate oligomers were common in sporophytes in the Laminariales and
Desmarestiales but not in their filamentous gametophyte stages. One species
(
Pylaiella littoralis
) from the Ectocarpales had an oxidative burst response but ten
other ectocarpalean species did not. Members of the Fucales had high constitutive
production of H
2
O
2
but most did not produce additional H
2
O
2
in response to alginate
oligomers. K
€
upper et al
.
(
2002
) also reported that axenic sporophytes of
Macrocystis
pyrifera
(Order Laminariales) were rapidly infected by pathogenic bacteria when the
oxidative burst response was blocked with an NAD(P)H oxidase inhibitor but not in
controls, and that when nonaxenic
M. pyrifera
or
L. digitata
sporophytes were
treated with the inhibitor, they were rapidly attacked by their natural bacterial
flora. These authors also demonstrated that the oxidative burst response is important
in resistance of both
M. pyrifera
and
L. digitata
to the pathogenic brown algal
endophytes,
Laminariocolax tomentosoides
and
Laminariocolax macrocystis
,
although the response took 7 days to occur and likely involves elicitation of other
structural or chemical defenses (K
€
€
upper et al
.
2002
).
11.4
Impacts of Close Associations
11.4.1 Community Context
The consequences of epibiotism and endobiosis for the host algae are not necessar-
ily negative, but instead depend on the community context as discussed recently in
Jormalainen and Honkanen (
2008
). Examples of positive effects of epibiont
removal by grazers are numerous and depend strongly of the type of interactions
established among hosts, epibiota, and grazers. In many cases grazers, often
gastropods, can drastically counteract the negative influences of epibiotism.
Epibiota on the host alga may modify the host's susceptibility to herbivores such
that it would decrease or increase susceptibility to herbivores. Wahl and Hay (
1995
)
took the host species as the reference point, and classified epibiosis-caused decreases
in herbivory as “associational resistance” and epibiosis-caused increases in herbivory
as “shared doom.” The same phenomena have also been called “protective coating”
and “co-consumption,” respectively (Karez et al.
2000
). Both these epibiosis-related
modifications of susceptibility to herbivory have been found in macroalgae (critically
reviewed by Jormalainen and Honkanen
2008
).
