Environmental Engineering Reference
In-Depth Information
having a direct effect on membranes structure. Also, the generation of lipid
peroxy radicals can induce further damage by participating in free radical
cascades (Murphy 1983).
The effects of UV-exposure in seaweeds are multiple, including a
decrease in the CO
2
-fi xation rate, oxygen evolution (Allen et al. 1997, Vass
1997), and photosynthesis activity due to the photodestruction of pigments
(Bischof et al. 2002, Poppe et al. 2003). Also, the UV-B induces a decline in the
Rubisco activity, which is related to the decreasing amount of its subunits as
well as the corresponding mRNA levels (Bischof et al. 2000, 2002). Another
effect of UV-B is the inactivation of the chloroplastic ATPase. Effects have
also been observed on the ultrastructural level, producing changes of the
fi ne structure of thylakoids and mitochondria (Holzinger et al. 2004).
Mechanisms to mitigate the UV radiation effects
Adaptation to UV radiation has equipped macroalgae with defensive
mechanisms to minimize UV-induced damages. Seaweeds are able to protect
themselves via avoidance, repair, and screening mechanisms (Karentz 2001).
An important mechanism to reduce the damaging impact of UV radiation
is the synthesis and accumulation of UV-absorbing compounds (UVAC).
These compounds as mycosporine-like amino acids (MAAs), scytonemin,
and phlorotannins have been found in many photosynthetic organisms.
They function as passive shielding solutes by dissipating the absorbed
short wavelength radiation energy in form of harmless heat generating
photochemical reactions (Bandaranayake 1998). Synthesis of UVAC has been
induced by UV-B in
Chondrus crispus
(Karsten et al. 1998),
Porphyra columbina
(Korbee-Peinado et al. 2004), and
Ulva pertusa
(Han and Han 2005). MAA
compounds also have other ecophysiological functions such as protectors
against desiccation or osmotic regulators, antioxidants, accessory pigments
(biosynthesis of several carotenoids) (Korbee et al. 2006), and intracellular
nitrogen storage (Korbee-Peinado et al. 2004, Korbee et al. 2006). De la
Coba et al. (2009) reported the potential antioxidant capabilities of purifi ed
aqueous extracts of the MAAs isolated from
Porphyra rosengurttii
,
Gelidium
corneum
and
Ahnfeltiopsis devoniensis
.
Supra-and eulittoral Antarctic species experience the strongest solar
radiation and synthesize and accumulate very high MAA contents, which
are positively correlated with the natural UV doses (Huovinen et al. 2004)
or affected by osmotic stress (Klisch et al. 2002) and/or nutrient availability
(Zheng and Gao 2009). Red algae have the highest percentage of species
that synthesize MAAs (Huovinen et al. 2004), followed by brown and green
algae.
Porphyra
contain high levels of MAAs, being up to 1% of their dry
weight (Hoyer et al. 2001).
The function of MAAs as intracellular screening agents has been
inferred from a decrease in their intracellular concentration with increasing
