Antioxidants and photoprotection in a lichen as compared with its isolated symbiotic partners

Abstract

Extreme desiccation and irradiation increase the formation of reactive oxygen species in organisms. Lichens are highly resistant to potential damage, but it is not known whether biochemical interaction between their fungal and algal partners is involved in conferring stress tolerance. Here, we show that antioxidant and photoprotective mechanisms in the lichen Cladonia vulcani are more effective by orders of magnitude than those of its isolated partners. When alone, both alga and fungus suffer oxidative damage during desiccation, but in the lichen, each appears to induce up-regulation of protective systems in the other. Without the fungal contact, the alga tolerates only very dim light and its photoprotective system is only partially effective; without the alga, the glutathione-based antioxidant system of the fungus is slow and ineffective. In the lichen, this mutually enhanced resistance to oxidative stress and, in particular, its desiccation tolerance are essential for life above ground. This lifestyle, in turn, increases the chance of dispersal of reproductive propagules and ensures their joint evolutionary success.glutathione ͉ desiccation tolerance ͉ oxidative stress ͉ xanthophyll cycle

Living strategy of cold-adapted fungi with the reference to several representative species

“…The widespread distribution of this life-form in ice-free areas in Antarctica could be favoured by the high frequency of rock-freeze-fracturing phenomena (Cowan and Tow 2004). Remarkably, lichen associations are able to integrate photoprotective systems which provide higher resistance to oxidative damages than alga or fungus alone (Kranner et al 2005). An increase of phenolic compounds content under UV exposition, which may prevent UV penetration into lichen thallus, as well as play a protective role as antioxidants, has also been observed (Buffoni Hall et al 2002).…”

Exploring functional contexts of symbiotic sustain within lichen-associated bacteria by comparative omics

“…This symbiotic design has evolved as a convergence in unrelated fungal lineages (Grube and Hawksworth, 2007;Honegger, 2012). It has been optimized not only for the association with carbon-providing algal photobionts (Kranner et al, 2005), but also for the enrichment of bacterial supporters. Genome sequences of the eukaryotic partners, which are now becoming available (for example, Wang et al, 2014), will further help to address the intricacies of one of the oldest known symbiosis and its interactions with their bacterial helpers.…”

“…Once the symbiotic phenotype is established, lichens may reach indeterminate ages and may even survive even the harshest conditions on earth (Øvstedal and Lewis-Smith, 2001). One reason for the ecological success of this fungal-algal partnership is the mutually enhanced ability to survive oxidative stress by suspended animation and rapid resumption of metabolism under permissive conditions (Kranner et al, 2005). However, additional and hitherto unidentified forces might have helped lichens to adapt to nutrient-poor and hostile habitats with strong fluctuation of abiotic parameters.…”

Habitat stress initiates changes in composition, CO2 gas exchange and C-allocation as life traits in biological soil crusts

“…We suggest these pools to have different functions within the lichendominated BSC. The short-chained sugars and sugar alcohols with low-molecular weight in the alcohol fraction have been assigned to many different roles in terms of stress resistance and survival, desiccation protection (Kranner et al, 2008), freezing protection (Tearle, 1987;Roser et al, 1992) or being antioxidants (Kranner et al, 2005;Green et al, 2011;Figure 4). No such roles have been described for the hot water soluble long-chain carbohydrates and we suggest this pool to be an intermediate storage mainly to support growth but also to sustain the short-chained sugar pool if necessary (absolute transfer rate from one compartment to another is 2.5 Â 10-4/h, Farrar, 1978).…”