Resilience of Xanthoria parietina under Mars-like conditions: photosynthesis and oxidative stress response

Ionizing radiation resilience: how metabolically active lichens endure exposure to the simulated Mars atmosphere

To deepen our understanding of lichen adaptation and their potential to colonize extraterrestrial environments, we aimed to identify physiological/biochemical responses of selected lichen species in a metabolically active state to simulated Mars-like conditions in the dark including exposure to X-rays. Our study is the first to demonstrate that the metabolism of the fungal partner in lichen symbiosis was active while being in a Mars-like environment. Diploschistesmuscorum was able to activate defense mechanisms effectively. In contrast, increased oxidative stress and associated damage were not effectively balanced in C.aculeata, which does not support the melanin's radioprotective function in this species. The heavy crystalline deposit on D.muscorum thallus might offer protection enhancing lichen resistance to extreme conditions. We concluded that metabolically active D.muscorum can withstand the X-ray dose expected on the Mars surface over one year of strong solar activity. Consequently, X-rays associated with solar flares and SEPs reaching Mars should not affect the potential habitability of lichens on this planet.

Decoding the physicochemical basis of resurrection: the journey of lichen Flavoparmelia caperata through prolonged water scarcity to full rehydration

Desiccation tolerance is a complex phenomenon observed in the lichen Flavoparmelia ceparata. To understand the reactivation process of desiccated thalli, completely dried samples were rehydrated. The rehydration process of this lichen occurs in two phases. The first phase, characterized by rapid rehydration, involves the conversion of non-functional reaction centers (RCs) into functional PSII RCs, and the accumulation of ROS along with the increment in SOD antioxidant enzyme. These coordinated mechanisms initiate the light reaction of photosynthesis by forming active light-harvesting complexes (LHCs). This adaptation ensures efficient recovery, as evidenced by specific energy fluxes (ABS/RC, TR/RC, ET/RC, and DI/RC), phenomenological fluxes (ABS/CS, TR/CS, ET/CS, and DI/CS), quantum efficiencies (ФP0, ФE0, and ФD0), primary and secondary photochemistry, photochemical and non-photochemical quenching, and performance index, highlighting the essential role of rapid water uptake in restoring turgor pressure for cell structure and function maintenance. The interconnected network of antioxidant defenses, including catalase (CAT) and peroxidase (POD), underscores the plant's ability to cope with oxidative stress during resilience. The acid phosphomonoesterase (PME) enzymatic activity corresponds to its role in releasing phosphate for essential cellular functions and post-rehydration thallus growth. The activity of CAT, GPOD, and PME signifies the gradual reactivation of lichen F. caperata. Moreover, the investigation into chlorophyll a fluorescence emphasizes the efficient reactivation of the photosynthetic process in F. caperata. In conclusion, lichen F. caperata demonstrates significant potential for desiccation tolerance through the rapid transformation of chloroplasts, chlorophylls, and PSII RCs from their inactive to active states upon rehydration. This research not only enhances our understanding of desiccation tolerance in resurrection plants but also highlights the importance of lichens, particularly F. caperata, as valuable models for studying plant resilience in challenging environments.