Dehydration rate and time of desiccation affect recovery of the lichenic algae Trebouxia erici: alternative and classical protective mechanisms

Abstract

The mechanisms involved in desiccation tolerance of lichens and their photobionts are still poorly understood. To better understand these mechanisms we have studied dehydration rate and desiccation time in Trebouxia, the most abundant chlorophytic photobiont in lichen. Our findings indicate that the drying rate has a profound effect on the recovery of photosynthetic activity of algae after rehydration, greater than the effects of desiccation duration. The basal fluorescence (F'(o)) values in desiccated algae were significantly higher after rapid dehydration, than after slow dehydration, suggesting higher levels of light energy dissipation in slow-dried algae. Higher values of PSII electron transport were recovered after rehydration of slow-dried Trebouxia erici compared to rapid-dried algae. The main component of non-photochemical quenching after slow dehydration was energy dependent (q (E)), whereas after fast dehydration it was photoinhibition (q (I)). Although q (E) seems to play a role during desiccation recovery, no significant variations were detected in the xanthophyll cycle components. Desiccation did not affect PSI functionality. Classical antioxidant activities like superoxide dismutase or peroxidase decreased during desiccation and early recovery. Dehydrins were detected in the lichen-forming algae T. erici and were constitutively expressed. There is probably a minimal period required to develop strategies which will facilitate transition to the desiccated state in this algae. In this process, the xanthophyll cycle and classical antioxidant mechanisms play a very limited role, if any. However, our results indicate that there is an alternative mechanism of light energy dissipation during desiccation, where activation is dependent on a sufficiently slow dehydration rate.

Unravelling the roles of desiccation-induced xanthophyll cycle activity in darkness: a case study in Lobaria pulmonaria

“…This may explain the apparent contradiction with previous studies with L. pulmonaria (Heber et al 2010), in which Z decreased when thalli were desiccated in darkness. The paramount importance of the drying rate in the engagement of photoprotection mechanisms and in the recovery of photosynthetic function after dehydration has been highlighted in the lichenic algae Trebouxia erici (Gasulla et al 2009). In fact, cellular mechanisms involved both in desiccation resistance and in recovery capacity after rewatering need a minimum time to be triggered (Cooper and Farrant 2002).…”

“…On one hand, it is implicated in the modulation of the rate of thermal energy dissipation Adams 1996, 2006) and, on the other hand, contributes to enhance antioxidative protection (Havaux and Niyogi 1999) and/or to membrane stabilisation (Havaux 1998). Since L. pulmonaria is a homoiochlorophyllous desiccation-tolerant lichen and chlorophyll molecules may represent a source of singlet oxygen during the dry state, the formation of Z in darkness could have an adaptive meaning as a photoprotective mechanism essential to avoid oxidative damage (Kranner and Birtic 2005), not only during desiccation but also during rewatering (Minibayeva and Beckett 2001;Gasulla et al 2009). However, the formation of Z reported in the present study could be simply the result of the unavoidable structural changes of thylakoid membranes during the last steps of dehydration, which generate lipid hexagonal structures favouring the access of VDE to its substrate (Latowski et al 2004).…”

Preliminary assessment of terrestrial microalgae isolated from lichens as testing species for environmental monitoring: Lichen phycobionts present high sensitivity to environmental micropollutants

“…These algae have features such as the possibility to obtain large quantities at low economic costs and tolerance to a wide range of operating temperatures (Gasulla et al, 2010). In addition unlike free-living algae have high tolerance to desiccation (high tolerance to hydric stress) (Gasulla et al, 2009(Gasulla et al, , 2013, qualities that free-living algae do not possess.…”

The organic air pollutant cumene hydroperoxide interferes with NO antioxidant role in rehydrating lichen

“…Lichens possess important antioxidant systems and a strong relation of glutathione with desiccation tolerance has been demonstrated (Kranner, 2002). However, this relation has not been found for other classical mechanisms and the role of nonclassical still remains to be elucidated (Gasulla et al, 2009). As a matter of fact, the lichen cell biology and the physiology of symbiosis remain mostly undeciphered.…”