Carbonic anhydrase(s) associated with lichens: in vivo activities, possible locations and putative roles.

The activity of the enzyme carbonic anhydrase (CA; E.C. 4.2. 1 . 1) was examined in eight specks of lichen in vivo measurements of 18O exchange from doubly labelled CO2 ( 12C18O18O) to water, with the aim of determining whether this enzyme is present in lichens and if so to what extent it participates in physiological processes. The lichens were chosen to represent different mycobiont (Heterodera, Leptogium, Lobaria, Peltigera, Pseudocyphellaria, Xantoparmelia) and photobiont (Coccomyxa, Dictyochloropsis, Mymecia, Nostoc, Trebouxia) genera as well as varying morphology. All lichens were found to possess considerable activity of CA, which varied by a factor of about four between the species when compared on a chlorophyl basis, arid by a factor of about 10 when related to the weight. Incubation of lichen thalli with ethoxyzolamide (EZA) and acetazolamide (AZA). which inhibit intracellular and extracellular CA respectively, showed that intracellular CA was present in all of the species. Incubation with EZA also resulted in inhibition to photosynthetic CO2 uptake in all species suggesting a role of internal CA in the CO2 acquisition process in all the investigated photobiont genera. A pan of the CA activity was inhibited by AZA in all except two of two four cyanobacterial Nostoc lichens, indicating the possible presence of extracellular forms of CA. This CA also appeared to he involved in the acquisition of CO2 as AZA inhibited photosynthesis CO2 uptake in these lichens. The CA inhibitors also affected CO2 efflux in the dark, i.e. fungal respiration, which was inhibited by both AZA and EZA in six of the species, suggesting that a proportion of the CA activity might be located in the mycobiont. [ABSTRACT FROM AUTHOR]