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Hormone therapy may protect partnership from problems
Lichens have a remarkable ability to tolerate hostile conditions. Many can withstand extended periods of severe water deficit and then resume normal metabolic activity. However, we actually know relatively little about desiccation tolerance in these fascinating ‘dual organisms’. It has been proposed that lichens that are normally exposed to long periods of desiccation may exhibit constitutive adaptation mechanisms whereas those that grow in mainly moist conditions, subject to briefer periods of drying, may possess inducible tolerance mechanisms. It was one of the latter, Peltigera polydactylon, that was investigated by Beckett et al., Scotsville, South Africa and Kazan, Russia (pp. 109–115). Peltigera polydactylon, a lichen in which the photobiont partner is a cyanobacterium, lives in South African forests, which, although mostly moist, are exposed to regular winter droughts. The authors suggest that in this habitat lichens may experience partial dehydration before the onset of the full drought. They gave P. polydactylon a 3-day partial dehydration followed by 1 day of re-hydration before exposing them to full scale drought for 15 or 30 days. This pre-treatment led to a more rapid recovery of net photosynthesis after 15 days drought (but not after 30 days) compared with control plants. The partial drought pre-treatment could be completely replaced by application of 100 µM ABA under hydrated conditions. This is consistent with ABA in the cyanobacterial photobiont partner being involved in responding to/adaptation to water deficit, as in green plants. However, ABA treatment did not appear to protect chlorophyll fluorescence or photosystem II activity from drought, so the more rapid recovery of net photosynthesis after ABA pre-treatment clearly merits further investigation. The final point to make is that the effects of the partial dehydration or ABA pre-treatments were not shared with the fungal partner: its respiration and heat output were similar in control and in pre-treated samples.
Professor J. A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk
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