Photo-oxidation modulates green fern spore longevity during dry storage

Desiccation tolerance and longevity of plant propagules in the dry state have significant implications for biotechnological applications. In this study fern spores were used as a unicellular model to characterize some of the mechanisms of ageing during dry storage of plant propagules (at relative humidity ca. 15%). More specifically, we compared the potential relationships among indicators of photo-oxidative stress and spore viability during dry storage between green (chlorophyllous) spores of Todea barbara and non-green spores of Christella dentata. Green spores stored under the light aged faster than those stored in the dark, and faster than light- and dark-stored non-green spores of C. dentata. This rapid ageing in light-stored green spores was associated with significantly lower antioxidant activity (relative to time zero and dark-stored spores) during storage, and a burst of hydrogen peroxide during the latter stages of storage, which was not a feature of dark-stored spores. We attribute these signs of enhanced oxidative-stress mediated ageing in light-stored spores to photo-oxidative processes, similar to those described in other homoiochlorophyllous organisms. Additionally, high antioxidant activity and low levels of reactive oxygen species in green spores compared with non-green spores suggests differing mechanisms of coping with life in the dry state.