Print PageHabitat transitions from water to land were key steps in the evolution and diversification of advanced life on Earth. Desiccation encountered on land particularly threatens photosynthetic organisms. Light absorption by photosynthetic pigments can cause photooxidative stress and damage to the photosynthetic apparatus, particularly when temperature and moisture are limiting. We are examining photosynthetic activity and photoprotection under desiccation and rehydration stress in multiple, independent lineages of desert green algae and their close aquatic relatives. Recently, a remarkably efficient “quencher” (energy-absorber) was identified in the literature as photoprotective in several desiccation-tolerant lichens and mosses.
Results/Conclusions
We have found that in several free-living desert algae, the chlorophyll (Chl) fluorescence emission spectrum measured at liquid nitrogen temperatures (77K), and room-temperature chlorophyll fluorescence during desiccation and rehydration, exhibit patterns similar to those associated with this recently identified quencher. Specifically, at room temperature, slow desiccation of a desert-derived Chlorella sp. (class Trebouxiophyceae) and a desert-derived Klebsormidium sp. (class Klebsormidiophyceae) over several hours results in declines in both variable (Fv) and basal Chl fluorescence (Fo’), and rehydration results in Fo’ recovering faster than Fv. Also, a blue-shift in the wavelength of peak Chl fluorescence emission is observed in desert vs.sister aquatic algae at 77K, in multiple green algal classes, along with an enigmatic 760nm bump in the emission spectrum that is reminiscent of spectral features in some lichens. These data from free-living green algae, combined with data from desiccation-tolerant chloro-lichens and mosses in the literature, suggest that the novel, desiccation-induced quencher first detected in chloro-lichens may be widely shared among terrestrial organisms in the broad green plant clade.
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