Accumulation of trehalose in response to desiccation and salt stress in the terrestrial cyanobacterium Nostoc commune

Changes in photosynthetic activity and trehalose levels in field-isolated, natural colonies of the terrestrial cyanobacterium Nostoc commune responding to desiccation and salt stress were investigated. As the water content decreased in N. commune colonies during desiccation, photosynthetic O-2-evolving activity decreased and no activity was detected in desiccated colonies. A high level of O-2 evolution was restored in the colonies as they absorbed atmospheric moisture, indicating that only a small amount of water is required for reactivation of photosynthesis. No detectable trehalose was found in fully hydrated N. commune colonies; however, trehalose accumulation occurred in response to water loss during desiccation and high levels of trehalose were detected in the air-dried colonies. Moreover, a 0.2 M NaCl treatment also induced trehalose accumulation to a level equivalent to that by desiccation. Photosynthetic O-2 evolution was inhibited by 0.2 M NaCl, indicating that N. commune can tolerate only low levels of salt. These results suggest that cessation of photosynthesis and trehalose accumulation occur in response to both matric water stress (desiccation) and osmotic water stress (high salt concentration), and that while trehalose may be a less effective osmoprotective compound than others, it is important for the extreme tolerance to desiccation observed in terrestrial cyanobacterium.