Viability of dried cells, and survivability and reproduction under water stress, low light, heat, and UV exposure in Chlorella vulgaris

Dried Chlorella vulgaris Beyerinck cells were 100% viable when stored in desiccators over fused CaCl2 for 2 days either in light or dark, but the viability decreased to 1% after 30 days at 20 degreesC in light. Neither dried nor wet cells remained viable after 10 days at 0 degreesC in dark. Tolerance of C. vulgaris cells to dry storage might be due either to their unicellular nature or to the chemical composition of cell wall containing sporopollenin. Osmotic regulation did not seem to occur, as the alga was salt-sensitive. Autospores or young vegetative cells were more sensitive than autospore mother cells to both physical and physiological water stress, imposed respectively by growing them on media with a high agar content or in salinized liquid media. The rupture of autospore mother cells and release of autospores did not occur even in 100 mM NaCl. The vegetative cells remained viable in darkness at 22 +/- 1 degreesC for 45 days, but the formation of autospore mother cells required light intensities of more than 10 mu mol m(-2) s(-1). The vegetative cells were sensitive to heat or UV.