Abstract
BackgroundTo find out how algal cells cope with and recover from heat stress, the small vegetative cells of the synchronous Scenedesmus vacuolatus culture were subjected to a heat pretreatment (46.5°C for 1 h) followed by dark recultivation. The changes in physiological activities and morphology of Scenedesmus cells were continuously monitored throughout the course of decline and recovery.ResultsIt was found that the heat treatment, though completely inhibited photosynthesis, did not kill Scenedesmus cells. These cells, during dark recultivation, could make a fast repair and regained the ability of proliferation. We suggest that they entered a ‘stand-by’ state, which was characterized by condensed chromatin, partially functional but morphologically altered chloroplasts, disappeared vacuoles, slightly shrunk protoplast and intact plasma membranes. These stressed cells, on the surface, seemingly were undergoing some kind of disintegration, could readily and quickly return to normal cells upon illumination. Cell death occurred only after a long period of darkness (>48 h).ConclusionsOur results suggest that the recovery of algal cells from stress damage may actually proceed in two steps. The middle “stand-by’ stage normally is gone through too rapidly to be detected unless cells are kept in the dark.Electronic supplementary materialThe online version of this article (doi:10.1186/1999-3110-54-3) contains supplementary material, which is available to authorized users.
Highlights
To find out how algal cells cope with and recover from heat stress, the small vegetative cells of the synchronous Scenedesmus vacuolatus culture were subjected to a heat pretreatment (46.5°C for 1 h) followed by dark recultivation
We suggest that the chloroplasts, in between 12 and 48 h of dark cultivation, entered a ‘stand-by’ state, in which the cell maintained intact chloroplasts and functional photosynthetic machinery, so that a quick recovery can resume when light became available
Cells entered a ‘stand-by’ state, which was characterized by condensed chromatin, partially functional but morphologically altered chloroplasts, disappeared vacuoles, slightly shrunk protoplast and intact plasma membranes
Summary
To find out how algal cells cope with and recover from heat stress, the small vegetative cells of the synchronous Scenedesmus vacuolatus culture were subjected to a heat pretreatment (46.5°C for 1 h) followed by dark recultivation. The changes in physiological activities and morphology of Scenedesmus cells were continuously monitored throughout the course of decline and recovery. Desiccated desert green algae can recover high levels of photosynthetic quantum yield within 1 h of rehydration (Gray et al, 2007). Eremosphaera tanganyikae, of Lake Tanganyika, East Africa, exhibited large variations in cell abundance and cell size in response to seasonal changes (Stoyneva et al, 2007). It has been shown that algae can reversibly enter different physiological states to accommodate the changed environment (Ferroni et al, 2009).
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