We have analyzed protein expression in the bleached small vegetative cells of synchronous Scenedesmus vacuolatus to investigate how unicellular algae lived through stress. These cells were subjected to heat treatment (46.5 °C for 1h in dark condition) and then cultured under continuous illumination for 24 h. Flow cytometry analysis of the chlorophyll autofluorescence intensity of S. vacuolatus cells indicated that heat-treated cells were completely bleached within 24 h of light cultivation. Transmission electron microscopy (TEM) images showed that bleached cells maintained thylakoid membrane structure, but with lower contrast. The bleached cells regained green color after 72 h, along with a recovery in contrast, which indicated a return of photosynthetic ability. Two-dimensional gel electrophoresis (2DE) showed that the protein expression patterns were very difference between control and bleached cells. ATP synthase subunits and glutamine synthetase were down-regulated among the many differences, while some of phototransduction, stress response proteins were up-regulated in bleached cells, elucidating bleached cells can undergo changes in their biochemical activity, and activate some stress response proteins to survive the heat stress and then revive. In addition, small heat shock proteins (HSPs), but not HSP40 and HSP70 family proteins, protected the bleaching cells.
Keywords: ATP synthase; chlorophyll; heat shock protein (HSP); heat stress; photobleaching; protein identification.