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Characterization of the decline and recovery of heat-treated Scenedesmus vacuolatus

View Article: PubMed Central

ABSTRACT

Background: 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.

Results: It 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).

Conclusions: Our 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 material: The online version of this article (doi:10.1186/1999-3110-54-3) contains supplementary material, which is available to authorized users.

No MeSH data available.


Related in: MedlinePlus

Representative transmission electron micrographs. (A) Untreated cell before dark cultivation (control) and the cells that had been heat treated and then cultured in the dark for (B) 0, (C) 2, (D) 6, (E) 12, (F) 24, (G) 48 and (H) 72 h, respectively. Bars = 1 μm. Abbreviations: c, chloroplast; m, mitochondrion; n, nucleus; nl, nucleolus; s, starch granule; v, vacuole. Arrows in (B): condensation of chromatin on the inner side of the nuclear membrane. Arrows in (E-G): exudation of organic substances between the cell wall and the cell membrane. Arrow in (H): rupture of cell membrane.
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Fig5: Representative transmission electron micrographs. (A) Untreated cell before dark cultivation (control) and the cells that had been heat treated and then cultured in the dark for (B) 0, (C) 2, (D) 6, (E) 12, (F) 24, (G) 48 and (H) 72 h, respectively. Bars = 1 μm. Abbreviations: c, chloroplast; m, mitochondrion; n, nucleus; nl, nucleolus; s, starch granule; v, vacuole. Arrows in (B): condensation of chromatin on the inner side of the nuclear membrane. Arrows in (E-G): exudation of organic substances between the cell wall and the cell membrane. Arrow in (H): rupture of cell membrane.

Mentions: The morphological variations were examined by TEM, and the untreated cells before dark cultivation were served as the control (Figure 5A). For heat-treated cells, there was no noticeable change in cell size, but slight shrinkage of the cytoplasm with some organic substances exuded into the space between the cell wall and the cell membrane was observed after 12 h dark cultivation (Figures 5E-G; arrows). Interestingly, the vacuole also disappeared after 12 h. The cell membranes remained intact until about 72 h, when the vast majority of cells appeared to be broken (Figure 5H, arrow).Figure 5


Characterization of the decline and recovery of heat-treated Scenedesmus vacuolatus
Representative transmission electron micrographs. (A) Untreated cell before dark cultivation (control) and the cells that had been heat treated and then cultured in the dark for (B) 0, (C) 2, (D) 6, (E) 12, (F) 24, (G) 48 and (H) 72 h, respectively. Bars = 1 μm. Abbreviations: c, chloroplast; m, mitochondrion; n, nucleus; nl, nucleolus; s, starch granule; v, vacuole. Arrows in (B): condensation of chromatin on the inner side of the nuclear membrane. Arrows in (E-G): exudation of organic substances between the cell wall and the cell membrane. Arrow in (H): rupture of cell membrane.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5383920&req=5

Fig5: Representative transmission electron micrographs. (A) Untreated cell before dark cultivation (control) and the cells that had been heat treated and then cultured in the dark for (B) 0, (C) 2, (D) 6, (E) 12, (F) 24, (G) 48 and (H) 72 h, respectively. Bars = 1 μm. Abbreviations: c, chloroplast; m, mitochondrion; n, nucleus; nl, nucleolus; s, starch granule; v, vacuole. Arrows in (B): condensation of chromatin on the inner side of the nuclear membrane. Arrows in (E-G): exudation of organic substances between the cell wall and the cell membrane. Arrow in (H): rupture of cell membrane.
Mentions: The morphological variations were examined by TEM, and the untreated cells before dark cultivation were served as the control (Figure 5A). For heat-treated cells, there was no noticeable change in cell size, but slight shrinkage of the cytoplasm with some organic substances exuded into the space between the cell wall and the cell membrane was observed after 12 h dark cultivation (Figures 5E-G; arrows). Interestingly, the vacuole also disappeared after 12 h. The cell membranes remained intact until about 72 h, when the vast majority of cells appeared to be broken (Figure 5H, arrow).Figure 5

View Article: PubMed Central

ABSTRACT

Background: 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.

Results: It 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).

Conclusions: Our 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 material: The online version of this article (doi:10.1186/1999-3110-54-3) contains supplementary material, which is available to authorized users.

No MeSH data available.


Related in: MedlinePlus