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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

The variation of photosynthetic activity (Fv/Fm). (A) The decay of Fv/Fm ratio as a function of the time of heat treatment. (B) The variations of the Fv/Fm of heat-treated cells are plotted as functions of the time of recultivation in the dark (○), and those with light (150 μmol photon m-2 s-1) turned on at 12 (∇), 24 (■), 36 (Δ), 48 (□), 60 (◊) and 72 h (♦), respectively. The Fv/Fm of untreated cells as a function of the time of dark cultivation is also shown (●). Each data point represents the mean ±SD of three independent measurements with two replicates each. The dotted line indicates the Fv/Fm (0.74 ± 0.02) of untreated cells at the beginning of dark cultivation.
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Fig2: The variation of photosynthetic activity (Fv/Fm). (A) The decay of Fv/Fm ratio as a function of the time of heat treatment. (B) The variations of the Fv/Fm of heat-treated cells are plotted as functions of the time of recultivation in the dark (○), and those with light (150 μmol photon m-2 s-1) turned on at 12 (∇), 24 (■), 36 (Δ), 48 (□), 60 (◊) and 72 h (♦), respectively. The Fv/Fm of untreated cells as a function of the time of dark cultivation is also shown (●). Each data point represents the mean ±SD of three independent measurements with two replicates each. The dotted line indicates the Fv/Fm (0.74 ± 0.02) of untreated cells at the beginning of dark cultivation.

Mentions: The photosynthetic activity was accessed by measuring the maximal quantum yield (Fv/Fm) of photosystem II of dark-adapted cells. The activity was completely inhibited after 20 min into the heat treatment (Figure 2A). However, as shown in Figure 2B, a quick recovery of the activity to a low level (~ 0.12) could be detected after about 12 h of dark recultivation. It then stayed steady until 48 h, but eventually declined to zero after 84 h. If light irradiation was provided sometime after 12 h, the Fv/Fm value would quickly rise to a value similar to that of untreated cells at time zero (~ 0.74), and the longer the dark period the faster the recovery. The result suggests that the repair started immediately after heat pretreatment, but a full recovery of photosynthetic activity required light. However, after 60 h of dark cultivation, the recovery upon illumination became slower and incomplete, and after 72 h, illumination simply abolished the remaining activity. The Fv/Fm of untreated cells (the control) decayed slowly during dark cultivation, and dropped only about 25% after 84 h.Figure 2


Characterization of the decline and recovery of heat-treated Scenedesmus vacuolatus
The variation of photosynthetic activity (Fv/Fm). (A) The decay of Fv/Fm ratio as a function of the time of heat treatment. (B) The variations of the Fv/Fm of heat-treated cells are plotted as functions of the time of recultivation in the dark (○), and those with light (150 μmol photon m-2 s-1) turned on at 12 (∇), 24 (■), 36 (Δ), 48 (□), 60 (◊) and 72 h (♦), respectively. The Fv/Fm of untreated cells as a function of the time of dark cultivation is also shown (●). Each data point represents the mean ±SD of three independent measurements with two replicates each. The dotted line indicates the Fv/Fm (0.74 ± 0.02) of untreated cells at the beginning of dark cultivation.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig2: The variation of photosynthetic activity (Fv/Fm). (A) The decay of Fv/Fm ratio as a function of the time of heat treatment. (B) The variations of the Fv/Fm of heat-treated cells are plotted as functions of the time of recultivation in the dark (○), and those with light (150 μmol photon m-2 s-1) turned on at 12 (∇), 24 (■), 36 (Δ), 48 (□), 60 (◊) and 72 h (♦), respectively. The Fv/Fm of untreated cells as a function of the time of dark cultivation is also shown (●). Each data point represents the mean ±SD of three independent measurements with two replicates each. The dotted line indicates the Fv/Fm (0.74 ± 0.02) of untreated cells at the beginning of dark cultivation.
Mentions: The photosynthetic activity was accessed by measuring the maximal quantum yield (Fv/Fm) of photosystem II of dark-adapted cells. The activity was completely inhibited after 20 min into the heat treatment (Figure 2A). However, as shown in Figure 2B, a quick recovery of the activity to a low level (~ 0.12) could be detected after about 12 h of dark recultivation. It then stayed steady until 48 h, but eventually declined to zero after 84 h. If light irradiation was provided sometime after 12 h, the Fv/Fm value would quickly rise to a value similar to that of untreated cells at time zero (~ 0.74), and the longer the dark period the faster the recovery. The result suggests that the repair started immediately after heat pretreatment, but a full recovery of photosynthetic activity required light. However, after 60 h of dark cultivation, the recovery upon illumination became slower and incomplete, and after 72 h, illumination simply abolished the remaining activity. The Fv/Fm of untreated cells (the control) decayed slowly during dark cultivation, and dropped only about 25% after 84 h.Figure 2

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