ISSN:
1615-6102
Keywords:
Cell cycle
;
Chloroplast nucleoids
;
DAPI staining
;
Illumination regime
;
Irradiance
;
Scenedesmus quadricauda
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Summary Synchronous cultures of the green algaScenedesmus quadricauda were grown at different mean irradiances (ranging from 15 Wm−2 to 130Wm−2). At each irradiance, the algae were exposed to illumination regimes which differed in light duration and dark intervals (2∶22 to 24∶0 hours). The cells from these cultures were sampled during their cycles, stained with DAPI and the number of nuclei and chloroplast nucleoids estimated. The nucleoids divided semisynchronously in steps which represented doublings in their number. For each doubling a constant amount of light energy (defined as the product of irradiance and light duration) had to be converted by the cells to become committed to this division. The times to the start of the nucleoid divisions were therefore inversely proportional to the irradiances applied and the final number of nucleoids was proportional to the light duration. Temporal relationships between nuclear and nucleoid divisions were also light dependent. Shortage of light energy caused delay in nucleoid division. The cell division rate was higher than the rate of nucleoid division and consequently, the cells tended to decrease their nucleoid number with decreasing irradiance. With increasing irradiance the start of nucleoid division was gradually shifted toward the beginning of the cell cycle. The rate of nucleoid division exceeded the rate of nuclear and cellular division, thus with increasing irradiance cells with increasing numbers of nucleoids were formed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01276790
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