ISSN:
1432-2048
Keywords:
Chloroplast senescence
;
Euglena
;
Nitrogen storage
;
Proteolysis
;
Ribulose-1,5-bisphosphate carboxylase/oxygenase (oxidative modification)
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract When photoheterotrophic Euglena gracilis Z Pringsheim was subjected to nitrogen (N)-deprivation, the abundant photosynthetic enzyme ribulose-1,5-bis-phosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) was rapidly and selectively degraded. The breakdown began after a 4-h lag period and continued for a further 8 h at a steady rate. After 12 h of starvation, when the amount of Rubisco was reduced to 40%, the proteolysis of this enzyme slowed down while degradation of other proteins started at a similar pace. This resulted in a decline of culture growth, chloroplast disassembly — as witnessed by chlorophyll (Chl) loss — and cell bleaching. Experiments with spectinomycin, an inhibitor of chloroplastic translation, indicated that there was an absolute increase in the rate of Rubisco degradation in the N-deprived culture as compared with control conditions, where no significant carboxylase breakdown was detected. Oxidative aggregation of Rubisco (as detected by non-reductive electrophoresis) and association of the enzyme to membranes increased with time of N-starvation. Fluorescent labeling of oxidized cysteine (Cys) residues with monobromobimane indicated a progressive oxidation of Cys throughout the first hours of N-deprivation. It is concluded that Rubisco acts as an N store in Euglena, being first oxidized, and then degraded, during N-starvation. The mobilization of Rubisco allows sustained cell growth and division, at almost the same rate as the control (non-starved) culture, during 12 h of N-deprivation. Afterwards, breakdown is extended to other photosynthetic structures and the whole chloroplast is dismantled while cell growth is greatly reduced.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00192532
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