ISSN:
1615-6102
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Summary The effects of myomycin (MM), a new bleaching antibiotic forEuglena gracilis, were investigated during the greening process of the alga. Dark-grown cells, after preincubation in the dark for 21 hours, were exposed to continuous light for 72 hours in both growing and resting conditions in the presence of 20, 35, 50, 100, 150 μg/ml of the antibiotic. In dividing cells, chlorophyll synthesis was strongly inhibited and practically suppressed with the two highest concentrations of MM, while in non-dividing cells, the process was only partially influenced. The cell division rate was also lowered, although in lesser degree than chlorophyll formation, but in any case a normal level of cell viability was maintained. Fluorescence and electron microscopic observations showed that the decrease in pigment synthesis corresponded to several stages of inhibition of the light-induced proplastid-to-chloroplast transformation. In particular, the plastids of the cells treated with the three lowest concentrations of MM showed an abnormal outline and a reduced number of thylakoids. In the presence of 100 and 150 μg/ml of the antibiotic, the thylakoids either did not form or were present as perforated or fragmented structures inside small plastids sometimes containing non-crystalline prolamellar bodies. In the permanently bleached cells, the plastids persisted as poorly differentiated bodies strictly resembling the proplastids of dark-grown cells. In any case, in spite of the profound plastidial alterations, the remnant cell was not apparently affected by the antibiotic. On the basis of the results obtained and the literature on bleaching agents, it can be inferred that the action of MM is due to a permanent block of protein synthesis on prokaryotic type plastidial ribosomes.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01287693
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