Charophytes is a green algal group closely related to land plants. We 
investigated the effects of antibiotics that interfere with peptidoglycan 
biosynthesis on chloroplast division in the desmid Closterium 
peracerosum-strigosum-littorale complex. To detect cells just after division, we 
used colchicine, which inhibits Closterium cell elongation after division. 
Although normal Closterium cells had two chloroplasts before and after cell 
division, cells treated with ampicillin, D-cycloserine, or fosfomycin had only 
one chloroplast after cell division, suggesting that the cells divided without 
chloroplast division. The antibiotics bacitracin and vancomycin showed no 
obvious effect. Electron microscopic observation showed that irregular-shaped 
chloroplasts existed in ampicillin-treated Closterium cells. Because antibiotic 
treatments resulted in the appearance of long cells with irregular chloroplasts 
and cell death, we counted cell types in the culture. The results suggested that 
cells with one chloroplast appeared first and then a huge chloroplast was 
generated that inhibited cell division, causing elongation followed by cell 
death.