The effects of continuous incubation in hydroxyurea (HU) solutions (0.2, 0.4, 0.8 mg/ml) on germination of rape seeds and growth of young seedling axes were studied during 132 hours from initial soaking. Germination turned out to be unaffected by the treatment. Root growth was first increasingly inhibited by the HU concentration tested, but after prolonged incubation a complete arrest of the root growth was noted at all HU concentrations. The elongation growth of hypocotyls was found to be stimulated by a HU 0.2 mg/ml concentration while it was markedly suppressed by 0.4 mg/ml, and completely arrested by 0.8 mg/ml Inhibition of growth of the upright hypocotyl part at higher HU concentration was found to be accompanied by the unbending of the hooked under-cotyledonary part. It is suggested that inhibition of nuclear endomitotic DNA synthesis In elongating hypocotyl cells, suppresses only partially their growth, whereas a complete inhibition of the hypocotyl growth results from arrest of the mitochondrial DNA synthesis.
Characterization of DNA synthesis at a restrictive temperature in the temperature-sensitive mutants, tsFT5 cells, that belong to the complementation group of ts85 cells containing a thermolabile ubiquitin-activating enzyme E1. Involvement of the ubiquitin-conjugating system in DNA replication