effect of physiological activation on nucleolar morphology in Allium cepa

When onion bulb epidermal cells are activated by exposure of turgid leaf bases to ambient atmosphere, nucleoli in cells adjacent to wound sites enlarge within three hours and change their shapes from round to oval and elongated-oval, and finally form dumbbell-shaped nucleoli. Nucleolar vacuoles were observed in 10% of the elongated-oval and dumbbell type nucleoli three hours after wounding and exposure to ambient atmosphere and in 70% of these 24 hours after treatment. These changes are inferred to be the result of activity at the molecular level (RNA transcriptional and ribosomal subunit processing).