INTERFERENCE BY NEAR ULTRAVIOLET AND GREEN LIGHT WITH MITOSIS IN ONION ROOT TIP MERISTEM

Near ultraviolet (365 nm) and green (546-577 nm) radiations suppress mitosis in cells of the onion root tip meristem. As short a period of time as one hour of radiation was sufficient to repress the mitotic index. Green radiations are less effective than the near-ultraviolet. Near-ultraviolet induces a relative increase in prophase mitotic figures and green light induces a relative increase in anaphase mitotic figures. Mitotic division in primary root tips of onion seedlings exhibits a diurnal rhythm with peaks of activity at noon and at midnight and secondary peaks at 7 AM and 7 PM. Irradiated roots do not deviate from this pattern.