Enhancement of micronuclei frequency in the Tradescantia /micronuclei testusing a long recovery time

The Tradescantia/micronuclei test (TRAD/MCN) is a well-validated test for m onitoring environmental genotoxicants. These pollutants induce at the early meiotic stage of pollen mother cells chromosome fragments which become mic ronuclei at the tetrad stage. The standard test protocol requires some hour s of exposure of the inflorescences and a recovery time of about 24 hours t o reach the early tetrad stage. Since the recovery period represents a crit ical step of the TRAD/MCN, experiments were performed to establish its leng th in plants of clone #4430 of the hybrid T. hirsutiflora x T. subacaulis w hich is widely used in environmental monitoring. The aim of the present res earch was to ascertain the exact duration of recovery time in order to impr ove the sensitivity of the TRAD/MCN test. First, studies were performed to select the flowers at the beginning of the meiosis, and then anthers were s ampled and studied for a period of 48-86 hours. The complete meiosis in the plants examined required about 80 hours. Second, exposure to genotoxic sub stances followed by different recovery times was carried out to demonstrate that effectiveness of the TRAD/MCN test is closely related to the duration of the recovery time. The test was carried out by exposing inflorescences to known mutagens (sodium azide and maleic hydrazide) for six hours followe d by different recovery times (24-72 hours). The results showed that the fr equency of micronuclei in the pollen mother cells increased with the length of the recovery time.