Frequency of micronuclei in root-tips of Tradescantia clone 02: Effects of diurnal temperature difference and Co gamma radiation

Frequency of micronuclei in root-tip cells was used to asses the influence and/or interaction of a large Diurnal Temperature Difference (DTD) on irradiated and non-irradiated Tradescantia Clone 02. Hydroponically grown plants were subjected to four different treatment combinations: no radiation/normal DTD (7.2°C), no radiation/large DTD (23.5°C), radiation (60R)/normal DTD, radiation/large DTD. An analysis of variance of Feulgen positive micronuclei arising from chromosome fragments in root-tip cells revealed that a 5-day chronic exposure to a large DTD without radiation does not significantly increase the frequency of cells with micronuclei (freq. = 0.53%). An accute 60 R radiation exposure, as expected, did significantly increase the frequency (freq. = 3.23%). None of the treatment interactions significantly altered micronuclei production. These data lend support to the contention that the mutation-induction mechanism of large DTD's, as expressed by variant color sectoring in stamen hair cells of this clone, is not mediated by chromosome breakage. Exposure to a large DTD, therefore, may be a method for inducing mutations in stamen hairs without concomitant chromosome breakage, and may also provide a good cytological means for analyzing somatic crossing over, which has been postulated as a possible mechanism for the expression of spontaneous mutations at the D⁺ locus. The frequency of micronuclei in irradiated tissue remained constant throughout the 5-day course of the experiments and several explanations for this occurrence are proposed.