Somatic Mutations Induced in Stamen Hairs ofTradescantiaClone 02 by Relativistic Muons

IntroductionSince a major component of the cosmic-ray background at sea-level arrives in the form of high-energy muons, there is considerable significance in determining the relative biological effectiveness (r.b.e.) of muons for inducing mutations.Of particular interest are measurements obtained at low doses and dose-rates .In previous studies of muon-induced mutations, special genetic stocks of Tradescantia (Davies, Sparrow, Woodley and Maschke 1963) and Zea mays (Micke, Smith, Woodley and Maschke 1964 a, b) were exposed to 2-8 GeV/c negative muons (µ-) at a dose-rate of 7 .5rads/hour and compared with standards of B0 Co gamma-rays and 250 kVp X-rays, respectively .The r.b .e. values obtained in the two experiments were 0 .79and 0 .81,respectively .However, the statistics were not sufficient to rule out r .b.e.= 1 .We report here on a study of the dose and dose-rate response of muon-induced blue-to-pink somatic mutations in the stamen hair cells of Tradescantia clone 02.The clone, which has blue petals and stamen hairs, is heterozygous for genes controlling flower pigments, so that mutant cells are predominantly pink .This blue-to-pink mutation is believed to be mainly the result of chromosomal deletions (Mericle and Mericle 1967), but point mutations cannot be ruled out .The blue-to-pink somatic mutation in Tradescantia clone 02 is particularly suited for low dose and dose-rate studies because of its high radiosensitivity .Extensive studies have been carried out for blue-to-pink mutations induced by X-rays, gamma-rays and neutrons (Nayar and Sparrow 1967, Underbrink, Sparrow, Sparrow and Rossi 1970and 1971, Sparrow Underbrink and Rossi 1972) .A dose-rate effect for this mutation has been found recently by Nauman, Underbrink, and Sparrow (to be published) .