THE RELATIONSHIP OF MUTATION RATE PER ROENTGEN TO DNA COiNTENT FER CHROMOSOME AND TO INTERPHASE CHROMOSOME VOLUME1

LOCALIZED phenot.ypic changes in petal color following X-irradiation and acute or chronic gainma irradiation have been reported for several species of higher plants (IBA, MA'rSUBARA, INOKOSHI, OKA and MESHITSUKA 1964; MATSUBARA, IBA, OKA and MESHITSUKA 1964, MoEs 1966; GUPTA and SAMATA 1963, 1964; RICHTER and SINGLETON 1955; SAGAWA and MEHLQUIST 1957; NEZU 1963b; MESHITSUKA, OKA, MATSUBARA and IBA 1963; MESHITSUKA, OKA, IBA, MATSUBARA and INOKOSHI 1963). Mutation rates for individual loci controlling flower color have been published for Antirrhinum majus (CUANY, SPARROW and POND 1958), Zmpatiem; balsamina (ALSTON and SPARROW 1962), Petunia hybrid~, Tradescantia (clone 02), Lilium testaceum (SPARROW, CUANY, MIKSCHE and SCHAIRER 1961), and Tulipa (NEZU 1963a). The possibility that mutation rate per roentgen (CUANY, SPARROW and JAHN 1958; CUANY, SPARROW and FOND 1958; SPARROW, CUANY, MIKSCHE and SCHAIRER 1961) or frequency of chromosome deletion per nucleus per roentgen (SPARROW and EVANS 1961) might be related to certain nuclear parameters was recognized several years ago, and some of the present data were reported in preliminary form in 1962 (SHAVER and SPARROW 1962). Further experiments confirming the relationship between chromosome size and induced somatic mutation rate are reported here (see also BAETCKE, SPARROW, SHAVER and POND 1967). It has been shown previously that plant radiosensitivity as measured by lethality. growth inhibition. etc. also depends partially on DNA content per chromosome (SPARROW and .MIKSCHE 1961; SPARROW, SPARROW, THOMPSON and SCHAIRER 1965; BAETCKE, SPARROW, NAUMAN and SCHWEMMER 1967). It therefore seemed appropriate to test whether mutation rate also might be at least partly dependent on DNA content per cell or per chromosome. The data presented below show that such a relationship does exist.