Radiosensitivity and interphase chromosome volume in the gymnosperms

Abstract

The sensitivities to acute 60Co γ-radiation of five species of gymnosperms were studied. The species were Pinus elliotti, Pinus palustris, Juniperus conferta, Podocarpus macrophylla and Zamia floridana. The nuclear and interphase chromosome volumes (nuclear volume divided by chromosome number) were calculated from measurements of shoot meristematic nuclei for each species. The plants, which were 1–2 year seedlings or 1-year old rooted cuttings, received acute radiation, taking care to shield the roots and thus simulate irradiation under natural growing conditions. The gymnosperms are a very radiosensitive group of plants; the 50 percent lethal doses (LD 50) for the species studied ranged from 500 to 760 R. The correlation between radiosensitivity and nuclear (or interphase chromosome) volume for the species studied agreed quite well with values obtained from other acutely irradiated woody species. A general curve of survival vs. exposure (in units of LD 50's) is given. It is useful for selecting in advance the appropriate exposures to deliver in order to obtain data in the exposure region of declining survival, if any exposure causing a given survival percentage is previously known or can be estimated. The data came from survival curves for 10 species of acutely irradiated woody plants. On the average, the LD 1(99% survival exposure) is 0·53 times the LD 50 the LD 99 (1% survival exposure) is 1·47 the LD 50.