RELATIVE BIOLOGICAL EFFICIENCY OF 14.1MeV FAST NEUTRONS AND ¹³⁷Cs GAMMA RAYS IN THE STAMEN HAIRS OF <i>TRADESCANTIA REFLEXA</i> RAFIN

Abstract

Most species of the genes Tyadescantia have many hairs on their stamen filaments. Each stamen hair is composed of a single chain of cells, and its development depends principally on the repeated division of the terminal cell. Thus the stamen hairs of this genus can be regarded as an essentially single-meristematic-cell system as demonstrated by Ichikawa and Sparrow (1967b), and can be used as an excellent plant material for radiobiological studies at the single-cell level (Davies 1963; Alvarez and Sparrow 1965;Nayar and Sparrow 1967; Ichikawa and Sparrow 1967a, 1967b, 1968, 1969 Ichikawa 1968; Ichikawa et al. 1969).The present study was undertaken to determine the relative biological efficiency (RBE) of 14.1 MeV fast neutrons as compared with 137Cs gamma rays in causing loss of reproductive integrity and in inducing somatic mutations in Tyadescantia stamen hairs.The main reason why this study was carried out is that extremely high RBE values of 10 to 50 sometimes more than 100 have been reported in plant materials for fast neutrons or other heavy particles by many authors (Matsumura et al. 1963;Neary et al. 1963;Smith et al. 1964; Matsumura 1966 and many others, see Discussion). The RBE values reported in animals and microorganisms are generally much closer to 1 (at most 5) (see Kondo 1964). It should be remembered that most of the extremely high RBE values in plants have been obtained from irradiation of dry seeds containing a small amount of water (about 8 to 15 percent).It is generally accepted that water content modifies the sensitivity to X rays or gamma rays greatly but that to neutrons relatively slightly (Ehrenberg et al. 1952; Ehrenberg and Nybom 1954; Ehrenberg 1955;Ikushima 1968; Fujii 1969). The present RBE study in the single meristematic cells of actively growing stamen hairs, which contain a comparable amount of water with other organisms, will offer information to help resolve the above discrepancy reported between plants and other organisms. MATERIAL AND METHODSA tetraploid Tyadescantia clone (KU 7, 2n=24) was used in the present investigation. This clone was recently isolated as a heterozygote for flower color (blue/pink, blue being 1) Contribution from 353.

SOMATIC MUTATION RATE AT LOW LEVELS OF CHRONIC GAMMA-RAY EXPOSURES IN <i>TRADESCANTIA</i> STAMEN HAIRS

“…2 affects somatic mutation frequency in Tradescantia stamen hairs. The above mutation rate of 3.36x 10 pink mutant events per hair per R effective exposure obtained for Period 1 is much lower than the earlier value of 1.56 X 10-3 pink mutant events per hair per rad obtained from the same clone but after 137Cs gammaray irradiation at very much higher dose rates of 18 to 45 rads/min (Ichikawa 1970). The present mutation rate is also significantly lower than the value of 9.03 x 10-4 pink mutant events per hair per R determined for a clone of T. virginiana (also tetraploid) irradiated with 137Cs gamma rays at the exposure rates of 6.25 to 31.25 R/hr (Ichikawa and Sparrow 1968), about 30 to 60 times higher exposure rates than those in the present study.…”

“…3. A pink mutant event is defined as two or more contiguous pink cells or a single pink cell, and is considered to have been derived from a mutation induced in a single meristematic hair cell (Ichikawa and Sparrow 1968;Ichikawa 1970). The data collected on days 11 and 12 are pooled as those for Period 1 because there is no significant difference in the data between those days.…”

“…Since no radiation effects are observed in the stamen hairs whose development had been completed by the time of irradiation (Ichikawa and Sparrow 1967a, 1967b, 1968Ichikawa 1968Ichikawa , 1970, gamma-ray exposures given after the com- pletion of the hair development can be considered to be "ineffective exposures". In the clone used, the hair development is completed seven days before flowering.…”

“…The present study was undertaken to obtain more informations on mutation rate at low levels of gamma-ray exposures and exposure rates, employing Tradescantia stamen hairs which have been demonstrated by us to be excellent experimental material for determining somatic mutation rate because of their essentially single-meristematic-cell nature (Nayar and Sparrow 1967;Sparrow 1968, 1969;Ichikawa 1970). The other purpose of this study was to test whether or not the Tradescantia stamen hair system can be used as a sensitive biometrical tool for detecting low levels of radiation exposures.…”

RELATIVE BIOLOGICAL EFFICIENCY OF 14.1MeV FAST NEUTRONS AND ¹³⁷Cs GAMMA RAYS IN THE PRESOAKED SEEDS OF <i>TRITICUM BOEOTICUM</i> BOISS. AND ITS AUTOTETRAPLOID

“…On the other hand, much lower RBEs (about 2 to 8) have been found in microspores (Conger et al 1958), stamen hairs (Ichikawa 1970), and growing plants (Donini et al 1967). The RBE values reported in microorganisms, animal cells and animals are also low (close to 1, sometimes higher but at most 5, see Kondo 1964).…”