| Right- and left-handedness in Triticum and Aegilops
III. The effects of external factors Hajime ONO Laboratory of Genetics, Hyogo Agricultural College, Sasayama, Hyogo Prefecture, Japan Each species of Triticum and Aegilops has its own specific value of C, as previously reported (Kojima, 1945). In the present experiments, it has been observed that the C value is affected in Triticum monococcum var. flavescens by nutritional conditions and X-ray irradiation. 1) Nutritional condition: the C value showed a significant difference between plants under normal conditions in the field and those under deficient nutrition in pots. A marked reduction in the C value was noticed when the nutrition was deficient at the time of spikelet differentiation. A quantitative analysis of the relationship between the concentration of culture media and the change of the C value was carried out under sand culture conditions recommended by Dr. Kasai of the Research Institute for Food Science, Kyoto University. Twelve pots, each with four plants at the time of spikelet differentiation, were divided into four groups, which were supplied with solutions of 1, 1/2, 1/10 and 1/30 of the standard cencentration, respectively. The result is shown in Table 1. According to the variance analysis, the regression mean square is significant, while the remainder mean square is not. The relation of C value to the solution concentration may be represented by a straight line; C=6.66 log (X)+84.15; that is, the relation will be expressed by a function of C value to the logarithm of the nutrient concentration. The value of C varies linearly, from 71.0% to 89.5%. 2) X-ray irradiation: in the middle of March the seedlings in a pot were subjected to X-rays. The C value of the spikelets, which developed after the irradiation, was remarkably reduced as shown in Table 2. The C value was much lower in these experiments than in the nutrition experiments described above. A reduction of the C value was also noticed in the subsequent generations, as indicated in Table 3. Regarding this peculiarity in the transmission of the effect of X-ray on the C value, two alternative mechanisms, genic and cytoplasmic, are possible. Namely, it may be due either to the drift of the frequencies of mutant genes from one generation to the next, or to a certain cytoplasmic change, which resembles the phenomenon of "Dauermodifikation" (Jollos. 1939). Accordingly, the following two experiments were carried out, namely, 1) the reciprocal crossing experiments between the X-rayed and non-treated plants, 2) the artificial selection of mutant genes concerning C value among the X-rayed plants. From the results of the preliminary experiments, it may be said that the transmissible X-ray effects on the C value are caused by some genic mutation and not by a cytoplasmic change, and that the remarkable reduction of the C value in X-rayed plants themselves may be due partly to a certain physiological disturbance caused by irradiation. |