On the Growth Ability of the Excised Seminal Roots of Rice Plant in vitro.

Abstract

During the course of the previous studies on the nutrient medium for the culture of excised roots of rice, it was repeatedly observed that these excised roots showed a remarkable variation in their growth even with the same nutrient medium. Since this variation was considered as an obstacle for further studies, investigations were carried out in order to clarify this situation. The explants were obtained from the seedlings of rice, variety Noorin No. 29, germinated aseptically under well-controlled as well as semi-controlled temperature. Throughout the studies, the 1cm root tips used to initiate experiments were excised from seminal roots and were cultured with the "improved medium" reported previously. All the cultures were maint-ained at about 27°C in the dark for the periods from half to one month, until the root growth ceased. A series of cultures, from November 1963 to October 1964, were performed using the rice seeds harvested in the Autumn of 1963. The results of these cultures showed a seasonal fluctuation in root growth ; the roots cultured in winter months grew definitely longer than those cultured in spring and summer months. Maximum elongation of roots in each cuture was almost within the range of 13 to 22 cm in winter cultures and 8 to 13 cm in spring and summer cultuers. On the basis of the above data, it was of interest to study the factor (s) involved in this seasonal fluctuation of root growth. In order to elucidate this, the authors carried out the following experiments. In the first experiments on the effect of various controlled temperature, at the time of seed germination, upon the root growth in cultures, it was found that the growth of excised roots was hardly influenced by the germination temperature. In the second experiments on the relation between the length of seminal roots, at the time of excising root tips, and the growth of excised root tips (1cm), it was found that the growing stage of the seminal root at the time of excision affected the growth of excised root tips in culture. At last, it was thought that the age of seeds might affect the growth of seminal root tips in culture. Accordingly, a number of comparisons were made between the growth of excised roots derived from the seeds harvested in the autum of 1963 and those harvested in the autum of 1964. The results of these experiments showed that the growth of excised roots derived from "new" seeds exceeded distinctly that of excised roots derived from "old" seeds. Furthermore, a series of cultures, using the seeds harvested in the autumn of 1964, were performed. In this experiment, root tips were excised from 1.5 cm seminal roots (at the same growing stage) and were cultured as mentioned above. In these cultures, again, the root growth showed a remarkable seasonal fluctuation. This phenomenon might be due to the aging of seeds. From these experiments, it may be concluded that there are at least two factors responsible for the variation in the growth of excised seminal roots; the growing stage of seminal root at the time of excising the inoculum and the age of seeds used.