Morphology of the Process of Shoot Formation in the Rice Callus Culture

Abstract

Although shoot differentiation in rice callus culture has been reported by several workers, details of gross morphology on the differentiation process are obscure. In this work, two methods (Saka and Maeda's and Nishi et al's) for shoot differentiation were compared and the gross morphological variation connected with shoot differentiation were investigated in rice callus culture. 1. Two different processes of shoot formation with relation to the change in region showing morphological variation were observed in the Saka and Maeda's medium. There is a developmental process which shows a series of changes from 'Dry' region to 'Protuberances' or 'Green', to 'Green protuberances', and finally to 'Green leaves'. And there is another process which shows a series of changes from 'White' region to 'White and green', and finally to 'Green leaves'. Two processes were compared in the time of appearance of the each region. 2. Similar variation was also observed in the rice callus in the Nishi et al's medium for shooting. However, few leaves but many roots were appeared in their medium. In many cases, the appearance of 'Green' region was related to the initiated roots. 3. The two methods were compared in time of appearance and number of regions representing leafy structure. As a result, it was ascertained that Saka and Maeda's method is available to our following histological and physiological investigations. 4. From the investigation with the effect of growth hormones on the variation in the Saka and Maeda's medium, it was revealed that the high level of kinetin is required mainly for the appearance of 'Dry' and 'Protuberances' regions, and the low level of 2, 4-D for 'White' and 'Green' regions. 5. Friable and compact callus tissues were inoculated separately into the Saka and Maeda's medium for shooting. The number of regions representing the variation was compared between both callus tissues. The appearance of 'Dry' region was poor in the friable callus tissues. 6. The region representing the variation was observed with stereomicroscope. Moreover fresh hand sections of a part of the region were made and observed histologically with ordinary microscope. As a result, it was, shown that (a) tiny protuberances and trichomes are accompanied with 'Dry' and 'Green' regions, respectively, and (b) green cells are always observed near to tracheary elements.