Callus formation of somatic hybrid of rice and soybean and characteristics of the hybrid callus.

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Abstract
Induction of calli from rice (strain A-58) and soybean (cv. Harosoy) protoplast mixtures treated by polyethyleneglycol (PEG) was successful, and hybrid calli were identified and selected by the observation of a blackish purple pigment of flavonoids in the rice calli and a softness in the soybean calli. The blackish purple pigment of hybrid calli disappeared rapidly after 1 or 2 subcultures. The peroxidase and esterase isozyme band patterns of all hybrid calli after several subcultures were that of soybean callus. Rice chromosomes are probably rapidly eliminated, while soybean nuclear genome may be retained in the hybrid calli. During subcultures of the hybrid calli, yellow, green and white calli were segregated. The soybean calli were usually yellow, but sometimes turned green. The rice calli were a blackish purple which was so unstable that whitish yellow calli were often obtained. When all these calli were transferred onto the medium containing 1-naphthaleneacetic acid (NAA) and kinetin, the whitish yellow calli of rice and the white calli segregated from the hybrids did not usually turn green. Nevertheless, the segregated white calli occasionally produced green parts in a mosaic pattern during long-term cultures. Soybean calli, and yellow and green calli segregated from the hybrids became green or remained green. Analysis of fraction I protein showed that the segregated green calli have soybean chloroplasts, while the white calli have both rice and soybean chloroplasts. The segregated green calli may have mainly soybean nuclei and soybean chloroplasts, while the white calli may have soybean nuclei, and rice and soybean chloroplasts in a mosaic pattern.