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Plant and Cell Physiology, 1981, Vol. 22, No. 5 827-835
© 1981

Article

Mechanism of Suppression of DOPA Accumulation in a Callus Culture of Stizolobium hassjoo

Hamako Obata-Sasamoto1, Noriko Nishi2 and Atsushi Komamine1

1Department of Botany, Faculty of Science, University of Tokyo Hongo, Tokyo 113, Japan
2Department of Biology, Faculty of Science, Ochanomizu University Otsuka, Tokyo 112, Japan

Mechanisms of suppression of 3,4-dihydroxyphenylalanine (DOPA) accumulation were investigated in a callus culture of Stizolobium hassjoo. DOPA was detected in the callus but in a much smaller amount than in the intact plant, and its content changed during culture.

Biosynthesis of DOPA from labeled tyrosine in callus was confirmed by obtaining the constant specific radioactivity of the formed DOPA after co-crystallizing it four times with an authentic specimen. The variation in the percentage of radioactivity incorporated from labeled tyrosine into the ethanol-insoluble fraction was a mirror image of that of the DOPA content during culture. The increase in incorporation of radioactivity from labeled tyrosine into DOPA preceded that of the DOPA content. The rate of incorporation of radioactivity from labeled tyrosine into the ethanol-insoluble fraction was lower in etiolated seedlings than in callus at every stage of growth. However, the rate of incorporation of radioactivity from labeled tyrosine into DOPA was about the same in etiolated seedlings as in 19-day-old callus, which showed the highest activity of DOPA synthesis during culture.

The results obtained here indicate that the biosynthetic pathway of DOPA from tyrosine operates in callus at any growth stage and that the shift of the metabolic flow of tyrosine from DOPA synthesis to other pathways, e.g., protein synthesis, can explain the change in DOPA content during callus culture, and partially the suppression of DOPA accumulation in callus.

(Received February 4, 1981; Accepted May 18, 1981)
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