REGULATION OF TRACHEARY ELEMENT DIFFERENTIATION BY EXOGENOUS L-METHIONINE IN CALLUS OF SOYA BEAN CULTIVARS

The relationship between the induction of tracheary element differentiation and exogenous L-methionine was examined in agar-grown cultures of soya bean callus initiated from G. max L. [cultivars] Wayne and Clark 63. Although cv. Wayne is a normal cultivar soya bean, seedlings of cv. Clark 63 exhibit abnormal growth at 25.degree. C due to excessive ethylene biosynthesis at this temperature. Cv. Wayne callus showed increased xylogenesis in the presence of exogenous L-methionine (3.7 .mu.g l-1) in comparison to IAA-KN controls at 20 and 25.degree. C. Cv. Clark 63 callus produced greater numbers of tracheary elements in response to exogenous L-methionine only at 25.degree. C. The induction of xylem differentiation was independent of the maintenance temperature of the stock cultures of both cultivars. Xylogenesis initiated by an IAA-KN medium was inhibited by the addition of AgNO3 (20 mg l-1) to the extent of 76.5% in cv. Wayne and 6% in cv. Clark 63. The inhibitory effect was partially reversed by the addition of L-methionine (3.7 .mu.g l-1) to the IAA-KN-AgNO3 medium. Evidently, xylogenesis in vitro involves auxin, cytokinin and ethylene.