Regulation of Tracheary Element Differentiation by Exogenous L-Methionine in Callus of Soya Bean Cultivars

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Abstract
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 Glycine max L. ‘Wayne’ and ‘Clark 63’. Although Wayne is a normal cultivar soya bean, seedlings of Clark 63 exhibit abnormal growth at 25 °C due to exessive ethylene biosynthesis at this temperature. Wayne callus showed increased xylogenesis in the presence of exogenous L-methionine (3.7 μg 1−1) in comparison to IAA–KN controls at both 20 and 25 °C. Clark 63 callus produced greater numbers of tracheary elements in response to exogenous L-methionine only at 25 °C. The induction of xylem differentiation was independent of the maintenance temperature of the stock cultures of both cultivars. Xylogenesis initiated byan IAA–KN medium was inhibited by the addition of AgNO3 (20 mg 1−1) to the extent of 76.5 per cent in cv. Wayne and 6 per cent in cv. Clark 63. The inhibitory effect was partially reversed by the addition of L-methionine (3.7 μg 1−1) to the IAA–KN–AgNO2 medium. These data support the hypothesis that xylogenesis in vitro involves auxin, cytokinin and ethylene.