Somatic embryos were obtained from leaf discs of juvenile red oak plants. Basal inductive nutrient medium was a modified Murashige and Skoog solution enriched with 500 mg L-' casein hydrolysate, 100 mg L-' polyvinylpyrrolidone, 5.4 @4 naphthaleneacetic acid and 0.09 w benzyladenine. Embryogenesis was obtained only from leaf discs in the presence of light and increased when the adaxial surface of the explants (with midrib or main veins present) was in contact with the medium. Large variation was observed in all experiments. Recurrent embryogenesis was observed at the base of embryo clusters with callus present; conversely, embryogenic potential was rapidly lost by subculturing full calli. Maturation, germination and development of isolated somatic embryos were obtained. However, the vast majority of embryos did not have viable apical bud meristems and on only a few occasions were shoots produced.

The effects of K-nutrition on growth (increase of fresh weight), bud formation (time of emergence, number of buds), and amine and hydroxycinnamic acid amide contents in foliar explants of Nicotiana tabacum cv Xanthi n.c. cultivated in vitro were examined. In K-deficient medium and in high K medium growth and bud formation were markedly inhibited. Marked changes of amine content (a diamine, putrescine; a phenolic amine, phenethylamine) were observed after a few days of culture. No apparent relationship was found between these amines and growth or bud differentiation. In contrast, changes in hydroxycinnamic acid levels were shown to correlate well with growth and bud formation. The greatest stimulation of budding and growth was correlated with the greatest accumulation of these amides. The highest contents of hydroxycinnamic acid amides were found during the first 15 days in culture when intensive cell division took place. Then they declined sharply after 26 days in culture as the rate of cell division decreased and differentiation occurred.Availability of K is known to have a large impact on plant growth, in part at least, because of the effects of K-status on certain aspects of leaf cell metabolism (5). K-deficiency induces an accumulation of PA2 and especially, accumulation of a diamine, Put. The largest and most consistent stress-induced changes in PA metabolism have been observed in K-deficient oat and barley seedlings (2,21,24). It has been shown that K deficiencies in tobacco leaves caused Put accumulation (22) but also gave rise to the accumulation of the di-and PA conjugates formed with the hydroxycinnamic acids (hydroxy-cinnamic acid amides, HCA amides) such as caffeoylputrescine and mono-and di-caffeoylspermidine (6). Increasing evidence suggests that the naturally occurring PAs (1,7,19,20) and HCA amides (3, 9-13, 16, 17) may act as modulators of some cellular and physiological processes during plant growth and development.The objectives of the present study were to determine the effects of K-nutrition on (a) growth and bud formation of foliar explants of Nicotiana tabacum cv Xanthi n.c. cultivated in vitro (b) the content of free amines and HCA amides. The relations between free amines, HCA amides, and growth and bud formation are examined and discussed. ' This paper is published with the approval ofthe director of the Dijon Agricultural Experiment Station.

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