MORPHOGENESIS OF POTATO PLANTS IN-VITRO .1. EFFECT OF LIGHT QUALITY AND HORMONES

Stem cuttings of potato plants (Solanum tuberosum L., cv. Miranda) wer e cultured in vitro on MS medium with sucrose either without or with a ddition of indole-3-acetic acid (IAA) or kinetin (K) under red light ( R) or blue light (B). Plants on medium without hormones under R were t hin, long, with very small leaves, and produced no or only a few micro tubers (after longer-lasting cultivations). In B, plants remained shor t, thick, with large, well-developed leaves and produced a significant amount of microtubers. Darkening of both roots and shoots strongly pr omoted tuber formation; the tubers were formed on the darkened part of the plant. IAA had no pronounced effect on plant development in B exc ept for slight lengthening of the stem, and, in longer cultivations, s lightly enhanced tuber formation as well. In R, IAA brought about seve ral significant effects: stem reduction and induction of tuber formati on being the most significant. Kinetin in R increased tuber formation slightly. In B, kinetin not only strongly stimulated tuber formation, but also increased the total fresh weight and root (+ stolons)/shoot r atio. Results are discussed with regard to the possible role of auxins and/or cytokinins in mediating the morphogenetic effects of light.