Thidiazuron-induced plant regeneration from hypocotyl cultures of St. John's wort (Hypericum perforatum. cv 'Anthos').

St. John's wort (Hypericum perforatum. cv 'Anthos') is a medicinal plant with evidence of efficacy as an anti-depressant. The present report describes the development of an in vitro regeneration system that utilizes thidiazuron [N-phenyl-N'-(1,2,3-thidiazol-yl)urea] for the induction of de novo shoots on etiolated hypocotyl segments of St. John's wort seedlings. The optimum level of thidiazuron supplementation to the culture medium was 5 µmol·l-1 for a 9-day induction period followed by subculture of induced hypocotyl explants on basal medium. Other plant growth regulators including benzyladenine and indoleacetic acid were not effective in inducing regeneration on St. John's wort hypocotyls. Histological examination of the cultures revealed that the regenerated plants were derived from de novo developed shoots. Transfer of the regenerated shoots into a liquid medium with no plant growth regulators resulted in the rapid and prolific growth of viable plantlets. The rapid and efficient micropropagation system for St. John's wort may be useful for both the genetic improvement of this crop and the production of high-quality phytopharmaceutical preparations for the treatment of neurological disorders.

Morphoregulatory role of thidiazuron: morphogenesis of root outgrowths in thidiazuron-treated geranium (Pelargonium x hortorum Bailey).

Root outgrowths formed on the root tissue of geranium (Pelargonium x hortorum Bailey cv. Kim and cv. Shone Helena) plants in response to treatment with the phenylurea derivative, thidiazuron (N-phenyl-N'-1,2,3-thiadiazol-5'-ylurea; TDZ). Treatment with the cytokinin N(6)-benzylaminopurine (BAP) or the auxin α-naphthaleneacetic acid (NAA) did not result in stimulation of similar abnormal structures on the root tissue. Significantly more outgrowths developed on roots of plants treated with 10 µM and 20 µM TDZ than on control plants or those treated with 1 µM TDZ for the eight-week treatment period. Some outgrowths produced shoots and plantlets while still attached to roots, and regenerants were easily separated from the root tissue and transferred to soil in the greenhouse where they grew to maturity. Histological observations suggested these outgrowths originated from the vascular cambium region of the root.