THE EFFECTS OF PROLINE, THIOPROLINE AND METHYLGLYOXAL-BIS-(GUANYLHYDRAZONE) ON SHOOT REGENERATION FREQUENCIES FROM STEM EXPLANTS OF BRASSICA-NAPUS

Internode segments from aseptic shoot cultures are the most prolific e xplants for the regeneration of Brassica shoots in vitro. These explan ts also have the advantage of not being subject to the genotypic varia tions in regeneration response observed in hypocotyl and cotyledon exp lants. Despite reports of 80-100% shoot regeneration from stem explant s, observed frequencies are typically 50-60%. Three media additives, p roline, thioproline and methylglyoxal-bis-(guanylhydrazone) (MGBG), we re tested for their efficacy in promoting shoot regeneration from stem explants of two B. napus varieties, Westar and Cobra. The effects of proline and thioproline on both varieties were neutral or deleterious. In Cobra the MGBG treatments caused a uniform reduction in explant re generation. However, at low concentrations (0.35 mu M) MGBG resulted i n a 50% increase, to 92%, in regeneration from Westar. The potential o f MGBG in promoting explant regeneration in B. napus is discussed in t he light of its interaction with the explant genotype.