Carrageenan oligosaccharides enhance stress-induced microspore embryogenesis in Brassica oleracea var. italica

Embryogenic induction in cultures of isolated microspores is a stress-dependent process, which can be triggered by heat shock, sucrose or nitrogen starvation or by anti-microtubular drugs. As they are known to mimic biotic stress, oligosaccharides were tested as an alternative source of compounds to induce microspore embryogenesis in Brassica oleracea var. italica. Among the eight oligosaccharide series that were investigated and the corresponding polysaccharides, namely pectin, alginate, fucan, laminarin, agar and kappa-, iota-, and lambda-carrageenans, only the carrageenan oligomers displayed significant effects on microspore induction. When supplied in combination to heat stress, they markedly enhanced the final yields of microspore-derived embryos, with a two-fold increase in the most reactive treatment, i.e. in the presence of lambda-carrageenan oligosaccharides. A 30 min treatment was enough to stimulate embryogenesis, and two optimal concentrations were observed, 170 nM and 34 &mgr;M.