Regulatory factors to affect sporophytic shoot formation of Equisetum arvense induced by exogenously supplied cytokinin

Abstract

Summary We examined the regulatory factors involved in the formation of the sporophytic shoot of Equisetum arvense , which is produced from the gametophyte in response to exogenously supplied cytokinin. Among the tested cytokinins (BA, BA-riboside, Kinetin, Zeatin and 4-PU), BA showed the highest effect. As the concentrations of the cytokinins except Zeatin increased to more than those optimal for shoot formation, callus was dominantly produced from the explanted gametophyte tissue instead of the sporophytic shoot. Although cytokinin played a key role in expression of the sporophytic genes in the haploid generation of E. arvense (Kuriyama et al. 1990 a), no apogamous shoout could form on the sugar-free medium even when it was cultured with exogenous cytokinin. For the production of a number of shoots, a suitable concentration of sugar was needed with a suitable concentration of cytokinin. The necessity of a sugar supply did not depend on increasing osmotic pressure of culture medium because sucrose was more effective than glucose, and sorbitol and mannitol had no effect on shoot formation. Illumination was not required for sporophytic shoot formation, but shoots formed in darkness were yellow or whitish and thinner or longer than those formed in the light. NAA, 2,4-D, ABA, and GA inhibited apogamous shoot formation.