Influence of gelling agents on culture medium gel strength, water availability, tissue water potential, and maturation response in embryogenic cultures of Pinus strobus L.

Maturation of somatic embryos of Pinus strobus L. was evaluated on media co ntaining various types (agars and gellan gum), brands and concentrations of gelling agents in the presence of 80 mu M ABA and 0.09 M sucrose. The medi a were characterized with respect to gel strength, water potential and wate r availability. Embryogenic tissue and somatic embryos cultured on medium w ith various concentrations of gellan gum were used to determine their water potential (Psi). Regardless of the type of gelling agent used, gel strengt h increased with gelling agent concentration and was critical to the matura tion response. High gel strength was associated with reduced water availabi lity from the medium to the cultures. The water potential of gelled maturat ion medium remained constant between 0.4 and 1.0% gellan gum. It is conclud ed that the embryogenic tissue was exposed to varying amounts of water at t he onset of and during the culture period, and that the amount of water in the culture environment in turn influenced the maturation response. Cotyled onary somatic embryos derived from gellan gum medium of high gel strength h ad a lower Psi than somatic embryos matured on medium of lower gel strength . Once somatic embryos developed to the cotyledonary stage on the maturatio n medium, they were transferred to the germination medium. The germination frequency and the number of morphologically normal germinants were higher f or somatic embryos matured on medium of high gel strength. Raising the conc entration of the gelling agent in the maturation medium may be an alternati ve to the use of solutes to restrict water available to the embryogenic cul tures.