MATURATION OF SOMATIC EMBRYOS OF PINUS-STROBUS IS PROMOTED BY A HIGH-CONCENTRATION OF GELLAN GUM

Application of somatic embryogenesis to Pinus strobus clonal propagati on and genetic improvement was hampered by the difficulty in achieving synchronous maturation of a large number of somatic embryos that woul d germinate and produce plants. Media containing abscisic acid (80 mu M) and osmotic agents such as sucrose, polyethylene glycol and/or dext ran did not sustain development of mature somatic embryos from plated embryonal masses. This indicated that factors other than osmotic agent s might be involved in sustaining development of Pinus strobus somatic embryos to maturity. It was subsequently found that media lacking osm otica but containing a high concentration of gellan gum (1%) induced s ignificant improvement in the development of mature somatic embryos in the presence of 80 or 120 mu M abscisic acid. This positive effect wa s independent of the genotype and all four tested lines displayed simi lar responses. Media containing gellan gum at concentrations from 0.4 to 1.2% formed gels that varied in their strength. Gel strength was pr oportional to the concentration of gellan gum in the specific medium b ut varied depending on the medium formulation, Gel strength increased with the duration of storage of the culture medium by 46% (SD 14) afte r 14 days oi storage. Preliminary results showed that embryos matured on high gellan gum media displayed improved germination frequencies. T hese results indicate that in Pinus strobus the water status and possi bly other medium characteristics that are influenced by increased conc entration of gelling agent have stimulatory effects on maturation of s omatic embryos.