No abstract

Maturation of somatic embryos of Pinus strobus L. was evaluated on media containing various types (agars and gellan gum), brands and concentrations of gelling agents in the presence of 80 mM ABA and 0.09 M sucrose. The media were characterized with respect to gel strength, water potential and water availability. Embryogenic tissue and somatic embryos cultured on medium with various concentrations of gellan gum were used to determine their water potential (C). Regardless of the type of gelling agent used, gel strength increased with gelling agent concentration and was critical to the maturation response. High gel strength was associated with reduced water availability from the medium to the cultures. The water potential of gelled maturation medium remained constant between 0.4 and 1.0% gellan gum. It is concluded that the embryogenic tissue was exposed to varying amounts of water at the onset of and during the culture period, and that the amount of water in the culture environment in turn influenced the maturation response. Cotyledonary somatic embryos derived from gellan gum medium of high gel strength had a lower C than somatic embryos matured on medium of lower gel strength. Once somatic embryos developed to the cotyledonary stage on the maturation medium, they were transferred to the germination medium. The germination frequency and the number of morphologically normal germinants were higher for somatic embryos matured on medium of high gel strength. Raising the concentration of the gelling agent in the maturation medium may be an alternative to the use of solutes to restrict water available to the embryogenic cultures.

Abstract:Leafy spurge (Euphorbia esula L.), a serious perennial weed of temperature range and pasture lands, has continued to colonize despite various control strategies. The persistence of this species can be attributed in part to the presence of an extensive root system containing abundant organic reserves. These components, established towards the end of the growing season, are remobilized to support early spring growth. Carbohydrates comprise the bulk of reserve material with late fall increments in free sugars being associated with reductions in starch content. Nitrogenous components undergo significant seasonal fluxes, with free amino acids and soluble proteins reaching maxima during late fall. Asparagine, glutamic acid, serine, ornithine, proline, arginine and aspartic acid all contribute significantly to the storage of nitrogen. Changes in nitrate content are associated with the overwintering process. These observations are indicative of the role that nitrogen plays in the overwintering strategy and regenerative capacity of leafy spurge roots.

Chicory (Cichorium itttyhus L.) and dandelion (Taraxacutn officinale L.) are persistent weeds, the aerial portions of which do not survive in winter. However, subterranean tissues remain viable and facilitate the rapid resumption of growth in early spring. The source of nutrients for gr-owth prior to the establishment of foliage is the r-oots. Carbohydrate and N reserves are accrued during late summer and attturnn, r-espectively. Hydrolysis of Iructans during late autumn occurs coincidentally with incr-ements in sucrose, the latter providing a readily accessible C pool. Nitr-ate, fr-ee amino acids and soluble protein all play substantial roles in nitrogen storage. Asparagine is the predominant amino acid in the free pool dur-ing winter, followed by glutamine, omithine, serine, aspartic acid and glutamic acid. Storage reserves remain at peak levels throughout winter and decline prior to the resumption of growth. The patterns observed here provide evidence that N is an important curr-ency of storage metabolism and, thus, a fr-amcwork has been provided for the examination of regulation of N storage in perennial weeds.

Roots are the overwintering structures of herbaceous perennial weeds growing in temperate climates. During the fall they accumulated reserves which are remobilized when growth resumes in the spring. An 18kDa (kilodalton) protein increases in both chicory and dandelion roots during the fall months. The proteins in both species are antigenically similar, and are recognized also by an antibody to a storage-protein deposited in Jerusalem artichoke (Helianthus tuberosus) tubers. In chicory, the protein is root-specific, but in dandelion it is detectable in the flowers, vestigial stem and the seed. Electrophoretic characterization of the 18-kDa protein shows that it is a single polypeptide, without subunits, with charge isomers of pI values close to pH 6.5. The major protein present in chicory and dandelion roots is unlike the vegetative storage proteins recently found in soybean or the storage proteins in the bark of trees.