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Trees bearing novel or exotic gene components are poised to contribute to the bioeconomy for a variety of purposes such as bioenergy production, phytoremediation, and carbon sequestration within the forestry sector, but sustainable release of trees with novel traits in large-scale plantations requires the quantification of risks posed to native tree populations. Over the last century, exotic hybrid poplars produced through artificial crosses were planted throughout eastern Canada as ornamentals or windbreaks and these exotics provide a proxy by which to examine the fitness of exotic poplar traits within the natural environment to assess risk of exotic gene escape, establishment, and spread into native gene pools. We assessed postzygotic fitness traits of native and exotic poplars within a naturally regenerated stand in eastern Canada ( Quebec City, QC). Pure natives ( P. balsamifera and P. deltoides spp. deltoides), native hybrids ( P. deltoides × P. balsamifera), and exotic hybrids (trees bearing Populus nigra and P. maximowiczii genetic components) were screened for reproductive biomass, yield, seed germination, and fungal disease susceptibility. Exotic hybrids expressed fitness traits intermediate to pure species and were not significantly different from native hybrids. They formed fully viable seed and backcrossed predominantly with P. balsamifera. These data show that exotic hybrids were not unfit and were capable of establishing and competing within the native stand. Future research will seek to examine the impact of exotic gene regions on associated biotic communities to fully quantify the risk exotic poplars pose to native poplar forests. [ABSTRACT FROM AUTHOR]

Hybridization and introgression are pervasive evolutionary phenomena that provide insight into the selective forces that maintain species boundaries, permit gene flow, and control the direction of evolutionary change. Poplar trees ( Populus L.) are well known for their ability to form viable hybrids and maintain their distinct species boundaries despite this interspecific gene flow. We sought to quantify the hybridization dynamics and postzygotic fitness within a hybrid stand of balsam poplar ( Populus balsamifera L.), eastern cottonwood ( P. deltoides Marsh.), and their natural hybrids to gain insight into the barriers maintaining this stable hybrid zone. We observed asymmetrical hybrid formation with P. deltoides acting as the seed parent, but with subsequent introgression biased toward P. balsamifera. Native hybrids expressed fitness traits intermediate to the parental species and were not universally unfit. That said, native hybrid seedlings were absent from the seedling population, which may indicate additional selective pressures controlling their recruitment. It is imperative that we understand the selective forces maintaining this native hybrid zone in order to quantify the impact of exotic poplar hybrids on this native system. [ABSTRACT FROM AUTHOR]

Advances in technology for in vitro propagation and genetic transformation have accelerated the development of genetically engineered trees during the past 15 years. At least 33 species of transformed forest trees have been successfully regenerated to date. Targeted traits include herbicide tolerance, pest resistance, abiotic stress tolerance, modified fiber quality and quantity, and altered growth and reproductive development. Commercial potential has been demonstrated in the field for a few traits, in particular herbicide tolerance, insect resistance, and altered lignin content. Now that commercial implementation is feasible, at least for the few genotypes that can be efficiently transformed and propagated, environmental concerns have become the main obstacle to public acceptance and regulatory approval. Ecological risks associated with commercial release range from transgene escape and introgression into wild gene pools to the impact of transgene products on other organisms and ecosystem processes. Evaluation of those risks is confounded by the long life span of trees, and by limitations of extrapolating results from small-scale studies to larger-scale plantations. Issues that are central to safe deployment can only be addressed by permitting medium- to large-scale release of transgenic trees over a full rotation. Current regulations restricting field releases of all transgenes in both time and space need to be replaced with regulations that recognize different levels of risk (as determined by the origin of the transgene, its impact on reproductive fitness, and nontarget impacts) and assign a commensurate level of confinement. The next step in determining acceptability of transgene technology for forest tree improvement is the unconfined release of constructs that pose little risk in terms of gene escape and nontarget impacts, such as lignin-altered poplar or pine, to permit evaluation of ecological risks and environmental or agronomic benefits at relevant scales. [ABSTRACT FROM AUTHOR]

We investigated the synthesis and accumulation of vegetative storage proteins (VSPs) in poplar plantlets and the homology between poplar seed storage proteins (SSPs) and VSPs. One-dimensional SDS polyacrylamide gel electrophoresis confirmed that both seed and vegetative storage proteins contained two predominant polypeptides of MW 32 and 36 kDa, but the subunit composition of the polypeptides differed. The 32- and 36-kDa polypeptides were highly abundant in basal leaves, stems, and roots of poplar plantlets. The 36-kDa subunit was synthesized in all plantlet tissues examined, but the 32-kDa subunit was not, suggesting that the 36-kDa polypeptide is a precursor of the 32-kDa polypeptide. The 36- and 32-kDa polypeptides of both SSPs and VSPs were glycosylated and both were found to be albumins. In addition, both polypeptides cross-reacted with a VSP antibody. Protein fingerprint patterns generated with two different proteolytic enzymes were identical for the 36-kDa polypeptide isolated from seeds or from stem tissue. Our study provides evidence that poplar SSPs and VSPs exhibit homology, and that expression is neither tissue-specific nor regulated solely by photoperiod. [ABSTRACT FROM PUBLISHER]

Isolating RNA from dry conifer seeds can be difficult because of a number of interfering compounds present in seeds. We describe a protocol for total RNA isolation from black spruce dry seeds, which is an adaptation of a method used for mouse myeloma tissues. The extraction relies on selective precipitation of RNA by using lithium chloride. [ABSTRACT FROM AUTHOR]

Butternut (Juglans cinerea L.) survival is threatened in North America by the fungus Sirococcus clavigignenti-juglandacearum. To date, there is no control for this fungal disease and long-term seed storage,to ensure survival of the species, is not a viable option. Initially, low (0, -5, -10, -15, and -400C) and ultralow (-1960C, cryopreservation) temperature tolerance of butternut embryonic axes isolated fromthe nuts collected from one tree was examined. Embryonic axes with approximately 3 mm of cotyledonary tissue attached to the hypocotyl area germinated after exposure to 0, -5, -10, -15, and -400C for 4 h and to -1960C for 24 h. Percent germination after exposure to 0 and -50C was 87 and 82%, respectively, and after -10 and -150C was 29 and 27%, respectively. Thirty-two percent of axes germinated after -400C, and 36% germinated after exposure to -1960C. Tolerance to -1960C was examined in the embryonic axes isolated from the nuts of 13 other trees. Significant tree-to-tree variation was found in the tolerance of the embryonic axes to low temperature. This variation corresponded to the water content of the embryonic axes; water contents of 4.8% and lower exhibited tolerance to -1960C. Reducing the water content of theembryonic axes by slow desiccation to 4.8% or less resulted in an increased tolerance to -1960C. These results suggest that low and ultralow temperature storage of embryonic axes may be a viable method for butternut ex situ conservation. [ABSTRACT FROM AUTHOR]