No abstract

Eucalyptus globulus is an important species for pulpwood production in many countries. The pattern and partitioning of variation is important baseline knowledge for tree breeding. Currently the species is divided into four subspecies: globulus, bicostata, pseudoglobulus and maidenii. Random Amplified Polymorphic DNA (RAPD) markers were used to analyse variation in 173 representatives of 37 natural populations of E. globulus: 31 localities of ssp. globulus (148 individuals), two localities each of ssp. bicostata (nine individuals), ssp. maidenii (ten individuals) and ssp. pseudoglobulus (six individuals). Ten 10-mer primers amplified a total of 162 scorable bands, of which 149 (91.9 per cent) were polymorphic. AMOVA analysis of a Euclidean distance matrix based on presence/absence of polymorphic bands found most variation within localities, but significant differences between localities and regions. Principal components analysis (PCA) identified a major latitudinal dine in RAPD phenotype that differentiated southern Tasmanian localities from other ssp. globulus localities on mainland Australia. Many localities previously identified as intermediate between subspecies globulus and other subspecies in morphology were not intermediate in RAPD phenotype. In some cases regions which showed marked differentiation between localities in capsule and juvenile leaf morphology showed little RAPD differentiation between localities. RAPDs also provided new insights into the affinities of outlying localities.Although RAPD technology has not yet been applied to many forest tree species, patterns of variation were similar to those found in other outcrossing species studied using both RAPDs and other molecular markers.

Olfactory ensheathing cells (OECs) represent an exciting possibility for promoting axonal regeneration within the injured spinal cord. A number of studies have indicated the ability of these cells to promote significant reactive sprouting of injured axons within the injured spinal cord, and in some cases restoration of functional abilities. However, the cellular and/or molecular mechanisms OECs use to achieve this are unclear. To investigate such mechanisms, we report for the first time the ability of OECs to promote post-injury neurite sprouting in an in vitro model of axonal injury. Using this model, we were able to differentiate between the direct and indirect mechanisms underlying the ability of OECs to promote neuronal recovery from injury. We noted that OECs appeared to act as a physical substrate for the growth of post-injury neurite sprouts. We also found that while post-injury sprouting was promoted most when OECs were allowed to directly contact injured neurons, physical separation using tissue culture inserts (1 mm pore size, permeable to diffusible factors but not cells) did not completely block the promoting properties of OECs, suggesting that they also secrete soluble factors which aid post-injury neurite sprouting. Furthermore, this in vitro model allowed direct observation of the cellular interactions between OECs and sprouting neurites using live-cell-imaging techniques. In summary, we found that OECs separately promote neurite sprouting by providing a physical substrate for growth and through the expression of soluble factors. Our findings provide new insight into the ability of OECs to promote axonal regeneration, and also indicate potential targets for manipulation of these cells to enhance their restorative ability.

No abstract

Although olfactory ensheathing cells (OECs) are used to promote repair in the injured spinal cord, little is known of their phenotype in this environment. In this study, using quantitative reverse transcriptase-polymerase chain reaction RT-PCR, expression of neuregulin-1 mitogen/survival factors and the axonal growth regulator Nogo was quantified in OECs and compared with other non-neuronal cells. Their expression was also compared with OECs which had previously been encapsulated in a porous polymer tube and implanted into the injured spinal cord. Similar to astrocytes and fibroblasts, OECs expressed various neuregulin subtypes including neu differentiation factor, glial growth factor and sensory and motorneuron-derived factor. Implanted OECs upregulated neu differentiation factor and secreted neuregulin, but downregulated expression of all other variants. OECs and oligodendrocytes expressed Nogo-A, -B and -ABC and were immunopositive for Nogo-A protein. The Nogo-A protein in OECs was found to be cytoplasmic rather than nuclear or cell surface associated. Unlike oligodendrocytes, OECs expressed Nogo-66 receptor (NgR) mRNA. Implanted OECs upregulated Nogo-A and -B, but downregulated Nogo-ABC and NgR.

The potential use of restriction fragment length polymorphisms (RFLPs) of chloroplast DNA to determine relationships at higher taxonomic levels in the genus Eucalptus was examined. Chloroplast DNA from 24 species, encompassing representatives of all the subgenera of Eucalyptus as well as one representative of the genus Angophora, was analysed using four 6-base restriction endonucleases. Eighty-four polymorphisms were obtained (twenty-eight autopomorphic) and the data matrix analysed using both cladistic and phenetic approaches. Results provided relatively good congruence with taxonomic perceptions based on morphological traits. Eucalyptus subgenera Blakella and Corymbia appear to be genetically similar to each other and to Angophora, although their phylogenetic relationships are not resolved in this study. Using Angophora alone, or together with the bloodwoods Blakella and Corynthia, as the outgroup for cladistic analysis, the two representatives of Eudesmia examined form a distinctly separate monophyletic group, which appears to be the sister taxon to Idiogenes, Gaubaen, Monocalyptus and Symphyomyrtus. The results provide some support for the close association of Idiogenes, Gauhaea and Monocalyptus and the hypothesis that they are the sister group of Symphyomyrtus. Taxonomically problematic species Eucalyptus guilfoylei, E. microcorys and E. deglupta were included in the study and it was found that E. guilfoylei appeared to diverge prior to the rest of the Symphyomyrtus, E. microcorys near the root of this clade, while the Telocalyptus representative E. deglupta fell within Symplgvontyrtus. The results obtained from the chloroplast DNA data provided independent support for previous morphological studies while generating new hypotheses and highlighting areas requiring closer examination.

Random amplified polymorphic DNA (RAPD) studies of a natural hybrid swarm between Eucalyptus amygdalina Labill. and E. risdonii Hook.f. and nearby allopatric stands revealed that, despite clear morphological differences, all bands were shared between species. However, frequency differences revealed genetic divergence between species, populations within species, and individuals within populations. Variation was greatest between individuals within populations and lowest between species. For both species, the direction of variation which distinguished the two populations was in a different direction to that which separated the two species, suggesting population differences were not due to introgression but were the result of genetic isolation and/or strong localised selection. Several morphologically typical individuals with intermediate RAPD profiles were detected in the hybrid swarm and nearby allopatric samples of both species, suggesting that some cryptic introgression may be occurring. Controlled F1 crosses generally had closer genetic affinity to E. risdonii, raising the possibility that some parents used may have been advanced generation hybrids. While natural hybrids selected for their intermediate leaf phenotype were usually also intermediate between the two species using RAPD markers, some deviated markedly toward E. risdonii. The study suggests that morphological appearance does not necessarily reflect genetic (RAPD) status and in some cases detectable RAPD differences between spatially close populations of the same species may be as great or greater than the differences between species.

Chloroplast DNA based phylogenetic studies using PCR-amplification and digestion (40 species) combined with Southern blotting (23 species) suggest that Angophora and some representatives of the Eucalyptus subgenera Corymbia and Blakella form a monophyletic group. The subgenera Eudesmia, Monocalyptus, Gaubaea, Idiogenes, Symphyoinyrtus and Telocalyptus appear to form a well defined monophyletic group encompassing most of Eucalyptus, but the exact sister taxon to this group remains unresolved. The results suggest that subgenera Corymbia and Blakella are paraphyletic and that Telocalyptus should be submerged within the subgenus Symnphyoinyrtus.