J.A. McComb

A comparison of changes in phenylalanine ammonia-lyase activity, lignin and phenolic synthesis in the roots of Eucalyptus calophylla (field resistant) and E. marginata (susceptible) when infected with Phytophthora cinnamomi

Inoculation of primary roots of Eucalyptus marginata (jarrah, susceptible) and E. calophylla (marri, field resistant) with Phytophthora cinnamomi zoospores caused a lesion to develop within 12–16 h. Lesions in roots of E. calophylla were restricted within 3–4 days and ceased extending whereas those in roots of E. marginata continued to extend. The temporal and spatial changes in phenylalanine ammonia lyase activity, lignin concentration and the concentration of soluble phenolics in roots were followed for 96 h after inoculation. PAL activity increased in inoculated roots of E. calophylla within 24 h of inoculation, beginning at the root tip and then declining to below control levels over the succeeding 24–48 h. A similar pattern of increase in PAL activity, followed by a decline was recorded for four of the five successive 1 cm root segments distal to the root tip. There were no increases in PAL activity in inoculated roots of E. marginata. After inoculation, the amount of lignin m roots of E. calophylla was increased above control levels by as much as 53%. Lignin concentrations in inoculated roots of E. marginata were unchanged. The concentration of suberin remained at pre-inoculation levels throughout the experiment in roots of both species. There were rapid increases in total soluble phenolics in roots of E. calophylla after inoculation, but only minor increases in roots of E. marginata. In the third root segment from the root tip in E. calophylla levels of total phenolics were at their maximum of 97% above controls. Thin layer chromatography of an aqueous methanol extract of infected roots of E. calophylla revealed the presence of several new compounds which were not present in control roots of E. marginata. Treatment of roots of E. calophylla with the PAL inhibitor, aminooxyacetate, altered the resistance response through changes in the concentration of lignin and phenolics and produced what phenotypically resembled susceptibility. These results implicate lignin and phenolic synthesis in the resistance of cucalypts to P. cinnamomi.

Salt tolerance screening of selected Australian woody species — a review

This review critically evaluates the strategies for selection of salt tolerant woody Australian species for land reclamation. There is evidence that in selecting material to screen, provenances from saline areas will show higher levels of salt tolerance than those from non-saline areas. However, there are sufficient numbers of exceptions to justify inclusion in trials of some material from non-saline areas. Because of the complexity and long term nature of field trials, large numbers of species and provenances have been screened as juvenile plants (up to 1 year old) in the glasshouse. For very few of these, has the match between performance in glasshouse and field been checked. In Eucalyptus, the genus for which most species have been screened, the assessment of salinity tolerance is the same in the field and glasshouse for 20 species, three appear more tolerant in the field than the glasshouse and five are less tolerant in the field than would be expected from glasshouse results. For 13 eucalypt species there are conflicting results between different glasshouse and/or field trials. A similar picture emerges for Melaleuca, Acacia and Casuarina though in these genera fewer species have been tested in both glasshouse and field. Glasshouse trials have a role where specific information is needed from juvenile plants such as the ability of a species to exclude salt from the leaves, or performance under controlled conditions of waterlogging or saline waterlogging. However, as the objective of most experiments is to identify superior salt tolerant lines for the field, despite the complexity and cost, well designed and monitored field trials are the ultimate test. Researchers are also encouraged to consider inclusion of appropriate standard lines of Eucalyptus camaldulensis and E. occidentalis to enable better comparisons between trials.

Transposable Elements: Powerful Contributors to Angiosperm Evolution and Diversity

Transposable elements (TEs) are a dominant feature of most flowering plant genomes. Together with other accepted facilitators of evolution, accumulating data indicate that TEs can explain much about their rapid evolution and diversification. Genome size in angiosperms is highly correlated with TE content and the overwhelming bulk (>80%) of large genomes can be composed of TEs. Among retro-TEs, long terminal repeats (LTRs) are abundant, whereas DNA-TEs, which are often less abundant than retro-TEs, are more active. Much adaptive or evolutionary potential in angiosperms is due to the activity of TEs (active TE-Thrust), resulting in an extraordinary array of genetic changes, including gene modifications, duplications, altered expression patterns, and exaptation to create novel genes, with occasional gene disruption. TEs implicated in the earliest origins of the angiosperms include the exapted Mustang, Sleeper, and Fhy3/Far1 gene families. Passive TE-Thrust can create a high degree of adaptive or evolutionary potential by engendering ectopic recombination events resulting in deletions, duplications, and karyotypic changes. TE activity can also alter epigenetic patterning, including that governing endosperm development, thus promoting reproductive isolation. Continuing evolution of long-lived resprouter angiosperms, together with genetic variation in their multiple meristems, indicates that TEs can facilitate somatic evolution in addition to germ line evolution. Critical to their success, angiosperms have a high frequency of polyploidy and hybridization, with resultant increased TE activity and introgression, and beneficial gene duplication. Together with traditional explanations, the enhanced genomic plasticity facilitated by TE-Thrust, suggests a more complete and satisfactory explanation for Darwin’s “abominable mystery”: the spectacular success of the angiosperms.

Alternating Cytokinins in Multiplication Media Stimulates in Vitro Shoot Growth and Rooting of Eucalyptus globulus Labill

Shoots of Eucalyptus globulus Labill. cultured on shoot multiplication media containing, on alternate subcultures, 6-benzylaminopurine (BAP) or 6-furfurylaminopurine (kinetin), showed better growth than cultures in which either of the cytokinins was used continuously, or both were used in an equimolar mixture. When BAP was used continuously in the medium (i.e. in every subculture), shoots multiplied but remained stunted and leaves became red and abscised. Kinetin or 6-dimethylallyaminopurine (2iP) used continuously in the medium induced very low multiplication but the shoots did not become red nor did the leaves abscise. Shoots taken from multiplication medium containing BAP and placed on rooting medium with 10 microM indole butyric acid (IBA) produced few roots and often died while on the rooting medium. In contrast, shoots from the multiplication medium containing kinetin produced more roots and remained healthy during the passage on the rooting medium.

The long-term ability of phosphite to control Phytophthora cinnamomi in two native plant communities of Western Australia

This study examined the ability of foliar applications of the fungicide phosphite to contain colonisation of Phytophthora cinnamomi in a range of plant species growing in natural plant communities in the northern sandplain and jarrah (Eucalyptus marginata) forest of south-western Australia. Wound inoculation of plant stems with P. cinnamomi was used to determine the efficacy of phosphite over time after application. Colonisation by P. cinnamomi was reduced for 5–24 months after phosphite was applied, depending on the concentration of phosphite used, plant species treated and the time of phosphite application. Plant species within and between plant communities varied considerably in their ability to take up and retain phosphite in inoculated stems and in the in planta concentrations of phosphite required to contain P. cinnamomi. As spray application rates of phosphite increased from 5 to 20 g L–1, stem tissue concentrations increased, as did the ability of a plant species to contain P. cinnamomi. However, at application rates of phosphite above 5 g L–1 phytotoxicity symptoms were obvious in most species, with some plants being killed. So, despite 10 and 20 g L–1 of phosphite being more effective and persistent in controlling P. cinnamomi, these rates are not recommended for application to the plant species studied. The results of this study indicate that foliar application of phosphite has considerable potential in reducing the impact of P. cinnamomi in native plant communities in the short-term. However, in order to maintain adequate control, phosphite should be sprayed every 6–12 months, depending on the species and/or plant community.

Vacuum infiltration of Petunia hybrida pollen with Agrobacterium tumefaciens to achieve plant transformation

Abstract Genetic transformation of Petunia hybrida with a reporter gene and selectable marker gene (35S-bar) was achieved in similar frequencies by pollinating flowers with pollen vacuum-infiltrated with Agrobacterium tumefaciens or applying a drop of Agrobacterium suspension to the stigma immediately prior to pollination. Nine percent of the T1, and 5% of the T2 progeny germinated in nutrient medium with 3 mgl/l BastaR. Polymerase chain reaction assays indicated that of the BastaR-resistant plants, 66% of the T1 plants, and 61% of the T2 plants harboured the GUS gene. Histochemical assays showed that 10% of the putatively transformed T1 plants and 5% of their progeny expressed GUS in leaf tissue, pistils and young anthers. Southern hybridization confirmed genomic integration of the bar gene in one to three places in selected T1 and T2 progeny.

Selection for NaCl tolerance in cell cultures of Medicago sativa and recovery of plants from a NaCl-tolerant cell line

Medicago sativa lines with a high incidence of regeneration were established as suspension cultures and used to select for NaCl tolerant lines. Attempts were then made to regenerate plants from these lines. Regeneration was severely depressed in NaCl tolerant calli and the only plants that were successfully regenerated were from one callus of M. sativa cv. Regen S which grew in 62.5 mM NaCl. Plants from this callus, and new calli derived from the recovered plants, have shown a tolerance to NaCl comparable to calli and plants from the initial seed stock rather than an improved level of tolerance.

Phylogenetic relationships between two rare acacias and their common, widespread relatives in south-western Australia

Knowledge of phylogenetic relationships betweentaxa is particularly valuable for conservationmanagement of threatened taxa in anevolutionarily diverse flora such as that foundin the south-west of Western Australia. Acacia sciophanes and A. lobulata aretwo threatened species that have restricteddistributions at the edge of the range of theirwidespread relatives, A. anfractuosa andA. verricula respectively. The phylogenyof these species pairs was investigated usingRFLP analysis of cpDNA. Both restricted specieswere shown to be phylogenetically distinct.Acacia sciophanes and A. anfractuosaare sister species and display the characteristics of a relatively recent evolutionary lineage. In comparison A. lobulata shows significant divergence from A. verricula and is not closely related to the species group in which A. verricula is placed. Acacia lobulataappears to represent an ancient lineage and ismost likely a relictual species. Acaciaverricula also has characteristics of a moreancient evolutionary lineage than A.sciophanes and A. anfractuosa. Ifpriority setting processes based onphylogenetic principles were to be applied tothese species A. lobulata would have thegreater biodiversity value for conservationmanagement.

Mating system studies in jarrah, Eucalyptus marginata (Myrtaceae)

Estimates of outcrossing rate were determined for four populations of Eucalyptus marginata from the jarrah forest in south-west Western Australia. The mean multilocus outcrossing rate (t = 0.81) was high in all populations and was towards the high end of the range of outcrossing rates that have been observed in other mass-flowering eucalypt species. A significant proportion of the inbreeding detected appeared to be due to biparental inbreeding, and the levels of correlated paternity were unexpectedly high. Differences between populations were generally not significant, although trees from a disturbed site affected by disease showed lower outcrossing, higher biparental inbreeding and higher correlated paternity, suggesting an increase in population structure compared with trees from disease-free sites.

Ability of phosphite applied in a glasshouse trial to control Phytophthora cinnamomi in five plant species native to Western Australia

The ability of phosphite to control Phytophthora cinnamomi Rands in five Western Australian native plant species was examined. Foliar application of phosphite slowed, but did not completely inhibit, colonisation of stems by P. cinnamomi. For example, in Banksia hookeriana Meisn. inoculated 2 weeks after phosphite application, 5 g phosphite/L inhibited the growth rate of P. cinnamomi by 57% compared with the non-phosphite-treated plants. The longevity of phosphite efficacy varied with plant species. Foliar application of 5 and 10 g phosphite/L decreased the growth rate of P. cinnamomi in Dryandra sessilis (Knight) Domin. for at least 12 months after it was applied. Application rates of 5 and 10 g phosphite/L for Banksia grandis Willd. and 10 g/L for B. hookeriana were effective for at least 18 months after application. In Hibbertia commutata Steud. and Dampiera linearis R.Br., phosphite was effective for less than 6 and 12 months, respectively. In a second trial, plants were inoculated with P. cinnamomi at different time periods after phosphite was applied and time to death was recorded. There was a range of responses depending on the plant species and time of year they were inoculated. The initial levels of phosphite in roots and stems of B. grandis, B. hookeriana and D. sessilis and the rate of decrease of phosphite in these tissues differed between plant species. In general, concentrations of phosphite in stems were higher or equivalent to those in roots. This study indicates that the long-term efficacy of phosphite depends on both the plant species treated and the time of year the plants are infected with P. cinnamomi.