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Over the past few decades, complementary and alternative treatments have become increasingly popular worldwide. The purported therapeutic characteristics of natural products have come under increased scrutiny both in vitro and in vivo as part of efforts to legitimize their usage. One such product is tea tree oil (TTO), a volatile essential oil primarily obtained from the native Australian plant, Melaleuca alternifolia , which has diverse traditional and industrial applications such as topical preparations for the treatment of skin infections. Its anti-inflammatory-linked immunomodulatory actions have also been reported. This systematic review focuses on the anti-inflammatory effects of TTO and its main components that have shown strong immunomodulatory potential. An extensive literature search was performed electronically for data curation on worldwide accepted scientific databases, such as Web of Science, Google Scholar, PubMed, ScienceDirect, Scopus, and esteemed publishers such as Elsevier, Springer, Frontiers, and Taylor & Francis. Considering that the majority of pharmacological studies were conducted on crude oils only, the extracted data were critically analyzed to gain further insight into the prospects of TTO being used as a neuroprotective agent by drug formulation or dietary supplement. In addition, the active constituents contributing to the activity of TTO have not been well justified, and the core mechanisms need to be unveiled especially for anti-inflammatory and immunomodulatory effects leading to neuroprotection. Therefore, this review attempts to correlate the anti-inflammatory and immunomodulatory activity of TTO with its neuroprotective mechanisms.

Melaleuca alternifolia (tea tree), family Myrtaceae, is endemic to the northern rivers of NSW, Australia. Since 1925, the volatile components of the hydro- and steam-distilled oils of the leaves have been studied in detail. However, the less-volatile compounds have not been investigated. Using an ethanolic extract of the seedling leaves, the non-volatile components were studied using gas chromatography-mass spectrometry (GC/MS) and liquid chromatography- mass spectrometry (LC/MS). Four of these less-volatile components were isolated by preparative-HPLC from young seedling leaves and identified as the acylphloroglucinols 1-(2,6-dihydroxy-4-methoxy-3-methylphenyl)-2-methylpropan-1-one, callisalignone A, 1-(2,6-dihydroxy-4-methoxyphenyl)-3-methylbutan-1-one and pulverulentone B described here for the first time from M. alternifolia. These compounds change in concentration in the leaf sets as later seedling leaves mature on the seedling., (© 2022 The Authors. Chemistry & Biodiversity published by Wiley-VHCA AG, Zurich, Switzerland.)

Prostanthera lasianthos (Lamiaceae) is commonly referred to as the 'Victorian Christmas Bush', a name that derives from the floral display it gives in the Christmas period. However, botanists recognise P. lasianthos as a heterogeneous species aggregate that includes several putative new species that are confined to disjunct locations. Recently one taxon was revised to P. eungella B.J.Conn & K.M.Proft. In the current study the chemistry of essential oils was determined for 25 specimens, representative of 8 taxa (including P. eungella). Chemical relationships were investigated using two types of multivariate analysis and several distinct chemical profiles were identified. One taxon (P. sp. Wollomombi Gorge) was sampled nine times from three different locations during the year to determine the effects of seasonal variation and subjectively-assessed soil moisture content. It was demonstrated that the chemistry of this taxon is strongly influenced by soil moisture independently of growth stage, but possibly influenced by periods of dry or wet weather. Two distinct chemotypes and one intermediate type were identified. These chemotypes differed by mediated expression of linalool and hence linalyl acetate. These metabolites were also present in specimens of P. sp. Bald Mountain, but as minor components. This latter taxon could be reliably distinguished by higher relative abundance of butanoic acid, 1-methylbutyl ester. As judged by a smaller sampling size for the other taxa, evidence that this pattern of mediated expression between terpene species was found. However, the identity of terpenes that demonstrated this mediated expression were different for each taxon; for example, volatiles from P. eungella demonstrated mediation between α-pinene and caryophyllene. Nevertheless, it is possible that chemical expression of all taxa in the heterogeneous species aggregate is strongly mediated by the moisture or nutrient content of soils. Thus, the dataset produced during this study can be used as a reference against other chemical data to investigate taxonomic placement in members of this group., Competing Interests: Declaration of competing interest None., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Which majestic ornamental tree, conspicuous in the Australian landscape, has ten million hectares in cultivation worldwide--yielding timber, fuel, essential oil and cut foliage? It could only be eucalyptus.

Analysis of five microsatellite loci in 500 Melaleuca alternifolia individuals produced 98 alleles that were useful for population genetic studies. Considerable levels of observed heterozygosity were recorded (HO = 0.724), with approximately 90% of the variability being detected within populations. A low level of selfing (14%) was suggested to be the principal cause of excess homozygosity in a number of populations (overall FIS = 0.073). This study showed low levels of inbreeding in certain populations as well as a significant isolation-by-distance model. Only two groups of populations (Queensland and New South Wales) constituted different genetic provenances as a result of geographical isolation. The M. alternifolia data suggest that microsatellite loci did not always arise by a stepwise mutation process but that larger jumps in allele size may be involved in their evolution.