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Macadamia nuts, scientifically designated as Macadamia integrifolia, are a highly valuable crop that originated in Australia. This study provides a comprehensive examination of the symbiotic relationships between various macadamia root systems and arbuscular mycorrhizal fungi (AMF). The four principal macadamia-producing regions in Yunnan Province were selected for investigation on the basis of meticulous criteria. To determine the AMF infection rate, the roots were stained. Furthermore, high-throughput sequencing was employed to conduct a comprehensive analysis of the fungal diversity in the rhizosphere soil. The findings were definitive, indicating that both normal and cluster roots are capable of establishing a symbiotic relationship with AMF. Secondary forests exhibited significantly elevated fungal diversity relative to normal roots, while cluster roots demonstrated the lowest diversity and notable regional variation, indicating that the environment exerts a considerable influence on inter-root fungi and AMF. The analysis of the fungal community composition revealed that the predominant groups were Ascomycetes and Basidiomycetes. The FUNGuild function prediction clearly indicated distinct differences in the fungal functions of secondary forests, cluster roots, and normal roots. This study provides a scientific foundation for the sustainable development of macadamia nuts and significantly contributes to a deeper comprehension of the intricate interactions between macadamia and AMF, thereby fostering the long-term stable and healthy growth of the macadamia nut industry.

To research the antioxidant activity and amino acid composition of antioxidant peptides from Macadamia integrifolia, the Macadamia integrifolia polypeptides were prepared by complex protease enzymatic hydrolysis, the constituents with optimal antioxidant activity (molecular weight less than 1000 Da) were obtained by macroporous resin and dialysis technology. The polypeptides were separated by Sephadex G-15 gel, and the scavenging and reducing ability of 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxyl and 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulfonate) radicals (ABTS+) of each component were evaluated. The optimal antioxidant components were separated and identified and analyzed by liquid chromatography and tandem mass spectrometry (LC-MS/MS). The results showed that, the G1, G2 and G3 were isolated by dextran gel column chromatography, G3 had the strongest antioxidant activity, its scavenging and reducing capacity of hydroxyl radicals was superior to glutathione with half maximal inhibitory concentration (IC50) of 6.18 mg/mL and 2.19 mg/mL, respectively. The half maximal inhibitory concentration (IC50) of scavenging capacity of DPPH and ABTS+ was 0.50 and 0.02 mg/mL, respectively. G3 was identified by liquid chromatography tandem mass spectrometry to contain 46 peptides, the length of each peptide was less than 10 amino acids. The molecular weights of the 9 peptides with matching scores more than 200 were 631~920 Da, and with no toxicity. The screened peptides with high antioxidant activity were HLLPK, KEFFP and KEFFPA, the molecular weights of them were 606.84, 666.83 and 737.92 Da, respectively. This research preliminarily revealed the antioxidant peptides composition of macadamia nut, deepened the research of antioxidant peptide of Macadamia integrifolia, and would provide a theoretical reference for the development and utilization of antioxidant peptide of Macadamia integrifolia.

Vacuum-fried products were prepared with macadamia kernels as raw material. Single factor experiment and response surface Box-Behnken test were used to optimize the vacuum frying process of macadamia kernels. Oil content, acid value, peroxidation value, color difference and sensory quality of vacuum-fried kernel were determined by comparing with raw kernel. The results showed that the effects of freezing temperature, vacuum frying temperature, vacuum frying time and vacuum degree on taste and flavor quality of macadamia kernels were significantly different (P

Macadamia nut polypeptides were prepared by enzymatic hydrolysis of macadamia nut meal, and suitable proteases for the preparation of macadamia antioxidant polypeptides were screened with ABTS+ radical scavenging effects as evaluation indicators. Four constituents (MNAP-1, MNAP-2, MNAP-3, MNAP-4) were obtained by DA201-C macroporous resin and dialysis technology. The scavenging capacity against 1,1-diphenyl-2-picrylhydrazyl radical (DPPH·), hydroxyl radical and 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulfonate radicals) radical (ABTS+·), and reducing power were investigated by comparing with glutathione as controls. The results showed that the suitable protease was complex protease for the preparation of macadamia antioxidant polypeptides, which was better than neutral protease, acid protease, alkaline protease, papain and bromelain at the same concentration. Antioxidant activities of different molecular weight macadamia nut polypeptides were different, which all had strong scavenging capacity against DPPH and ABTS+ radicals, and also had certain scavenging capacity against hydroxyl radical and reducing power. MNAP-4 (molecular weight less than 1000 Da) had the strongest scavenging capacity against DPPH, ABTS+ and hydroxyl radicals and the highest reducing power with half maximal inhibitory concentration (IC50) of 0.36, 6.75, 0.08 and 3.19 mg/mL, respectively, which was lower than other molecular weight polypeptides. Correlation analysis showed different molecular weight macadamia nut polypeptides had good correlations with their DPPH, hydroxyl and ABTS+ radicals scavenging capacity and reducing power with r values of 0.947, 0.964, 0.948 and 0.856 (P

Macadamia is an evergreen tree belonging to the Proteaceae family. The two commercial macadamia species, Macadamia integrifolia and M. tetraphylla, are highly prized for their edible kernels. The M. integrifolia genome was recently sequenced, but the genome of M. tetraphylla has to date not been published, which limits the study of biological research and breeding in this species. This study reports a high-quality genome sequence of M. tetraphylla based on the Oxford Nanopore Technologies technology and high-throughput chromosome conformation capture techniques (Hi-C). An assembly of 750.87 Mb with 51.11 Mb N50 length was generated, close to the 740 and 758 Mb size estimates by flow cytometry and k-mer analysis, respectively. Genome annotation indicated that 61.42% of the genome is composed of repetitive sequences and 34.95% is composed of long terminal repeat retrotransposons. Up to 31,571 protein-coding genes were predicted, of which 92.59% were functionally annotated. The average gene length was 6,055 bp. Comparative genome analysis revealed that the gene families associated with defense response, lipid transport, steroid biosynthesis, triglyceride lipase activity, and fatty acid metabolism are expanded in the M. tetraphylla genome. The distribution of fourfold synonymous third-codon transversion showed a recent whole-genome duplication event in M. tetraphylla. Genomic and transcriptomic analysis identified 187 genes encoding 33 crucial oil biosynthesis enzymes, depicting a comprehensive map of macadamia lipid biosynthesis. Besides, the 55 identified WRKY genes exhibited preferential expression in root as compared to that in other tissues. The genome sequence of M. tetraphylla provides novel insights for breeding novel varieties and genetic improvement of agronomic traits.

Background Macadamia is a true dicotyledonous plant that thrives in a mild, humid, low wind environment. It is cultivated and traded internationally due to its high-quality nuts thus, has significant development prospects and scientific research value. However, information on the genetic resources of Macadamia spp. remains scanty. Results The mitochondria (mt) genomes of three economically important Macadamia species, Macadamia integrifolia, M. ternifolia and M. tetraphylla, were assembled through the Illumina sequencing platform. The results showed that each species has 71 genes, including 42 protein-coding genes, 26 tRNAs, and 3 rRNAs. Repeated sequence analysis, RNA editing site prediction, and analysis of genes migrating from chloroplast (cp) to mt were performed in the mt genomes of the three Macadamia species. Phylogenetic analysis based on the mt genome of the three Macadamia species and 35 other species was conducted to reveal the evolution and taxonomic status of Macadamia. Furthermore, the characteristics of the plant mt genome, including genome size and GC content, were studied through comparison with 36 other plant species. The final non-synonymous (Ka) and synonymous (Ks) substitution analysis showed that most of the protein-coding genes in the mt genome underwent negative selections, indicating their importance in the mt genome. Conclusion The findings of this study provide a better understanding of the Macadamia genome and will inform future research on the genus.

Macadamia (Macadamia spp.) has been widely planted in southern China and has been now developed into an important industry. China has the largest area of macadamia plantation in the world but provides only 3% production of the world. Current farming systems have a fertilizer surplus of about 73 g of nitrogen (N), 103 g of phosphorus (P), and 24 g of potassium (K) per macadamia plant per year in southern China. Optimizing fertilization recommended for macadamia improves production by about 5 kg per plant. Macadamia develops cluster roots (i.e., proteoid roots) in a P-starvation environment. Overuse of P fertilizers restrains the development of cluster roots as well as rhizosphere processes, thus decreasing the P-use efficiency. Excessive fertilization, especially P fertilization, is one of the major limiting factors in China macadamia production. This study is the first to analyze current management practices and then discuss approaches of improving nutrient management based on the specific root biology of macadamia. For a sustainable macadamia industry, it is imperative to develop appropriate nutrient management by integrating root-zone soil nutrient supply, fertilizer application, and rhizosphere processes. [ABSTRACT FROM AUTHOR]