Fresh-cut Chinese water chestnuts (CWC) turn yellow after being peeled, reducing their shelf life and commercial value. Metabolomics, the systematic study of the full complement of small molecular metabolites, was useful for clarifying the mechanism of fresh-cut CWC etiolation and developing methods to inhibit yellowing. In this study, metabolic alterations associated with etiolation at different growth stages (0 day, 2 days, 3 days, 4 days, 5 days) from fresh-cut CWC were investigated using LC–MS and analyzed by pattern recognition methods (principal component analysis (PCA), partial least squares-discriminant analysis (PLS-DA), and orthogonal projection to latent structures-discriminant analysis (OPLS-DA)). The metabolic pathways of the etiolation molecules were elucidated. The main metabolic pathway appears to be the conversion of phenylalanine to p-coumaroyl-CoA, followed by conversion to naringenin chalcone, to naringenin, and naringenin then following different pathways. Firstly, it can transform into apigenin and its derivatives; secondly, it can produce eriodictyol and its derivatives; and thirdly it can produce dihydrokaempferol, quercetin, and myricetin. The eriodictyol can be further transformed to luteolin, cyanidin, dihydroquercetin, dihydrotricetin, and others. This is the first reported use of metabolomics to study the metabolic pathways of the etiolation of fresh-cut CWC.

This study aims to understand the main nutrient composition and comprehensively evaluate the differences in the mineral element contents of fruits of different macadamia cultivars, as well as screen good cultivars that are suitable for use in rocky desert mountains. Nine macadamia nut cultivars were selected as test materials in rocky desert mountain orchards. The contents of crude fat, crude protein, and total soluble sugar in kernels and N, P, K, Ca, Mg, Fe, Mn, Cu, Zn, and B in peels and kernels were determined, respectively. Then, the kernels’ mineral element contents were comprehensively evaluated based on principal component analysis. The results showed that the kernels were rich in crude fat, protein, and soluble sugar, with the crude fat content reaching 75% or greater, and the variation among cultivars was small. However, the variation in soluble sugar content was extensive. The content of mineral elements varied in different cultivars and parts of the fruit, with the average macronutrient content being K > N > Ca > P > Mg in the pericarp and N > K > P > Mg > Ca in the kernel, and the content of micronutrients in the pericarp and the kernel being Mn > Fe > Zn > Cu > B. By principal component analysis, the 10 mineral nutrient indexes were calculated as four principal components, with a cumulative contribution rate of 88.051%. Using the affiliation function value method and the calculation of the comprehensive evaluation value, the nine cultivars could be classified into three categories. The cultivar with the highest comprehensive evaluation value of the mineral element content was O.C. The one with the lowest value was H2, which indicated that O.C is a suitable variety for popularization in rocky desert mountainous areas. Stepwise regression analysis concluded that P, K, Fe, Mn, and Cu were the indicators significantly influencing the mineral element content of macadamia nuts and fruits in rocky desert mountains.

The pericarp of Macadamia integrifolia represents a promising but underexplored source of functional flavonoids. To systematically elucidate their biosynthesis and enhance the industrial potential of this by-product, we conducted integrated transcriptomic and metabolomic profiling of pericarps across five developmental stages (50, 80, 110, 140, and 170 days after flowering). Our analysis reveals, for the first time, a distinct temporal shift in both gene expression and metabolite accumulation. Early stages were characterized by high expression of PAL, 4CL, CHS, and FLS, coupled with abundant flavonols and anthocyanins. In contrast, late stages exhibited upregulation of CHI and F3’5’H, redirecting the metabolic flux toward flavanones and isoflavones. This dynamic profile was closely associated with jasmonate and gibberellin signaling pathways and was likely regulated by key transcription factors (MYB, NAC, bHLH). These findings provide a multi-omics framework that elucidates the temporal flavonoid biosynthesis in macadamia pericarp, thereby laying the groundwork for its future industrial valorization.

The kernel oil content of macadamia can reach up to 80%, yet the molecular basis underlying cultivar-dependent variation in lipid accumulation remains insufficiently understood. In this study, four macadamia cultivars with contrasting oil traits (O.C, QA1, QA2, and QA3) were investigated using integrated transcriptomic, metabolomic, and nutritional analyses to explore the metabolic pathways associated with kernel oil accumulation. Phenotypic evaluation revealed significant differences in fruit characteristics and nutritional composition among cultivars, with O.C exhibiting the highest crude fat content and QA1 showing the highest crude protein content. Transcriptomic analysis identified numerous differentially expressed genes (DEGs), which were mainly enriched in glycerolipid metabolism, α-linolenic acid metabolism, and amino acid biosynthesis pathways. Metabolomic profiling detected 778 metabolites, among which lipid-related compounds represented a major proportion. Integrated analysis revealed three major metabolic pathways associated with oil accumulation, including amino acid biosynthesis, glycerolipid metabolism, and linoleic acid metabolism. In the amino acid biosynthesis pathway, differential accumulation of amino acids and expression changes of genes including ASNS, GLUL, and MAT were observed among cultivars. In glycerolipid metabolism, differential expression of TAG biosynthesis-related genes (DGAT and PDAT) and variation in phospholipid-related metabolites, including LysoPC and LysoPE, were detected among cultivars. In linoleic acid metabolism, differential expression of fatty acid desaturation and elongation genes (SAD, FAD2, FAD3, and FAE1/KCS) was accompanied by cultivar-dependent differences in the abundance of several fatty acid-related metabolites. Overall, this study provides a comprehensive characterization of transcriptomic and metabolic variation associated with crude fat content and fatty acid-related metabolites in macadamia kernels and identifies candidate genes for further functional validation and molecular breeding studies.

Macadamia integrifolia is a valuable tropical and subtropical crop, yet its large-scale propagation remains constrained by difficulties in adventitious rooting. ‘Guire 1’, the dominant cultivar in Guangxi, China, accounts for over 65% of the local planting area, but its rooting ability and the underlying regulatory mechanisms remain poorly understood. Using one-year-old lignified branches of ‘Guire 1’, we examined structural, physiological, and molecular characteristics during the rooting process. Measurements included nutrient content, oxidase activity, and endogenous hormone levels across developmental stages, while integrated transcriptomic and metabolomic analyses were conducted to identify key pathways and genes. The findings demonstrated that macadamia cuttings rooted through the callus formation pathway. During rooting, malondialdehyde (MDA), soluble sugar, and soluble protein levels gradually declined, with no significant changes in later stages. Activities of superoxide dismutase (SOD) and peroxidase (POD) gradually decreased, with peroxidase maintaining relatively high activity in later stages. Free proline, abscisic acid (ABA), and jasmonic acid (JA) contents peaked at early stages and then decreased, whereas indole-3-acetic acid (IAA) peaked at the root primordium initiation stage. Zeatin riboside (ZR) and salicylic acid (SA)were highest at the initial stage. During the rooting process, a total of 1722 differential metabolites (DAMs), 14,482 differentially expressed genes (DEGs), and 699 transcription factors were identified. Integrated analyses identified plant hormone signal transduction, phenylpropanoid biosynthesis, flavonoid biosynthesis, and starch and sucrose metabolism as the crucial pathways involved in macadamia cutting rooting. These pathways regulated hormone balance, lignin synthesis, vascular differentiation, reactive oxygen species scavenging, and energy supply during rooting. This study elucidates the rooting mechanism in macadamia cuttings, supporting germplasm preservation and large-scale propagation techniques.