New sights into lipid metabolism regulation by low temperature in harvested Torreya grandis nuts

Metabolomics reveal changes in flavor quality and bioactive components in post-ripening Torreya grandis nuts and the underlying mechanism

Secondary metabolites are a group of small molecules with critical roles in plants fitness in addition to their potential bioactivities in humans. Most of these compounds are associated with the flavor and quality formation of fruits or nuts during the development or the postharvest stages. Change in metabolic profiles and shifts underpinning the post-ripening process in T. grandis nuts are not yet reported. In this study, a large scale untargeted metabolomics approach was employed in T. grandis nuts, revealing for a total of 140 differential accumulated metabolites. Among them, nearly 60% of metabolites belonging to terpenoids, coumarins and phenolic acids, and phytohormones were showed a gradual accumulation pattern, while most of compounds in flavonoids were decreased during post-ripening. An in-depth analysis of changes in these metabolite classes suggest a framework for post-ripening process effect associated with the postharvest quality of T. grandis nuts for the first time.

The effect of ethylene on squalene and β-sitosterol biosynthesis and its key gene network analysis in Torreya grandis nuts during post-ripening process

Squalene and β-sitosterol are health-benefit compounds due to their nutritional and medicinal properties. It has been reported that the content of these bioactive compounds is relatively high in Torreya grandis nuts. However, it is not yet known what changes in squalene and β-sitosterol accumulation occur during the special post-ripening process of T. grandis nuts and the effect of the well-known ripening hormone ethylene on the regulatory mechanism of their biosynthetic pathways. Thus, we performed transcriptome and metabolite analyses. The results showed that ethylene not only promoted the post-ripening process but also enhanced the accumulation of squalene by inducing gene expression in the mevalonate pathway. At the same time, ethylene treatment also promoted the accumulation of other sterols but inhibited gene expression in the β-sitosterol biosynthesis pathway. In addition, co-expression and correlation analysis suggested a framework for the transcriptional regulation of squalene and β-sitosterol biosynthesis genes under ethylene treatment.

The interaction of temperature and relative humidity affects the main aromatic components in postharvest Torreya grandis nuts

The postharvest ripening stage is necessary for Torreya grandis (T. grandis) nuts to complete aromatic synthesis, which requires appropriate temperature and relative humidity (RH). Currently, scarce information is available regarding the changes in aroma profiles in T. grandis nuts and the relationship with their response to different environmental conditions. Therefore, the interaction of temperature (20 °C or 30 °C) and relative humidity (70% RH or 90% RH) was investigated on aromatic substances after harvest. The results showed that 56 aromatic components were detected by a gas chromatography-mass spectrometer (GC-MS) and mainly divided into five categories, among which terpenes were the most abundant (56.2-86.7%). Principal component analysis (PCA) showed that both temperature and humidity can affect the aroma composition, and terpenes were mainly influenced by humidity. Specifically, d-limonene occupied the largest proportion of terpenes (63.0-90.8%) and was significantly upregulated by high humidity.

Linum usitatissimum FAD2A and FAD3A enhance seed polyunsaturated fatty acid accumulation and seedling cold tolerance in Arabidopsis thaliana

Flax (Linum usitatissimum) seed oil is rich in polyunsaturated fatty acids (PUFAs), particularly linolenic acid, which is converted from linoleic acid. Studies have indicated that the biosynthesis of linoleic acid and linolenic acid is controlled by FAD2 and FAD3, respectively. However, the functional distinctions of different LuFAD2 and LuFAD3 copies from L. usitatissimum in governing the biosynthesis of linoleic acid or linolenic acid, respectively, remain unclear. In this study, five LuFAD2 and three LuFAD3 cDNAs were cloned from the L. usitatissimum cultivar 'Longya 10', and GC-MS results demonstrated that LuFAD2A and LuFAD3A play predominant roles in the accumulation of linoleic acid and linolenic acid, respectively. Their simultaneous overexpression in Arabidopsis thaliana seeds led to a significant increase in fatty acid contents, especially PUFAs. Additionally, LuFAD2A and LuFAD3A promoted the biosynthesis of jasmonic acid by increasing the levels of linolenic acid, which, in turn, enhanced plant cold tolerance. When the amount of linolenic acid is not sufficient, plants adapt to low temperature via the accumulation of anthocyanins. These findings provide insights into the higher accumulation of PUFAs in L. usitatissimum seeds, and provide potential targets for improving oil quality of other oil-producing crops through molecular manipulation.

Novel Insight into the Relationship between Metabolic Profile and Fatty Acid Accumulation Altering Cellular Lipid Content in Pineapple Fruits at Different Stages of Maturity

Pineapple fruits are usually harvested at different stages of maturity, based on consumer demands. The stage of maturity significantly affects the storage tolerance due to alterations in the cellular lipid homeostasis in the fruits. The characteristic abundance of metabolites and fatty acids (FAs) can provide vital information giving insight into the cellular lipid changes that occur during the ripening process in the fruits. Here, liquid chromatography-tandem mass spectrometry, largely based on the analysis of widely targeted metabolomics, was applied to evaluate the differences in the metabolites among the pineapple at three different stages of maturity namely, pineapples at the young fruit (YF), mature fruit (MF), and fully mature fruit (FMF) stages. In this study, 466 metabolites were annotated and identified. Among these, 59 lipids, including the glyceride esters, fatty acids and conjugates, and lysophospholipids (LPLs) were characterized. Notably, the LPLs were down-regulated in their relative abundance in the MF compared with the YF, and subsequently they remained almost stable in the FMF stage. The FA profiling results revealed the presence of certain unsaturated fatty acids (UFAs); besides, the total monounsaturated fatty acid (MUFA) to saturated fatty acid (SFA) ratio, as well as the polyunsaturated fatty acids (PUFA) to SFA ratio, showed noticeable decrease during the ripening process. The differential accumulation patterns of the LPLs, MUFAs, PUFAs, and SFAs imply that the lipid degradation and peroxidation take place in the pineapple fruits from the YF to MF and YF to FMF stages, respectively. The present study provides new insights into the alterations in the cellular lipid metabolism underlying the metabolite profiles and accumulation of FAs in pineapple fruits during ripening.

Effect of Temperature and Humidity on Oil Quality of Harvested Torreya grandis cv. Merrillii Nuts During the After-Ripening Stage

Temperature and relative humidity (RH) influence post-harvest ripening, a crucial stage for quality promotion in some oil plants or fruits. Torreya grandis cv. Merrillii nuts, which are rich in unsaturated fatty acids (UFA), are easily affected by temperature and humidity, and they oxidize quickly during the post-harvest ripening stage, leading to the deterioration of nut quality. In this study, the main nutraceutical components, fatty acid composition, and related metabolic parameters of lipid rancidity under four treatments (20°C and 70% RH, T20-LH; 30°C and 70% RH, T30-LH; 20°C and 90% RH, T20-HH; 30°C and 90% RH, T30-HH) were measured. The post-harvest ripening process was advanced under HH treatments (T20-HH and T30-HH) compared to LH treatments (T20-LH and T30-LH) and was associated with a shorter time for the seed coat to turn dark black and a faster reduction in starch content. The amount of unsaturated fatty acids significantly increased under the T20-HH treatment, but significantly decreased under the T30-HH treatment from 12 to 16 d of ripening time. The acid value (AV) and lipase activity under the T30-HH treatment remained virtually constant from 12 to 16 d of ripening time, and this was accompanied by a dramatic increase in peroxide value (POV), lipoxygenase (LOX) activity, and relative expression of the LOX2 gene. Meanwhile, a significant positive correlation between LOX activity and POV, malondialdehyde (MDA) content, and O2⋅- content was observed. The results imply that the lower amount of oxidative rancidity induced by the T20-HH treatment is related to the LOX activity induced by down-regulation of the LOX2 gene during the late after-ripening stage. Therefore, the T20-HH treatment not only promoted the post-harvest process of T. grandis 'Merrillii' nuts but also delayed lipid oxidation, which was ultimately associated with better oil quality at the late after-ripening stage.