Use of TD-GC-TOF-MS to assess volatile composition during post harvest storage in seven accessions of rocket salad (Eruca sativa)

An important step in breeding for nutritionally enhanced varieties is determining the effects of the post-harvest supply chain on phytochemicals and the changes in VOCs produced over time. TD- GC-TOF-MS was used and a technique for the extraction of VOCs from the headspace using portable tubes is described. Forty-two compounds were detected; 39 were identified by comparison to NIST libraries. Thirty-five compounds had not been previously reported in Eruca sativa. Seven accessions were assessed for changes in headspace VOCs over 7 days. Relative amounts of VOCs across 3 time points were significantly different - isothiocyanate-containing molecules being abundant on 'Day 0'. Each accession showed differences in proportions/types of volatiles produced on each day. PCA revealed a separation of VOC profiles according to the day of sampling. Changes in VOC profiles over time could provide a tool for assessment of shelf-life

Multi-omic approaches to investigate molecular mechanisms in peach post-harvest ripening

Peach post-harvest ripening is a complex developmental process controlled by a plethora of genetic and epigenetic factors. Specifically, it leads to protein, lipid and nucleic acid degradation, all resulting in cell death. Substantial research has been directed at investigating peach regulatory mechanisms underlying genomic, metabolomic and transcriptomic modifications occurring during this stage, and much progress has been made thanks to the advent of Next Generation Sequencing technologies. This review is focused on the latest multi-omics studies, with the aim of highlighting the most significant results and further investigating the regulation of the key genes involved in peach post-harvest processes and related physiology. By offering an exhaustive overview of peach omics profiles, it provides a comprehensive description of gene expression changes and their correlation with ripening stages, including some post-harvest treatments, as well as with volatile organic compound modifications. However, the present work highlights that, due to the complexity of the process, recent investigations do not elucidate all underlying molecular mechanisms, making further studies still necessary. For this reason, some key points for future research activities and innovative peach breeding programs are discussed, relying on trusted multi-omic approaches

Multi-omics approaches to study molecular mechanisms in Cannabis sativa

Cannabis (Cannabis sativa L.), also known as hemp, is one of the oldest cultivated crops, grown for both its use in textile and cordage production, and its unique chemical properties. However, due to the legislation regulating cannabis cultivation, it is not a well characterized crop, especially regarding molecular and genetic pathways. Only recently have regulations begun to ease enough to allow more widespread cannabis research, which, coupled with the availability of cannabis genome sequences, is fuelling the interest of the scientific community. In this review, we provide a summary of cannabis molecular resources focusing on the most recent and relevant genomics, transcriptomics and metabolomics approaches and investigations. Multi-omics methods are discussed, with this combined approach being a powerful tool to identify correlations between biological processes and metabolic pathways across diverse omics layers, and to better elucidate the relationships between cannabis sub-species. The correlations between genotypes and phenotypes, as well as novel metabolites with therapeutic potential are also explored in the context of cannabis breeding programs. However, further studies are needed to fully elucidate the complex metabolomic matrix of this crop. For this reason, some key points for future research activities are discussed, relying on multi-omics approaches

Molecular mechanisms underlying potential pathogen resistance in cannabis sativa

Cannabis (Cannabis sativa L.) is one of the earliest cultivated crops, valued for producing a broad spectrum of compounds used in medicinal products and being a source of food and fibre. Despite the availability of its genome sequences, few studies explore the molecular mechanisms involved in pathogen defense, and the underlying biological pathways are poorly defined in places. Here, we provide an overview of Cannabis defence responses against common pathogens, such as Golovinomyces spp., Fusarium spp., Botrytis cinerea and Pythium spp. For each of these pathogens, after a summary of their characteristics and symptoms, we explore studies identifying genes involved in Cannabis resistance mechanisms. Many studies focus on the potential involvement of disease-resistance genes, while others refer to other plants however whose results may be of use for Cannabis research. Omics investigations allowing the identification of candidate defence genes are highlighted, and genome editing approaches to generate resistant Cannabis species based on CRISPR/Cas9 technology are discussed. According to the emerging results, a potential defence model including both immune and defence mechanisms in Cannabis plant–pathogen interactions is finally proposed. To our knowledge, this is the first review of the molecular mechanisms underlying pathogen resistance in Cannabis

Using volatile organic compounds to monitor shelf-life in rocket salad

Rocket salad (Diplotaxis tenuifolia or Eruca sativa) is a perishable product of increasing interest due to its high content of nutritionally relevant compounds including glucosinolates and vitamin C. There is an increasing consumption of ready-to-eat salads which are sold to the consumer in bags, often packed under modified atmosphere. Shelf-life and sell-by dates are commonly applied to these products and are usually dictated by the appearance of the product rather than its nutritional value. During shelf-life, postharvest deterioration leads to a loss of nutritionally relevant compounds such as vitamin C. This is accelerated by suboptimal conditions during storage and transport such as breaches of the cold-chain. Volatile organic compounds (VOCs) are easy and quick to sample use of thermal desorption gas chromatography time of flight mass spectroscopy (TD-GC-TOF-MS) enables remote sampling and a very sensitive analysis of VOC profiles. We have used TD-GC-TOF-MS to sample VOCs from rocket salad bags sourced from a local supermarket to assess changes during the shelf-life of the product. Using statistical analyses that treat the whole VOC profile as a single variable we show that it is possible to differentiate between day of purchase, use by date and time points beyond sale. We conclude that this methodology is therefore of use for assessing rocket salad quality through the supply chain

Multi-trait analysis of post-harvest storage in rocket salad (Diplotaxis tenuifolia) links sensorial, volatile and nutritional data

AbstractRocket salad (Diplotaxis tenuifolia; wild rocket) is an important component of ready to eat salads providing a distinct peppery flavour and containing nutritionally relevant compounds. Quality deteriorates during post-harvest, in relation to time and storage temperature amongst other factors. Volatile organic compounds (VOCs) are easily measurable from rocket leaves and may provide useful quality indicators for e.g. changes in isothiocyanates derived from nutritionally important glucosinolates. VOC profiles discriminated storage temperatures (0, 5 and 10°C) and times (over 14days). More specifically, concentrations of aldehydes and isothiocyanates decreased with time paralleling a fall in vitamin C and a reduction in sensorial quality at the two higher temperatures. Sulphur containing compounds rise at later time-points and at higher temperatures coincident with an increase in microbial titre, mirroring a further drop in sensorial quality thus indicating their contribution to off-odours

Physiological, metabolite and volatile analysis of cut size in melon during postharvest storage

Melons are an important component of fresh fruit salads, however, they suffer from limited shelf life. Processing of melon fruit for use in fruit salads induces a number of changes including alterations in colour and texture. In addition, respiration rate and ethylene production are affected. Processing also elicits changes in flavour (sweetness) and aroma (production of volatile organic compounds – VOCs), of critical importance to the consumer. Several parameters govern shelf life; temperature is a critical factor. In this study we tested whether cut size is another parameter that can affect quality indicators. Melon (Cucumis melo ‘Arapaho’) cubes of three sizes were stored at 4°C and assessed for quality at five time-points over a 15-day period. We assessed a number of parameters including firmness, loss of fresh weight, respiration rate, antioxidant capacity, phenolic compounds and carotenoid content. In addition we measured VOC profiles to assess whether there were any qualitative changes associated with storage period and/or cut size. Fresh weight (FW) loss and respiration rate increased significantly with storage time and FW loss was affected by cut size. Total carotenoid levels remained stable during the storage time as did antioxidant capacity in all cut sizes. However, cinnamic acid levels tended to decrease in the last stage of the storage period and changes in β-carotene content correlated with cut size (though not significantly). We were also able to separate the VOC profiles from the different cut sizes indicating that VOCs may be useful markers as indicators of the effects of cut size and storage time on quality

Detection of Listeria monocytogenes in cut melon fruit using analysis of volatile organic compounds

Ready-to-eat fresh cut fruits and vegetables are increasingly popular, however due to their minimal processing there is a risk of contamination with human pathogens. Listeria monocytogenes is of particular concern as it can multiply even at the low temperatures used to store fresh cut products pre-sale. Current detection methods rely on culturing, which is time consuming and does not provide results in the time frame required. Growth of bacteria on a substrate alters its chemical composition affecting the profile of volatile organic compounds (VOCs) emitted. Use of VOCs as a detection method has been hampered by lack of sensitivity and robust sample collection methods. Here we use thermal desorption gas chromatography time of flight mass spectrometry (TD-GC-TOF-MS) followed by analysis with PerMANOVA to analyse VOC profiles. We can discriminate between fresh cut melon cubes inoculated with 6 log CFU/g of L. monocytogenes and uninoculated controls, as well as melon cubes inoculated with <1 log CFU/g of L. monocytogenes stored for 7 days at 4 °C and following equilibration for 6 h at 37 °C. This is a substantial advance in sensitivity compared to previous studies and additionally the collection method used allows remote sampling and transport of the VOCs, greatly facilitating analyses

Effect of temperature and cut size on the volatile organic compound profile, and expression of Chorismate synthase in fresh-cut melon

The postharvest quality of fresh-cut melon is strongly affected by storage conditions to which it is subjected. During postharvest, fruit undergoes several stresses and its physiology is similar to that in senescent tissues. This affects both its biochemistry and the expression of genes involved in secondary metabolite biosynthesis. Volatile organic compounds (VOCs) have been used previously to assess quality of fresh cut melon as they reflect changes in flavor and also changes in overall metabolism. Chorismate synthase (CS) is a key enzyme in the shikimate pathway and catalyzes the formation of chorismate, which is the precursor of numerous aromatic compounds in plants. In this work the effects of different storage temperatures and cut-sizes were studied, with the aim of identifying effects on flavor through changes in VOCs, and molecular responses of the CmCS gene to different postharvest conditions. Melon (Cucumis melo L. 'Macigno') fruits were harvested at a fully ripened commercial stage, were washed in a chlorine water solution, and the mesocarp (pulp) was cut in cube-shaped portions; two sizes were chosen, 1×1 and 3×2 cm. Melon cubes were then stored at 20 or 4°C. VOCs were assessed in the 3×2 cut size at both temperatures and showed clear changes during storage. A subset of VOCs were shown to correlate negatively with storage time and temperature and from these, specific compounds can be identified that act as markers for an overall change in VOC profiles. CmCS was more affected by temperature, showing decreased levels of expression during storage at 20°C with respect to harvest and to cold storage. On the other hand, cut-size did not result in changes in its expression in 3×2 cut size

Expression of Arabidopsis WEE1 in Tobacco Induces Unexpected Morphological and Developmental Changes

WEE1 regulates the cell cycle by inactivating cyclin dependent protein kinases (CDKs) via phosphorylation. In yeast and animal cells, CDC25 phosphatase dephosphorylates the CDK releasing cells into mitosis, but in plants, its role is less clear. Expression of fission yeast CDC25 (Spcdc25) in tobacco results in small cell size, premature flowering and increased shoot morphogenetic capacity in culture. When Arath;WEE1 is over-expressed in Arabidopsis, root apical meristem cell size increases, and morphogenetic capacity of cultured hypocotyls is reduced. However expression of Arath;WEE1 in tobacco plants resulted in precocious flowering and increased shoot morphogenesis of stem explants, and in BY2 cultures cell size was reduced. This phenotype is similar to expression of Spcdc25 and is consistent with a dominant negative effect on WEE1 action. Consistent with this putative mechanism, WEE1 protein levels fell and CDKB levels rose prematurely, coinciding with early mitosis. The phenotype is not due to sense-mediated silencing of WEE1, as overall levels of WEE1 transcript were not reduced in BY2 lines expressing Arath;WEE1. However the pattern of native WEE1 transcript accumulation through the cell cycle was altered by Arath;WEE1 expression, suggesting feedback inhibition of native WEE1 transcription