The volatile esters of (Z)-3-hexenol with acetic, propionic, isobutyric, or butyric acids are synthesized by alcohol acyltransferases (AAT) in plants. These compounds are differentially emitted when tomato plants are efficiently resisting an infection with Pseudomonas syringae pv. tomato. We have studied the defensive role of these green leaf volatile (GLV) esters in the tomato response to bacterial infection, by analyzing the induction of resistance mediated by these GLVs and the phenotype upon bacterial infection of tomato plants impaired in their biosynthesis. We observed that treatments of plants with (Z)-3-hexenyl propionate (HP) and, to a greater extent with (Z)-3-hexenyl butyrate (HB), resulted in stomatal closure, PR gene induction and enhanced resistance to the bacteria. HB-mediated stomatal closure was also effective in several plant species belonging to Nicotiana, Arabidopsis, Medicago, Zea and Citrus genus, and both stomatal closure and resistance were induced in HB-treated NahG tomato plants, which are deficient in salicylic acid (SA) accumulation. Transgenic antisense AAT1 tomato plants, which displayed a reduction of ester emissions upon bacterial infection in leaves, exhibited a lower ratio of stomatal closure and were hyper-susceptible to bacterial infection. Our results confirm the role of GLV esters in plant immunity, uncovering a SA-independent effect of HB in stomatal defense. Moreover, we identified HB as a natural stomatal closure compound with potential agricultural applications.

Diverse fatty acid structures from different plant species are important renewable resources for industrial raw materials and as liquid fuels with high energy density. Because of its immense geographical and topographical variations, China is a country with enormous diversity of plant species, including large numbers of plants endemic to China. The richness of this resource of species provides a wide range of fatty acids in seeds or other tissues, many of which have been identified by Chinese scientists. However, in the past, most publications describing analysis of these plants were written in Chinese, making access for researchers from other countries difficult. In this study, we investigated reports on seed and fruit oil fatty acids as described in Chinese literature. Six books and more than one thousand papers were collected and the identified fatty acids and relevant plant species were summarized. In total, about 240 fatty acids from almost 1,500 plant species were identified from available Chinese literature. Only about one third of these species were retrieved in the PhyloFAdb and SOFA online databases of plant fatty acids. By referring to a summary of plant species endemic to China, 277 Chinese endemic species from 68 families have been surveyed for seed fatty acids. These account for <2% of total Angiosperm species endemic to China indicating the scope of species yet to be surveyed. To discover additional new fatty acid structures that might benefit society, it is important in the future to study oilseed fatty acids of the many other Chinese endemic plants. As an example, seeds of five unsurveyed species were collected and their fatty acids were analyzed. Ricinoleic acid was detected for the first time in the Salicaceae family.

During seed imbibition, lipids are engaged in membrane reorganization while facing free radical-mediated oxidative injury. In the present work, we explored changes in lipid components at different timepoints of imbibition (0.5, 2, 4, 6, and 8 h) in the legume Medicago truncatula, by combining biochemical approaches with targeted lipidomics and untargeted metabolomics. ROS and RNS (reactive oxygen and nitrogen species) accumulation was observed throughout the tested timepoints whereas lipid peroxidation increased at 4 h of imbibition. The seed response to oxidative damage was evidenced by a significant increase in tocopherols starting from 0.5 h of imbibition as well as by the reduction in total thiol content occurring at 2 h of imbibition. Since under physiological conditions, the proper functions of the cell membranes are strongly dependent on the qualitative and quantitative balance of fatty acid residues in phospholipids, the investigation was expanded to the fatty acid cohort of M. truncatula seeds. Total saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs), polyunsaturated fatty acids (PUFAs), omega(ω)-3 and omega(ω)-6 fatty acids showed fluctuations during seed imbibition. The most remarkable finding was the profile of the ω-3 PUFA docosopentaenoic acid (DPA, 7 cis, 10 cis, 13 cis, 16 cis, and 19 cis-22:5) that showed a peak (up to 1.0% of the total fatty acid content) at 0.5 and 8 h of imbibition, concomitant with the peaks observed in tocopherol levels. It is possible that the observed changes in DPA alter the physical properties of membranes, as reported in animal cells, triggering signaling pathways relevant for the cell defense against oxidative injury. Furthermore, the content and balance between tocopherols and PUFAs is regarded as a determinant of storage stability. No enhancement in trans-fatty acids occurred throughout imbibition, suggesting for a proper antioxidant response carried by the seed. Fatty acids profiles were integrated with data from untargeted metabolomics showing changes in lipid sub-pathways, among which fatty acid amide, lyso-phospholipids, and phospholipid metabolism. The emerging lipid profiles and dynamics are discussed in view of the overall imbibition damage generated during M. truncatula seed imbibition.

Carboxylesterases (CXE) and methylesterases (MES) are hydrolytic enzymes that act on carboxylic esters and are involved in plant metabolic processes and defense responses. A few functions of plant CXE and MES genes have been identified but very little information is available about the role of most members. We made a comprehensive study of this gene family in a commercially important species, peach (Prunus persica L. Batsch). A total of 33 peach CXE genes and 18 MES genes were identified and shown to be distributed unevenly between the chromosomes. Based on phylogenetic analysis, CXEs and MESs clustered into two different branches. Comparison of the positions of intron and differences in motifs revealed the evolutionary relationships between CXE and MES genes. RNA-seq revealed differential expression patterns of CXE/MESs in peach flower, leaf, and ripening fruit and in response to methyl jasmonate (MeJA) and ultraviolet B treatment. Transcript levels of candidate genes were verified by real-time quantitative PCR. Heterologous expression in Escherichia coli identified three CXEs that were involved in the hydrolysis of volatile esters in vitro. Furthermore, two recombinant MES proteins were identified that could hydrolyze MeJA and methyl salicylate. Our results provide an important resource for the identification of functional CXE and MES genes involved in the catabolism of volatile esters, responses to biotic and abiotic stresses and activation of signaling molecules such as MeJA and methyl salicylate.

Drought is a persistent challenge for horticulture, affecting various aspects of fruit development and ultimately fruit quality, but the effect on nutritional value has been under-investigated. Here, fruit quality was studied on six tomato genotypes and one goji cultivar under deficit irrigation (DI), from fruit composition to in vitro bioaccessibility of carotenoids. For both species, DI concentrated most health-related metabolites in fresh fruit. On a dry mass basis, DI increased total phenolic and sugar concentration, but had a negative or insignificant impact on fruit ascorbic acid, organic acid, and alcohol-insoluble matter contents. DI also reduced total carotenoids content in tomato (-18.7% on average), especially β-carotene (-32%), but not in goji berry DW (+15.5% and +19.6%, respectively). DI reduced the overall in vitro bioaccessibility of carotenoids to varying degrees depending on the compound and plant species. Consequently, mixed micelles produced by digestion of fruits subjected to DI contained either the same or lesser quantities of carotenoids, even though fresh fruits could contain similar or higher quantities. Thus, DI effects on fruit composition were species and genotype dependent, but an increase in the metabolite concentration did not necessarily translate into greater bioaccessibility potentially due to interactions with the fruit matrix.

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.

Flower color is an important trait in plants. However, genes responsible for the white flower trait in Chinese cabbage are rarely reported. In this study, we constructed an F2 population derived from the Y640-288 (white flower) and Y641-87 (yellow flower) lines for the fine mapping of the white flower gene BrWF3 in Chinese cabbage. Genetic analysis indicated that BrWF3 was controlled by a single recessive gene. Using BSA-seq and KASP assays, BrWF3 was fine-mapped to an interval of 105.6 kb. Functional annotation, expression profiling, and sequence variation analyses confirmed that the AtPES2 homolog, Bra032957, was the most likely candidate gene for BrWF3. Carotenoid profiles and transmission electron microscopy analysis suggested that BrWF3 might participate in the production of xanthophyll esters (particularly violaxanthin esters), which in turn disrupt chromoplast development and the formation of plastoglobules (PGs). A SNP deletion in the third exon of BrWF3 caused the loss of protein function, and interfered with the normal assembly of PGs, which was associated with reduced expression levels of genes involved in carotenoid metabolism. Furthermore, we developed and validated the functional marker TXBH83 for BrWF3. Our results provide insight into the molecular mechanism underlying flower color pigmentation and reveal valuable information for marker-assisted selection (MAS) breeding in Chinese cabbage.

Acyl-CoA-binding proteins (ACBPs), conserved at the acyl-CoA-binding domain, can bind acyl-CoA esters as well as transport them intracellularly. Six ACBPs co-exist in each model plant, dicot Arabidopsis thaliana (thale cress) and monocot Oryza sativa (rice). Although Arabidopsis ACBPs have been studied extensively, less is known about the rice ACBPs. OsACBP4 is highly induced by salt treatment, but down-regulated following pathogen infection, while OsACBP5 is up-regulated by both wounding and pathogen treatment. Their differential expression patterns under various stress treatments suggest that they may possess non-redundant functions. When expressed from the CaMV35S promoter, OsACBP4 and OsACBP5 were subcellularly localized to different endoplasmic reticulum (ER) domains in transgenic Arabidopsis. As these plants were not stress-treated, it remains to be determined if OsACBP subcellular localization would change following treatment. Given that the subcellular localization of proteins may not be reliable if not expressed in the native plant, this study addresses OsACBP4:GFP and OsACBP5:DsRED expression from their native promoters to verify their subcellular localization in transgenic rice. The results indicated that OsACBP4:GFP was targeted to the plasma membrane besides the ER, while OsACBP5:DsRED was localized at the apoplast, in contrast to their only localization at the ER in transgenic Arabidopsis. Differences in tagged-protein localization in transgenic Arabidopsis and rice imply that protein subcellular localization studies are best investigated in the native plant. Likely, initial targeting to the ER in a non-native plant could not be followed up properly to the final destination(s) unless it occurred in the native plant. Also, monocot (rice) protein targeting may not be optimally processed in a transgenic dicot (Arabidopsis), perhaps arising from the different processing systems for routing between them. Furthermore, changes in the subcellular localization of OsACBP4:GFP and OsACBP5:DsRED were not detectable following salt and pathogen treatment, respectively. These results suggest that OsACBP4 is likely involved in the intracellular shuttling of acyl-CoA esters and/or other lipids between the plasma membrane and the ER, while OsACBP5 appears to participate in the extracellular transport of acyl-CoA esters and/or other lipids, suggesting that they are non-redundant proteins in lipid trafficking.

Blue mold and core rot caused by Penicillium expansum and Trichothecium roseum are major diseases of apple fruit in China; however, their differential aggressiveness in apples and effect on fruit postharvest physiology are unclear. The effects of colonization of apples cv. Red Delicious by both pathogens were compared to physiological parameters of ripening and release of volatile compounds (VOCs). P. expansum colonization showed increased aggressiveness compared to T. roesum colonization of apple fruits. P. expansum enhanced colonization occurred with differential higher ethylene production and respiratory rate evolution, lower membrane integrity and fruit firmness in correspondence with the colonization pattern of inoculated apples. Moreover, P. expansum caused lower contents of total soluble solid and titratable acid, and higher malondialdehyde compared with T. roesum colonization. While both pathogen infections enhanced VOCs release, compared with T. roseum inoculated apples, P. expansum inoculated apple showed a higher total VOCs production including alcohols, aldehydes and esters, being the C6 alcohols, aldehydes and esters amount. PLS-DA analysis indicated that hexanoic acid was the most important factor to distinguish the inoculated fruits from the controls. Interestingly, propyl acetate and hexyl benzoate, and undecylenic acid and hexadecane were only identified in the P. expansum and T. roseum inoculated fruits, respectively. Taken together, our findings indicate that both fungi inoculations promote apple fruit ripening and release specific VOCs; moreover, apple fruits are more susceptible to P. expansum colonization than T. roesum.

The green microalga Lobosphaera incisa accumulates triacylglycerols (TAGs) with exceptionally high levels of long-chain polyunsaturated fatty acid (LC-PUFA) arachidonic acid (ARA) under nitrogen (N) deprivation. Phosphorous (P) deprivation induces milder changes in fatty acid composition, cell ultrastructure, and growth performance. We hypothesized that the resource-demanding biosynthesis and sequestration of ARA-rich TAG in lipid droplets (LDs) are associated with the enhancement of catabolic processes, including membrane lipid turnover and autophagic activity. Although this work focuses mainly on N deprivation, a comparative analysis of N and P deprivation responses is included. The results of lipidomic profiling showed a differential impact of N and P deprivation on the reorganization of glycerolipids. The formation of TAG under N deprivation was associated with the enhanced breakdown of chloroplast glycerolipids and the formation of lyso-lipids. N-deprived cells displayed a profound reorganization of cell ultrastructure, including internalization of cellular material into autophagic vacuoles, concomitant with the formation of LDs, while P-deprived cells showed better cellular ultrastructural integrity. The expression of the hallmark autophagy protein ATG8 and the major lipid droplet protein (MLDP) genes were coordinately upregulated, but to different extents under either N or P deprivation. The expression of the Δ5-desaturase gene, involved in the final step of ARA biosynthesis, was coordinated with ATG8 and MLDP, exclusively under N deprivation. Concanamycin A, the inhibitor of vacuolar proteolysis and autophagic flux, suppressed growth and enhanced levels of ATG8 and TAG in N-replete cells. The proportions of ARA in TAG decreased with a concomitant increase in oleic acid under both N-replete and N-deprived conditions. The photosynthetic apparatus's recovery from N deprivation was impaired in the presence of the inhibitor, along with the delayed LD degradation. The GFP-ATG8 processing assay showed the release of free GFP in N-replete and N-deprived cells, supporting the existence of autophagic flux. This study provides the first insight into the homeostatic role of autophagy in L. incisa and points to a possible metabolic link between autophagy and ARA-rich TAG biosynthesis.

Many plants accumulate high levels of hydroxycinnamoyl esters and amides in their tissues, presumably to protect against biotic and abiotic stress. Red clover (Trifolium pretense) leaves accumulate high levels [5-15 mmol/kg fresh weight (FW)] of caffeic acid derivatives, including phaselic acid (2-O-caffeoyl-L-malate). Oxidation of caffeoyl-malate by an endogenous polyphenol oxidase (PPO) has been shown to help preserve forage protein after harvest and during storage as silage, which should improve N use efficiency in dairy and other ruminant production systems. The widely grown forage alfalfa lacks both PPO and PPO substrates and experiences substantial loss of protein following harvest. We previously identified a hydroxycinnamoyl-coenzyme A (CoA):malate hydroxycinnamoyl transferase (HMT, previously called HCT2) responsible for phaselic accumulation in red clover. With the goal of producing PPO-oxidizable compounds in alfalfa to help preserve forage protein, we expressed red clover HMT in alfalfa. Leaves of these alfalfa accumulated mainly p-coumaroyl- and feruloyl-malate (up to 1.26 and 0.25 mmol/kg FW, respectively). Leaves of HMT-expressing alfalfa supertransformed with an RNA interference (RNAi) construct to silence endogenous caffeoyl-CoA acid O-methyltransferase (CCOMT) accumulated high levels of caffeoyl-malate, as well as the p-coumaroyl and feruloyl esters (up to 2.16, 2.08, and 3.13 mmol/kg FW, respectively). Even higher levels of caffeoyl- and p-coumaroyl-malate were seen in stems (up to 8.37 and 3.15 mmol/kg FW, respectively). This level of caffeoyl-malate accumulation was sufficient to inhibit proteolysis in a PPO-dependent manner in in vitro experiments, indicating that the PPO system of post-harvest protein protection can be successfully adapted to alfalfa.

Carotenoids are essential in human diet, so that the development of programs toward carotenoid enhancement has been promoted in several crops. The cereal tritordeum, the amphiploid derived from the cross between Hordeum chilense Roem. et Schulz. and durum wheat has a remarkable carotenoid content in the endosperm. Besides, a high proportion of these carotenoids are esterified with fatty acids. The identification of the gene(s) responsible for xanthophyll esterification would be useful for breeding as esterified carotenoids show an increased ability to accumulate within plant cells and have a higher stability during post-harvest storage. In this work, we analyzed five genes identified as candidates for coding the xanthophyll acyltransferase (XAT) enzyme responsible for lutein esterification in H. chilense genome. All these genes were expressed during grain development in tritordeum, but only HORCH7HG021460 was highly upregulated. Sequence analysis of HORCH7HG021460 revealed a G-to-T transversion, causing a Glycine to Cysteine substitution in the protein of H290 (the only accession not producing quantifiable amounts of lutein esters, hereinafter referred as zero-ester) of H. chilense compared to the esterifying genotypes. An allele-specific marker was designed for the SNP detection in the H. chilense diversity panel. From the 93 accessions, only H290 showed the T allele and the zero-ester phenotype. Furthermore, HORCH7HG021460 is the orthologue of XAT-7D, which encodes a XAT enzyme responsible for carotenoid esterification in wheat. Thus, HORCH7HG021460 (XAT-7Hch) is a strong candidate for lutein esterification in H. chilense and tritordeum, suggesting a common mechanism of carotenoid esterification in Triticeae species. The transference of XAT-7Hch to wheat may be useful for the enhancement of lutein esters in biofortification programs.

Oxylipins are crucial components in plant wound responses that are mobilised via the plant vasculature. Previous studies have shown that the overexpression of an Arabidopsis acyl-CoA-binding protein, AtACBP3, led to an accumulation of oxylipin-containing galactolipids, and AtACBP3pro::BETA-GLUCURONIDASE (GUS) was expressed in the phloem of transgenic Arabidopsis. To investigate the role of AtACBP3 in the phloem, reverse transcription-polymerase chain reaction and western blot analysis of phloem exudates from the acbp3 mutant and wild type revealed that the AtACBP3 protein, but not its mRNA, was detected in the phloem sap. Furthermore, micrografting demonstrated that AtACBP3 expressed from the 35S promoter was translocated from shoot to root. Subsequently, AtACBP3 was localised to the companion cells, sieve elements and the apoplastic space of phloem tissue by immunogold electron microscopy using anti-AtACBP3 antibodies. AtACBP3pro::GUS was induced locally in Arabidopsis leaves upon wounding, and the expression of wound-responsive jasmonic acid marker genes (JASMONATE ZIM-DOMAIN10, VEGETATIVE STORAGE PROTEIN2, and LIPOXYGENASE2) increased more significantly in both locally wounded and systemic leaves of the wild type in comparison to acbp3 and AtACBP3-RNAi. Oxylipin-related fatty acid (FA) (C18:2-FA, C18:3-FA and methyl jasmonate) content was observed to be lower in acbp3 and AtACBP3-RNAi than wild-type phloem exudates using gas chromatography-mass spectrometry. Experiments using recombinant AtACBP3 in isothermal titration calorimetry analysis showed that medium- and long-chain acyl-CoA esters bind (His)6-AtACBP3 with KD values in the micromolar range. Taken together, these results suggest that AtACBP3 is likely to be a phloem-mobile protein that affects the FA pool and jasmonate content in the phloem, possibly by its binding to acyl-CoA esters.

Volatile organic compounds (VOCs) emitted by plants are secondary metabolites that mediate the plant interaction with pathogens and herbivores. These compounds may perform direct defensive functions, i.e., acting as antioxidant, antibacterial, or antifungal agents, or indirectly by signaling the activation of the plant's defensive responses. Using a non-targeted GC-MS metabolomics approach, we identified the profile of the VOCs associated with the differential immune response of the Rio Grande tomato leaves infected with either virulent or avirulent strains of Pseudomonas syringae DC3000 pv. tomato. The VOC profile of the tomato leaves infected with avirulent bacteria is characterized by esters of (Z)-3-hexenol with acetic, propionic, isobutyric or butyric acids, and several hydroxylated monoterpenes, e.g., linalool, α-terpineol, and 4-terpineol, which defines the profile of an immunized plant response. In contrast, the same tomato cultivar infected with the virulent bacteria strain produced a VOC profile characterized by monoterpenes and SA derivatives. Interestingly, the differential VOCs emission correlated statistically with the induction of the genes involved in their biosynthetic pathway. Our results extend plant defense system knowledge and suggest the possibility for generating plants engineered to over-produce these VOCs as a complementary strategy for resistance.

The chloroplast is a self-independent organelle and contains its own transcription and translation systems. The establishment of genetic systems is vital for normal plant growth and development. We isolated a rice zebra leaf 16 (zl16) mutant derived from rice cultivar 9311. The zl16 mutant showed chlorotic abnormalities in the transverse sectors of the young leaves of seedlings. The use of transmission electron microscopy (TEM) demonstrated that dramatic defects occurred in variegated zl16 leaves during the early development of a chloroplast. Map-based cloning revealed that ZL16 encodes a β-hydroxyacyl-ACP dehydratase (HAD) involved in de novo fatty acid synthesis. Compared with the wild type, a missense mutation (Arg164Trp) in the zl16 mutant was identified, which significantly reduced enzymatic activity and altered the three-dimensional modeling structure of the putative protein. ZL16 was ubiquitously expressed in various plant organs, with a pronounced level in the young leaf. A subcellular localization experiment indicated that ZL16 was targeted in the chloroplast. Furthermore, we analyzed the expression of some nuclear genes involved in chloroplast development, and found they were altered in the zl16 mutant. RNA-Seq analysis indicated that some genes related to cell membrane constituents were downregulated in the mutant. An in vivo metabolic assay revealed that the total fatty acid content in the mutant was significantly decreased relative to the wild type. Our results indicate that HAD is essential for the development of chloroplasts by regulating the synthesis of fatty acids in rice.

At the cellular level, membrane damage is a fundamental cause of yield loss at high temperatures (HT). We report our investigations on a subset of a peanut (Arachis hypogaea) recombinant inbred line population, demonstrating that the membrane lipid remodeling occurring at HT is consistent with homeoviscous adaptation to maintain membrane fluidity. A major alteration in the leaf lipidome at HT was the reduction in the unsaturation levels, primarily through reductions of 18:3 fatty acid chains, of the plastidic and extra-plastidic diacyl membrane lipids. In contrast, levels of 18:3-containing triacylglycerols (TGs) increased at HT, consistent with a role for TGs in sequestering fatty acids when membrane lipids undergo remodeling during plant stress. Polyunsaturated acyl chains from membrane diacyl lipids were also sequestered as sterol esters (SEs). The removal of 18:3 chains from the membrane lipids decreased the availability of susceptible molecules for oxidation, thereby minimizing oxidative damage in membranes. Our results suggest that transferring 18:3 chains from membrane diacyl lipids to TGs and SEs is a key feature of lipid remodeling for HT adaptation in peanut. Finally, QTL-seq allowed the identification of a genomic region associated with heat-adaptive lipid remodeling, which would be useful for identifying molecular markers for heat tolerance.

The swelling agent is a plant growth regulator that alters the composition and content of nutrients and volatile gases in the fruit. To identify whether grape fruit had been treated with swelling agent, the odor information and quality indexes of grape berries treated with different concentrations of swelling agent were examined by using electronic nose technology and traditional methods. The contents of soluble sugars, soluble solids, soluble proteins and vitamin C were significantly increased in N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU) treated fruit. The contents of hexanal, (E)-2-hexenal, and nonanal aldehydes decreased significantly. Similarly, the levels of phenyl ethanol, 1-octanol, ethanol, and ethyl acetate alcohols and esters also decreased noticeably. Additionally, the levels of damascenone, linalool, and geraniol ketones and terpenoids decreased. However, the contents of benzaldehyde, D-limonene, acetic acid and hexanoic acid increased. In addition, the electrical signals generated by the electronic nose (e-nose) were analyzed by linear discriminant analysis (LDA), support vector machine (SVM) and random forest (RF). The average recognition rate of SVM was 94.4%. The results showed that electronic nose technology can be used to detect whether grapes have been treated with swelling agent, and it is an economical and efficient detection method.

Green leaf volatiles (GLVs) consist of six-carbon volatile aldehydes, alcohols, and their esters. They are formed from polyunsaturated fatty acids and are involved in the defense of plants against herbivores and pathogens. GLVs generally have low concentrations in intact healthy plant tissues, but the biosynthetic pathway to form GLVs is quickly activated by mechanical damage to tissues, an event called the GLV-burst. Most seed plants have the ability to implement GLV-burst; however, this potential in non-seed plants has not been extensively researched. In this study, we examined the GLV-burst capacity of monilophytes, lycophytes, and bryophytes, and confirmed that monilophytes and lycophytes showed substantial GLV-burst ability, while bryophytes did not, with a few exceptions. When the genome sequence of a model lycophyte, Selaginella moellendorffii was reviewed, 10 genes were found that showed high similarity with the non-canonical cytochrome P450 enzymes, CYP74s, specialized in oxylipin formation. Recombinant proteins expressed with Escherichia coli showed that one of them had the ability to encode allene oxide synthase, and another encoded hydroperoxide lyase (HPL), preferring linolenic acid 13-hydroperoxide, and it was inferred that this gene was responsible for GLV-burst in S. moellendorffii. Based on the phylogenetic tree constructed with CYP74s of non-seed and seed plants, we hypothesized that HPL was acquired independently in the lycophyte and seed plants through diversification of CYP74 genes.

Foliar pathogens face heterogeneous environments depending on the maturity of leaves they interact with. In particular, nutrient availability as well as defense levels may vary significantly, with opposing effects on the success of infection. The present study tested which of these factors have a dominant effect on the pathogen's development. Poplar leaf disks of eight maturity levels were inoculated with the poplar rust fungus Melampsora larici-populina using an innovative single-spore inoculation procedure. A set of quantitative fungal traits (infection efficiency, latent period, uredinia size, mycelium quantity, sporulation rate, sporulation capacity, and spore volume) was measured on each infected leaf disk. Uninfected parts of the leaves were analyzed for their nutrient (sugars, total C and N) and defense compounds (phenolics) content. We found that M. larici-populina is more aggressive on more mature leaves as indicated by wider uredinia and a higher sporulation rate. Other traits varied independently from each other without a consistent pattern. None of the pathogen traits correlated with leaf sugar, total C, or total N content. In contrast, phenolic contents (flavonols, hydroxycinnamic acid esters, and salicinoids) were negatively correlated with uredinia size and sporulation rate. The pathogen's fitness appeared to be more constrained by the constitutive plant defense level than limited by nutrient availability, as evident in the decrease in sporulation.

Green leaf volatiles (GLVs) are C6-molecules - alcohols, aldehydes, and esters - produced by plants upon herbivory or during pathogen infection. Exposure to this blend of volatiles induces defense-related responses in neighboring undamaged plants, thus assigning a role to GLVs in regulating plant defenses. Here we compared Arabidopsis thaliana ecotype Landsberg erecta (Ler) with a hydroperoxide lyase line, hpl1, unable to synthesize GLVs, for susceptibility to Pseudomonas syringae pv. tomato (DC3000). We found that the growth of DC3000 was significantly reduced in the hpl1 mutant. This phenomenon correlated with lower jasmonic acid (JA) levels and higher salicylic acid levels in the hpl1 mutant. Furthermore, upon infection, the JA-responsive genes VSP2 and LEC were only slightly or not induced, respectively, in hpl1. This suggests that the reduced growth of DC3000 in hpl1 plants is due to the constraint of JA-dependent responses. Treatment of hpl1 plants with E-2-hexenal, one of the more reactive GLVs, prior to infection with DC3000, resulted in increased growth of DC3000 in hpl1, thus complementing this mutant. Interestingly, the growth of DC3000 also increased in Ler plants treated with E-2-hexenal. This stronger growth was not dependent on the JA-signaling component MYC2, but on ORA59, an integrator of JA and ethylene signaling pathways, and on the production of coronatine by DC3000. GLVs may have multiple effects on plant-pathogen interactions, in this case reducing resistance to Pseudomonas syringae via JA and ORA59.