ABSTRACT L-phenylalanine (Phe) is converted via the phenylpropanoid pathway into phenolic compounds, and elevated phenolic/flavonoid levels are generally associated with enhanced plant resistance. We previously showed that exogenous Phe suppresses the necrotrophic fungus Botrytis cinerea in petunia, chrysanthemum, determinant tomato, and several postharvest diseases. Here, we expanded evaluation to a broad range of pathosystems, including an indeterminate greenhouse tomato cultivar, multiple dicot species, and the monocot wheat. Phe, applied as spray or drench across concentrations, was consistently effective at ≥4 mM. It reduced disease severity in diverse systems: Sclerotinia sclerotiorum (tomato, sweet basil, cucumber, lettuce), Leveillula taurica and Oidium neolycopersici (tomato), Podosphaera xanthii (cucumber), wheat foliar pathogens ( Blumeria graminis f. sp. tritici , Zymoseptoria tritici , Puccinia triticina , P. striiformis f. sp. tritici ), the oomycetes Pseudoperonospora cubensis (cucumber leaves) and Pythium aphanidermatum (roots), bacterial pathogens ( Pseudomonas syringae pv. tomato and Clavibacter michiganensis subsp. michiganensis ) and Tomato brown rugose fruit (ToBRFV) that belongs to the Tobamovirus genus. Phe was effective on both young and mature leaves and often performed comparably to chemical fungicides; combinations rarely improved control, except for enhanced activity with pyrimethanil against B. cinerea in tomato. Synergistic effects were observed when Phe was combined with an adjuvant against tomato powdery mildews. A formulated product (NaturaFend 550 SP) was more effective than non-formulated Phe in B. cinerea (tomato) and P. xanthii (cucumber). Application timing also influenced efficacy, with treatment 5 days before infection providing superior control compared with 0, 3, or 7 days. Overall, Phe effectively controlled biotrophic and necrotrophic fungi, oomycetes, bacterial pathogens and a virus across diverse crops under experimental greenhouses and commercial like conditions.

Anthocyanin coloration of fruit, foliage, and flowers is dependent both on pigment synthesis and degradation. Our previous comprehensive study on in planta anthocyanin degradation was conducted on the purple Brunfelsia calycina flowers, whitening due to a one-step process, involving a single vacuolar peroxidase. Here, we reveal a novel two-step in planta degradation process in the purple Solanum macranthum flowers, as they whiten. This process involves both vacuolar β-glucosidases and peroxidases, similar to the in vitro processes described in fruit juices, with β-glucosidase enzymes stripping the pigments from their sugar moieties, followed by enzymes oxidizing the aglycones. We show that the activities of both β-glucosidase and peroxidase are crucial for the in planta degradation to occur in S. macranthum flowers. A specific vacuolar β-glucosidase (SmBGL7) and two peroxidase isozymes (SmPrx01, SmPrx02) increased in their activity parallel to the degradation process. One vacuolar β-glucosidase gene and two peroxidase genes are induced in the flower tissue just prior to the onset of anthocyanin degradation, with MWs related to those found for the corresponding isozymes of all three enzymes. SmPrx01 has an identical active site proximal heme-ligand signature sequence to the B. calycina degrading peroxidase gene, BcPrx01, and binds both malvidin (the main aglycone in B. calycina) and petunidin (the main aglycone in S. macranthum) equally. The second peroxidase, unique to S. macranthum, SmPrx02, has a stronger binding to petunidin than to malvidin, suggesting potential variability and synergistic involvement of peroxidases in anthocyanin degradation.

Tuta absoluta ("leafminer"), is a major pest of tomato crops worldwide. Controlling this insect is difficult due to its efficient infestation, rapid proliferation, and resilience to changing weather conditions. Furthermore, chemical pesticides have only a short-term effect due to rapid development of T. absoluta strains. Here, we show that a variety of tomato cultivars, treated with external phenylalanine solutions exhibit high resistance to T. absoluta, under both greenhouse and open field conditions, at different locations. A large-scale metabolomic study revealed that tomato leaves absorb and metabolize externally given Phe efficiently, resulting in a change in their volatile profile, and repellence of T. absoluta moths. The change in the volatile profile is due to an increase in three phenylalanine-derived benzenoid phenylpropanoid volatiles (BPVs), benzaldehyde, phenylacetaldehyde, and 2-phenylethanol. This treatment had no effect on terpenes and green leaf volatiles, known to contribute to the fight against insects. Phe-treated plants also increased the resistance of neighboring non-treated plants. RNAseq analysis of the neighboring non-treated plants revealed an exclusive upregulation of genes, with enrichment of genes related to the plant immune response system. Exposure of tomato plants to either benzaldehyde, phenylacetaldehyde, or 2-phenylethanol, resulted in induction of genes related to the plant immune system that were also induced due to neighboring Phe-treated plants. We suggest a novel role of phenylalanine-derived BPVs as mediators of plant-insect interactions, acting as inducers of the plant defense mechanisms.

Plants can easily uptake and metabolize externally given phenylalanine to numerous specialized metabolites, related to fragrance, increased resistance to pathogens, and fruit aroma. Despite the resulting improved quality, there are several drawbacks associated with the characteristics of phenylalanine molecules that might delay its commercial use. One is the fact that phenylalanine can serve as a carbon and nitrogen source for microorganisms when kept in aqueous solutions for extended periods. This may cause, for example, clogging of cut stems dipped in phenylalanine solutions. Another drawback is the remaining of phenylalanine residues on the plants, causing damage. Here we present a novel carboxymethyl cellulose derivate for efficient encapsulation of phenylalanine, reducing the effect of stem clogging and improving its uptake into plant tissues. This formulation is a carboxymethyl cellulose derivative with butyl substituents, termed CMC-4, which can self-assemble spontaneously, and has a dynamic structure enabling encapsulation of not only hydrophobic, but also hydrophilic and even ionic molecules. Petunia foliar application of phenylalanine encapsulated into CMC-4 increases the efficiency of phenylalanine uptake and metabolism. Furthermore, CMC-4 delayed drying of phenylalanine solution droplets sprayed on plants, resulting in less residue deposition on the leaves and flowers, and allowing treatments with higher phenylalanine concentrations.

Phenylalanine has a unique role in plants as a source of a wide range of specialized metabolites, named phenylpropanoids that contribute to the adjustment of plants to changing developmental and environmental conditions. The profile of these metabolites differs between plants and plant organs. Some of the prominent phenylpropanoids include anthocyanins, phenolic acids, flavonoids, tannins, stilbenes, lignins, glucosinolates and benzenoid phenylpropanoid volatiles. Phenylalanine biosynthesis, leading to increased phenylpropanoid levels, is induced under stress. However, high availability of phenylalanine in plants under non-stressed conditions can be achieved either by genetically engineering plants to overproduce phenylalanine, or by external treatment of whole plants or detached plant organs with phenylalanine solutions. The objective of this review is to portray the many effects that increased phenylalanine availability has in plants under non-stressed conditions, focusing mainly on external applications. These applications include spraying and drenching whole plants with phenylalanine solutions, postharvest treatments by dipping fruit and cut flower stems, and addition of phenylalanine to cell suspensions. The results of these treatments include increased fragrance in flowers, increased aroma and pigmentation in fruit, increased production of health promoting metabolites in plant cell cultures, and increased resistance of plants, pre- and post-harvest, to a wide variety of pathogens. These effects suggest that plants can very efficiently uptake phenylalanine from their roots, leaves, flowers and fruits, translocate it from one organ to the other and between cell compartments, and metabolize it into phenylpropanoids. The mechanisms by which Phe treatment increases plant resistance to pathogens reveal new roles of phenylpropanoids in induction of genes related to the plant immune system. The simplicity of treatments with phenylalanine open many possibilities for industrial use. Many of the phenylalanine-treatment effects on increased resistance to plant pathogens have also been successful in commercial field trials.

Pathogenic fungi cause most postharvest decay. Phenylalanine (Phe) is an eco-friendly treatment that increased fruit resistance to various pathogenic fungi including Colletotrichum gloeosporioides, the main postharvest pathogen of mango fruit. The mode of action of Phe-induced fruit tolerance against C. gloeosporioides was examined after harvest, post-treatment, and post-inoculation by transcriptome, metabolome, and biochemical assays. Phe treatment induced defense response-related genes including Ca2+ signaling, MAP kinase, WRKY transcription factors, and activation of the phenylpropanoid pathway, which lead to an accumulation of flavonols and anthocyanins. In addition, after Phe application and C. gloeosporioides inoculation, the levels of the antioxidant, total phenolic, and flavonoid were induced. The increase in antioxidants in Phe-treated fruit was correlated with reduced lipid peroxidation. Phenolic extract of mango peel treated with Phe reduced conidia germination and hyphal growth of various pathogenic fungi including C. gloeosporioides, Botrytis cinerea, Alternaria alternata, and Lasiodiplodia theobromae. Furthermore, the application of peel extracts from fruit treated with Phe reduced decay against C. gloeosporioides and A. alternata in mango fruit. Overall, the novelity of this study show that postharvest Phe treatment induces the fruit defense response and the biosynthesis of antioxidant and antifungal flavonoids, which can effectively control fungal growth and disease development, indicating its applicative potential as postharvest control against fungal pathogens.

Anthocyanins are secondary metabolites responsible for the red coloration of mango and apple. The red color of the peel is essential for the fruit’s marketability. Anthocyanins and flavonols are synthesized via the flavonoid pathway initiated from phenylalanine (Phe). Anthocyanins and flavonols have antioxidant, antifungal, and health-promoting properties. To determine if the external treatment of apple and mango trees with Phe can induce the red color of the fruit peel, the orchards were sprayed 1 to 4 weeks before the harvest of mango (cv. Kent, Shelly, and Tommy Atkins) and apple fruit (cv. Cripps pink, Gala and Starking Delicious). Preharvest Phe treatment increased the red coloring intensity and red surface area of both mango and apple fruit that was exposed to sunlight at the orchard. The best application of Phe was 2–4 weeks preharvest at a concentration of 0.12%, while a higher concentration did not have an additive effect. A combination of Phe and the positive control of prohydrojasmon (PDJ) or several applications of Phe did not have a significant added value on the increase in red color. Phe treatment increased total flavonoid, anthocyanin contents, and antioxidant activity in treated fruit compared to control fruits. High Performance Liquid Chromatography analysis of the peel of Phe treated ‘Cripps pink’ apples showed an increase in total flavonols and anthocyanins with no effect on the compound composition. HPLC analysis of ‘Kent’ mango fruit peel showed that Phe treatment had almost no effect on total flavonols content while significantly increasing the level of anthocyanins was observed. Thus preharvest application of Phe combined with sunlight exposure offers an eco–friendly, alternative treatment to improve one of the most essential quality traits—fruit color.

Cold is the best means of prolonging fruit storage. However, tropical fruit are susceptible to cold storage. The mode of action of mango fruit tolerance to suboptimal cold temperature of 7 or 10 degrees C after postharvest appli-cation of 8 mM phenylalanine was investigated using transcriptomic and metabolomic analyses of mango fruit during suboptimal cold storage. Phenylalanine-treated fruit had less chilling injuries-black spot and pitting electrolyte leakage,-and reduced decay after suboptimal cold storage. Phenylalanine treatment induced genes related to plant-pathogen interactions, plant hormone signal transduction, and the phenylpropanoid pathway, increasing the levels of the flavonoids quercetin and kaempferol glycosides and anthocyanins, and antioxidant content. Reduced oxidation led to lower lipid peroxidation, and a reduction in fatty acid-degradation products, e. g., volatile aldehydes. Treatment with phenylalanine, therefore, enhances chilling tolerance of mango fruit through regulation of metabolic and defense-related pathways, maintaining high levels of flavonoids, and an-tioxidants enzyme activity, and reducing H2O2 content, lipid peroxidation, and volatile aldehydes.

Elicitation treatments of grape cell cultures with methyl jasmonate (MeJA), ultraviolet-C (UV-C) irradiation, and sucrose induce mild production of stilbenes and flavonoids due to limited substrate availability. However, these treatments cause a synergistic boost of stilbenes production when applied to two phenylalanine (Phe)-enriched transgenic grape cell lines, AroG* + STS and AroG* + FLS. The combined treatment of UV-C elicitation on the Phe-fed AroG* + STS line resulted in the highest content of stilbenes (37.8-fold increase, 17.39 mg/g dry weight (DW)) mainly due to resveratrol (64-fold, 3.23 mg/g DW) and viniferin (1343-fold, 13.43 mg/g DW). The synergistic increase following either UV-C or MeJA elicitation was due to the induction of stilbene-related genes, while sucrose treatment had no effect on gene expression levels and served as an additional carbon source for phenylpropanoids. The combined strategy presented may enable future usage of grape cell cultures for the production of stilbenes and in particular viniferin.

Stilbenes and flavonoids are two major health-promoting phenylpropanoid groups in grapes. Attempts to promote the accumulation of one group usually resulted in a decrease in the other. This study presents a unique strategy for simultaneously increasing metabolites in both groups in V. vinifera cv. Gamay Red grape cell culture, by overexpression of flavonol synthase (FLS) and increasing Phe availability. Increased Phe availability was achieved by transforming the cell culture with a second gene, the feedback-insensitive E. coli DAHP synthase (AroG*), and feeding them with Phe. A combined metabolomic and transcriptomic analysis reveals that the increase in both phenylpropanoid groups is accompanied by an induction of many of the flavonoid biosynthetic genes and no change in the expression levels of stilbene synthase. Furthermore, FLS overexpression with increased Phe availability resulted in higher anthocyanin levels, mainly those derived from delphinidin, due to the induction of F3'5'H. These insights may contribute to the development of grape berries with increased health benefits.

Mango fruit exposed to sunlight develops red skin and are more resistant to biotic and abiotic stresses. Here we show that harvested red mango fruit that was exposed to sunlight at the orchard is more resistant than green fruit to Colletotrichum gloeosporioides. LCMS analysis showed high amounts of antifungal compounds, as glycosylated flavonols, glycosylated anthocyanins, and mangiferin in red vs. green mango skin, correlated with higher antioxidant and lower ROS. However, also the green side of red mango fruit that has low levels of flavonoids was resistant, indicated induced resistance. Transcriptomes of red and green fruit inoculated on their red and green sides with C. gloeosporioides were analyzed. Overall, in red fruit skin, 2,187 genes were upregulated in response to C. gloeosporioides. On the green side of red mango, upregulation of 22 transcription factors and 33 signaling-related transcripts indicated induced resistance. The RNA-Seq analysis suggests that resistance of the whole red fruit involved upregulation of ethylene, brassinosteroid, and phenylpropanoid pathways. To conclude, red fruit resistance to fungal pathogen was related to both flavonoid toxicity and primed resistance of fruit that was exposed to light at the orchard.

Fragrance is a desirable characteristic for cut flowers, but is rare among commercial cultivars. To date, there are no transformed commercial flower cultivars with increased fragrance, despite the fact that genetic engineering can generate fragrance in ornamentals without compromising on other commercial traits. One of the major volatile groups responsible for fragrance of flowers such as roses, petunia, snapdragon and clarkia, are the phenylalanine-derived benzenoid phenylpropanoids (BPVs). Here we show that a variety of commercial flowers, belonging to taxonomically distant plant species have the potential of producing fragrant BPVs when treated with exogenous phenylalanine. This group of flowers includes chrysanthemums, roses, anemones, Ornithogalum dubium and gerberas. Chrysanthemums, among the five leading flowers in the cut flower industry, lack flowery fragrance. However, treatment of cut chrysanthemums with phenylalanine resulted in an increase in BPVs preexisting in the flowers, producing a flowery fragrance clearly distinguished by a sensory panel. Similarly, phenylalanine treatment of anemones, also lacking fragrance, resulted in fragrant flowers. However, unlike chrysanthemums, in anemones, in addition to increasing preexisting BPVs, phenylalanine treatment resulted in production of new BPVs, not detected in non-treated flowers. Production of novel compounds due to phenylalanine treatment suggests that concealed metabolic pathways do exist in plants, may be activated by increased substrate availability. This study presents the potential of phenylalanine treatment as a way for increasing flowery fragrance in a large variety of non-fragrant commercially important plants.

Stilbenes are phytoalexins with health-promoting benefits for humans. Here, we boost stilbenes' production, and in particular the resveratrol dehydrodimer viniferin, with significant pharmacological properties, by overexpressing stilbene synthase (STS) under unlimited phenylalanine (Phe) supply. Vitis vinifera cell cultures were co-transformed with a feedback-insensitive E. coli DAHP synthase (AroG*) and STS genes, under constitutive promoters. All transgenic lines had increased levels of Phe and stilbenes (74-fold higher viniferin reaching 0.74 mg/g DW). External Phe feeding of AroG* + STS lines caused a synergistic effect on resveratrol and viniferin accumulation, achieving a 26-fold (1.33 mg/g DW) increase in resveratrol and a 620-fold increase (6.2 mg/g DW) in viniferin, which to date is the highest viniferin accumulation reported in plant cultures. We suggest that this strategy of combining higher Phe availability and STS expression generates grape cell cultures as potential factories for sustainable production of stilbenes with a minor effect on the levels of flavonoids.

Lisianthus (Eustoma grandiflorum), a leading plant in the cut flower industry, is scentless. Here we show that lisianthus flowers have potential to produce several fragrant benzenoid-phenylpropanoids when substrate availability is not limited. To enable hyperaccumulation of substrates for the production of volatile benzenoid-phenylpropanoids, lisianthus commercial hybrid "Excalibur Pink" was transformed via floral dipping with a feedback-insensitive Escherichia coli DAHP synthase (AroG*) and Clarkia breweri benzyl alcohol acetyltransferase (BEAT), under constitutive promoters. The T1 progeny of "Excalibur Pink" plants segregated into four visual phenotypes, with pink or white colored petals and multiple or single petal layers. Interestingly, transformation with AroG* and BEAT caused no significant effect in the pigment composition among phenotypes, but did increase the levels of down-stream fragrant volatile benzenoids. All the transgenic lines exclusively accumulated methyl benzoate, a fragrant benzenoid, either in their petals or leaves. Furthermore, feeding with benzyl alcohol resulted in the accumulation of two novel benzenoids, benzyl acetate (the product of BEAT) and benzoate, as well as a dramatic increase in the concentrations of additional benzenoid-phenylpropanoid volatiles. Presumably, the degree of benzaldehyde overproduction after benzyl alcohol feeding in both leaves and flowers revealed their reverse conversion in lisianthus plants. These findings demonstrate the concealed capability of lisianthus plants to produce a wide array of fragrant benzenoid-phenylpropanoids, given high substrate concentrations, which could in turn open opportunities for future scent engineering.

SummaryFlowers are the most vulnerable plant organ to infection by the necrotrophic fungus Botrytis cinerea. Here we show that pre‐treatment of chrysanthemum (Chrysanthemum morifolium) flowers with phenylalanine (Phe) significantly reduces their susceptibility to B. cinerea. To comprehend how Phe treatment induces resistance, we monitored the dynamics of metabolites (by GC/LC‐MS) and transcriptomes (by RNAseq) in flowers after Phe treatment and B. cinerea infection. Phe treatment resulted in accumulation of 3‐phenyllactate and benzaldehyde, and in particular induced the expression of genes related to Ca2+ signaling and receptor kinases, implicating an induction of the defense response. Interestingly, the main effects of Phe treatment were observed in flowers exposed to B. cinerea infection, stabilizing the global fluctuations in the levels of metabolites and transcripts while reducing susceptibility to the fungus. We suggest that Phe‐induced resistance is associated to cell priming, enabling rapid and targeted reprogramming of cellular defense responses to resist disease development. After Phe pre‐treatment, the levels of the anti‐fungal volatiles phenylacetaldehyde and eugenol were maintained and the level of coniferin, a plausible monolignol precursor in cell wall lignification, was strongly increased. In addition, Phe pre‐treatment reduced ROS generation, prevented ethylene emission, and caused changes in the expression of a minor number of genes related to cell wall biogenesis, encoding the RLK THESEUS1, or involved in Ca2+ and hormonal signaling processes. Our findings point to Phe pre‐treatment as a potential orchestrator of a broad‐spectrum defense response which may not only provide an ecologically friendly pest control strategy but also offers a promising way of priming plants to induce defense responses against B. cinerea.

Summary Fruit defense against pathogens relies on induced and preformed mechanisms. The present contribution evaluated performed resistance of red and green mango fruit against the fungal pathogen Colletotrichum gloeosporioides and identified the main active antifungal components. High‐performance liquid chromatography analysis of nonhydrolyzed mango peel extracts identified major anthocyanin peaks of glycosylated cyanidin and methylcyanidin, and flavonol peaks of glycosylated quercetin and kaempferol, which were more abundant on the 'red side' of red mango fruit. Organic extracts of red vs green mango peel were more efficient in inhibiting C. gloeosporioides . Transcriptome analysis of the mango– C. gloeosporioides interaction showed increased expression of glucosidase genes related to both fungal pathogenicity and host defense. Glucosidase treatment of organic peel extract increased its antifungal activity. Additionally, quercetin and cyanidin had significantly higher antifungal activity than their glycosylated derivatives. Peel extract volatiles treated with glucosidase had antifungal activity. GCMS analysis identified 15 volatiles after glucosidase hydrolysis, seven of them present only in red fruit. These results suggest that the fruit obtains a concealed arsenal of glycosylated flavonoids in its peel when they are hydrolyzed by β‐glucosidase that is induced in both fungus and host during infection process, become more toxic to the fungal pathogen, inhibiting decay development.

More than 40% of harvested fruit is lost, largely due to decay. In parallel, restrictions on postharvest fungicides call for eco-friendly alternatives. Fruit's natural resistance depends mainly on flavonoids and anthocyanins-which have antioxidant and antifungal activity-synthesized from the phenylpropanoid pathway with phenylalanine as a precursor. We hypothesized that phenylalanine could induce fruit's natural defense response and tolerance to fungal pathogens. The postharvest application of phenylalanine to mango and avocado fruit reduced anthracnose and stem-end rot caused by Colletotrichum gloeosporioides and Lasiodiplodia theobromae, respectively. The postharvest application of phenylalanine to citrus fruit reduced green mold caused by Penicillium digitatum. The optimal phenylalanine concentrations for postharvest application were 6 mM for citrus fruits and 8 mM for mangoes and avocadoes. The preharvest application of phenylalanine to strawberries, mangoes, and citrus fruits also reduced postharvest decay. Interestingly, citrus fruit resistance to P. digitatum inoculated immediately after phenylalanine application was not improved, whereas inoculation performed 2 days after phenylalanine treatment induced the defense response. Five hours after the treatment, no phenylalanine residue was detected on/in the fruit, probably due to rapid phenylalanine metabolism. Additionally, in vitro testing showed no inhibitory effect of phenylalanine on conidial germination. Altogether, we characterized a new inducer of the fruit defense response-phenylalanine. Preharvest or postharvest application to fruit led to the inhibition of fungal pathogen-induced postharvest decay, suggesting that the application of phenylalanine could become an eco-friendly and healthy alternative to fungicides.

C. morifolium are obligate short day plants that can be induced to flower throughout the year and their stem length can be controlled by maintaining artificial long days before the onset of flowering. The ability to strictly control the flowering of chrysanthemums enabled this crop to become one of the leading ornamentals grown for the cut flower industry. The most effective inhibition of chrysanthemum flowering was found to be red light, while blue light had no inhibitory effect, and in some studies was even suggested to induce flowering. Here the effect of light quality and duration of day length illumination on chrysanthemum growth and flowering was examined. In contrast to previous studies, the results presented here suggest that blue light does inhibit chrysanthemum flowering, but the efficiency of inhibition is dependent on the duration of the lighting. Overnight illumination with blue LED lights, resulting in inhibition of flowering of three chrysanthemum cultivars, and had no significant effect on their growth. When illumination time was shortened blue light was found to be less efficient than white or red light in preventing flowering. Red LED lights were also tested in a larger scale experiment in a greenhouse, in preventing flowering of two chrysanthemum cultivars. Plants were illuminated for six hours after sundown, with either constant or intermittent red LED lights and harvested two months after the lighting was turned off. Red intermittent light resulted in somewhat shorter stems and lower quality branches in comparison to constant light.

Red-blushed skin color is important for mango fruit quality and marketability. Preharvest spraying of 'Kent', 'Shelly' and 'Maya' mangoes with 0.1, 0.2 or 0.4% prohydrojasmon (PDJ) induced red skin color (areal coverage and intensity) and anthocyanins accumulation especially in fruit from the outer side of tree canopy, which were exposed to sunlight Maximum red blush was achieved with 0.2% ('Shelly') and 0.4 % ('Kent' and 'Maya') PDJ in fruit from outside the canopy, with an increase of three fold in anthocyanins and two fold increase in flavonols. HPLC analysis of non-hydrolyzed samples showed that the major anthocyanin peaks were cyanidin-3-galactoside and 7-O-methylcyanidin-3-O-beta-D-galactopyranoside, and the major flavonol peaks were glucoside derivatives of quercetin and kaempferol. Thus, PDJ activated the phenylpropanoid and anthocyanin pathways mainly with exposure to sunlight, allowing potential production of specific antioxidant and antifungal flavonols and anthocyanins. Induced red skin color in most of the experiments reduced postharvest decay, which may enhance commercial value and extend shelf life.

Ethylene plays a major role in the regulation of flower senescence, including in the ethylene-sensitive Vanda 'Sansai Blue' orchid flowers. This cut flower is popular in Thailand due to its light blue big size florets possessing a beautiful shape pattern. In the present study, we further examined the rapid ethylene-induced process of active anthocyanin degradation in cut Vanda 'Sansai Blue' flowers, which occurred much before detection of other typical senescence-related symptoms. For this purpose, the cut inflorescences were exposed to air (control), 1 or 10 μl L-1 ethylene for 24 h, or to 0.2 μl L-1 1-methylcyclopropene (1-MCP) for 6 h followed by 10 μl L-1 ethylene for 24 h at 21°C, and the effects of these treatments on various parameters were assayed. While the fading-induced effect of ethylene was not concentration-dependent in this range, the ethylene treatment significantly reduced the flower vase life in a concentration-dependent manner, further confirming the separation of the bleaching process from senescence. Exposure of the inflorescences to 1-MCP pre-treatment followed by 10 μl L-1 ethylene, recovered both inflorescence color and anthocyanin content to control levels. Quantification of total anthocyanin content, performed by HPLC analysis on the basis of cyanidin-3-glocuside equivalents, showed that ethylene reduced and 1-MCP recovered the anthocyanins profile in non-hydrolyzed anthocyanin samples of Vanda 'Sansai Blue' florets, assayed at half bloom and bloom developmental stages. The results showed that the ethylene-induced color fading, observed immediately after treatment, resulted from a significant reduction in the levels of the two main anthocyanidins, cyanidin and delphinidin, as well as of other anthocyanidins present in low abundance, but not from changes in the levels of flavonols, such as kaempferol. This anthocyanin degradation process seems to operate via ethylene-increased peroxidase activity, detected at the bud stage. Taken together, our results suggest that the ethylene-induced rapid color bleaching in petals of cut Vanda 'Sansai Blue' flowers is an outcome of in-planta anthocyanin degradation, partially mediated by increased peroxidase activity, and proceeds independently of the flower senescence process.