Improving the Red Color and Fruit Quality of ‘Kent’ Mango Fruit by Pruning and Preharvest Spraying of Prohydrojasmon or Abscisic Acid

Metabolome, Plant Hormone, and Transcriptome Analyses Reveal the Mechanism of Spatial Accumulation Pattern of Anthocyanins in Peach Flesh

Anthocyanins are important secondary metabolites in fruits, and anthocyanin accumulation in the flesh of peach exhibits a spatial pattern, but the relevant mechanism is still unknown. In this study, the yellow-fleshed peach, cv. 'Jinxiu', with anthocyanin accumulation in the mesocarp around the stone was used as the experimental material. Red flesh (RF) and yellow flesh (YF) were sampled separately for flavonoid metabolite (mainly anthocyanins), plant hormone, and transcriptome analyses. The results showed that the red coloration in the mesocarp was due to the accumulation of cyanidin-3-O-glucoside, with an up-regulation of anthocyanin biosynthetic genes (F3H, F3'H, DFR, and ANS), transportation gene GST, and regulatory genes (MYB10.1 and bHLH3). Eleven ERFs, nine WRKYs, and eight NACs were also defined as the candidate regulators of anthocyanin biosynthesis in peach via RNA-seq. Auxin, cytokinin, abscisic acid (ABA), salicylic acid (SA), and 1-aminocyclopropane-1-carboxylic acid (ACC, ethylene precursor) were enriched in the peach flesh, with auxin, cytokinin, ACC, and SA being highly accumulated in the RF, but ABA was mainly distributed in the YF. The activators and repressors in the auxin and cytokinin signaling transduction pathways were mostly up-regulated and down-regulated, respectively. Our results provide new insights into the regulation of spatial accumulation pattern of anthocyanins in peach flesh.

The Role of ABA in the Interaction between Citrus Fruit and Penicillium digitatum

Abscisic acid (ABA) protects citrus fruit against Penicillium digitatum infection. The global mechanisms involved in the role of ABA in the P. digitatum-citrus fruit interaction are unknown. Here, we determine the transcriptome differences between the Navelate (Citrus sinensis (L.) Osbeck) orange and its ABA-deficient mutant Pinalate, which is less resistant to infection. Low ABA levels may affect both the constitutive mechanisms that protect citrus fruit against P. digitatum and early responses to infection. The repression of terpenoid, phenylpropanoid and glutation metabolism; of oxidation-reduction processes; and of processes related to the defense response to fungus and plant hormone signal transduction may be one part of the constitutive defense reduced in the mutant against P. digitatum. Our results also provide potential targets for developing P. digitatum-citrus fruit-resistant varieties. Of those up-regulated by ABA, a thaumatin protein and a bifunctional inhibitor/LTP, which are relevant in plant immunity, were particularly remarkable. It is also worth highlighting chlorophyllase 1 (CLH1), induced by infection in Pinalate, and the OXS3 gene, which was down-regulated by ABA, because the absence of OXS3 activates ABA-responsive genes in plants.

Preharvest Application of Phenylalanine Induces Red Color in Mango and Apple Fruit’s Skin

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.

Pre-Harvest Application of Salicylic Acid, Abscisic Acid, and Methyl Jasmonate Conserve Bioactive Compounds of Strawberry Fruits during Refrigerated Storage

The short shelf-life and loss of bioactive compounds of strawberry fruit are the most important problems during strawberry refrigerated storage. This study was carried out to evaluate the effect of the pre-harvest foliar application of salicylic acid (SA) (2 and 4 mM), abscisic acid (ABA) (0.25 and 0.50 mM), and methyl jasmonate (MeJA) (0.25 and 0.50 mM) three times, 10 d apart, at fruit development and ripening stages on storage ability and bioactive compounds of strawberry fruit (cv. Festival) stored at 4 °C for 12 d. Our results showed that fruit obtained from both concentrations of ABA and 0.25 mM MeJA was firmer and had higher total soluble solids (TSS) than fruit from non-treated plants. However, all previous applications had no significant effect on weight loss, pH, or color. Applications of 4 mM SA and 0.25 mM MeJA conserved fruit from ascorbic acid (AsA) loss compared to control at the end of the storage period. In addition, all pre-harvest applications remained higher in total phenolic compounds (TPC) and anthocyanin contents compared to controls at the last storage period. Hence, the pre-harvest application of SA, ABA, and MeJA could be used to conserve TPC and anthocyanin as well as the quality of strawberry fruits during refrigerated storage.

Analysis of Light-Independent Anthocyanin Accumulation in Mango (Mangifera indica L.)

Light dependent anthocyanin accumulation contributes to the red pigmentation of the fruit skin of mango (Mangifera indica L.). Light-independent pigmentation has also been reported, but remains poorly characterized. In this study, the pigmentation patterns in the skin of two red mango cultivars, ‘Ruby’ and ‘Sensation’, were evaluated. Metabolomic profiling revealed that quercetin-3-O-glucoside, cyanidin-3-O-galactoside, procyanidin B1, and procyanidin B3 are the predominant flavonoid compounds in the skin of ‘Ruby’ and ‘Sensation’ fruit. Young fruit skin mainly accumulates flavonol and proanthocyanidin, while anthocyanin is mainly accumulated in the skin of mature fruit. Bagging treatment inhibited the biosynthesis of flovonol and anthocyanin, but promoted the accumulation of proanthocyanidin. Compared with ‘Sensation’, matured ‘Ruby’ fruit skin showed light red pigmentation at 120 days after full bloom (DAFB), showing a light-independent anthocyanin accumulation pattern. However, the increase of anthocyanin concentration, and the expression of key anthocyanin structural and regulatory genes MiUFGT1, MiUFGT3, and MiMYB1 in the skin of bagged ‘Ruby’ fruit versus ‘Sensation’ at 120 DAFB was very limited. There was no mutation in the crucial elements of MiMYB1 promoter between ‘Ruby’ and ‘Sensation’. We hypothesize that the light-independent anthocyanin accumulation in the skin of mature ‘Ruby’ fruit is regulated by plant hormones, and that ‘Ruby’ can be used for breeding of new more easily pigmented red mango cultivars.

Prohydrojasmon Promotes the Accumulation of Phenolic Compounds in Red Leaf Lettuce

Prohydrojasmon (PDJ) is a synthetic jasmonate derivative that is primarily used as a growth regulator, but its mechanism of action is unclear. In this study, we elucidated the effects of PDJ on phytochemical production in red leaf lettuce. The PDJ treatments promoted the accumulation of phenolic compounds in aerial plant parts. An LC-MS analysis revealed that these accumulated compounds were identified as cyanidin-3-O-glucoside, cyanidin-3-O-(6″-O-malonyl)-glucoside and cyanidin-3-O-(6″-O-malonyl)-glucoside methyl ester. The abundance of these compounds in lettuce extracts increased significantly in response to the PDJ treatment. Additionally, the LC-MS analysis also identified the accumulated phenolic compounds in the extracts of PDJ-treated lettuce, including caffeoyltartaric acid, chlorogenic acid, caffeoylmalic acid, chicoric acid, and dicaffeoylquinic acid. Gene expression analyses indicated the PDJ treatments upregulated the expression of PAL, F3H, and ANS genes in lettuce. These results suggest that PDJ treatments enhance the expression of genes involved in the synthesis of anthocyanins and phenolic compounds, resulting in an increase in the quantities of these compounds, which reportedly have various functions affecting human physiology.