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The novel loquat cultivar ‘Chunhua No.1′ (CH1) is a promising commercial cultivar. However, CH1 has texture characteristics different from those of common loquat, and its formation mechanism remains unclear. Here, we first identified the phenolic compounds of CH1 and its parent (‘Dawuxing’, DWX) and the effect on texture formation. The special presence of stone cells explained the flavor differences in CH1. Chlorogenic acid, neochlorogenic acid, and coniferyl alcohol were the main phenolic compounds in loquat, and the high content of coniferyl alcohol was a potential factor for the rough texture of CH1. Transcriptome reveals that phenylpropanoid metabolism was activated during CH1 fruit texture formation. Kyoto Encyclopedia of Genes and Genomes (KEGG) identified 51 structural genes involved in phenylpropanoid biosynthesis, and Weighted Gene Co-expression Network Analysis (WGCNA) identified four structural genes and 88 transcription factors. These findings provide new insights into the phenolic metabolism and flavor formation of loquat fruit.

Pomegranate (Punica granatum L.), with its abundant phenolic substances and strong antioxidant activity, holds significant research and utilization potential across various organs. However, there have been few studies on the phenolic content and antioxidant activity of different parts of pomegranate, especially the placenta. This study investigated the phenolic content and antioxidant activity of fruits, flowers, and leaves of two pomegranate varieties, ‘Tunisia’ and ‘Qingpi’, throughout their growth and development. Results indicated significant variations in phenolic content among different organs, with petals exhibiting the highest total polyphenol content (TPC, 49.40 mg GAE/g FW) and total anthocyanin content (TMAC, 1938.54 nmol/g FW). Placenta contained the highest levels of total flavonoids (TFC, 173.58 mg RE/g FW) and punicalagin (109.30 mg/g FW). The peel had the highest content of total flavanols (TFAC, 19.42 mg CE/g FW). Over the course of pomegranate development, total polyphenols, total flavonoids, total flavanols, punicalagin, and antioxidant activity declined in different organs. Antioxidant activity followed the order: fruit > flower > leaf, with the placenta exhibiting the highest antioxidant activity among fruits. Antioxidant activity showed a significant positive correlation with total polyphenols (R2 = 0.77-1.00), total flavonoids (R2 = 0.71-0.99, except tegmens), and punicalagin (R2 = 0.71-1.00). This study provides a comparative analysis of the phenolic content and antioxidant activity in different organs of pomegranate, highlighting the placenta as the primary source of punicalagin. This study provides a theoretical basis for the development and utilization of pomegranate phenolic compounds.

MADS-box is a large transcription factor family in plants and plays a crucial role in various plant developmental processes; however, it has not been systematically analyzed in kiwifruit. In the present study, 74 AcMADS genes were identified in the Red5 kiwifruit genome, including 17 type-I and 57 type-II members according to the conserved domains. The AcMADS genes were randomly distributed across 25 chromosomes and were predicted to be mostly located in the nucleus. A total of 33 fragmental duplications were detected in the AcMADS genes, which might be the main force driving the family expansion. Many hormone-associated cis-acting elements were detected in the promoter region. Expression profile analysis showed that AcMADS members had tissue specificity and different responses to dark, low temperature, drought, and salt stress. Two genes in the AG group, AcMADS32 and AcMADS48, had high expression levels during fruit development, and the role of AcMADS32 was further verified by stable overexpression in kiwifruit seedlings. The content of α-carotene and the ratio of zeaxanthin/β-carotene was increased in transgenic kiwifruit seedlings, and the expression level of AcBCH1/2 was significantly increased, suggesting that AcMADS32 plays an important role in regulating carotenoid accumulation. These results have enriched our understanding of the MADS-box gene family and laid a foundation for further research of the functions of its members during kiwifruit development.

Soil in most areas of the world is selenium (Se) deficient, which results a low Se content in agricultural products. To improve the fruit tree Se accumulation, the effects of different Artemisia argyi water extract concentrations (0, 100, 200, 300, and 400-fold dilutions) on the growth and Se accumulation of peach seedlings were studied by a pot experiment. A 300- and 400-fold dilution of A. argyi water extract increased the root and shoot biomass (dry weight), leaf chlorophyll a content, superoxide dismutase (SOD) activity, and peroxidase (POD) activity of peach seedlings, but decreased the leaf chlorophyll a/b. Different A. argyi water extract concentrations had no significant effects on peach leaf chlorophyll a content of peach seedlings, but increased the leaf carotenoid content, catalase (CAT) activity, and soluble protein content. Different A. argyi water extract concentrations increased the total Se, inorganic Se, and organic contents in roots and shoots of peach seedlings to some extent. Furthermore, A. argyi water extract concentration exhibited a linear relationship with the root and shoot total Se contents. Compared with the control, the 100-, 200-, 300-, and 400-fold dilutions of A. argyi water extract increased the shoot total Se content by 18.95%, 31.31%, 39.32%, and 51.59%, respectively. Different A. argyi water extract concentrations also increased the leaf Se metabolism-related enzyme activities of peach seedlings, including the activities of adenosine triphosphate sulfurase (ATPS), adenosine 5’-phosphosulfate reductase (APR), and serine acetyltransferase (SAT), as well as selenocysteine methyltransferase (SMT) to some extent. Moreover, correlation and grey relational analyses revealed the root total Se content, CAT activity, and ATPS activity to be closely associated with the total shoot Se content. Therefore, applying A. argyi water extract can thus promote the growth and Se uptake of peach seedlings, and the future study should focus on the application effects of Se uptake in peach fruits.

This study was conducted to investigate the visual appearance and physicochemical changes of postharvest jujube fruits (Ziziphus jujuba Mill. cv. Shucuizao) stored under 0 °C for 15 days. The fruits were dipped in 0 (control), 50, 100, 200 and 400 µM melatonin solutions after harvest. The results showed that treatment with a suitable melatonin concentration improved the rate of crisp fine fruits, delayed weight loss and firmness decline, and suppressed changes in total soluble solids (TSS) and titratable acidity (TA) contents of jujube fruits compared with the control. In addition, jujube fruits soaked with melatonin showed improved antioxidant capacity through increased ascorbic acid (AsA) content, enhanced superoxide dismutase (SOD) activity, and decreased malonaldehyde (MDA) content. As a result, 50 µM melatonin showed the greatest improvement of visual appearance and quality maintenance, and could be used as an effective treatment to preserve postharvest jujube fruit.

Cadmium (Cd) contamination of paddy soil affects safe crop production. This study aimed to evaluate the effects of plant biostimulant amino acid fertilizer on the phytoremediation capability of an emergent accumulator plant Nasturtium officinale R. Br. for Cd-contaminated paddy soils. A pot study was carried out to study the effects of different concentrations of amino acid fertilizer on the Cd accumulation of N. officinale grown in Cd-contaminated paddy soil. The amino acid fertilizer increased the biomass of N. officinale. The amino acid fertilizer concentration exhibited a quadratic polynomial regression relationship with the root and shoot biomass. The fertilizer also increased the photosynthetic pigment (chlorophyll and carotenoid) contents, peroxidase (POD; EC 1.11.1.7) activity, and catalase (CAT; EC 1.11.1.6) activity of N. officinale, but decreased the soluble protein content and had no significant effect on the superoxide dismutase (SOD; EC 1.15.1.1) activity. Furthermore, the amino acid fertilizer increased the Cd content and Cd extraction of N. officinale. The shoot Cd extraction increased by 29.06%, 63.05%, 77.22%, and 17.40% at 1500-, 1200-, 900-, and 600-fold dilutions of the amino acid fertilizer, respectively, compared with the control. Moreover, the amino acid fertilizer promoted the Cd transport from the roots to shoots of N. officinale. The amino acid fertilizer concentration also exhibited a quadratic polynomial regression relationship with the root Cd content, shoot Cd content, root Cd extraction, and shoot Cd extraction, respectively. The correlation, grey relational, and path analyses revealed that the root biomass, shoot biomass, chlorophyll content, catalase activity, shoot Cd content, and root Cd extraction were closely associated with the shoot Cd extraction. Therefore, the amino acid fertilizer can promote Cd uptake and improve the phytoremediation capability of N. officinale to remediate Cd-contaminated paddy soils, and 900-fold dilution is the most suitable concentration.

Plums are good sources of various bioactive phytochemical compounds such as vitamins, anthocyanins, and carotenoids, whereby all of which are noted for multiple potential health benefits. However, knowledge regarding plum carotenoid profiles remains limited. Hence, the total and individual carotenoids in the edible parts (skin and flesh) of ten plum cultivars were determined using a spectrophotometer and high-performance liquid chromatography–diode array detection, respectively. Total and individual carotenoid contents in skin were significantly higher (p < 0.05) than those in flesh among all plum cultivars tested. The cultivars with the highest content of total carotenoids in skin were Naili (36.73 μg/g FW), followed by Yinhongli (21.81 μg/g FW) and Yuhuangli (19.70 μg/g FW), with the lowest in Angeleno (8.97 μg/g FW). Lutein, zeaxanthine, β-cryptoxanthin, α-carotene, and β-carotene were the major types of carotenoids detected, with lutein and β-carotene being the predominant constituents of the skin and flesh tissues, respectively. Lutein, zeaxanthine, and total carotenoid contents were positively correlated with the expressions of PSY, LCYB, and LCYE, and negatively correlated with the expressions of PDS and CRTISO. Characterizing the carotenoid profiles and investigating variations in carotenoid biosynthetic gene expressions among plum cultivars are crucial for advancing genetic improvements in plums.

The selenium (Se) deficiency is threatening the human health, and the increase of Se content in food can prevent the Se deficiency of human body. To increase the Se content in fruit trees and alleviate the Se stress to fruit trees, the effects of gibberellic acid (GA) on the growth and Se accumulation in Cyphomandra betacea under Se stress were studied. Although GA increased the biomass of C. betacea, it did not significantly affect the root/shoot ratio. The root and shoot biomass had a quadratic polynomial regression relationship with the GA concentration. Furthermore, GA increased the photosynthetic pigment content, photosynthetic parameters, and antioxidant enzyme activity of C. betacea. GA also increased the Se content in C. betacea, peaking at 300 mg/L GA. For instance, GA (300 mg/L) increased the Se contents in roots and shoots of C. betacea by 70.31 and 22.02%, respectively, compared with the control. Moreover, the root Se and shoot Se contents had a quadratic polynomial regression relationship with the GA concentration. Correlation and gray relational analyses showed that the carotenoid, chlorophyll a, and chlorophyll b contents were closely related to the Se uptake in C. betacea under the GA application. These results show that GA (300 mg/L) can promote the growth and Se uptake of C. betacea under Se stress.

Potassium (K) is the most important element for fruit quality improvement. This study aimed at determining the best K fertilizer type that can promote grape growth and nutrient uptake. Specifically, four types of K fertilizers (complex fertilizer, potassium nitrate, potassium sulfate, and potassium dihydrogen phosphate) were applied to grapevines grown in plastic pots, and then their effects on grape growth and nutrient uptake were explored. Results showed that the complex fertilizer and potassium nitrate treatments increased the biomass of the grapevine plants, whereas the other fertilizers had no significant effects on the biomass. Only the potassium nitrate treatment increased the contents of photosynthetic pigments in grapevine leaves. The complex fertilizer and potassium nitrate treatments increased the total N content in the grapevine plants to some extent, whereas the other fertilizer treatments decreased the total N content to some extent. It was also evident that all four K fertilizers increased the total P and K contents in the grapevine plants. Compared to the control, the complex fertilizer, potassium nitrate, potassium sulfate, and potassium dihydrogen phosphate treatments increased the scion total P content by 20.18%, 9.77%, 12.52%, and 30.81%, respectively, and increased the scion total K content by 15.37%, 8.41%, 20.15%, and 26.48%, respectively. In addition, correlation and grey relational analyses showed that the rootstock stem total N content, rootstock root biomass, and soil alkali-hydrolyzable N concentration were the top three indicators most closely associated with the scion total N content, whereas the rootstock root total P content, soil available P concentration, and rootstock stem total P content were the top three indicators most closely associated with the scion total P content. Additionally, the rootstock root total K content, soil available K concentration, and rootstock root total P content were the top three indicators most closely associated with the scion total K content. Overall, the different K fertilizers can all promote the uptake of P and K by grapevine plants, and the potassium dihydrogen phosphate fertilizer is the best choice.

Loquats have gained increasing attention from consumers and growers for their essential nutrients and unusual phenology, which could help plug a gap period at market in early spring. Fruit acid is a critical contributor to fruit quality. The dynamic changes in organic acid (OA) during fruit development and ripening of common loquat (Dawuxing, DWX) and its interspecific hybrid (Chunhua, CH) were compared, as well as the corresponding enzyme activity and gene expression. At harvest, titratable acid was significantly lower (p ≤ 0.01) in CH (0.11%) than in DWX loquats (0.35%). As the predominant OA compound, malic acid accounted for 77.55% and 48.59% of the total acid of DWX and CH loquats at harvest, followed by succinic acid and tartaric acid, respectively. PEPC and NAD-MDH are key enzymes that participate in malic acid metabolism in loquat. The OA differences in DWX loquat and its interspecific hybrid could be attributed to the coordinated regulation of multiple genes and enzymes associated with OA biosynthesis, degradation, and transport. The data obtained in this work will serve as a fundamental and important basis for future loquat breeding programs and even for improvements in loquat cultural practices.

Gamma amino butyric acid (GABA), an important free amino acid in plant tissues, plays an essential role in all stages of plant growth and development. In this study, we aimed to explore the effects of GABA on the nutrient absorption of loquat [Eriobotrya japonica (Thunb.) Lindl.] seedlings. The effects of applying exogenous GABA in different concentrations (0.0, 0.5, 1.0, 1.5, and 2 g L−1) on the nutrient uptake of loquat seedlings were studied. GABA increased the biomass (dry weight) and contents of photosynthetic pigments in loquat seedlings to a certain extent. GABA concentration exhibited a quadratic polynomial regression relationship with the biomass. Exogenous GABA in different concentrations increased the total nitrogen (N) and phosphorus (P) contents in loquat seedlings, whereas only 0.5 and 1.0 g L−1 of GABA increased the potassium (K) content. Similarly, GABA concentration also had a polynomial regression relationship with the total N, P, and K contents. Compared to the control, 0.5, 1.0, 1.5, and 2.0 g L−1 of GABA increased the shoot total N content by 27.30, 32.99, 15.41, and 12.93%, respectively, and also increased the shoot total P content by 26.12, 37.52, 21.99, and 9.61%, respectively. Furthermore, correlation and grey relational analyses showed that the carotenoid content, root biomass, and soil alkali-hydrolyzable N concentration were the indicators most closely associated with the uptakes of N, P, and K in shoots. This study shows that exogenous GABA can promote the growth and nutrient uptake of loquat seedlings at an optimum concentration of 1.0 g L−1.

Loquats have drawn much attention due to their essential nutrients and unusual phenology, which fills a market gap in early spring. Fruit firmness (FF) is one of the most important quality attributes. Dynamic changes in FF, cell wall (CW) polysaccharides, CW hydrolase activity, and expression of CW metabolism-related genes during the fruit development and ripening stages of two contrasting loquat cultivars were compared. Although the two cultivars possessed similar FF at the initial fruitlet stage, Dawuxing was significantly firmer than Ninghaibai at all subsequent time points. FF was positively correlated with the contents of covalent-soluble pectin and hemicellulose, activity of peroxidase, and gene expressions of PME, EG, CAD6, and POD; and negatively correlated with the contents of water-soluble pectin, activities of polygalacturonase, endo-glucanase, cellobiohydrolase, and xylanase, and gene expressions of PG, EG2, PAL1, PAL3, and CAD5. Identifying molecular mechanisms underlying the differences in FF is useful for fundamental research and crop improvement in future.

Fruit aromas are composed of a complex mixture of volatile organic compounds, which are essential attributes associated with the overall flavor and consumer preference. Muscadine grape (MG; Vitis rotundifolia Michx.) is an aroma-dense fruit crop. However, there is very scarce information on its volatile profiles. In this study, the volatile constituents of five newly introduced MG cultivars, including Alachua, Carlos, Fry, Granny Val, and Noble, were profiled using headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC/MS) combined with multivariate statistical analysis. A total of 44 compounds, including esters, aldehydes, alcohols, fatty acids, terpenes, ketones, and furan, were identified and relatively quantified. Principal component analysis (PCA) and partial least-squares discriminant analysis (PLS-DA) evidently discriminated against the five MG cultivars based on their volatile profiles. The specific volatiles that contributed the most to this discrimination were highlighted. Geraniol and cinnamyl alcohol were demonstrated to be essential for characterizing the Alachua MG cultivar, whereas ethyl trans-2-butenoate and propyl acetate were shown to be important compounds to characterize the Noble MG cultivar. The results further showed that 2-Ethyl-1-hexanol, (Z)-3-hexenal, and (E)-2-hexenol were closely related to Carlos, Fry, and Granny Val cultivars, respectively. This investigation is the first in-depth exploration of the volatile profiles of the aroma-dense muscadine grape, which is essential for future genetic or biotechnological improvements to attain a cultivar with the desired flavor.

Plums are widely consumed, contain high levels of phenolic compounds, and have strong antioxidant activity. In this study, the main Sichuan cultivars ‘Qiangcuili’ and ‘Cuihongli’ were used to study the changes in the appearance, internal quality, phenolic compounds, and antioxidant activities during fruit development and the expression of phenolic-compound-related structural genes. The results showed that, during development of the two plums, the total soluble solid and soluble sugar contents were highest at the mature stage. The phenolic contents (total phenol content (TPC), total flavonoid content (TFC), and total flavanol content (TFAC)) trended gradually downward as the fruits of the two cultivars matured, while the total anthocyanin content gradually increased in ‘Cuihongli’. The main phenolic components were neochlorogenic acid, chlorogenic acid, ferulic acid, benzoic acid, rutin, and proanthocyanidin B1. The changes in the DPPH and FRAP scavenging activities decreased with fruit ripening. The antioxidant capacity was positively correlated with the TPC, TFC, and TFAC. In the two cultivars, the total phenols, phenolic components, and antioxidant capacity were higher in the peel than in the pulp. CHS, PAL3, and HCT1 may be the regulatory genes related to the accumulation of phenolic substances in the pericarp and pulp of ‘Qiangcuili’ and ‘Cuihongli’. HCT1 may be an important regulator involved in the accumulation of chlorogenic acid in plums. The changes in the quality of the phenols, phenolic components, and antioxidant activity were elucidated during the development of the main plum cultivars in Sichuan, particularly the changes that provided a theoretical basis for the development of bioactive substances in local plum cultivars.

Abstract Background Grape buds exhibit non-uniform, or delayed, break in early spring in subtropical regions because the accumulation of chilling is insufficient. Hydrogen cyanamide (H2CN2, HC) can partially replace chilling to effectively promote bud sprouting and is used widely in warm winter areas. However, the exact underlying mechanism of grape bud release from endodormancy induced by HC remains elusive. Results In this study, the transcriptome of grape winter buds under in vitro conditions following HC and water treatment (control) was analyzed using RNA-seq technology. A total of 6772 differentially expressed genes (DEGs) were identified. Furthermore, the gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that starch and sucrose metabolism and plant hormone signaling transduction were most enriched out of the 50 total pathways. HC treatment induced the upregulated expression of sucrose synthase (SUS), sucrose phosphate synthase (SPS), α-amylase (AM), and β-amylase (BM) and downregulated expression of sucrose invertase (INV), hexokinase (HK), fructokinase (FK), soluble starch synthase (SS), and granule-bound starch synthase (GBSS). Hence, the starch concentration in the HC-treated group was significantly lower than that in control, whereas soluble sugar content in the HC-treated group increased quickly and was higher than that in control between 0 and 8 d. The concentration of indoleacetic acid (IAA) and zeatin (ZT) increased, whereas that of abscisic acid (ABA) and gibberellin (GA) decreased in HC treated group, which coincided with the expression level of genes involved in above hormone signals. The content of hydrogen peroxide (H2O2) and enzyme activity of superoxide dismutase (SOD) and peroxidase (POD) were increased in grape buds with HC treatment, whereas catalase (CAT) activity was decreased. HC treatment increased the expression of POD, SOD, primary amine oxidase (PAO), polyamine oxidase (PAOX), and glutathione peroxidase (GSH-Px). Conclusion Based on these results, it is possible to propose a mechanistic model that underlies the regulation of endodormancy release in grapevine buds by exogenous HC application.

Jujube is a characteristic light-demanding fruit tree, but fruit quality is frequently degraded because of the weak light in protected cultivation facilities in south China. In this study, a black shade net was used to set three light intensities artificially: no shading (0%, control, NS), moderate shading (45%, MS), and severe shading (76%, SS) to investigate the effect of low light on sugar metabolism of jujube. Compared with NS, chlorophyll and carotenoid contents in shaded leaves were increased, while specific leaf weight was decreased. A decrease in sucrose content, rather than fructose and glucose, was the main factor affecting sugar content in shaded leaves and fruits. Low expression of ZjSS2 and ZjSS3 inhibited sugar synthesis in shaded leaves, thereby reducing sucrose content by 23.7% in SS leaf than that in NS. Compared with NS, sucrose content in SS fruit was decreased by 58.1%, which was mainly caused by the down-regulated expression of ZjSS2 and ZjSPS1. In conclusion, sugar accumulation in leaf and fruit with shading treatment was suppressed, which was associated with differential transcription levels of related metabolic genes. The study provides new insights into sugar metabolism in leaf and fruit of phototropic plants under low light environments, such as jujube.

Carrizo citrange [Citrus sinensis (L.) Osbeck × Poncirus trifoliata (L.) Raf., CC] is one of the most widely used rootstocks in citriculture worldwide, but its cytogenetic study has been hampered by its inherent small size, morphological similarity to mitotic chromosomes, and lack of accessible cytological landmarks. In our previous study, a spontaneously occurring tetraploid CC seedling was discovered. The main goals of this study were to elucidate the chromosome constitution and construct the karyotypes of diploid CC rootstock and its corresponding spontaneously occurring tetraploid. To accomplish these, the chromosomal characteristics were investigated by sequential multicolor fluorescence in situ hybridization (FISH) with eight properly labeled repetitive DNA sequences, including a centromere-like repeat, four satellite repeats, two rDNAs, and an oligonucleotide of telomeric (TTTAGGG)n repeat. The results nicely demonstrated that these repetitive DNAs are reliable cytogenetic markers that collectively facilitate simultaneous and unequivocal identification of homologous chromosome pairs. Based on chromosome size and morphology together with FISH patterns of repetitive DNAs, an integrated karyotype of CC rootstock was constructed, consisting of 2n = 2x = 12m (1sat) + 6sm with karyotype asymmetry degree being divided into 2B category. Cytogenetically speaking, the variable and asymmetric distribution patterns of these repetitive DNAs were fully confirmed the hybrid nature of CC rootstock. In addition, comparative distribution patterns and chromosomal localizations of these repetitive DNAs convincingly showed that this tetraploid CC material arose from somatic chromosome doubling of diploid CC rootstock. This study revealed, for the first time, the integrated karyotype and chromosomal characteristics of this important citrus rootstock as well as its spontaneously occurring tetraploid plant. Furthermore, this study is a good prospective model for study species with morphologically indistinguishable small chromosomes.

In this study, third-generation full-length (FL) transcriptome sequencing was performed of loquat using single-molecule real-time(SMRT) sequencing from the pooled cDNA of embryos of young loquat fruit under different low temperatures (three biological replicates for treatments of 1°C, -1°C, and -3°C, for 12 h or 24 h) and the control group(three biological replicates for treatments of room temperature), Illumina sequencing was used to correct FL transcriptome sequences. A total of 3 PacBio Iso-Seq libraries (1-2 kb, 2-3 kb and 3-6 kb) and 21 Illumina transcriptome libraries were constructed, a total of 13.41 Gb of clean reads were generated, which included 215,636 reads of insert (ROIs) and 121,654 FL, non-chimaric (FLNC) reads. Transcript clustering analysis of the FLNC reads revealed 76,586 consensus isoforms, and a total of 12,520 high-quality transcript sequences corrected with non-FL sequences were used for subsequent analysis. After the redundant reads were removed, 38,435 transcripts were obtained. A total of 27,905 coding DNA sequences (CDSs) were identified, and 407 long non-coding RNAs (lncRNAs) were ultimately predicted. Additionally, 24,832 simple sequence repeats (SSRs) were identified, and a total of 1,295 alternative splicing (AS) events were predicted. Furthermore, 37,993 transcripts were annotated in eight functional databases. This is the first study to perform SMRT sequencing of the FL transcriptome of loquat. The obtained transcriptomic data are conducive for further exploration of the mechanism of loquat freezing injury and thus serve as an important theoretical basis for generating new loquat material and for identifying new ways to improve loquat cold resistance.

Reference genes are used for the correction of qRT-PCR data, and it is necessary to investigate the optimum reference gene under certain conditions. The expression levels of seven traditional reference genes ACT1, ACT2, GAPDH, 18S rRNA, UBQ, TUB and CYP were analyzed using qRT-PCR in different varieties, tissues, developmental stages and hormone (or pollen polysaccharide) treatments in kiwifruit. Gene expression stability was assessed with the help of three common software (geNorm, NormFinder, BestKeeper), and the minimum number of reference genes necessary for normalization was also determined. GAPDH, ACT1 and ACT2 were selected as reference genes for different genotypes of kiwifruit. GAPDH and UBQ were the best combinations of reference genes for root, stem, leaf, flower and fruit. GAPDH and ACT1 could be the preferred reference genes for normalization of qRT-PCR data during fruit development. The pairing of ACT1 and UBQ constituted the optimal combination of reference genes in kiwifruit treated with different hormones (or pollen polysaccharide). This study provides a new and reliable option for the use of reference genes in the analysis of gene expression patterns of interest in kiwifruit.

Although the effects of melatonin on plant abiotic and biotic stress resistance have been explored in recent decades, the accumulation of endogenous melatonin in plants and its influence on fruit quality remains unclear. In the present study, melatonin accumulation levels and the expression profiles of five synthesis genes were investigated during fruit and leaf development in sweet cherry (Prunus avium L.). Melatonin was strongly accumulated in young fruits and leaves, then decreased steadily with maturation. Transcript levels of PacTDC and PacSNAT were highly correlated with melatonin content in both fruit and leaves, indicating their importance in melatonin accumulation. Furthermore, application of 50 and 100 μmol·L−1 of melatonin to leaves had a greater influence on fruit quality than treatments applied to fruits, by significantly improving fruit weight, soluble solids content, and phenolic content including total phenols, flavanols, total anthocyanins, and ascorbic acid. Meanwhile, melatonin application promoted the antioxidant capacity of fruit assayed by 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azinobis (3-ethylben zothiazoline-6-sulfonic acid) (ABTS), and ferric reducing antioxidant power (FRAP). These results provide insights into the physiological and molecular mechanisms underlying melatonin metabolism of sweet cherry.

PAL, UFGT as structural genes and MYB10 as a regulatory gene play an important role in the accumulation of anthocyanins in plants. In this experiment, ‘Cuihongli’ and ‘Qiangcuili’ were used as materials to clone PAL, UFGT and MYB10 related to anthocyanin synthesis by homologous sequence cloning. The results showed that the full length of PAL was 2160 bp, encoding 719 amino acids; the full length of UFGT was 1428 bp, encoding 475 amino acids, and the differences of PAL and UFGT between the two cultivars were one amino acid and three amino acids, respectively. The sequence length of ‘Cuihongli’ MYB10 gene is 732 bp, which encodes 243 amino acids and belongs to the superfamily of SANT family. Homology analysis and phylogenetic tree analysis showed that the proteins encoded by PAL, UFGT and MYB10 genes were short and closely related to Prunus persica, Prunus avium, Prunus armeniaca and Prunus cerasifera in Rosaceae.

MYB10, bHLH and WD40 are correlative regulatory factors of anthocyanin. In this paper, the expression of MYB10, bHLH and WD40 in the peel and the pulp of two plum cultivars were analyzed with the materials of ‘Cuihongli’ and ‘Qiangcuili’. The results showed that, with the development of the fruit of ‘Cuihongli’, the expression of MYB10 in the peel was downregulated firstly then upregulated, and the expression of MYB10 was not detected in the flesh of ‘Cuihongli’s pulp and the peel and the pulp of the ‘Qiangcuili’. The expression of bHLH and WD40 showed that the they had no significant correlation with the accumulation of anthocyanin in the two cultivars. It is suggested that the deletion of MYB10 gene expression result in the lack of anthocyanin in the flesh of ‘Qiangcuili’ .

Melatonin, a multiple signal molecule, plays important roles in delaying senescence during the development of plants. Because few species have been studied for the effect of exogenous melatonin on anti-aging, the plausible mechanism of melatonin of anti-aging effects on other plant species has remained largely unknown. In the present study, the effects of exogenous melatonin on leaf senescence in kiwifruit were examined during natural aging after melatonin (200 μM) or water (Control) pretreatment. The decreased membrane damage and lower hydrogen peroxide (H2O2) content due to the enhanced scavenging activity of antioxidant enzymes peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) demonstrated that melatonin effectively delayed the aging of kiwifruit leaves. Likewise, owing to up-regulated expression of chlorophyll a/b-binding protein (CAB) gene in the sampled leaves pretreated with melatonin, chlorophyll degradation decreased. Therefore, osmoregulatory substances in sampled leaves accumulated (e.g., soluble sugar and soluble protein) and seedling cell environment stability was maintained. Simultaneously, melatonin decreased H2O2 concentration owing to increased glutathione (GSH) and ascorbate (AsA) content, and the expression levels of glutathione reductase (GR), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDAR), dehydroascorbate reductase (DHAR) were up-regulated by melatonin application, indicating that the increase of GSH and AsA was attributed to the expression of these genes. In addition, a large amount of flavonoids accumulated in seedlings pretreated with melatonin, and transcript levels of eight genes involved in flavonoid synthesis, including phenylalanine ammonia-lyase (PAL), cinnamate-4-hydroxymate (C4H), chalcone synthase (CHS), flavanone 3-hydroxylase (F3H), flavonol synthase (FNS), leucoanthocyanin reductase (LAR), anthocyanin reductase (ANR), flavonoid 3-O-glucosyltransferase (UFGT) were enhanced in response to melatonin application. These results indicated that melatonin delayed aging of kiwifruit leaves by activating the antioxidant capacity and enhancing flavonoid biosynthesis. All of these results can provide clear proof that melatonin plays a key roles in delaying leaf senescence.

Evidence exists to suggest that melatonin (MT) is important to abiotic stress tolerance in plants. Here, we investigated whether exogenous MT reduces heat damage on biological parameters and gene expression in kiwifruit (Actinidia deliciosa) seedlings. Pretreatment with MT alleviates heat-induced oxidative harm through reducing H2O2 content and increasing proline content. Moreover, MT application raised ascorbic acid (AsA) levels and the activity of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). We also observed elevation in the activity of enzymes related to the AsA-GSH cycle, such as ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR). Furthermore, MT application increased the expression of 28/31 glutathione S-transferase (GST) genes, reducing oxidative stress. These results clearly indicate that in kiwifruit, MT exerts a protective effect against heat-related damage through regulating antioxidant pathways.