Post-harvest quality of melon accessions subjected to salinity.

The objective was to evaluate the behavior of melon genotypes (Cucumis melo L.) in the physical, chemical and biochemical quality of melon fruits as a function of electrical conductivity irrigation water levels (ECw). The experimental design adopted was randomized blocks in a 5 x 3 factorial scheme with five replications. The first factor was represented by five salinity levels (0.5, 1.5, 3.0, 4.5, and 6.0 dS m-1) and the second factor by accessions A35, and A24, and the hybrid Sancho. The physical, chemical and biochemical variables showed a reduction in production, with smaller fruits, with less weight, smaller cavity, with increased pulp thickness for Sancho. Vitamin C and yellow flavonoids increased indicating antioxidant power against ROS. The genotypes showed similar post-harvest behavior, however, the hybrid Sancho stood out over the others, possibly because it is an improved material. Accession A24 presented physiological and biochemical responses that classify it as intolerant.

Novel Bisexual Flower Control Gene Regulates Sex Differentiation in Melon (Cucumis melo L.).

The sex-control system involves several mechanisms in melon. The present study identified a novel bisexual flower control gene from the hermaphroditic melon germplasm, different from the previously recognized one. Genetic analysis showed that a single recessive gene in the newly identified locus b controlled the bisexual flower phenotype in melons. We generated 1431 F2 segregating individuals for genetic mapping of locus b, which was delimited to a 47.94 kb region. Six candidate genes were identified in the delimited interval, and candidate No. 4 encoding melon CPR5 protein was selected as the suitable one for locus b and was denoted CmCPR5. CPR5 reportedly interacted with ethylene receptor ETR1 to regulate ethylene signal transduction. Moreover, the ethephon assays showed that the parental lines (unisexual line and bisexual line) had contrasting expression patterns of CmCPR5. The BiFC and LCI assays also confirmed that CmCPR5 interacted with CmETR1 in 0426 but not in Y101. However, crossover tests showed that CmETR1 functioned normally in both parental lines, suggesting CPR5 malfunction in Y101. This study proposed a corollary mechanism of bisexual flower regulation during stamen primordium development in which the inhibition of stamen primordia development was prevented by the malfunctioning CmCPR5, resulting in bisexual flowers.

In vivo antioxidant potential of fruit mucilage from two varieties of Cucumis melo subsp. agrestis against oxidative stress induced toxicity.

To evaluate in-vivo antioxidant potential of fruit mucilage from Cucumis melo variety momordica (PM) and variety agrestis (KM) using rats as experimental animals, the fruits were collected, identified, dried and pulverized. Mucilages were isolated from the fruit powders by microwave-assisted method. Aqueous extracts obtained were filtered to remove fruit pulp. Each filtrate was centrifuged at 4000xg rpm for 15 min. Each supernatant was precipitated with 3 volumes of 95% ethanol and maintained overnight at 4°C. These precipitates were filtered and lyophilized. In vivo antioxidant activity was determined using rats for 14 days. Paracetamol (75mg/Kg, i.p.) for inducing oxidative stress and Vitamin C & Vitamin E (200mg/Kg each, p.o.) as standard treatment were used. PM and KM were given in 500mg/Kg and 1000mg/Kg, p.o. doses in separate groups. SOD, MDA, GSH and CAT levels were estimated in organs (liver, kidney, heart, brain) of all groups using standard procedures. Toxic control showed prominent toxicity in the liver. The levels of GSH, CAT and SOD were raised and MDA levels were reduced in all organs of test and standard groups. The levels of antioxidant biomarkers varied in all remaining groups. The overall results are significant suggesting strong antioxidant potential of PM and KM.

Foliar application of putrescine before a short-term heat stress improves the quality of melon fruits (Cucumis melo L.).

BACKGROUND: Climate change has caused an increase in the frequency and intensity of heatwaves, worldwide, which subject plants to thermal stress for short periods; this can affect the quality of melon fruits, both negatively and positively. Since the application of putrescine has been shown to help increase tolerance of abiotic stresses, the objective of this work is to determine the effects of the foliar application of putrescine (1.5 and 5 mmol L-1 ) before a short heat stress (HS) on the quality of melon fruits. RESULTS: The results indicate that HS had a positive effect on the quality of melon fruits, since it increased the total sugars and polyamines contents and the antioxidant capacity, and reduced the presence of substances undesirable in foods such as nitrate. However, the fruit quality was further increased by the combination of HS and putrescine (5 mmol L-1 ). In this case, the melon fruits showed increases in their antioxidant capacity and contents of polyamines, amino acids and minerals beneficial to health. The nitrate concentration was even lower than in the control fruits. CONCLUSION: This novel study highlights the possibility of improving the nutritional quality of melon pulp by applying foliar putrescine in combination with a short period of high temperature. © 2020 Society of Chemical Industry.

CmLOX10 positively regulates drought tolerance through jasmonic acid -mediated stomatal closure in oriental melon (Cucumis melo var. makuwa Makino).

Drought stress severely impairs plant growth and production. Lipoxygenase (LOX), a master regulator for lipid peroxidation, is critical for direct or indirect response to abiotic stresses. Here, we found that drought stress induced the transcription of CmLOX10 in leaves of oriental melon seedlings. Reverse genetic approaches and physiological analyses revealed that silencing CmLOX10 increased drought susceptibility and stomatal aperture in oriental melon seedlings, and that ectopic overexpression of CmLOX10 in Arabidopsis enhanced drought tolerance and decreased the stomatal aperture. Moreover, the transcription of jasmonic acid (JA)-related genes and JA accumulation were significantly induced in CmLOX10-overexpressed Arabidopsis, which were reversely suppressed in CmLOX10-silenced seedlings during the stage of drought stress. Foliar application of JA further verified that JA enhanced drought tolerance and induced stomatal closure in leaves of melon seedlings. In addition, the feedback regulation of CmLOX10 was induced by JA signaling, and the expression level of CmMYC2 was increased by JA and drought treatment. Yeast one-hybrid analysis showed that CmMYC2 directly bound to the promoter of CmLOX10. In summary, we identified the important roles of CmLOX10 in the regulation of drought tolerance in oriental melon seedlings through JA- mediated stomatal closure and JA signaling-mediated feedback through CmMYC2.

iTRAQ-based quantitative proteomics analysis of cantaloupe (Cucumis melo var. saccharinus) after cold storage.

BACKGROUND: Cantaloupe is susceptible to cold stress when it is stored at low temperatures, resulting in the loss of edible and commercial quality. To ascertain the molecular mechanisms of low temperatures resistance in cantaloupe, a cold-sensitive cultivar, Golden Empress-308 (GE) and a cold-tolerant cultivar, Jia Shi-310 (JS), were selected in parallel for iTRAQ quantitative proteomic analysis. RESULTS: The two kinds of commercial cultivars were exposed to a temperature of 0.5 °C for 0, 12 and 24 days. We found that the cold-sensitive cultivar (GE) suffered more severe damage as the length of the cold treatment increased. Proteomic analysis of both cultivars indicated that the number of differentially expressed proteins (DEPs) changed remarkably during the chilly treatment. JS expressed cold-responsive proteins more rapidly and mobilized more groups of proteins than GE. Furthermore, metabolic analysis revealed that more amino acids were up-regulated in JS during the early phases of low temperatures stress. The DEPs we found were mainly related to carbohydrate and energy metabolism, structural proteins, reactive oxygen species scavenging, amino acids metabolism and signal transduction. The consequences of phenotype assays, metabolic analysis and q-PCR validation confirm the findings of the iTRAQ analysis. CONCLUSION: We found that the prompt response and mobilization of proteins in JS allowed it to maintain a higher level of cold tolerance than GE, and that the slower cold responses in GE may be a vital reason for the severe chilling injury commonly found in this cultivar. The candidate proteins we identified will form the basis of future studies and may improve our understanding of the mechanisms of cold tolerance in cantaloupe.

Lignin synthesized by CmCAD2 and CmCAD3 in oriental melon (Cucumis melo L.) seedlings contributes to drought tolerance.

KEY MESSAGE: CmCAD2 and CmCAD3 function more positively than CmCAD1 in oriental melon for lignin synthesis which is important to ensure internal water status and thus for drought tolerance. Well-lignification may be the guarantee of efficient axial water transport and barrier of lateral water flow in oriental melon tolerating drought stress, however remains to be verified. As an important enzyme in monolignol synthesis pathway, five cinnamyl alcohol dehydrogenase (CAD) genes were generally induced in melon seedlings by drought. Here we further revealed the roles of CmCAD1, 2, and 3 in lignin synthesis and for drought tolerance. Results found that overexpressing CmCAD2 or 3 strongly recovered CAD activities, lignin synthesis and composition in Arabidopsis cadc cadd, whose lignin synthesis is disrupted, while CmCAD1 functioned modestly. In melon seedlings, silenced CmCAD2 and 3 individually or collectively decreased CAD activities and lignin depositions drastically, resulting in dwarfed phenotypes. Reduced lignin, mainly composed by guaiacyl units catalyzed by CmCAD3, is mainly due to the limited lignification in tracheary elements and development of Casparion strip. While CmCAD1 and 2 exhibited catalysis to p-coumaraldehyde and sinapaldehyde, respectively. Compared with CmCAD1, drought treatments revealed higher sensitivity of CmCAD2 and/or 3 silenced melon seedlings, accompanying with lower relative water contents, water potentials and relatively higher total soluble sugar contents. Slightly up-regulated expressions of aquaporin genes together with limited lignification might imply higher lateral water loss in stems of silenced lines. In Arabidopsis, CmCAD2 and 3 transgenic lines enhanced cadc cadd drought tolerance through recovering lignin synthesis and root development, accompanying with decreased electrolyte leakage ratios and increased RWCs, thus improved survival rates. Briefly, lignin synthesized by CmCAD2 and 3 functions importantly for drought tolerance in melon.

High-density NGS-based map construction and genetic dissection of fruit shape and rind netting in Cucumis melo.

Melon is an important crop that exhibits broad variation for fruit morphology traits that are the substrate for genetic mapping efforts. In the post-genomic era, the link between genetic maps and physical genome assemblies is key for leveraging QTL mapping results for gene cloning and breeding purposes. Here, using a population of 164 melon recombinant inbred lines (RILs) that were subjected to genotyping-by-sequencing, we constructed and compared high-density sequence- and linkage-based recombination maps that were aligned to the reference melon genome. These analyses reveal the genome-wide variation in recombination frequency and highlight regions of disrupted collinearity between our population and the reference genome. The population was phenotyped over 3 years for fruit size and shape as well as rind netting. Four QTLs were detected for fruit size, and they act in an additive manner, while significant epistatic interaction was found between two neutral loci for this trait. Fruit shape displayed transgressive segregation that was explained by the action of four QTLs, contributed by alleles from both parents. The complexity of rind netting was demonstrated on a collection of 177 diverse accessions. Further dissection of netting in our RILs population, which is derived from a cross of smooth and densely netted parents, confirmed the intricacy of this trait and the involvement of major locus and several other interacting QTLs. A major netting QTL on chromosome 2 co-localized with results from two additional populations, paving the way for future study toward identification of a causative gene for this trait.

Sieve element occlusion provides resistance against Aphis gossypii in TGR-1551 melons.

Feeding behavior and plant response to feeding were studied for the aphid Aphis gossypii Glover on susceptible and resistant melons (cv. Iroquois and TGR-1551, respectively). Average phloem phase bout duration on TGR-1551 was <7% of the duration on Iroquois. Sixty-seven percent of aphids on TGR-1551 never produced a phloem phase that attained ingestion (EPG waveform E2) in contrast to only 7% of aphids on Iroquois. Average bout duration of waveform E2 (scored as zero if phloem phase did not attain E2) on TGR-1551 was <3% of the duration on Iroquois. Conversely, average bout duration of EPG waveform E1 (sieve element salivation) was 2.8 times greater on TGR-1551 than on Iroquois. In a second experiment, liquid nitrogen was used to rapidly cryofix leaves and aphids within a few minutes after the aphids penetrated a sieve element. Phloem near the penetration site was then examined by confocal laser scanning microscopy. Ninety-six percent of penetrated sieve elements were occluded by protein in TGR-1551 in contrast to only 28% in Iroquois. Usually in TGR-1551, occlusion was also observed in nearby nonpenetrated sieve elements. Next, a calcium channel blocker, trivalent lanthanum, was used to prevent phloem occlusion in TGR-1551, and A. gossypii feeding behavior and the plant's phloem response were compared between lanthanum-treated and control TGR-1551. Lanthanum treatment eliminated the sieve element protein occlusion response and the aphids readily ingested phloem sap from treated plants. This study provides strong evidence that phloem occlusion is a mechanism for resistance against A. gossypii in TGR-1551.

Drought mediated physiological and molecular changes in muskmelon (Cucumis melo L.).

Water deficiency up to a certain level and duration leads to a stress condition called drought. It is a multi-dimensional stress causing alteration in the physiological, morphological, biochemical, and molecular traits in plants resulting in improper plant growth and development. Drought is one of the major abiotic stresses responsible for loss of crops including muskmelon (Cucumis melo. L). Muskmelon genotype SC-15, which exhibits high drought resistance as reported in our earlier reports, was exposed to deficient water condition and studied for alteration in physiological, molecular and proteomic profile changes in the leaves. Drought stress results in reduced net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration (E) rate. With expanded severity of drought, declination recorded in content of total chlorophyll and carotenoid while enhancement observed in phenol content indicating generation of oxidative stress. In contrary, activities of catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX), and guaiacol (POD) were increased under drought stress. Peptide mass fingerprinting (PMF) showed that drought increased the relative abundance of 38 spots while decreases10 spots of protein. The identified proteins belong to protein synthesis, photosynthesis, nucleotide biosynthesis, stress response, transcription regulation, metabolism, energy and DNA binding. A drought-induced MADS-box transcription factor was identified. The present findings indicate that under drought muskmelon elevates the abundance of defense proteins and suppresses catabolic proteins. The data obtained exhibits possible mechanisms adopted by muskmelon to counter the impacts of drought induced stress.

Non-destructive monitoring of netted muskmelon quality based on its external phenotype using Random Forest.

The internal phenotypes of netted muskmelon (Cucumis melo L. var. eticulates Naud.) are always associated with its external phenotypes. In this study, the parameters of external phenotypic traits were extracted from muskmelon images captured by machine vision, and the internal phenotypes of interest to us were measured. Pearson analysis showed that most external phenotypic traits were highly correlated with these internal phenotypes in muskmelon fruit. In this study, we used the random forest algorithm to predict muskmelon fruit internal phenotypes based on the significantly associated external parameters. Carotenoids, sucrose, and total soluble solid (TSS) were the three most accurately monitored internal phenotypes with prediction R-squared (R2) values of 0.947 (root-mean-square error (RMSE) = 0.019 mg/100 g), 0.918 (RMSE = 3.233 mg/g), and 0.916 (RMSE = 1.089%), respectively. Further, a simplified model was constructed and validated based on the top 10 external phenotypic parameters associated with each internal phenotype, and these parameters were filtered with the varImp function from the random forest package. The top 10 external phenotypic parameters correlated with each internal phenotype used in the simplified model were not identical. The results showed that the simplified models also accurately monitored the melon internal phenotypes, despite that the predicted R2 values decreased 0.3% to 7.9% compared with the original models. This study improved the efficiency and accuracy of real-time fruit quality monitoring for greenhouse muskmelon.

The impacts of γ-Fe2O3 and Fe3O4 nanoparticles on the physiology and fruit quality of muskmelon (Cucumis melo) plants.

Iron fertilizers are worthy to be studied due to alleviate the Fe deficiency. Different forms of iron oxide nanoparticles are selected to better understand possible particle applications as an Fe source for crop plants. In this study, we assessed the different effects of γ-Fe2O3 and Fe3O4 NPs on the physiology and fruit quality of muskmelon plants in a pot experiment for five weeks. Results showed that no increased iron content was found under NPs treatment in root, stem, leaf and fruit, except 400 mg/L Fe3O4 NPs had a higher iron content in muskmelon root. With the extension of NPs exposure, both γ-Fe2O3 and Fe3O4 NPs began to promote plant growth. In addition, γ-Fe2O3 and Fe3O4 NPs could increase chlorophyll content at a certain stage of exposure. Happily, 200 mg/L γ-Fe2O3 NPs and 100, 200 mg/L Fe3O4 NPs significantly increased fruit weight of muskmelon by 9.1%, 9.4% and 11.5%. It is noteworthy that both γ-Fe2O3 and Fe3O4 NPs caused positive effects on VC content, particularly 100 mg/L Fe3O4 NPs increased the VC content by 46.95%. To the best of our knowledge, little research has been done on the effect of nanoparticles on the whole physiological cycle and fruit quality of melon. The assessment of physiology and fruit quality of muskmelon plants in vitro upon γ-Fe2O3 and Fe3O4 NPs exposure could lay a foundation for NPs potential impact at every growth period of muskmelon plants.

Transcriptome analysis of differentially expressed genes during anther development stages on male sterility and fertility in Cucumis melo L. line.

The genic male sterility (MS) plays a major role in melon hybrids production, it could reduce the cost of pollination and increase the yield and quality. However, the molecular mechanism underlying genetic male sterility is yet poorly understood. The morphological differences of flower buds of melon were observed showed that the flower buds were tetrad when they were 1 mm stage and monocyte microspore when they were 2 mm stage. Electron microscopy showed that there was significant difference between MS lines and MF (male fertility) lines. In order to detect the global expression of the genes during the melon anther development and association with MS, 12 DEGs (differentially expressed genes) libraries were constructed from the anther of MS and MF in the bud stage with 1 and 2 mm diameter, respectively. A total of 765 DEGs expressed in anther during different developmental stage (MS 1 mm vs. MS 2 mm), 148 and 309 DEGs were found to be related to MS as compared to MF (MS 1 mm vs. MF 1 mm, and MS 2 mm vs. MF 2 mm) at a false discovery rate FDR <0.01. Among these, 10 DEGs were expressed in all the three comparisons, including transcription factor bHLH genes. Among the DEGs in RNA-seq analysis, 28 were validated by qRT-PCR. Of these, a number of genes were involved in ABC transfactor B family, cytochrome-related genes, hormone-related genes (auxin transporter, gibberellin-regulated protein), MADS-box protein genes, F-box protein genes, peroxidase-related, and Zinc finger protein genes. These genes are involved in many biological pathways, including starch and sucrose metabolism, signal transduction mechanisms and transcription factors, etc. Compared to the same developmental stage of MS and MF, the different developmental stages of MS indicated diverse gene regulation pathways involved in the anther development in MS. These results would provide novel insight into the global network to male sterility in melon.

Morphophysiological and molecular evidence supporting the augmentative role of Piriformospora indica in mitigation of salinity in Cucumis melo L.

Salinity is one of the major limiting factors in plant growth and productivity. Cucumis melo L. is a widely cultivated plant, but its productivity is significantly influenced by the level of salinity in soil. Symbiotic colonization of plants with Piriformospora indica has shown a promotion in plants growth and tolerance against biotic stress. In this study, physiological markers such as ion analysis, antioxidant determination, proline content, electrolyte leakage and chlorophyll measurement were assessed in melon cultivar under two concentrations (100 and 200 mM) of NaCl with and without P. indica inoculation. Results showed that the endophytic inoculation consistently upregulated the level of antioxidants, enhanced plants to antagonize salinity stress. The expression level of an RNA editing factor (SLO2) which is known to participate in mitochondria electron transport chain was analyzed, and its full mRNA sequence was obtained by rapid amplification of cDNA ends (RACE). Under salinity stress, the expression level of SLO2 was increased, enhancing the plant's capability to adapt to the stress. However, P. indica inoculation further elevated the expression level of SLO2. These findings suggested that the symbiotic association of fungi could help the plants to tolerate the salinity stress.

Isolation and functional validation of the CmLOX08 promoter associated with signalling molecule and abiotic stress responses in oriental melon, Cucumis melo var. makuwa Makino.

BACKGROUND: Lipoxygenases (LOXs) play significant roles in abiotic stress responses, and identification of LOX gene promoter function can make an important contribution to elucidating resistance mechanisms. Here, we cloned the CmLOX08 promoter of melon (Cucumis melo) and identified the main promoter regions regulating transcription in response to signalling molecules and abiotic stresses. RESULTS: The 2054-bp promoter region of CmLOX08 from melon leaves was cloned, and bioinformatic analysis revealed that it harbours numerous cis-regulatory elements associated with signalling molecules and abiotic stress. Five 5'-deletion fragments obtained from the CmLOX08 promoter-2054 (LP1), 1639 (LP2), 1284 (LP3), 1047 (LP4), and 418 bp (LP5)-were fused with a GUS reporter gene and used for tobacco transient assays. Deletion analysis revealed that in response to abscisic acid, salicylic acid, and hydrogen peroxide, the GUS activity of LP1 was significantly higher than that of the mock-treated control and LP2, indicating that the - 2054- to - 1639-bp region positively regulates expression induced by these signalling molecules. However, no deletion fragment GUS activity was induced by methyl jasmonate. In response to salt, drought, and wounding treatments, LP1, LP2, and LP4 promoted significantly higher GUS expression compared with the control. Among all deletion fragments, LP4 showed the highest GUS expression, indicating that - 1047 to - 1 bp is the major region regulating promoter activity and that the - 1047 to - 418-bp region positively regulates expression induced by salt, drought, and wounding, whereas the - 1284 to - 1047-bp region is a negative regulatory segment. Interestingly, although the GUS activity of LP1 and LP2 was not affected by temperature changes, that of LP3 was significantly induced by heat, indicating that the - 1284- to - 1-bp region is a core sequence responding to heat and the - 2054- to - 1284-bp region negatively regulates expression induced by heat. Similarly, the - 1047- to - 1-bp region is the main sequence responding to cold, whereas the - 2054- to - 1047-bp region negatively regulates expression induced by cold. CONCLUSIONS: We cloned the CmLOX08 promoter and demonstrated that it is a signalling molecule/stress-inducible promoter. Furthermore, we identified core and positive/negative regulatory regions responding to three signalling molecules and five abiotic stresses.

Ultrastructure of compatible and incompatible interactions in phloem sieve elements during the stylet penetration by cotton aphids in melon.

Resistance of the melon line TGR-1551 to the aphid Aphis gossypii is based on preventing aphids from ingesting phloem sap. In electrical penetration graphs (EPGs), this resistance has been characterized with A. gossypii showing unusually long phloem salivation periods (waveform E1) mostly followed by pathway activities (waveform C) or if followed by phloem ingestion (waveform E2), ingestion was not sustained for more than 10 min. Stylectomy with aphids on susceptible and resistant plants was performed during EPG recording while the stylet tips were phloem inserted. This was followed by dissection of the penetrated leaf section, plant tissue fixation, resin embedding, and ultrathin sectioning for transmission electron microscopic observation in order to study the resistance mechanism in the TGR. The most obvious aspect appeared to be the coagulation of phloem proteins inside the stylet canals and the punctured sieve elements. Stylets of 5 aphids per genotype were amputated during sieve element (SE) salivation (E1) and SE ingestion (E2). Cross-sections of stylet bundles in susceptible melon plants showed that the contents of the stylet canals were totally clear and also, no coagulated phloem proteins occurred in their punctured sieve elements. In contrast, electron-dense coagulations were found in both locations in the resistant plants. Due to calcium binding, aphid saliva has been hypothesized to play an essential role in preventing/suppressing such coagulations that cause occlusion of sieves plate and in the food canal of the aphid's stylets. Doubts about this role of E1 salivation are discussed on the basis of our results.

Somatic embryogenesis of muskmelon (Cucumis melo L.) and genetic stability assessment of regenerants using flow cytometry and ISSR markers.

A new protocol for in vitro regeneration through direct somatic embryogenesis for two muskmelon cultivars (Cucumis melo L., "Mashhadi" and "Eivanaki") is reported. Somatic embryos were obtained culturing 4- and 8-day-old cotyledons, seeds, and hypocotyls on Murashige and Skoog medium supplemented with three different hormonal combinations never tested so far for melon (naphthoxyacetic acid (NOA) + thidiazuron (TDZ), NOA + 6-banzylaminopurine (BAP), and 2,4-dichlorophenoxyacetic acid (2,4-D) + N-(2-chloro-4-pyridyl)-N'-phenylurea (4-CPPU)). Results were compared with those obtained when explants were cultivated in the presence of 2,4-D + BAP, previously used on melon. Embryogenesis occurred more successfully in 4-day-old cotyledons and seeds than hypocotyls and 8-day-old cotyledons. The best result was achieved with NOA + BAP. Genotypes significantly affected embryogenesis. The number of embryos in "Eivanaki" was significantly higher than that in "Mashhadi." Embryo proliferation when explants were maintained in jars (9.3%) was found to be higher compared to that in petri dishes. For the first time, genetic stability of regenerated melon plants was evaluated using inter-simple sequence repeat markers. Polymerase chain reaction (PCR) products demonstrated a total of 102 well-resolved bands, and regenerants were 93% similar compared to the mother plant. Somaclonal changes during embryogenesis were evaluated by flow cytometry, showing 91% of the same patterns in regenerated plants. The results suggest that the new hormone components are effective when applied for in vitro embryogenesis of muskmelon as they show a high frequency in regeneration and genetic homogeneity.

Phloem Loading through Plasmodesmata: A Biophysical Analysis.

In many species, Suc en route out of the leaf migrates from photosynthetically active mesophyll cells into the phloem down its concentration gradient via plasmodesmata, i.e. symplastically. In some of these plants, the process is entirely passive, but in others phloem Suc is actively converted into larger sugars, raffinose and stachyose, and segregated (trapped), thus raising total phloem sugar concentration to a level higher than in the mesophyll. Questions remain regarding the mechanisms and selective advantages conferred by both of these symplastic-loading processes. Here, we present an integrated model-including local and global transport and kinetics of polymerization-for passive and active symplastic loading. We also propose a physical model of transport through the plasmodesmata. With these models, we predict that (1) relative to passive loading, polymerization of Suc in the phloem, even in the absence of segregation, lowers the sugar content in the leaf required to achieve a given export rate and accelerates export for a given concentration of Suc in the mesophyll and (2) segregation of oligomers and the inverted gradient of total sugar content can be achieved for physiologically reasonable parameter values, but even higher export rates can be accessed in scenarios in which polymers are allowed to diffuse back into the mesophyll. We discuss these predictions in relation to further studies aimed at the clarification of loading mechanisms, fitness of active and passive symplastic loading, and potential targets for engineering improved rates of export.

Influence of environmental factors on Cucumis melo L. var. agrestis Naud. seed germination and seedling emergence.

Cucumis melo L. var. agrestis Naud. (field muskmelon) is an annual invasive weed in many parts of Asia. However, there is very little available information about the germination and emergence of this species. Therefore, laboratory experiments were conducted to evaluate the effects of light, temperature, salt stress, osmotic stress, pH, and depth of planting on field muskmelon germination and seedling emergence. Light had no effect on seed germination, and the seeds germinated at a wide range of temperatures. More than 90% of the seeds germinated at constant temperatures between 20°C and 35°C, and fluctuating day/night temperatures between 15/25 and 30/40°C. The seeds were tolerant to salinity as germination occurred up to the 200 mM NaCl treatment. However, the seeds were sensitive to osmotic stress as seed germination was completely inhibited at -0.6 MPa. The seeds germinated over a pH range of 4 to 10, which suggested that pH was not a limiting factor for germination. Seedling emergence was greatest (97.86%) when the seeds were planted on the soil surface, but emergence declined as the burial depth increased. Information from this study can be used to predict future infestations in China and help develop strategies to manage this species.

Physiological analysis and transcriptome comparison of two muskmelon (Cucumis melo L.) cultivars in response to salt stress.

Melon (Cucumis melo L.) is an important vegetable crop that ranks second in salt tolerance among the Cucurbitaceae. Previous studies on the two muskmelon cultivars 'Bing XueCui' (BXC) and 'Yu Lu' (YL) revealed that they had different characteristics under salt stress, but the molecular basis underlying their different physiological responses is unclear. Here, we combined a physiological study with a genome-wide transcriptome analysis to understand the molecular basis of genetic variation that responds to salt stress in the melon. BXC performed better under salt stress than YL in terms of biomass and photosynthetic characteristics, because it exhibited less reduction in transpiration rate, net photosynthesis rate, and stomatal conductance under 150-mM NaCl stress than YL. A transcriptome comparison of the leaves of the cultivars revealed that 1171 genes responded to salt stress in BXC while 1487 genes were identified as salt-stress-responsive in YL. A real-time polymerase chain reaction analysis of 12 of the responsive genes revealed that there was a strong, positive correlation with RNA sequencing data. The genes were involved in several pathways, including photosynthesis, the biosynthesis of secondary metabolites, metabolism, and plant hormone signal transduction, and their expression levels differed between the two cultivars in response to salt stress. This study provides a molecular perspective of two melon cultivars in response to salt stress, and its results could be used to investigate the complex molecular mechanisms underlying salt tolerance in the melon.