Red Tangerine Research Articles

Effects of rootstocks and developmental time on the dynamic changes of main functional substances in 'Orah' (Citrus reticulata Blanco) by HPLC coupled with UV detection.

Citrus fruit is rich in important functional constituents such as flavonoids, phenolic acids terpenes and other functional substances that play an important role for treating clinical diseases or controlling major agricultural diseases and pests. Plant secondary metabolites have become one of the most important resources of novel lead compounds, especially young citrus fruits contain multiple functional substances. 'Orah', a type of citrus reticulata, is known for its fine appearance, productivity, delicious sweetness, late-maturing characteristics, and is widely cultivated in China. Fruit thinning and rootstock selection are commonly used agronomic measures in its production to ensure its quality and tree vigor. However, few studies have demonstrated the effects of these agronomic measures on the functional substances of 'Orah'. In this study, we used HPLC coupled with UV to detect the dynamic changes of fruit quality, 13 main flavonoids, 7 phenolic acids, 2 terpenes, synephrine and antioxidant capacity in both peel and pulp of citrus fruits grafted on four rootstocks (Red orange Citrus reticulata Blanco cv. red tangerine, Ziyang xiangcheng Citrus junos Sieb. ex Tanaka, Trifoliate orange Poncirus trifoliata L. Raf, and Carrizo citrange Citrus sinensis Osb.×P.trifoliate Raf) at six different developmental stages (from 90 DAF to 240 DAF). The results indicated that rootstock can significantly affect the contents of functional constituents and antioxidant capacity in 'Orah'. Additionally, it was found that pruning at either 90 DAF (days after flowering) or 150 DAF produced the most favorable outcomes for extracting functional substances. We also identified rootstock 'Trifoliate orange' has the highest total soluble solids (TSS) and 'Ziyang xiangcheng' to be the optimal in terms of comprehensive sensory of fruit quality, while 'Red orange' and 'Ziyang xiangcheng' are optimal in terms of functional substance quality, and 'Red orange' excels in antioxidant capacity. Overall, the findings demonstrate the important role of rootstocks and developmental stage in shaping fruit sensory quality and functional substance synthesis, providing valuable insights for guiding rootstock selection, determining thinning time, and utilizing pruned fruits in a more informed manner.

Widely Targeted Metabolomic Analysis Provides New Insights into the Effect of Rootstocks on Citrus Fruit Quality.

The use of different rootstocks has a significant effect on the content of flavor components and overall fruit quality. However, little information is available about the metabolic basis of the nutritional value of citrus plants. In this study, UPLC-MS/MS (ultra-performance liquid chromatography-tandem mass spectrometry) was performed to analyze the metabolites of three late-maturing hybrid mandarin varieties ('Gold Nugget', 'Tango' and 'Orah') grafted on four rootstocks ('Trifoliate orange', 'Carrizo citrange', 'Red tangerine' and 'Ziyang Xiangcheng'). A total of 1006 metabolites were identified through OPLS-DA (Orthogonal Partial Least Squares-Discriminant Analysis) analysis. KEGG (Kyoto Encyclopedia of Genes and Genomes) analysis revealed the most critical pathways among the different pathways associated with genes grafted on the four rootstocks that were differentially activated, including tryptophan metabolism and sphingolipid metabolism in 'Gold Nugget'; tryptophan metabolism, phenylpropanoid biosynthesis and sphingolipid metabolism in 'Tango'; and pantothenate and CoA biosynthesis- and photosynthesis-related biosynthesis in 'Orah'. A considerable difference between the different rootstocks was also observed in the accumulation of lipids, phenolic acids and flavonoids; further analysis revealed that the rootstocks regulated specific metabolites, including deacetylnomylinic acid, sudachinoid A, amoenin evodol, rutaevin, cyclo (phenylalanine-glutamic acid), cyclo (proline-phenylalanine), 2-hydroxyisocaproic acid, and 2-hydroxy-3-phenylpropanoic acid. The results of this study provide a useful foundation for further investigation of rootstock selection for late-maturation hybrid mandarin varieties.

Mycorrhizal Symbiosis Enhances P Uptake and Indole-3-Acetic Acid Accumulation to Improve Root Morphology in Different Citrus Genotypes

Arbuscular mycorrhizal fungi (AMF) are known to enhance plant growth via stimulation of root system development. However, the extent of their effects and underlying mechanisms across different citrus genotypes remain to be fully elucidated. This study investigates the impact of Funneliformis mosseae (F. mosseae) inoculation on plant growth performance, root morphology, phosphorus (P), and indole-3-acetic acid (IAA) concentrations, as well as the expression of related synthesis and transporter genes in three citrus genotypes: red tangerine (Citrus tangerine ex. Tanaka), kumquat (Fortunella margarita L. Swingle), and fragrant citrus (Citrus junos Sieb. ex. Tanaka). Following 12 weeks of inoculation, significant improvements were observed in plant height, shoot and root biomass, total root length, average root diameter, second-order lateral root development, root hair density, and root hair length across all genotypes. Additionally, F. mosseae inoculation significantly increased root P and IAA concentrations in the three citrus genotypes. Notably, phosphatase activity was enhanced in F. margarita but reduced in C. tangerine and C. junos following inoculation. Gene expression analysis revealed a universal upregulation of the P transporter gene PT5, whereas expressions of the auxin synthesis gene YUC2, transporter gene LAX2, and phosphatase gene PAP1 were commonly downregulated. Specific to genotypes, expressions of YUC5, LAX5, PIN2, PIN3, PIN6, and expansin genes EXPA2 and EXPA4 were significantly upregulated in C. tangerine but downregulated in F. margarita and C. junos. Principal component analysis and correlation assessments highlighted a strong positive association between P concentration, P and auxin synthesis, and transporter gene expressions with most root morphology traits, except for root average diameter. Conversely, IAA content and phosphatase activities were negatively correlated with these root traits. These findings suggest that F. mosseae colonization notably enhances plant growth and root system architecture in citrus genotypes via modifications in P transport and IAA accumulation, indicating a complex interplay between mycorrhizal symbiosis and host plant physiology.

Determination of Synephrine and Caffeine in Citrus Species Herbal Medicines and Weight-Loss Supplements from Taiwan by High-Performance Liquid Chromatography (HPLC)

Synephrine is widely found in Chinese herbs of the Rutaceae family and is commonly used as a primary substitute for ephedrine in sports supplements. However, its potential cardiotoxicity has necessitated governmental regulations regarding its use. This study determined the contents of synephrine, phenylephrine, and caffeine in 30 Chinese herbal preparations (including five single herbs) and 16 supplements promoted for weight loss. The presence of naturally occurring synephrine was detected in all Chinese herbal medicines, with immature bitter orange having the highest synephrine content (ranging from 233.1 to 505.3 mg/100 g). This was followed by three herbs with comparable amounts of up to 317.7 mg/100 g, namely bitter orange, red tangerine exocarp, and tangerine peel. Euodia fruit had the lowest synephrine content, measuring up to 4.9 mg/100 g. None of these herbal medicines were found to contain detectable phenylephrine. On the other hand, weight-loss supplements, comprising complex combinations of herbal extracts, were found to contain synephrine in concentrations up to 1159.0 mg/100 g and caffeine up to 1659.1 mg/100 g. The synephrine content of these products did not exceed the regulatory limit of six percent, nor did they surpass the respective daily consumption of 20 mg. However, one product was found to contain both synephrine and caffeine, albeit at low concentrations, which could potentially breach the regulation prohibiting the combined use of bitter orange and caffeine as food ingredients.

Transcriptome sequencing analyses uncover mechanisms of citrus rootstock seedlings under waterlogging stress.

Citrus plants are sensitive to waterlogging, which can cause yield reduction. Their production heavily depends on the rootstock being used for grafting of scion cultivars, and the rootstock is the first organ to be affected by waterlogging stress. However, the underlying molecular mechanisms of waterlogging stress tolerance remain elusive. In this study we investigated the stress response of two waterlogging-tolerant citrus varieties (Citrus junos Sieb ex Tanaka cv. Pujiang Xiangcheng and Ziyang Xiangcheng), and one waterlogging-sensitive variety (red tangerine) at the morphological, physiological, and genetic levels in leaf and root tissues of partially submerged plants. The results showed that waterlogging stress significantly decreased the SPAD value and root length but did not obviously affect the stem length and new root numbers. The malondialdehyde (MDA) content and the enzyme activities of superoxide dismutase (SOD), guaiacol peroxidase (POD), and catalase (CAT) were enhanced in the roots. The RNA-seq analysis revealed that the differentially expressed genes (DEGs) were mainly linked to 'cutin, suberine, and wax biosynthesis', 'diterpenoid biosynthesis', and 'glycerophospholipid metabolism' in the leaves, whereas were linked to 'flavonoid biosynthesis', 'biosynthesis of secondary metabolites and metabolic pathways' in the roots. Finally, we developed a working model based on our results to elucidate the molecular basis of waterlogging-responsive in citrus. Therefore, our data obtained in this study provided valuable genetic resources that will facilitate the breeding of citrus varieties with improved waterlogging tolerance.

Tolerance and Physiological Responses of Citrus Rootstock Cultivars to Boron Toxicity

Boron (B) is an essential trace nutrient element for citrus, but excessive B levels are frequently encountered in citrus production, potentially resulting in citrus toxicity. To better understand the tolerance and physiological responses of citrus rootstocks to excess B levels, Trifoliate orange, Ziyangxiangcheng, Carrizo citrange, and Red tangerine were treated with four B concentrations (0.05, 0.2, 0.8, and 3.2 mmol/L). High B concentrations resulted in leaf yellowing and shedding and eventual plant death. Chlorophyll content and photosynthetic capacity declined in response to high B concentrations, and relative leaf cell conductivity rose significantly. Trifoliate orange was the first to exhibit symptoms of B toxicity, with the highest levels of B-associated injury. As B concentrations rose, the height increment ratio declined, as did belowground and aboveground dry fresh weight. Soluble protein content initially rose and then fell, while proline content, SOD activity, and POD activity rose with B concentrations. B levels in these rootstocks also increased significantly, with the greatest increases in the leaves. Principal component analysis and subordinate function results revealed that the relative rank order for the B tolerance of citrus rootstocks was: Red tangerine > Carrizo citrange > Ziyangxiangcheng > Trifoliate orange.

A Mini Review of Citrus Rootstocks and Their Role in High-Density Orchards.

Dwarfing is an important agricultural trait for intensive cultivation and effective orchard management in modern fruit orchards. Commercial citrus production relies on grafting with rootstocks that reduce tree vigor to control plant height. Citrus growers all over the world have been attracted to dwarfing trees because of their potential for higher planting density, increased productivity, easy harvest, pruning, and efficient spraying. Dwarfing rootstocks can be used to achieve high density. As a result, the use and development of dwarfing rootstocks are important. Breeding programs in several countries have led to the production of citrus dwarf rootstocks. For example, the dwarfing rootstocks 'Flying Dragon', 'FA 517', 'HTR-051', 'US-897', and 'Red tangerine' cultivated in various regions allow the design of dense orchards. Additionally, dwarf or short-stature trees were obtained using interstocks, citrus dwarfing viroid (CDVd) and various chemical applications. This review summarizes what is known about dwarf citrus rootstocks and the mechanisms underlying rootstock-scion interactions. Despite advances in recent decades, many questions regarding rootstock-induced scion development remain unanswered. Citrus rootstocks with dwarfing potential have been investigated regarding physiological aspects, hormonal communication, mineral uptake capacity, and horticultural performance. This study lays the foundation for future research into the genetic and molecular mechanisms underlying citrus dwarfing.

Uptake of cadmium (Cd) by selected citrus rootstock cultivars

Cadmium (Cd) is a primary heavy metal causing crops toxicity, however, Cd uptake by citrus is little studied and largely unknown. In this study, nine (9) citrus rootstock cultivars were selected and grown under Cd stress at concentrations of 0, 2.5, 10, 20, 50, and 100 mg L−1 (Cd0, Cd2.5, Cd10, Cd20, Cd50 and Cd100, respectively) for 30 d, and citrus growth, Cd concentration, Cd transport ratio (TR%), and Cd uptake factor (PUF%) were measured. Results showed that after 30 d treatments, all selected citrus rootstocks remained alive under a relatively low Cd concentrations (Cd0, Cd2.5 and Cd10), but the mortality rate increased with increasing Cd concentrations beyond Cd20, and all citrus completely died at Cd100. Cd exposure significantly suppressed seedling growth. At 20 % growth reduction, tissue Cd concentrations were Cleopatra mandarin (C. reticulate Blanco) < Brazil sour orange (C. aurantium) < ‘Swingle’ citrumelo (C. paradisi × Poncirus. trifoliate Raf.) < Ziyang Xiangcheng (C. junos Sieb. ex Tanaka) < Carrizo citrange (C. sinensis Osb. × P. trifoliate Raf.) < Goutou sour orange (C. aurantium) < Yichang Cheng (C. ichangensis Swingle) < Red tangerine (C. tangerine) < Trifoliate orange (P. trifoliata Raf.). Moreover, the Cd accumulation in the roots was much higher than in the leaves, and the accumulation was elevated with increasing Cd concentration. Principal component analysis (PCA), including fresh weight growth rate of root and shoot, Cd concentration in root and shoot, transport ratio (TR%), plant uptake factor (PUF%), indicated that selected 9 cultivars could be classified into 4 categories: (1) Trifoliate orange possessed a weak capacity for Cd uptake and accumulation, and its growth was less affected, (2) Goutou sour orange had a weak Cd uptake capacity, but a strong capacity for Cd accumulation and translocation, (3) Ziyang Xiangcheng and Cleopatra mandarin exhibited relatively a strong capacity for both Cd uptake and translocation, (4) The others did not clearly show changes in physiological Cd transport features. This comprehensive evaluation showed that Trifoliate orange was high tolerance to Cd, and Goutou sour orange was low tolerance to Cd, whereas Ziyang Xiangcheng and Cleopatra mandarin were intolerant of Cd.

Metabolic adaptation following genome doubling in citrus doubled diploids revealed by non-targeted metabolomics

Polyploidy is a widespread phenomenon in nature and is thought to play a major role in the evolution of flowering plants. Additionally, polyploidization produces novel phenotypes that through plant breeding have enhanced the production of biomass and improved the stress tolerance of major economic crops. However, the effect of polyploidization on plant metabolism is still unclear. In order to test whether there are common metabolic responses following genome doubling, we performed a comparative metabolomic analysis of mature leaves from doubled diploids and the corresponding diploids of red tangerine (Citrus reticulata Blanco), trifoliate orange (Poncirus trifoliata L. Raf.) and precocious trifoliate orange (P. trifoliata). Non-targeted and targeted metabolic profiling of mature leaves from three doubled diploids and their diploid controls were performed by using liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS) and gas chromatography–mass spectrometry (GC–MS). About 11–34% of the detected metabolic features differentially accumulated in the doubled diploids, mostly by less than fivefold. The levels of primary metabolites tended to increase in the doubled diploids. Concentrations of tricarboxylic acid cycle intermediates—citric acid, malic acid, fumaric acid and succinic acid, enhanced in all of the doubled diploids. The levels of secondary metabolites, including phenylpropanoids and terpenoids, tended to decrease in the doubled diploids. This is consistent with the lower C/N ratios in the doubled diploids. Polyploidization had a significant but relatively limited influence on the accumulation of metabolites in these citrus species. We conclude that primary metabolism takes priority over secondary metabolism in doubled diploid plants to relieve the “genomic stress” encountered during the early stages of genome doubling, probably to promote vitality and growth.

Changes in the phenolic contents and antioxidant activities of citrus peels from different cultivars after in vitro digestion

SummaryThe aim of this study was to investigate the effects of in vitro digestion on the phenolic contents and antioxidant activities of citrus peels. Three different varieties of citrus peels (mandarin, ponkan and red tangerine) were treated with simulated gastric fluid (SGF) and simulated intestinal fluid (SIF). The results showed that the SGF or SIF treatments of the citrus peels did not significantly increase the total phenolic content (TPC) or total flavonoid content (TFC), except for that of the TFC of ponkan peel treated with SGF. However, simulated in vitro digestion did improve the antioxidant activities measured with FRAP and ABTS methods. The effect of SGF was more positive than those of SIF for the FRAP assay, but the opposite was true for ABTS. Notably, both simulated digestion techniques decreased the DPPH free radical scavenging abilities. Simulated digestion in vitro changed the antioxidant activities of the citrus peels.

Transcriptome Profiling to Understand the Effect of Citrus Rootstocks on the Growth of 'Shatangju' Mandarin.

To obtain insight into potential mechanisms underlying the influence of rootstock on scion growth, we performed a comparative analysis of ‘Shatangju’ mandarin grafted onto 5 rootstocks: Fragrant orange (Citrus junons Sieb. ex. Tanaka), Red tangerine (Citrus reticulata Blanco), ‘Shatangju’ mandarin (Citrus reticulata Blanco), Rough lemon (Citrus jambhiri Lush) and Canton lemon (Citrus limonia Osbeck). The tree size of ‘Shatangju’ mandarin grafted onto Canton lemon and Rough lemon were the largest, followed by self-rooted rootstock trees, and the lowest tree sizes correspond to ones grafted on Red tangerine and Fragrant orange rootstocks. The levels of indoleacetic acid (IAA) and gibberellin (GA) were significantly and positively related to growth vigor. The differences of gene expression in leaves of trees grafted onto Red tangerine, Canton lemon and ‘Shatangju’ mandarin were analyzed by RNA-Seq. Results showed that more differentially expressed genes involved in oxidoreductase function, hormonal signal transduction and the glycolytic pathway were enriched in ‘Red tangerine vs Canton lemon’. qRT-PCR analysis showed that expression levels of ARF1, ARF8, GH3 and IAA4 were negatively correlated with the growth vigor and IAA content. The metabolism of GA was influenced by the differential expression of KO1 and GA2OX1 in grafted trees. In addition, most of antioxidant enzyme genes were up-regulated in leaves of trees grafted onto Red tangerine, resulting in a higher peroxidase activity. We concluded that different rootstocks significantly affected the expression of genes involved in auxin signal transduction pathway and GA biosynthesis pathway in the grafted plants, and then regulated the hormone levels and their signal pathways.

Community analysis of arbuscular mycorrhizal fungi in roots of Poncirus trifoliata and Citrus reticulata based on SSU rDNA.

Morphological observation of arbuscular mycorrhizal fungi (AMF) species in rhizospheric soil could not accurately reflect the actual AMF colonizing status in roots, while molecular identification of indigenous AMF colonizing citrus rootstocks at present was rare in China. In our study, community of AMF colonizing trifoliate orange (Poncirus trifoliata L. Raf.) and red tangerine (Citrus reticulata Blanco) were analyzed based on small subunit of ribosomal DNA genes. Morphological observation showed that arbuscular mycorrhizal (AM) colonization, spore density, and hyphal length did not differ significantly between two rootstocks. Phylogenetic analysis showed that 173 screened AMF sequences clustered in at least 10 discrete groups (GLO1~GLO10), all belonging to the genus of Glomus Sensu Lato. Among them, GLO1 clade (clustering with uncultured Glomus) accounting for 54.43% clones was the most common in trifoliate orange roots, while GLO6 clade (clustering with Glomus intraradices) accounting for 35.00% clones was the most common in red tangerine roots. Although, Shannon-Wiener indices exhibited no notable differences between both rootstocks, relative proportions of observed clades analysis revealed that composition of AMF communities colonizing two rootstocks varied severely. The results indicated that native AMF species in citrus rhizosphere had diverse colonization potential between two different rootstocks in the present orchards.

Glomalin-related soil protein and water relations in mycorrhizal citrus (Citrus tangerina) during soil water deficit

Glomalin-related soil protein (GRSP), a glycoprotein of arbuscular mycorrhizal fungi (AMF) secreted into soil, governs the aggregate stability, but the role of GRSP in soil and plant water is sparsely studied. The 24-week-old red tangerine (Citrus tangerina) inoculated with Glomus etunicatum and G. mosseae were subjected to a soil drying for 12 days as soil water deficit (SWD). Length of SWD significantly reduced mycorrhizal colonization, soil hyphal length, and leaf and soil water potential (Ψ), but increased total GRSP (T-GRSP), easily extractable GRSP (EE-GRSP), and proportion of water-stable aggregates (WSAs) in >0.25 mm size, irrespective of AMF source. The AMF-inoculated seedlings showed significantly higher T-GRSP, EE-GRSP, and leaf/soil Ψ than non-AMF seedlings during SWD. A significantly positive correlation was observed for mycorrhizal colonization versus leaf or soil Ψ, and hyphal length versus leaf Ψ, suggesting that root intra- and extra-radical hyphae participated in water transport. Interestingly, in GRSP fractions, only T-GRSP was significantly positively correlated with 0.25–1 and >0.25 mm WSA and negatively with leaf and soil Ψ. These results revealed a strong glue function of T-GRSP (not EE-GRSP and hyphae) to alter the proportional distribution of WSA size, thereby aiding toward prevention of soil water loss for improving soil–plant water relations.

The physiological and nutritional responses of seven different citrus rootstock seedlings to boron deficiency

Carrizo citrange was the most tolerant citrus rootstock to B-deficiency and some physiological performance could be attributed to the decreased mineral nutrient concentrations caused by B-deficiency. Boron (B) is an essential microelement for normal growth and development in vascular plants, and adequate B nutrition is crucial for agricultural production. Although citrus plants are not classified as the most sensitive species to B-deficiency, the occurrence of B-deficiency has been reported in the major citrus producing countries of the world, including the east and south of China. In this study, in order to evaluate the effects of B-deficiency on plant growth, root-morphological traits, B and other nutritional responses of citrus rootstock and to investigate the relationship between this physiological performance and mineral nutrients seven common rootstock seedlings, including Trifoliate orange (TO), Carrizo citrange (CC), Chongyi tangerine (CT), Red tangerine (RT), Cleopatra mandarin (CM), Fragrant citrus (FC), and Sour orange (SO), were treated by B-deficiency (0 mg L−1) or moderate B (0.25 mg L−1). All the seedlings were grown in hydroponics situation with modified 1/2-strength Hoagland’s solution under greenhouse conditions for 10 weeks. The results showed that B-deficiency inhibited the growth and development of all tested citrus rootstocks, but substantial differences were observed among these rootstocks. Different visible symptoms were observed both in the leaf and root. Corking of the leaf veins and leaf yellowing symptoms were observed on all rootstock genotypes except on CC, which exhibited a little discoloration at the end of the experiment. In addition, root growth of the citrus seedlings were also decreased by B-deficiency, but the decreases were more obvious in TO and FC. It was worth noting that B-deficiency inhibited lateral root growth and development more significantly than tap root, but not in lateral root initiation. The different performance of these rootstock genotypes indicated that CC was the most tolerant while TO was the most sensitive to B-deficiency. In addition, under B-deficiency conditions, not only the B concentration, but also the other mineral nutrient concentrations were influenced, especially in Mg, Fe and Mn. This change in nutrient concentrations might partly contribute to the seedlings’ physiological performances under B-deficiency.

Arbuscular mycorrhizal fungi induce sucrose cleavage for carbon supply of arbuscular mycorrhizas in citrus genotypes

Arbuscular mycorrhizas (AMs) must gain carbohydrates (mainly glucose) through sucrose cleavage from their plant hosts. Using the AM fungus Funneliformis mosseae inoculated or non-inoculated citrus genotypes [red tangerine (Citrus tangerina Hort. ex Tanaka), kumquat (Fortunella margarita Lour. Swingle), and trifoliate orange (Poncirus trifoliata L. Raf.)], we tested the hypothesis that the sucrose cleavage would depend on sucrose-cleaving enzyme types and/or host genotypes for carbon supply to the AM development. Mycorrhizal inoculation significantly increased biomass production and glucose contents of leaf, root, and total plant, irrespectively of citrus genotypes. In contrast, under mycorrhization similar leaf sucrose contents were observed between these three citrus genotypes, whereas significantly higher sucrose contents were in roots of red tangerine and kumquat, and in total plant (leaf plus root) of red tangerine and trifoliate orange. Root AM colonization was significantly positively correlated with leaf and total plant glucose but not with root glucose or with sucrose in either leaf and/or root. Root AM colonization increased the activity of leaf acid invertase (AI) and sucrose synthase (SS) and root neutral invertase (NI) in trifoliate orange, leaf SS and root AI in kumquat, and root NI in red tangerine, but decreased leaf NI in all three citrus genotypes, leaf SS in red tangerine, root AI in red tangerine and trifoliate orange, and root SS in kumquat and trifoliate orange. These results support our hypothesis that the sucrose cleavage highly depended on both citrus genotypes and sucrose-cleaving enzyme types/activity, and thus may provide higher glucose as carbon source to support their fungal partners.

Structure–Activity Relationship of Citrus Polymethoxylated Flavones and Their Inhibitory Effects on Aspergillus niger

Citrus peels are rich in polymethoxylated flavones (PMFs) and are potential sources of natural preservatives. Six PMFs extracts, isolated and purified from the peels of three mandarins (Citrus reticulata) and three sweet oranges (Citrus sinensis), were identified and quantitated. Their inhibitory effects on Aspergillus niger were evaluated using a microbroth dilution assay. The Red tangerine variety exhibited the greatest antifungal activity (MIC = 0.2 mg/mL), while Jincheng showed the lowest activity (MIC = 1.8 mg/mL). An analysis of principal components was applied to the results in order to elucidate the structure-activity relationships of the citrus PMFs. The structure-activity relationship analysis revealed that, for good inhibitory effect, the 5-OH, 3-OCH₃, and 8-OCH₃ functionalities were essential, while the presence of 3-OH and 3'-OCH₃ greatly reduced inhibition. The findings of this study provide important information for the exploitation and utilization of citrus PMFs as natural biopreservatives.

Arbuscular mycorrhizas alter root system architecture of Citrus tangerine through regulating metabolism of endogenous polyamines

Arbusculuar mycorrhizal fungi (AMF) optimize root system architecture (RSA) of their host plants, whilst polyamines (PAs), including putrescine (Put), spermidine (Spd) and spermine (Spm), play an important role in primary, lateral and adventitious root development. However, the interaction of AMF and PAs on RSA is less studied. In a pot study, 0, 5, 10, 20 and 40 g fresh inocula of Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe were inoculated into rhizosphere of 9-day-old red tangerine (Citrus tangerine Hort. ex. Tanaka) seedlings. After 164 days of inoculation, AM colonization ranged from 26.6 to 54.2% and increased with the increase of G. mosseae inocula amount. Mycorrhization generally significantly increased RSA traits such as total length, projected area, surface area, volume, 0–1 cm classified root length, and the ratio of the 0–1 cm classified root length to the total length, but decreased root average diameter and the proportion of 1–2 cm classified root length. Mycorrhization also generally increased both leaf and root arginine and ornithine decarboxylase (ADC and ODC) activity, thus stimulating the synthesis of Put. In leaves, more Put was converted to Spd, but not to Spm, resulting in a Spd increment in leaf. By contrast, root Put was induced by AMF, which indirectly improved the root average diameter and proportion of fine roots, since the RSA traits were significantly correlated with root Put synthetases through ADC and ODC. Our results indicate that AMF might regulate endogenous PAs metabolism, thus resulting in a synergetic impact on RSA.

Growth, root morphology and boron uptake by citrus rootstock seedlings differing in boron-deficiency responses

Boron (B) is an essential microelement for higher plants and has important physiological functions in plant growth and development. Citrus plants are frequently exposed to B-deficiency, but knowledge regarding the effects of B-deficiency on rootstock growth, root morphology and genotypic variations in citrus is limited. To evaluate the variations in plant-growth parameters in response to B-deficiency, five citrus rootstocks seedlings that grown in modified 1/2-strength Hoagland's solution that contained 0.25 μM H 3BO 3 (moderate B-level, Control) or 0 μM H 3BO 3 (B-deficiency, −B) were investigated before and 90 days after treatment. There are significant genotypic variations in plant-growth parameters (dry mass, leaf area and seedling height), root-morphological traits and B-concentrations. B-deficiency inhibited plant dry mass and leaf area expansion of Fragrant citrus, Sour orange and Trifoliate orange seedlings significantly ( P < 0.05), whereas no effect was found on the total dry mass of Carrizo citrange and Red tangerine seedlings. Further, B-deficiency reduced the root number, root length and root surface area in Fragrant citrus and Trifoliate orange significantly ( P < 0.05); however, no significant effect was detected on these root morphological traits of Carrizo citrange and Red tangerine ( P > 0.05). In addition, B-deficiency reduced the B-concentration in the leaves of all the five genotypes and the B-concentration in the roots of Fragrant citrus and Sour orange, none effect was observed on the B-concentration in stems of all studied genotypes and roots. However, there were significant relationships between the root-morphological traits and B-uptake efficiency. These results showed that Carrizo citrange and Red tangerine are B-efficient, Trifoliate orange is the moderate B-efficient genotypic rootstocks, whereas Fragrant citrus and Sour orange are B-inefficient genotypic rootstocks. In addition, Trifoliate orange was the moderate B-efficient rootstocks of five genotypes. The root-to-shoot dry mass ratio ( R/ S) and longer root numbers were higher in the Carrizo citrange and Red tangerine than that of Trifoliate orange, Fragrant citrus and Sour orange genotypes. That is to say, maintaining higher R/ S and numerous longer lateral roots is very important in improving the B-efficiency and thus contribute much to the resistance of seedlings to B-deficiency in the Carrizo citrange and Red tangerine genotypes.

Spermine pretreatment confers dehydration tolerance of citrus in vitro plants via modulation of antioxidative capacity and stomatal response

Polyamines, small aliphatic polycations, have been suggested to play key roles in a number of biological processes. In this paper, attempts were made to investigate the possibility of improving dehydration tolerance of citrus in vitro plants by exogenous application of spermine (Spm). 'Red Tangerine' (Citrus reticulata Blanco) in vitro plants pretreated with 1 mM Spm exhibited less wilted phenotype and lower water loss and electrolyte leakage than the control under dehydration. Spm-pretreated plants contained higher endogenous polyamine content during the course of the experiment relative to the control, particularly at the end of dehydration, coupled with higher expression levels of ADC and SPMS. Histochemical staining showed that the Spm-pretreated leaves were stained to a lower extent than those without Spm pretreatment, implying generation of less reactive oxygen species (ROS). On the contrary, activities of peroxidase (POD) and superoxide dismutase (SOD) in the Spm-pretreated samples were higher than the control at a given time point or during the whole experiment, suggesting that Spm exerted a positive effect on antioxidant systems. In addition, significantly smaller stomatal aperture size was observed in Spm-pretreated epidermal peels, which showed that stomatal closure was promoted by polyamines. All of these data suggest that Spm pretreatment causes accumulation of higher endogenous polyamines and accordingly leads to more effective ROS scavenging (less tissue damage) and stimulated stomatal closure (lower water loss) upon dehydration, which may function collectively to enhance dehydration tolerance.

Arbuscular mycorrhizal enhancement of iron concentration by Poncirus trifoliata L. Raf and Citrus reticulata Blanco grown on sand medium under different pH

The effect of the arbuscular mycorrhizal (AM) fungus (Glomus versiforme) on iron contents by two citrus rootstocks (trifoliate orange [Poncirus trifoliata L. Raf] and red tangerine [Citrus reticulata Blanco]) was studied in sand culture under different pH conditions. Seeds were sown in a mixed substrate (perlite/sand, 1:1 [v/v]) inoculated with or without mycorrhizal inoculum. The experiment was carried out at four pH levels by applying nutrient solution at pH 5.0, 6.0, 7.0, or 8.0 to P. trifoliata and pH 5.2, 6.2, 7.2, or 8.2 to C. reticulata. No AM colonization was found in uninoculated control (NM) and plants, and root colonization in AM plants was depressed under iron deficiency at high pH. Colonization by G. versiforme led to higher dry weights of shoots compared with NM treatments, suggesting that G. versiforme enhanced plant growth. Higher concentration of chlorophyll and active iron, lower ratios of P/Fe and 50(10P+K)/Fe were present in AM plants than NM treatments. Nevertheless, G. versiforme improved root Fe (III) chelate reductase activity of P. trifoliata and C. reticulata. The data indicate that plant uptake and translocation of iron were enhanced and AM fungi may be considered as a potential tool for bioremediation of citrus iron deficiency.