Phenolics, flavonoids and antioxidant capacities in<i>Citrus</i>species with different degree of tolerance to Huanglongbing

Hijaz, Faraj; Al‐Rimawi, Fuad; Manthey, John A.; Killiny, Nabil

doi:10.1080/15592324.2020.1752447

Cited by 42 publications

(33 citation statements)

References 37 publications

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“…The formation of the CTAC–phenol complex (yellow color) could also reduce the fluorescence intensity by absorbing the applied or emitted light. Our previous study showed that citrus leaves are rich in phenols and flavonoids [ 17 ]. The level of phenols and flavonoids in citrus leaves were 3–15 and 0.2–1 mg g −1 fresh weight, respectively [ 17 ].…”

Section: Discussionmentioning

confidence: 99%

Development of Europium-Sensitized Fluorescence-Based Method for Sensitive Detection of Oxytetracycline in Citrus Tissues

et al. 2021

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Antimicrobial compounds have been successfully used to control many plant and animal diseases. Recently, oxytetracycline (OTC) and streptomycin have been approved for the treatment of Huanglongbing in citrus. Since the application of OTC is under strict regulations, several methods have been developed to determine and monitor its levels in the environment including high-performance liquid chromatography, ELISA, colorimetric, and fluorometric assays. In this study, we developed a fluorometric method for the determination of OTC in plant tissues based on its complexation with europium. Our preliminary trials showed that phenols and flavonoids interfere with the europium assay by reacting with the sensitizing reagent, cetyltrimethylammonium chloride. Consequently, we used the 60 mg hydrophilic–lipophilic balanced (HLB) cartridges to purify the OTC from the plant matrix. The recovery of OTC from spiked leaf samples was 75 ± 7.6%. Using the 500 mg HLB, we were able to detect 0.3 ppm OTC in the final sample extract, which corresponds to 3 µg g−1 fresh weight (FWT). The developed method was successfully used to measure the level of OTC in leaves obtained from trunk-injected trees. The results obtained by the europium method were similar to those obtained using the ELISA assay. We also tested the cross-reactivity of OTC metabolites with the europium method. The 4-epi-OTC showed a high cross-reactivity (50.0 ± 3.6%) with europium assay, whereas α-apo-OTC and β-apo-OTC showed small cross-reactivity. We showed that the europium-sensitized fluorescence-based method can be successfully used to assess OTC in citrus plant tissues after a cleanup step. Our results showed that this method was sensitive, reproducible, and can be used to analyze many samples simultaneously.

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Section: Discussionmentioning

confidence: 99%

Development of Europium-Sensitized Fluorescence-Based Method for Sensitive Detection of Oxytetracycline in Citrus Tissues

et al. 2021

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“…Gallic acid and catechin were chosen as a representative for phenols and flavonoids, respectively. Gallic acid and catechin are commonly used to estimate total phenols and flavonoids in plants [ 18 ].…”

Section: Methodsmentioning

confidence: 99%

Citrate Mediated Europium-Based Detection of Oxytetracycline in Citrus Tissues

et al. 2021

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Oxytetracycline (OTC) and streptomycin have been used for the control of several plant diseases and were recently permitted for the control of citrus greening disease, Huanglongbing. Consequently, sensitive and reliable methods are highly needed for the detection of OTC in citrus tissues. Herein, we studied the replacement of cetyltrimethylammonium chloride (CTAC) by citrate (Cit) as a sensitizing agent for the analysis of OTC in citrus tissues using the recently established europium (Eu) method. In addition, we determined the optimal conditions for the formation of the Eu-OTC-Cit ternary complex in tris buffer. Our results showed that the plant matrix significantly decreased the fluorescence intensity of the Eu-OTC-Cit complex even after the replacement of CTAC. Our investigations showed that phenols such as gallic acid degrade slowly at high pH and their degradation was enhanced in the presence of the (Eu+3) cation. To reduce the plant matrix interference, the sample extract was cleaned using solid-phase extraction (SPE). The OTC recoveries from spiked healthy and Candidatus Liberibacter asiaticus (CLas)-infected trees were 91.4 ± 7.8% and 82.4 ± 3.9%, respectively. We also used the citrate method to determine the level of OTC in trunk-injected trees. The level of OTC as measured using the Eu-OTC-Cit complex (117.5 ± 20.3 µg g−1 fresh weight “FWT”) was similar to that measured using Eu-OTC-CTAC complex (97.5 ± 14 µg g−1 FWT). In addition, we were able to visualize the OTC in citrus leaf extract, under ultraviolet light (400 nm), after it was cleaned with the SPE. Our study showed that the citrate can be successfully used to replace the harmful CTAC surfactant, which could also react with phenols.

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“…On the other hand, some HLB-tolerant citrus genotypes might be superior in antioxidant mechanism or phloem regeneration. Intriguingly, it was reported that HLB-tolerant varieties contain higher levels of antioxidant capacities than the susceptible varieties 41 . ‘Sugar Belle’ mandarin, which is HLB-tolerant, has more vigorous phloem regeneration than the HLB-susceptible C. sinensis varieties 42 .…”

Section: Discussionmentioning

confidence: 99%

Citrus Huanglongbing is an immune-mediated disease that can be treated by mitigating reactive oxygen species triggered cell death of the phloem tissues caused by Candidatus Liberibacter asiaticus

Pang

Huang

et al. 2021

Preprint

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The immune system is critical for keeping animals and plants healthy from pathogens. However, immune-mediated diseases are also common for human. Immune-mediated diseases have not been reported for plants. Here, we present evidence that citrus Huanglongbing (HLB), caused by phloem-colonizing Candidatus Liberibacter asiaticus (CLas), is an immune-mediated disease. CLas infection of Citrus sinensis stimulated systemic and chronic immune response in the phloem tissues including reactive oxygen species (ROS) production as indicated by H2O2, callose deposition, and induction of immune related genes. Systemic cell death of companion and sieve element cells, but not surrounding parenchyma cells, was observed following ROS production triggered by CLas. ROS production triggered by CLas localized in phloem tissues. The H2O2 concentration in exudates extracted from phloem enriched bark tissue of CLas infected plants reached a threshold of killing citrus protoplast cells, which was suppressed by uric acid (a ROS scavenger) and gibberellin. Foliar spray of HLB positive citrus with antioxidants (uric acid and rutin) and gibberellin significantly reduced both H2O2 concentrations and cell death in phloem tissues induced by CLas and reduced HLB symptoms. RNA-seq analyses of CLas infected and health C. sinensis support that CLas causes oxidative stress. In sum, HLB is an immune-mediated disease and both mitigating ROS via antioxidants and promoting plant growth can reduce cell death of the phloem tissues caused by CLas, thus controlling HLB.

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Phenolics, flavonoids and antioxidant capacities inCitrusspecies with different degree of tolerance to Huanglongbing

Cited by 42 publications

References 37 publications

Development of Europium-Sensitized Fluorescence-Based Method for Sensitive Detection of Oxytetracycline in Citrus Tissues

Development of Europium-Sensitized Fluorescence-Based Method for Sensitive Detection of Oxytetracycline in Citrus Tissues

Citrate Mediated Europium-Based Detection of Oxytetracycline in Citrus Tissues

Citrus Huanglongbing is an immune-mediated disease that can be treated by mitigating reactive oxygen species triggered cell death of the phloem tissues caused by Candidatus Liberibacter asiaticus

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