Evaluation of the Use of Different Solvents for Phytochemical Constituents, Antioxidants, and In Vitro Anti-Inflammatory Activities of Severinia buxifolia

Severinia buxifolia (Rutaceae) is a promising source of bioactive compounds since it has been traditionally used for the treatment of various diseases. The present study aimed at evaluating the impact of different solvents on extraction yields, phytochemical constituents and antioxidants, and in vitro anti-inflammatory activities of S. buxifolia. The results showed that the used solvents took an important role in the yield of extraction, the content of chemical components, and the tested biological activities. Methanol was identified as the most effective solvent for the extraction, resulting in the highest extraction yield (33.2%) as well as the highest content of phenolic (13.36 mg GAE/g DW), flavonoid (1.92 mg QE/g DW), alkaloid (1.40 mg AE/g DW), and terpenoids (1.25%, w/w). The extract obtained from methanol exhibited high capacity of antioxidant (IC50 value of 16.99 μg/mL) and in vitro anti-inflammatory activity (i.e., albumin denaturation: IC50 = 28.86 μg/mL; antiproteinase activity: IC50 = 414.29 μg/mL; and membrane stabilization: IC50 = 319 μg/mL). The antioxidant activity of the S. buxifolia extract was found to be 3-fold higher than ascorbic acid, and the anti-inflammatory activity of S. buxifolia extract was comparable to aspirin. Therefore, methanol is recommended as the optimal solvent to obtain high content of phytochemical constituents as well as high antioxidants and in vitro anti-inflammatory constituents from the branches of S. buxifolia for utilization in pharmacognosy.

Live Population Dynamics of ‘Candidatus Liberibacter asiaticus’, the Bacterial Agent Associated with Citrus Huanglongbing, in Citrus and Non-Citrus Hosts

Citrus huanglongbing (HLB) is a century-old destructive disease which presents an unprecedented challenge to citrus industries worldwide. In Florida, HLB is associated with the phloem-limited bacterium ‘Candidatus Liberibacter asiaticus’ and is mainly transmitted by Asian citrus psyllid (Diaphorina citri). Quantification of the pathogen population in a host aids in investigation of virulence mechanisms and disease management. Recently a procedure was developed to detect live bacterial populations using a novel DNA-binding dye, propidium monoazide, in conjunction with real-time polymerase chain reaction (PMA-qPCR). Chinese box orange (Severinia buxifolia) is a common ornamental present in Florida which could host D. citri and ‘Ca. L. asiaticus’. For 20 months, the change of the live ‘Ca. L. asiaticus’ populations in graft- and psyllid-transmitted Valencia sweet orange (Citrus sinensis ‘Valencia’) and S. buxifolia plants was monitored by PMA-qPCR. Our results showed that the live ‘Ca. L. asiaticus’ population was significantly lower in the months of December, January, and February than the rest of the year in both hosts. No statistically significant pattern in the total bacterial population was observed in either host. This pattern may indicate a seasonal growth of ‘Ca. L. asiaticus’ along with the growth of both plants. These new findings should provide useful information on HLB management.

Severibuxine, Isolated from Severinia buxifolia, Induces Apoptosis in HL-60 Leukemia Cells

In an ongoing search for cancer-preventing compounds derived from plant sources, we isolated the quinolin-2,4-dione alkaloid severibuxine from the root bark of Severinia buxifolia collected in Taiwan and then examined the apoptotic effect of this compound. Severibuxine showed cytotoxicity to leukemia HL-60 cells (IC50 = 12.3±0.6 μM). Fluorescence microscopic analysis of cells stained with Hoechst 33342 indicated that the percentage of apoptotic cells showing nuclear condensation and fragmentation increased in a time-dependent manner. In addition, the activities of caspase-9 and caspase-3 were also enhanced in a time-dependent manner upon treatment with severibuxine. The addition of caspase-9 and caspase-3 inhibitors blocked severibuxine-mediated apoptosis. Upon treatment with severibuxine, the mitochondrial membrane potential decreased in a time-dependent manner. Severibuxine induced apoptosis in HL-60 cells through activation of the caspase-9/caspase-3 pathway, which is triggered by mitochondrial dysfunction.

Sources of Resistance to Diaprepes Weevil in Subfamily Aurantiodeae, Rutaceae

Commercially used citrus rootstocks can all be seriously damaged by larvae of the sugar cane root weevil, Diaprepes abbreviatus (L.). Six greenhouse challenge experiments were used to compare the resistance of 24 selections of citrus rootstocks and related species to this weevil by measuring root damage, and larval growth and survival. The commercial rootstocks tested were found to be susceptible, while at least seven other species within the subfamily Aurantiodeae were observed to be significantly more resistant. The species Balsamocitrus dawei Stapf. was most resistant to weevil larvae, exhibited less root damage than commonly used rootstock cultivars, and significantly depressed larval growth and survival. The species Glycosmis pentaphylla (Retz.) Correa, Microcitrus australis (Planch.) Swing., Eremocitrus glauca (Lindl.) Swing., Severinia buxifolia (Poir.) Tenore, Triphasia trifolia (Burm. f.) P. Wils., and Citrus hystrix DC. suffered as much damage from the weevil as common rootstock cultivars but significantly depressed growth of larvae feeding on them. One new hybrid rootstock, HRS-801, also significantly depressed D. abbreviatus larval growth, but this effect has not yet been verified as having significance in a long-term or field situation. Several strategies are discussed for developing citrus rootstocks resistant to D. abbreviatus.