Cultivation studies on two commercially important plants; seasonal variation of Ceratonia siliqua and propagation trials on Athrixia phylicoides

Abstract

The use of plant extracts or derivatives in the field of medicine, nutraceuticals and cosmeceuticals has occurred for a long time. This is due to the diversity of compounds present in plants. The cosmetic industry has a number of products that include plant actives to combat ageing, pigmentation and blemishes. Extensive studies, such as the seasonal variation of bioactive compounds, are required to be carried out on the plant extracts before they can be included in such products. The present study focused on two commercially important plants: Ceratonia siliqua L. (C. siliqua) and Athrixia phylicoides DC. (A. phylicoides). A. phylicoides is an indigenous plant commonly known as bush tea because an infusion of this plant is a common traditional tea. This plant has a number of medicinal properties and commercialisation of the tea would benefit many. In order to enhance the propagation of the plant, a hormone rooting field trial was carried out on apical cuttings of A. phylicoides during spring and autumn. Cuttings were dipped in liquid hormone solutions of 1-Naphthaleneacetic acid (NAA), Indole-3-butyric acid (IBA), Indole-3-acetic acid (IAA) and Gibberellic acid (GA); all of which were tested at 0.1% and 0.3%. During spring, IBA at 0.1% had the highest rooting percentage of 58.33% and highest sprouting percentage of 60%. Following closely behind was NAA at 0.1% with a rooting percentage of 51.67%. IBA and NAA at 0.3% had the highest number of roots for the entire trial: 38.72 and 31.00, respectively. During autumn, NAA at 0.1% was found to have the highest sprouting percentage of 78.33% and at 0.3%, the highest rooting percentage of 83.33%. The highest number of roots formed was 7.88 by NAA at 0.3% with IAA forming 6.67 roots at 0.3%. IBA at 0.1% formed 6.41 roots. IBA was confirmed as an effective hormone for this plant but this study introduced an additional hormone, NAA, to serve the same purpose at a lower cost. Ethanol extracts of A. phylicoides were tested for potential anti-tyrosinase and antimicrobial studies due to the high antioxidant activities of the extracts. At the highest concentration tested (400 μg/ml plant extract) activity was not detected in either assay. C. siliqua is a popular plant commonly known as carob and is used globally for its bean gum and pods. Previous studies indicated that the leaf extract of this plant has the potential to be used in the cosmetic field. The present study investigated the seasonal variation of five previously isolated bioactive compounds in the leaves of C. siliqua (1,2,3,6-tetra-o-galloyl-β- D-glucose, Quercetin-3-o-α-L-rhamnoside, Myricetin-3-o-α-L-rhamnoside, Myricetin-3-o- glucoside and Gallocatechin-3-o-gallate). Thin Layer Chromatography (TLC), High Performance Liquid Chromatography (HPLC) and the tyrosinase inhibition assay were used in the study. Seasonal samples from three age groups were collected in order to determine the season and age at which optimal levels of the bioactive compounds were present. The leaf extracts prepared from the samples collected from autumn small, autumn medium and summer medium were found to be the most effective at inhibiting the tyrosinase enzyme with inhibitory concentration (IC50) values of 51.77±0.058 μg/ml, 59.49±0.1 μg/ml and 53.62±0.71 μg/ml, respectively. The positive control for the tyrosinase inhibition assay was kojic acid with an IC50 of 6.99±0.14 μg/ml. HPLC detected the highest amount of the key bioactive compounds, based on their previously identified melanin inhibition properties: 1,2,3,6-tetra-o-galloyl-β-D-glucose in winter large (327.92 mg/kg plant material) samples and quercetin-3-o-α-L-rhamnoside in summer medium (2216.84 mg/kg). A significant amount of variation of bioactive compounds of C. siliqua was identified amongst the large plants during the season trial. Follow up variation identification trials were carried out based on plant gender and the drying method of leaf material. TLC and the tyrosinase inhibition assay were used for these trials. Female plants of C. siliqua were found to have lower IC50 values overall for the tyrosinase inhibition assay. A female plant growing in the LC area in Hatfield was found to have the highest activity with an IC50 value of 103.70 μg/ml. The drying study found that leaves that were crushed after harvesting, without drying, led to an extract with the highest tyrosinase inhibition activity. The IC50 obtained for the fresh leaf extract was 139.60 μg/ml. The IC50 value of the control averaged to 7.75 μg/ml for the variation identification trials. The present study concluded that NAA was successful, in addition to IBA, as a rooting hormone for apical cuttings of A. phylicoides. Bioactivity of C. siliqua was found to be higher in summer and autumn.