2.10.2 Culture Conditions
The leaf as explant was cultured on MS, B5, and Schenk & Hidebrandt (SH) media supplemented with different combination of different NAA with BA and Kin for shoot induction. Maximum shoot induction rate observed in MS medium supplemented with NAA and BA in leaf explants (Sathyaprabha et al. 2010; Lakshmi and Padmaja 2011). Similarly maximum rooting was obtained on B5 medium supplemented with NAA and roots developed within 25 days after inoculation (Abdi et al. 2013). The exposure of dark period enhanced the production of 3,4-dihydro-2,4,8,9-tetrahydroxy-6-methyl-1(2H)-anthracenone-4-O-β-D-glucopyranoside and 3,4-dihydro-2-methoxy-4,8,9-trihydroxy-6-methyl-1(2H)-anthracenone-4-O-β-D-glucopyranoside in cell cultures of A. barbadensis (Yagi et al. 1998).
This is a medicinal plant in which useful secondary metabolites are found sufficiently. The secondary products including as aloe emodin and chrysophanol synthesized via a plant-specific type III polyketide biosynthesis pathway. Authors also examined the effect of endogenous elicitors on the type III polyketide biosynthesis pathway and identified the metabolic changes induced in elicitor-treated A. vera adventitious roots. Salicylic acid, methyl jasmonate, and ethephon were used to treat A. vera adventitious roots cultured on MS liquid media with IBA for five weeks. The production of aloe emodin and chrysophanol was enhanced by the salicylic acid treatment up to 13-fold as compared with control. Ultra performance liquid chromatography- mass spectrometry (UPLC-MS) analysis confirmed the presence of 37 compounds induced by salicylic acid, including aloe emodin and chrysophanol. This analysis also confirmed that these metabolic pathways change the expression of octaketide synthase genes and decreases in malonyl-CoA. In addition, anti-inflammatory activity was enhanced in extracts of salicylic acid-treated adventitious roots. It has been proved that salicylic acid has an important role in induction of the plant-specific type III polyketide biosynthetic pathway and so that the efficacy of A. vera can be increased through salicylic acid treatment (Lee et al. 2013).
The effects of different abiotic elicitors including nano-Ag, nano-TiO2, NH4NO3, and sucrose on cell suspension culture of A. vera were investigated. The maximum production (127-fold) of aloin was obtained with NH4NO3 at 48 hours of treatment. Aloin content was increased with nano elicitors at 48 hours after treatment and decreased gradually after that (Raei et al. 2014). A. barbadensis, the miracle plant, is the most widely cultivated species and has been widely used for medicines and cosmetics. The leaf discs of A. barbadensis were used as explants and maximum callus induction was obtained in MS medium supplemented with 2,4-D and Kin. This combination of growth hormone also increased the anthraquinone production, while NAA and IAA demonstrated very poor response (Supe 2013). Maximum adventitious root induction was observed in MS culture medium with supplementation of NAA and BA with suitable concentrations. The accumulation of phenolic compounds in the media that was adsorbed polyvinylphyrollidine