Enrichment of alliin in different in vitro grown tissues of Allium sativum through CdCl2 elicitation as revealed by high performance thin layer chromatography (HPTLC)

Abstract

Plant cell tissue and organ culture techniques provide an efficient way for the biosynthesis of high-value secondary metabolites in which elicitation has been recognized to be a potent approach in enriching the bioactive compounds. In this study, an effort was made to assess the influence of Cadmium chloride (CdCl2) on alliin yield of different in vitro grown tissues such as callus, somatic embryos, leaves and roots of Allium sativum. The tissues were cultured in MS amended with various levels of CdCl2 [control (0 mM), T1 (0.05 mM), T2 (0.1 mM), T3 (0.15 mM) and T4 (0.2 mM)] and the yield of alliin was quantified by using high performance thin layer chromatography (HPTLC). Biochemical analyses revealed that sample tissues under increasing CdCl2 conditions accumulated higher levels of sugar, protein and proline with maximum content of sugar (19.61 mg g−1 FW), protein (6.01 mg g−1 FW) and proline (12.19 mg g−1 FW) in leaves at T3 after 4 days of elicitor treatment. Changes within the activities of varied antioxidant enzymes like catalase (CAT), superoxide dismutase (SOD) and ascorbate peroxidase (APX) was assayed as the addition of CdCl2 in the medium causes stress. We noted that with an elevated level of CdCl2, antioxidant enzyme activity increased linearly with the highest activity observed in leaves at T4 of 6 days of elicitation (4.97 EU min−1 mg−1 protein CAT, 6.30 EU min−1 mg−1 protein SOD and 1.125 EU min−1 mg−1 protein APX). Increased activities of enzymes are involved in negating the cellular stress triggered due to the overproduction of ROS. The yield of alliin in response to varying levels of CdCl2 was estimated by using a simple, rapid, and sensitive HPTLC method. The best separation was achieved using butanol:propanol:acetic acid:water (3:1:1:1) as mobile phase. For analysis of alliin, the plates were scanned at 550 nm after spraying with ninhydrin and a good resolution was achieved with Rf value of 0.66. In our study, the alliin yield enhanced in all tested cultures with the elicitor level up to T3. In leaves, maximum accumulation of alliin (3.37 μg g−1 dry wt.) was noted on 0.15 mM (T3) CdCl2 added medium. Our data indicated the increase of alliin in CdCl2 added cultures, which suggests that the use of elicitors as a potential strategy for augmenting secondary metabolite synthesis.