RESUMO
In vitro cultures play a promising role for production of pharmaceutically important plant secondary metabolites and the use of elicitation can mitigate the low productivity of active compounds. In the present study, the influence of cadmium chloride (CdCl2) elicitation on alkaloid yield was investigated in Rauvolfia serpentina. This heavy metal was employed to enhance the yield of reserpine and ajmalicine in leaf derived callus, leaves, stems and roots of in vitro grown cultures. Different concentrations [0.05 mM (C1), 0.10 mM (C2), 0.15 mM (C3) and 0.20 mM (C4)] of CdCl2 were added to the MS medium. The elicitor's influence on callus biomass, biochemical attributes and the yield of alkaloids was monitored at regular intervals. The amendment of CdCl2 improved growth and maximum callus biomass (1.29 g fresh weight and 0.16 g dry weight) was noted at 0.15 mM (C3) after 6 days of elicitation. The addition of elicitor in medium caused cellular stress and to analyse the role of CdCl2 in plant defence responses various antioxidant enzymes, i.e., superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) activities were measured in treated and non-treated cultures. The antioxidant enzyme activity increased linearly with elevated levels of CdCl2 in medium; highest APX (0.88 EU min-1 mg-1protein), SOD (5.40 EU min-1 mg-1protein) and CAT (4.21 EU min-1 mg-1protein) activity were observed in leaves of in vitro regenerated plants at C4. The quantitative analyses of reserpine and ajmalicine were conducted in different elicitated tissues using high-performance thin-layer chromatography (HPTLC) method. The study reveals enriched level of reserpine and ajmalicine in cultivated tissues and the enhancement was noted up to C3 (0.15 mM) elicitor level. Reserpine yield was maximum (0.191 mg g-1 DW) in roots of in vitro regenerated plants. The accumulation of ajmalicine was, however, better in leaf derived callus at C3 (0.131 mg g-1 DW). Higher elicitor dose (0.20 mM) inhibited callus biomass growth and subsequent alkaloid accumulation. The present study indicates the use of CdCl2 as a propitious method in enhancing reserpine and ajmalicine yield in R. serpentina.
RESUMO
BACKGROUND: Somatic embryogenesis (SE) is an intricate molecular and biochemical process principally based on cellular totipotency and a model in studying plant development. In this unique embryo-forming process, the vegetative cells acquire embryogenic competence under cellular stress conditions. The stress caused by plant growth regulators (PGRs), nutrient, oxygenic, or other signaling elements makes cellular reprogramming and transforms vegetative cells into embryos through activation/deactivation of a myriad of genes and transcriptional networks. Hundreds of genes have been directly linked to zygotic and somatic embryogeneses; some of them like SOMATIC EMBRYOGENESIS LIKE RECEPTOR KINASE (SERK), LEAFY COTYLEDON (LEC), BABYBOOM (BBM), and AGAMOUS-LIKE 15 (AGL15) are very important and are part of molecular network. MAIN TEXT (OBSERVATION): This article reviews various genes/orthologs isolated from different plants; encoded proteins and their possible role in regulating somatic embryogenesis of plants have been discussed. The role of SERK in regulating embryogenesis is also summarized. Different SE-related proteins identified through LC-MS at various stages of embryogenesis are also described; a few proteins like 14-3-3, chitinase, and LEA are used as potential SE markers. These networks are interconnected in a complicated manner, posing challenges for their complete elucidation. CONCLUSIONS: The various gene networks and factors controlling somatic embryogenesis have been discussed and presented. The roles of stress, PGRs, and other signaling elements have been discussed. In the last two-to-three decades' progress, the challenges ahead and its future applications in various fields of research have been highlighted. The review also presents the need of high throughput, innovative techniques, and sensitive instruments in unraveling the mystery of SE.