Modulation in the enzymatic antioxidants, MDA level and elicitation in conessine biomolecule in (medicinal tree) cultures exposed to different heavy metals: Ni, Co, Cr and As.

Nodal explants of , an important medicinal tree, were cultured on Murashige and Skoog's medium (MS) containing 15 µM BA (control) alone and on medium supplemented with different concentrations (0, 1, 5, 25, 50, 100 and 200 mg/L) of heavy metals such as NiCl, CoCl, AsO and CrO to study their toxic effect. After 28 days of treatments, the nodal segments were harvested to assess the average number of shoots per explants, average shoot length, malondialdehyde content, proline content, conessine accumulation and antioxidant enzymatic activity. Among all the metals tried, best morphogenic response was achieved at 5 mg/L CrO where 80% culture differentiated an average of 3.21 ± 0.08 shoots per explant having 0.95 ± 0.018 cm average shoot length. Highest concentration (200 mg/L) of all the heavy metals proved lethal for morphogenesis. Maximum inhibition in average shoot number and average shoot length was observed in nodal explants treated with 25 mg/L AsO where an average of 0.49 ± 0.047 shoots having an average shoot length of 0.3 ± 0.02 cm. Contrarily, addition of heavy metals in culture medium proved strong elicitors, exhibiting significant enhancement in the biosynthesis of conessine, an important bioactive compound. HPLC analysis of the crude extract of in vitro grown untreated nodal cultures revealed an average of 117.06 ± 2.59 µg/g d. w. of conessine, whereas those treated with 100 mg/L of CoCl accounted for 297.1 ± 7.76 µg/g d. w. (an increase of 156% over control). Among the heavy metals tried, CoCl proved to be the best for conessine enhancement which was in the order of CoCl > CrO > NiCl > AsO in the nodal explants. Concomitantly, MDA content, the antioxidant enzymes activities of catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GR) and ascorbate peroxidase (APX) were also observed to be differentially expressed with the increase in the heavy metals concentration from 1 to 200 mg/L. Free proline, too, increased up to 3.5-fold over control. The results obtained during the present investigation revealed that the overall response of the nodal explants in terms of morphogenesis, conessine content and antioxidant enzyme activities was metal specific as well as dose dependent.