Ultraviolet-B (280-320 nm) enhanced radiation induced changes in secondary metabolites and photosystem-II of medicinal plant Withania somnifera Dunal.

Abstract

This study investigated supplemental UV-B radiation effects on medicinal plant Withania somnifera. Photosynthetic pigments decreased upon exposure to UV-B radiation. Non photosynthetic pigments anthocyanin was enhanced by UV-B treatment. Similar changes were also noted in the photochemical activities (PS I and PS II). Photosystem II (PS II) core complex of higher plants and cyanobacteria is composed of more than 20 polypeptide subunits. This paper reports the results obtained by application of MALDI mass spectrometry directly to isolate complexes prepared from Withania. In plants grown under ambient light conditions, PS II core complex was not affected in which D1 and D2 proteins appeared at m/z 39175±8 (r775) and m/z 39074±9 (r1994), respectively. Three unidentified peaks were observed at m/z 39214±9, 38995±6 and 177798±8. Upon exposure to UV-B enhanced radiation, the degradation of D1 protein together with the other thylakoid subunits at m/z 15214±8 CP47 (r2311), m/z 39071±7 CP43 (r1441), m/z 15636±9 PsbJ (r2516), m/z 39182±6 PsbH (r1720), m/z 31126±8 PsbK (r2631), and m/z 39129±8 PsbM (r623) were observed. In addition to this, three other peaks have been detected at m/z 38977(r2104), 39019(r649) and 24102(r2378). Ten significantly different chromatographic peaks were found by HPTLC finger print after UV-B induction. One compound identified was withaferin A and it was increased 3% by dry weight. Key words: Withania somnifera, withaferin A, UV-B, photosynthesis, HPTLC, MALDI-TOF.