Alterations in growth, antioxidative defense and medicinally important compounds of Curcuma caesia Roxb. under elevated ultraviolet-B radiation

Ultraviolet-B (UV-B) radiation is a well-known stress factor, as involved in the generation of free radicals, and induction factor which permutates growth, metabolic processes, and secondary metabolites synthesis of plants. However, its impact on medicinal plants is less explored particularly in relation to secondary metabolites associated with the medicinally important rhizomes. An endangered medicinal plant (Curcuma caesia Roxb.) grown under natural field conditions was exposed to elevated UV-B (ambient +/- 9.6 kJ m(-2) d(-1)) to assess changes in growth, antioxidant profile, defense strategy and the secondary metabolites of the rhizome. Results showed that eUV-B induced the generation of different reactive oxygen species (center dot O-2(-) radical and H2O2) which were counteracted by induction of UV absorbing pigments (flavonoids and anthocyanin), non-enzymatic (ascorbic acid) and enzymatic antioxidants (peroxidase, ascorbate peroxidase and catalase) at different growth stages. However, phenol, thiol and superoxide dismutase activity showed reduction at all the growth stages. Protection from UV-B was also manifested by an increase in total free radical scavenging activity, metal chelation and reducing activity. Alterations in biomass allocation might be a possible mechanism of defense which persuaded to higher increment in above ground biomass and tuber biomass with 47 % diminution of rhizome biomass. Among the four classes of compounds identified, sterols were increased whereas reductions were more prominent in fatty acids followed by monoterpenes and sesquiterpenes. Increased production of epicurzereonone, elemene, pinandiol, and 1,8-cineole whereas curcumenol, D-camphor, eucalyptol, curcumenone, isocurcumenol, and zederone were reduced. Elevated UV-B also induced the production of some anti-cancerous compounds such as furanodiene and caryophyllene.