Ultraviolet-B induced changes in physiology, phenylpropanoid pathway, and essential oil composition in two Curcuma...

Ultraviolet-B is an important fraction of sunlight which influences the plant performance either positively or adversely in terms of growth, physiology, biochemistry, and major active compounds. The static nature of plants constrains them to be subjected to various adverse environmental conditions. Several studies performed with plants and UV-B with fewer reports are available on medicinal plants having rhizome. The present study focuses on transformation induced in two Curcuma spp. (C. caesia and C. longa) under the influence of elevated UV-B (eUV-B) (ambient ±9.6 kJ m^-2 d^-1) under natural field conditions to analyse the changes in physiological, biochemical and essential oil of the test plants. eUV-B significantly reduced the photosynthetic activities such as photosynthetic rate (P_s), stomatal conductance (g_s), transpiration (T_r), internal CO₂ (C_i), and photochemical efficiency (F_v/F_m) with higher reductions in C. longa as compared to C. caesia. The enzymatic activities of PAL, CHI, and CAD showed higher stimulation in C. caesia whereas C. longa showed increment only in CAD. The essential oil content was increased by 16% and 9% in C. caesia and C. longa, respectively. C. caesia showed increased monoterpenes than sesquiterpenes, whereas almost equal increase of both the terpenoid found in C. longa. C. caesia showed induction of aromatic compounds (epiglobulol, germacrene, 4-terpineol), whereas anticancerous compounds; aphla-terpinolene (61%), beta-caryophyllene (60%), and beta-sesquiphellandrene (32%) were increased in C. longa. C. caesia acted well in terms of both physiology and major active compound (1, 8-cineole), but overall most of the compounds increased in C. longa under eUV-B.