Effects of elevated ultraviolet-B on the floral and leaf characteristics of a medicinal plant Wedelia chinensis (Osbeck) Merr. along with essential oil contents

Wedelia chinensis (Osbeck) Merr. is a perennial thermotolerant bioherbicidal plant species spread in tropical and subtropical regions. The impacts of ultraviolet-B (UV-B) radiation on the floral morphology, stomatal characteristics, biochemical properties and essential oil content in leaves have not been investigated in medicinally important ornamental plants like W. chinensis. The present study has evaluated the growth, its leaf, stomatal, and floral characteristics, photosynthetic pigments, various metabolites as well as the essential oil content of W. chinensis under ambient and elevated (ambient + 7.2 kJ m(-2) d(-1)) UV-B (eUV-B) radiation. UV-B exposure stimulated the growth of the test plant indicating the greater chances of its survival under harsh conditions which could be beneficial for ecological sustainability. The leaf thickness, wax deposition, and metabolites such as phenol, proline, anthocyanin, and flavonoids were significantly increased under eUV-B, while the reverse trend was observed for the specific leaf area (SLA) and photosynthetic pigments. Adaxial stomatal density (34.2%) and abaxial stomatal pore surface (146.1%) was also increased; however, the opposite trend was found in abaxial stomatal density (48.6%) and adaxial stomatal pore surface (41.5%). The floral characteristics were positively influenced by the eUV-B. However, yield loss in the form of essential oil content by 39.9% was recorded under eUV-B. Based on GC-MS analysis, an increase in mono-, di-, tri-terpenes, and fatty acids were observed, while sesquiterpene and other aliphatic hydrocarbons showed a reduction under eUV-B treatment. Moreover, alpha-Pinene, beta-Caryophyllene, beta-Thujene, beta-Myrcene, alpha-Phellandrene, L-Limonene, Germacrene D, Bicyclogermacrene, delta-Cadinene, Spathulenol, and Shyobunol were identified as the major components of the essential oil. The study concludes that exposure of UV-B radiation was directly beneficial for the floral morphology and unable to aggravate any morphological damage, the protective pigments, and antioxidants which played a strong defensive role in UV-B tolerance. Whereas, UV-B radiation exposure is deleterious to the plant's commercial importance in terms of yield of essential oil.