Stress response of Trichosanthes cucumerina L. (Cucurbitaceae) to elevated UV-B doses

UV-B radiation induced alterations in the contents of photosynthetic pigments, antioxidants (phenolics and ascorbic acid) and chlorophyll fluorescence in two tropical variants of Trichosanthes cucumerina L. – Cucurbitaceae. The Green (Variant A) and Light Green (Variant B) variants of T. cucumerina, which had earlier been shown to differ in their total phenolics contents, were used for the study. The plants were exposed to two UV-B doses of 11.9 kJ m–2 corresponding to 4 h, 23.8 kJ m–2 corresponding to 8 h and a control (without UV-B treatment). The maximum photochemical efficiency of the control plant (0.75) was significantly higher than those of the plants exposed to UV-B for 4 h (0.63) and 8 h (0.44). The chlorophyll a and total chlorophyll contents of the control plant were significantly higher than those of plants exposed to UV-B for 4 h and 8 h. The chlorophyll b contents were not significantly affected by the UV-B exposure.We report a significant decline in the total phenolics and ascorbic acid composition at 4 hours after exposure to UV-B. However, at 8 h after exposure, the total phenolics and ascorbic acid contents increased significantly compared to 4 h after exposure. The UV-B doses had no significant effect on the concentrations of Mg and micronutrients (Fe, Zn, Mn, and Cu) in the two variants of T. cucumerina used for this study. The physiological explanations for these results are discussed.