Acclimation of Polygonum minus Huds. to Low Light Irradiance and Its Effects on Growth, Leaf Gas Exchange and Antioxidant Defense

Polygonum minus Huds. has massive potential to be commercialized following many current discoveries of its medicinal properties. We investigated the growth and physiology changes of P. minus under different shading and treatment durations. The effects of four shading levels: 0% (T1), 30% (T2), 50% (T3) and 70% (T4) and two treatment durations of 10 weeks and 20 weeks were studied. Significant effects of shading levels and treatment durations were observed on the transpiration rate (E), leaf resistance, pigment content in leaves (Chl a, Chl b and Car), carbohydrate, ascorbic acid, total anthocyanin, phenolic and flavonoid contents. Enzyme activity of superoxide dismutase and ascorbate peroxidase were also significantly affected by shading levels and treatment durations. The highest antioxidant activities were recorded under T4 of both treatment durations along with the high content of Chl a, Chl b and Car. The leaf, stem and root extracts of P. minus were also subjected to HPLC analysis for quantification of selected flavonoid compounds. It was observed that longer treatment duration of 20 weeks reduced the amount of flavonoid.