Association of Metabolite Accumulation with Seasonal Variations in Evening Primrose (Oenothera biensis)

Abstract

Medicinal plants are important due to their antioxidant, antimicrobial properties. Of these evening primrose (Oenothera biensis L.) is used in the treatment of a number of diseases due to its distinct antioxidative and medicinal properties. The studies pertaining to seasonal patterns of growth behavior, survival strategies and secondary metabolites accumulation in leaves of different ages are not reported thus far. In this research, evening primrose was investigated for changes in the levels of secondary products, osmoprotectants, oxidants and antioxidants, vitamins, photosynthetic pigments and nutritional characteristics in penultimate, middle and bottom leaves on monthly intervals. Results revealed that plant showed better growth in spring (Feb-Apr) and autumn (Aug‒Oct) season, while summer (May‒Jul) and winter (Nov‒Jan) conditions were entirely damaging to growth. The osmoprotectants were highest in summer season followed by winter season, while in spring and autumn seasons the osmoprotectants remained low. These changes were sharper in penultimate followed by middle leaves while bottom leaves did not accumulate these compounds in sufficient quantities. The change in season had a great impact on the generation of hydrogen peroxide and malondialdehyde, which were the highest in summer season followed by winter and spring seasons. The activities of three enzymatic antioxidants were highest in summer season, while in winter season they were markedly lesser than summer but were normal in spring and autumn seasons. However, their accumulation was greater in penultimate and middle leaves than bottom leaves. Levels of vitamins including niacin, riboflavin and ascorbic acid in leaves were highest in summer season while inter season plants showed their significantly lesser levels. Penultimate leaf exhibited the sharper changes in their levels than other leaves. The accumulation of alkaloids, saponins, tannins, phenolics and flavonoids increased substantially in the summer season than other seasons. The anthocyanins, however, were low in summer but higher in in spring and autumn season. Chlorophylls were highest in spring season but decreased steadily towards summer season. Carotenoids synthesis was the highest in summer but the lowest in the spring season. Results regarding nutritional characteristics showed that K content decreased in winter season but was higher in summer season. The NO 3- -N, PO 43- -P, SO 42- -S and cellulose contents increased from spring to summer seasons but declined in autumn and winter seasons. Leaf starch content declined during summer season but was the highest in spring and autumn seasons. NDF, ADF and ADL increased in summer season but were quite low in winter season and showed moderate quantities in spring and autumn seasons. Soluble proteins were higher in summer and winter but low in spring and autumn. Changes in all these parameters were more conspicuous seen in penultimate and middle than aged bottom leaf. The correlations established amongst the monthly meteorological data and changes in the values of all the physiological attributes revealed that seasonal changes were the key drivers in modulating the growth and physiological responses of evening primrose. These changes switch the plant metabolic phenomena in a way that plant survival is ensured under harsher conditions.