Influence of Climatic Conditions and Phenological Stages on Chemical Composition, Essential Oils and Anatomical Characteristics of Ajuga iva (L.) Schreb.

Abstract

Many species of Ajuga have medicinal values and widely used to treat many diseases. The medicinal values of Ajuga iva are associated with the containment of many pharmaceutical compounds as essential oils, diterpenoids, triterpenes and phenolic compounds. No information is currently available concerning the effect of different climatic conditions and phenological stages on chemical composition, essential oils or anatomical features of Ajuga iva. Therefore, this study aimed to investigate the effect of different climatic conditions and phenological stages on the contents of free sugars, phytohormone and essential oils, as well as anatomical characteristics of Ajuga iva (L.) Schreb. The leaves of Ajuga iva, showed the presence of high frequency of trichomes in upper and lower leaf surfaces which may limit light absorption, thereby reducing the risk of photoinhibition. The results indicated that the contents of chlorophyll a, total carbohydrates and most of the detected sugars were significantly increased during the flowering stage in dry season. HPLC analysis of Ajuga extracts identified 14 phenolic compounds most of which tended to increase in the flowering stage. Where the concentrations of pyrogallol increased 3.7-fold and gallic acids increased 4.6-fold, also the concentrations of catechol and vanillic acid increased intensely 8 and 7-fold, respectively. The results indicated that the yield of essential oils of the aerial parts of Ajuga iva have depended on the phenological stages and significantly increased in winter. The data of headspace GC-MS analysis of volatile oils indicated that the essential oils of Ajuga iva were dominated by volatile monoterpenes (C10H16) which have been shown to play important ecological roles in plant defence mechanisms. Sabinene was the main constituent in the essential oil of Ajuga, followed by α -thujene and α-pinene. The results indicated that the full flowering stage was considered as an ideal period for harvesting the high yield of plant hormones, sugars and phenolic compounds, as well as α-Thujene from Ajuga iva.