Altitude Related Variation of Antioxidant Properties of Tea Leaf (Camellia sinensis)

Resumé

Places, in the high altitude are subject to higher UV radiation as compared to places of low altitude, provided they bear the same latitudinal location. Here, in this investigation, the oxidative stress and associated cell protection in tea plants growing in Mysore (12°30′ N 76°65′ E, 770 m) and Ooty (Dodabeta – 11°4090′ N, 76°6966′ E, 2623 m) has been studied. The UV radiation varies in these two places – in Ooty it is measured during February, 2012 during the first flush of tea leaves. Such variations in UV irradiance cause oxidative stress in tea plants growing in both the places. Being exposed to this necessary evil, plants have evolved cell protective/repair mechanisms (viz. antioxidants) that equip them to grow and flourish under ambient UV radiation. The positive effect of UV radiation is affected by signaling of defense genes that confer cell protection. Such positive UV effects include signal transduced transcription (upregulation) of phenylalanine ammonia lyase (PAL); this enzyme through the phenylpropanoid pathway causes the production of flavonoids that acts as a receptor of UV radiation. The molecular profile (with designed primer for PAL) shows intensified band pattern in case of high altitude grown tea clones. The compounds serve as biological “UV screens” in plants and also as scavengers of reactive oxygen species (ROS) through redox reaction due to its possession of quinone rings. Flavonoids including free flavonoids as well as flavonoid glycosides, accumulating in plants in response to UV, are in turn cleaved by ï¢-D glucosidase that is also known to be enhanced in transcription under stress (presumably including UV stress) conditions. ï¢-D glucosidase in plants cleaves flavonoid glycosides into its aglycon and glycon moieties. Aglycone flavonoids possess anti-oxidative capacity. According to the data, the enhanced PAL and ï¢-D glucosidase activities are shown to increase. The total antioxidant potential, UV absorbing compounds are also higher in Ooty tea clones. Moreover, antioxidant compounds (flavonoid glycosides – detected by TLC) are higher in high latitude grown Ooty tea clones showing greater amount of reactive oxygen species scavenging. Thus, the altitude related variations tea physiology has helped them to adopt in the UV enriched condition.Keywords: tea, flavonoids, antioxidants, reactive oxygen species