Redox status and oxalate exudation determines the differential tolerance of two contrasting varieties of ‘Assam tea’ [Camelia sinensis (L.) O. Kuntz] in response to aluminum toxicity

Abstract

The tea plant [Camellia sinensis (L.) O. Kuntz] is a well-known hyper-accumulator of aluminum (Al3+) that can grow in acidic soils contaminated with excess levels of Al3+. In this work, we used various assays for ascorbate–glutathione cycle components and other antioxidant enzymes to show that the alterations in the redox status after Al3+ treatment on tea cultivars, TV23 (tolerant) and S3A1 (sensitive), is responsible for their differential tolerance to Al3+ stress. A lower dose of Al3+ stress hastened the growth rate as suggested by an increase in biomass with respect to the control in both roots and leaves, but on further increasing the dose, the reverse occurred. Organic acid exudation has a major role in Al3+ detoxification. This study also reports the involvement of oxalate as a major exudate, since the activity of glycolate oxidase (GO) was found to drastically increase under the Al3+ stress condition. The increment in reactive oxygen species production and accumulation was quantitated in terms of malondialdehyde (MDA), super oxide anion (O2−), and hydrogen peroxide (H2O2), which was followed by a rapid increase in the activity of many stress-responsive antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POX). The results indicated that differential tolerance to Al3+ toxicity in tea varieties is linked to their oxidative stress response; and, antioxidant enzymes, as a crucial constituent of the defense response, appear to function differentially in the two cultivars. This is the first report showing differential tolerance of two contrasting varieties of ‘Assam Tea’ to Al3+ stress.