Physiological and metabolic responses to aluminum toxicity reveal differing resistance mechanisms to long-term exposure in highbush blueberry cultivars

Aluminum (Al) toxicity is a major environmental stress that affects the growth and development of plants in acid soils. Plants have developed different mechanisms and strategies of Al resistance based on the biosynthesis of organic compounds and the formation of non-phytotoxic complexes with Al. In this study we use three cultivars traditionally cultivated of highbush blueberry (Vaccinium corymbosum L., 'Brigitta', 'Star', and 'Duke') and two cultivars from the USA ('Camelia' and 'Cargo') that were recently introduced in southern Chile. Physiological and biochemical parameters were evaluated on plants grown at 0 and 200 mu M Al in Hoagland solution (pH 4.5) for 0, 7, 14, and 21 days. We found that the Al concentration increased in roots and shoots in all cultivars and that the relative growth rate was reduced only in shoots of 'Star' plants, an Al-sensitive cultivar. Photosynthetic pa-rameters were reduced under Al treatment only in 'Star' and 'Brigitta'. The concentration of photosynthetic pigments was reduced in 'Star', but increased in 'Cargo' and 'Brigitta' under Al toxicity. 'Duke' had a higher concentration of sugars and polyphenols, increased antioxidant activity, and low lipid peroxidation in leaves under Al treatment. The levels of ascorbate (ASC) and dehydroascorbate (DHA) increased in 'Camellia' leaves and Duke roots. The ASC/DHA ratio in roots increased in 'Star', and 'Camellia', but decreased in 'Duke' and 'Brigitta' leaves in the Al treatment. Cultivars 'Cargo' and 'Brigitta' increased oxalate exudation from roots under Al-toxicity, whereas 'Star' had low oxalate exudation. The results suggest a possible strategy related to internal detoxification via carbohydrates and phenolic compounds to reduce the long term toxic effect of Al in 'Duke', 'Cargo', and 'Camellia' cultivars of V. corymbosum under acidic conditions.