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Background: Aloe vera, a plant with crassulacean acid metabolism naturally adapted to water deficit, was introduced in the semi-arid regions of Chile in 1999.

Aims: Our objective was to evaluate how A. vera scavenged the superoxide ion (O-2(center dot)-), formed during oxidative stress, induced by water deficit.

Methods: Total and specific activity, enzyme accumulation and expression of genes encoding superoxide dismutase (SOD) were determined in leaf tips and leaf bases collected from plants subjected to different levels of water deficit.

Results: Two isoenzymes, Mn-SOD and Cu/Zn-SOD, accumulated significantly under water deficit, with a higher accumulation of Mn-SOD in the leaf bases, and of Cu/Zn-SOD in the leaf tips of plants under different degrees of water deficit (soil water availability ranged from 100% to 25% of field capacity; FC). The expression of sod genes increased only in gradually stressed individuals, where plants were pre-treated at 75% FC or 50% FC prior to being subjected to a severe water deficit of 25% FC. The superoxide ion levels increased more in the tips than in the leaf bases when plants were grown at 50% and 25% FC. Under gradually increasing water stress conditions, the accumulation of superoxide ions decreased to 50% of that of the control plants, associated with an increment in Cu/Zn-SOD accumulation and a higher expression of the mn-sod and cu/zn-sod genes.

Conclusions: These results indicate that A. vera plants are stressed under severe water deficit and suggest that SOD is a key enzyme to decrease the reactive oxygen species levels induced by water deficit.