Differential antioxidative responses in transgenic peanut bear no relationship to their superior transpiration efficiency under drought stress

Abstract

To counter the effects of environmental stresses, the plants must undergo detoxification that is crucial to avoid the accumulation of damaging free oxygen radicals (ROI). Here, we detail the oxidative damage, the antioxidant composition, and the osmoprotection achieved in transgenic plants of peanut overexpressing the AtDREB1A transgene, driven by a stress-inducible promoter (Atrd29A) when exposed to progressive water stress conditions. This study explored the biochemical mechanisms where (i) the antioxidants such as superoxide dismutase (SOD), ascorbate peroxidase (APOX), and glutathione reductase (GR) accumulated in the transgenic plants at comparably higher levels than their untransformed counterparts under dry soil conditions, (ii) a significant increase in the proline levels in the transgenic plants was observed in dry soils, and (iii) a dramatic increase in the lipid peroxidation in the untransformed controls in drier soils. Most of the biochemical parameters related to the antioxidative machinery in the tested peanut transgenics were triggered by the overexpression of AtDREB1A that appeared to differ from the untransformed controls. The antioxidants showed a negative correlation with the fraction of transpirable soil water (FTSW) thresholds, where the normalized transpiration rate (NTR) started decreasing in the tested plants. However, no significant relationship was observed between any of these biochemical indicators and the higher transpiration efficiency (TE) values found in the transgenic events. Our results show that changes in the antioxidative machinery in these transgenic peanut plants (overexpressing the AtDREB1A transcription factor) under water-limiting conditions played no causative role in improved TE.