Role of salicylic acid-seed priming in the regulation of chromium (VI) and UV-B toxicity in maize seedlings

Seed priming is a crucial method to induce tolerance capabilities in plants against various abiotic stresses. Seed priming is associated with an induction of number of physiological and biochemical changes in plants by the treatment of natural and/or synthetic compounds to the seeds before their germination. The aim of this study was to investigate whether salicylic acid (SA)-seed priming is involved in the regulation of hexavalent chromium [Cr(VI)] and UV-B toxicity in maize seedlings. For this, the accumulation of dry mass, Cr and SA, chlorophyll fluorescence, oxidative stress markers i.e. reactive oxygen species (ROS; O ₂ ·⁻ , ·OH and H₂O₂) and antioxidants were determined. Treatment of Cr(VI) (50 and 250 µM) declined growth and chlorophyll fluorescence parameters- Fᵥ/Fₘ, Fᵥ/F₀, Fₘ/F₀ and qP which accompanied by an increase in NPQ and the accumulation of Cr, and a decline in level of SA. The UV-B also exerts similar effects on growth, chlorophyll fluorescence and level of SA, and damaging effects become intense when combined with Cr(VI). SA-seed priming reduced Cr(VI) and UV-B toxicity on growth which accompanied by a decline in the accumulation of Cr. Cr(VI) and UV-B enhanced generation of O ₂ ·⁻ , ·OH and H₂O₂ which subsequently cause damage to lipids and proteins and thus, a decrease in membrane stability was noticed. Both stresses enhanced activities of superoxide dismutase and ascorbate peroxidase while activities of catalase and glutathione reductase were inhibited significantly. Furthermore, the results show that Cr(VI) and UV-B declined contents of total ascorbate and glutathione. This study suggests that Cr(VI) and UV-B might alter biosynthesis of SA as indicated by a decreased level of SA. However, SA-seed priming might act as a signal that reduces the accumulation of Cr and ROS and triggers up-regulation of antioxidants, which subsequently counteract Cr(VI) and UV-B toxicity and hence an improved growth was noticed.