Morphophysiological Effects of Chromium in Sour Orange (Citrus aurantium L.)

Abstract

This is the first study on the performance of sour orange (Citrus aurantium L.) in soil contaminated with chromium (Cr). A greenhouse experiment was conducted to determine the phytotoxic effect of Cr on seed germination and seedling growth of sour orange. Cr treatments were applied as Cr(NO3)3 in five concentrations (0, 50, 100, 150, and 200 ppm). A gradual increase in Cr concentration leads to inhibition of seed germination and other growth parameters. Phytotoxicity, relative water content (RWC), seed vigor index (SVI), and the tolerance index (TI) show a significant decrease up to 100 ppm as a result of the presence of metal. Biochemical constituents, nutrient uptake, antioxidative enzymes, and lipid peroxidation under Cr stress were also investigated. The results indicate that concentrations greater than 100 ppm Cr cause an increase in plant antioxidative enzymes—superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX)—and increased lipid peroxidation. On the other hand, sour orange effectively generated an enzymatic antioxidant defense system (especially CAT) to scavenge hydrogen peroxide (H2O2), resulting in less H2O2 in shoots with greater Cr concentrations. A majority of Cr accumulated in the shoots and low translocations to shoots. However, sour orange is the best universal rootstock for citrus because of its resistance to salinity and disease. It also grows well in heavy soils. Based on the results of this study, sour orange might be a potential candidate plant for phytofiltration of contaminated water and phytostabilization of Cr-contaminated soils.