Alterations of Amino Acid Concentrations and Photosynthetic Indices in Light Irradiated Arabidopsis thaliana during Phytoextraction

Abstract

Hyperaccumulation of heavy metals is substantial in some hyperaccumulators; however, few studies have been conducted to reveal the effect of light irradiation on the variations of representative amino acids and photosynthetic indices, which can represent the antioxidant capacity of plants during phytoremediation. The physiochemical responses of Arabidopsis thaliana to Cd stress were compared during six light irradiation treatments. The results of the experiment showed that the stress adaptation of A. thaliana was enhanced in all light irradiation treatments, except for monochromatic blue-light irradiation. The concentrations of glutamic acid and glutamine decreased significantly in pure blue light compared with the other treatments. The decrease in the concentrations of these two amino acids might be induced by an intensive biosynthesis of defensive factors, as manifested in the declined photosynthetic indices. Concentrations of aspartic acid and asparagine involved in the ammonification, absorption, and transportation of nitrogen in vascular plants increased in the red and blue combined irradiation treatments compared with the control, corresponding to the improved photosynthetic capacity of the species. The concentration of proline, which can represent environmental stresses including metal toxicity and excessive light energy, generally increased with an increasing ratio of blue light. This study proposes the key roles of amino acids and photosynthetic indices in light-motivated Cd pollution responses in A. thaliana.