Effect of arsenic on δ-aminolevulinic acid formation in greening maize leaf segments

Abstract

Supply of 0.5 mM Na2AsO4 significantly decreased the δ-amino levulinic acid (ALA) content and total chlorophylls in greening maize leaf segments with the effect being more substantial for the later. Inclusion of precursors of chlorophyll also affected the ALA content. Thus, % decrease by arsenic (As) was significantly reduced in the presence of glutamine and MgCl2, but was increased by glycine and succinate. ALA formation and chlorophyll content were significantly decreased by 0.5 mM Na2AsO4 during levulinic acid treatment in light as well as dark with more severe effect in light. Difference in ALA accumulation in light and dark (L–D) was also substantially decreased by higher concentrations of As. Inclusion of succinate and MgCl2, respectively, increased and decreased the % inhibition of ALA formation in light. In dark the addition of 2-oxoglutaric acid (2-OG), succinate and glycine caused an increase in % inhibition of ALA formation, while glutamate caused a decrease in inhibition. Inclusion of adenosine tri phosphate (ATP) increased the ALA formation in light in presence of As only, while pyridoxal phosphate (PLP) and MgCl2 enhanced it under both conditions. The results demonstrate more prominent decrease in total chlorophylls than ALA content and/or formation in the presence of As, indicating the involvement of other steps of chlorophyll biosynthesis in addition to ALA synthesis. Substantial decrease under dark at higher concentrations of As and protective effect of cofactors, such as, MgCl2, PLP and ATP in ALA formation in light suggests that chloroplastic ALA synthesizing activity is more sensitive to the presence of As.