Incidence of Metal Specific Hyper-Accumulation (HMA4) Gene in Wild and Cultivated Plant Species

Plant hyper-accumulate metals, leading to exceedingly high levels in the plant tissues, with biochemical and possible molecular evidences of this phenomenon. The present work attempts to ascertain the molecular imprint of heavy metal hyper-accumulation in plants using HMA4 gene. Four hyper-accumulating plant species; Eichhornia crassipes, Ludwigia decurrens, Pistia stratiotes and Solanum melongena were analyzed for heavy metal content using Inductively Coupled Plasma-Mass Spectrometer. The presence of a member gene; HMA4 that expresses heavy metal ATPase for Cadmium (Cd) and Zinc (Zn) within the hyper-accumulation gene-complex HMA complex was analyzed using Polymerase Chain Reaction and Sanger sequencing. The results show that the elemental contents accumulated in the plant species investigated followed the order; Fe > Mn > Na > Zn > Cu > Ni > Cr > Cd > Co, with Se and Pb varying. Pistia stratiotes recorded higher concentration of Cd and Cr (1.48 and 16.06ppm) respectively. Other plants range between 0.94 - 0.95 and 6.38 - 9.63 for Cd and Cr respectively. The plant species significantly accumulated higher metal content than permissible levels (ρ = 0.05). However, none of the species showed significant accumulating prowess than the others (ρ = 0.05). Only Pistia stratiotes expressed the HMA4 gene; indicating, the gene is probably responsible for the active uptake of Cd and Cr and thus is specific for Cd uptake in Pistia stratiotes. The results hold environmental as well as crop improvement potential for the species- Pistia stratiotes.