Effects Of Pre-Sowing Treatment With Synthetic And Natural Plant Growth Regulators On The Response Of Maize (Zea Mays L.) To Lead Stress

Effects of the pre-treatment of maize seeds with synthetic (Thidiazuron (TDZ), Cytodef, Kinetin, Epin-extra) and natural (Ribav-extra) plant growth regulators (PGRs) on maize (Zea mays L. cultivar Tzaritza) seedlings exposed to lead (Pb2+) were investigated in this research. The influence of PGRs on Pb2+ allocation in maize root tissues, the seedlings' axial growth, and the activity of catalase (CAT) in leaves was determined. The seeds of maize were treated with different PGRs and grown for 7 days on 1 mu M, 10 mu M, 0.1 mM, 1 mM Pb2+ solutions. At the end of the experiment, the growth of shoot and root, and the activity of catalase (CAT) in maize leaves were recorded. To detect the effect of PGRs on Pb2+ allocation in maize root tissues, the seeds were treated with solutions containing different PGRs, then 5-day-old seedlings were treated with 1 mM Pb2+ for 3 days. Transverse root slices were stained with dithizone and observed under a microscope. The results showed that the pre-treatment of maize seeds with solutions containing different PGRs modified the allocation of Pb2+ in root tissues. PGRs Thidiazuron enhanced while Epin-extra impaired the absorption of Pb2+ in root tissues. The effect of the pre-sowing treatment of seeds with each PGR on seedlings growth depended on the concentration of Pb2+ in the growth medium. The pre-sowing treatment of seeds with Epin-extra, Ribav-extra and Kinetin was the most effective for axial growth of maize under a high (0.1 and 1 mM) Pb2+ concentration, whereas the pre-sowing treatment of seeds with Epin-extra was effective for CAT activity in maize leaves under higher Pb2+ exposure. The efficiency of PGRs against high Pb2+ concentrations decreased as follows: Epin-extra approximate to Ribav-extra > Kinetin > Cytodef > TDZ.