The role of gibberellic acid and kinetin in alleviation of heavy metal stress during germination of sorghum seeds

In this study, the roles of gibberelic acid (GA3/G), kinetin (K) and a combination of these two plant growth regulators (PGR) on the effects of heavy metals on some growth parameters of the germination of the seeds and subsequently, of the seedlings from the seeds grown for 21 days in a growth chamber under conditions of 25±1 °C constant temperature, continuous fluorescent light (8000 lux) and 60%±5 moisture were studied.Lead (Pb), zinc (Zn) and cadmium (Cd) both delayed and prevented the germination of the seeds with the increases of their concentrations. The most adverse effect on the germination was done by Cd, and followed by Pb and Zn respectively. PGR pretreatments could not mostly reduce the preventing and delaying effects of Pb and Cd on germination, while they could reduce these negative effects caused by Zn. All three heavy metals prevented coleoptile/shoot growth, especially radicle/root growth significantly both in germination and seedling growth stages. In the both stages radicle/root growth was more sensitive than coleoptile/shoot growth against those three heavy metals. PGR failed to reduce the restraining effects of these heavy metals on radicle/root elongation during both germination and seedling growth stages. All the used PGR, especially K+G were considerably successful at the reducing of the adverse effects of Pb, Zn and Cd on coleoptile growth in germination stage. While the inhibitory effects of Pb and Zn on shoot elongation could be reduced with GA3 pretreatment, the ones of Cd could not be alleviated with any treatment. Adverse effects of studied heavy metals on fresh weight and water content percentage of the seedlings during germination could mostly be reduced with PGR treatments, mainly K and K+G. All three heavy metals were determined to have negative effects mainly on fresh weight, dry weight and water content percentage of the seedlings and that PGR pretreatment could not reduce these effects in the stage of seedling growth.