The Role Of Exogenous Abscisic Acid In Lead Tolerance Of Rice Seedlings

Plumbum (Pb) was one of the heavy metal considered as a potent environmental pollutant. It has gained more and more attention in recent years. In our experiment, the role of ABA in Rice seedlings under lead stress was studied, expected to alleviate the Pb toxicity. Abscisic acid (ABA) is a plant hormone. Endogenous ABA in plants plays an active role in physiology responses of plants to various external stresses such as drought, cold and salt. But the effects of exogenous ABA on the growth of rice seedling after long-term Pb stress remains unknown.The possible effects of ABA on the growth of rice seedlings and germimatinting rice seeds under Pb stress in solution culture were studied and a common cultivar Oryza sativa L. cv. Nanjing40 was used. The pre-treatment with 0.1mg/L ABA for 48 h partially protected seedlings from 0.25 mM Pb stress, which was considered as low and moderately toxic concentration. The results showed that the chlorophyll contents in leaves of ABA pre-treated seedlings were higher than that of Pb-exposed plants at the same Pb intensity. ABA modulated the H₂O₂ level in leaves of seedlings by repressing the activity of superoxide dismutase (SOD) and up regulating the activity of catalase (CAT) and ascorbate peroxidase (APX), which could take response to lead stress. The oxidative activity of roots of rice seedlings responded to the lead stress indicated that the roots play a vital role in enhancing the activity of lead tolerance of rice seedlings by partially preventing Pb²⁺ from transporting to stems and leaves of seedlings. There is no rapid accumulation of endogenous free proline, which acts as an osmosis regulating substance of plants appeared in the alleviating grew seedlings. It may show that the osmosis stress is not the primary determination factor caused by lead toxicity to plants at the concentration of 0.25mM Pb stress for 7days. The effects of ABA on the seeds germination under Pb stress were investigated during the first 7 days of germination. Pb had mild inhibition on the embryo development, but serious toxicity on radicle.