Effects of exogenous ABA on cold stress resistance in Hevea brasiliensis. The four-month-old Hevea brasiliensis seedlings grown in the soil were transferred to 10 °C and watered with water or 10 μM, 25 μM, 50 μM, or 75 μM ABA solution for the indicated days. (A) Phenotype of control, ABA-treated rubber tree seedlings before and after cold treatment (7 days at 10 °C). (B) Electrolyte leakage; (C) malondialdehyde (MDA) concentration; (D) free proline accumulation; (E) chlorophyll content, in CK, cold-treated (10 °C), and cold +50 μM ABA-treated leaves for the indicated time periods. CK, plants grown under normal conditions; FW, fresh weight. Error bars show standard deviation (SD) from three replicates.