Effects of exogenous hormones on physiological characteristics and drought resistance of Lolium perenne under drought stress

In order to investigate the effects of different exogenous hormones on the growth and physiological characteristics of perennial ryegrass (Lolium perenne) under drought stress, this experiment used a pot water control method (CK₁), drought stress (CK₂), and drought stress with four concentrations of exogenous hormones: 50 μmol·L⁻¹ melatonin (MT) + drought (T₁), 0.1 μmol·L⁻¹ 2,4-epibrassinolide (EBR) + drought (T₂), 10 μmol·L⁻¹ abscisic acid (ABA) + drought (T₃), and 200 mg·L ⁻¹ gibberellin (GA₃) + drought (T₄). The effects of four exogenous hormones on the relative water content, relative electrical conductivity, malondialdehyde, osmotic regulator, antioxidant activity, and endogenous hormone contents of perennial ryegrass leaves under each treatment were measured; drought resistance was evaluated by subordinate function. The results show that, with the increase in drought stress days, the relative water content of ryegrass decreased, the relative electrical conductivity, proline, soluble sugar, and malondialdehyde contents increased, superoxide dismutase (SOD) and peroxidase (POD) enzyme activity increased, and soluble protein and catalase (CAT) enzyme contents first increased then decreased. After 9 days of drought stress, compared with CK₂, ryegrass relative water content and soluble protein contents increased in the presence of four exogenous hormones; meanwhile, the relative conductivity, proline, soluble sugar, malondialdehyde contents, and SOD and POD enzyme activities decreased. Under drought stress, zeatin riboside (ZR), GA₃, ABA, and auxin (IAA) contents in ryegrass increased. GA₃ contents increased, ZR and ABA contents decreased after exogenous hormones were applied, and IAA contents decreased under other hormone treatments (except T₂). The order of drought resistance was CK > T₄ > T₃ > T₂ > T₁ > CK₂, indicating that the application of exogenous hormones improved ryegrass drought resistance; T₄ treatment was the best. The results provide theoretical guidance for the application of exogenous plant hormones in ryegrass production.