Seed germination and seedling physiological characteristics of Zygophyllum xanthoxylum under salt and drought stress

The seeds of Zygophyllum xanthoxylum were used as experimental materials to explore the changes in seed germination characteristics, antioxidant enzyme activity and the level of soluble sugar (SS), soluble protein (SP), free proline (Pro), and malondialdehyde (MDA) in seedlings under different degrees of salt and drought stress. Germination rate and germination potential showed a decreasing trend with increasing stress, although there were significant difference between NaCl treatments. There was no significant difference in germination rate and germination potential of seeds under 5%～10% PEG (P > 0.05). However, under the treatment of 30% PEG solution, the germination rate, germination potential, and germination index were significantly reduced. As the stress increased, the content of MDA, Pro, SS, and SP also increased. With the increase in NaCl concentration, the activity of superoxide dismutase (SOD) and peroxidase (POD) initially increased and then decreased. The activity of SOD and POD reached a maximum at 60 mmol·L⁻¹ NaCl. With the increase in PEG content, the activity of SOD also gradually increased, whereas the activity of POD increased firstly and then decreased. Salt and drought stress inhibited the germination of Z. xanthoxylum seeds. With the increasing severity of the stress, the time of germination was delayed and the cumulative germination rate was low. The cell membrane of seedlings was found to be damaged by salt and drought stress. The accumulation of higher levels of proline, soluble sugar, and soluble protein may be the main mechanism by which the plants adapt to salt and drought stress.