*2.5. Plant Materials and Stress Treatment*

The plant materials used in this study were collected from Institute of Botany, Jiangsu Province, and the Chinese Academy of Sciences (Nanjing Botanical Garden Mem. Sun Yat-Sen). Healthy and well-developed *H. hamabo* seeds were placed in a refrigerator at 4 ◦C for vernalization for 20 days. The seeds were then treated with concentrated sulfuric acid for 15 min and then rinsed thoroughly with running water before planting in plastic pots with a substrate composed of peat and vermiculite (1:1) and placing in a phytotron with a photoperiod of 16/8 h and day/night temperatures of 24/20 ◦C. Seedlings with 8–10 true leaves were transplanted into 1/2 MS solution for 7 days, followed with abiotic stress and hormone treatments.

High and low temperature stress treatments consisted of exposing the seedlings to 42 ◦C or 4 ◦C, respectively. A certain number of seedlings were exposed in 400 mM NaCl or 500 mM mannitol for high salt or drought treatment, respectively. Other seedlings were sprayed with 200 μM salicylic acid (SA), 1 mM methyl jasmonate (MeJA), or 50 μM abscisic acid (ABA) until the leaves were completely moist. The youngest fully expanded leaf from each plant was collected at 1, 2, 6, 12, and 24 h after treatment and then frozen in liquid nitrogen before storage at −80 ◦C. The youngest fully expanded leaf from each plant of untreated seedlings was similarly collected as control material. Three biological replicates with nine different plants, three plants in a group, were produced for each treatment.
