2.1. Plant material and growth conditions
The experiment was conducted in a modern climate-controlled
greenhouse located at Gansu Agricultural University in Lanzhou,
Gansu (northwest China). Mini Chinese cabbage (Brassica pekinen-sis cv. “Jinwa no. 2”) seeds were obtained from Gansu Academy of
Agricultural Sciences. The seeds were soaked in water for 2 h then
placed on moist filter paper in petri dish, and finally kept in the
dark to germinate at 25
◦
C for 16 h. After germination, uniformly
geminated seeds were sown in pots filled with clean quartz sand
and cultured with half-strength whole Hoagland’s nutrient solu-tion for ten days. At the two-leaf stage, uniform seedlings were
transferred to containers (38 cm × 28 cm × 12 cm) with 6 L nutrient
solutions and aerated intermittently (1 h at 4 h intervals). Seedlings
were attached to a plastic plate with a strip of sponge and grown
in a greenhouse at 25 ± 2
◦
C/18 ± 2
◦
C day/night temperature