Plant material
The SRPs were obtained from 1539-1 and 1637-2 cell lines through somatic
embryogenesis. The 1539-1 and 1637-2 cell lines were initiated in
nematode-resistant P. thunbergii families 39 and 37,
respectively. The protocols for somatic embryogenesis in
nematode-resistant P. thunbergii was conducted according to our
previous group report (Sun et al. 2019). Briefly, embryogenic cells were
isolated from immature cones and cultured on a maintenance medium for
proliferation. Subsequently,
the
embryogenic cells (fresh weight 1g) were transferred to Erlenmeyer
flasks (including 30 mL of liquid proliferation medium) and placed on an
orbital shaker at 90 rpm for 1
week.
The 2 mL suspension was transferred to a maturation medium for 10 weeks
in the dark at 23 ± 1℃. After 10 weeks of culturing (without intervals),
the cotyledon somatic embryos were taken from the maturation medium and
transferred to the germination medium for four weeks under cool white
fluorescent light (16/8 h) at
23±1℃.
The post-germination SRPs were selected as the experimental samples.