Cynanchum bungei Decne is a rare, endemic, and important medicinal plant species in China. Seed germination and early seedling growth of large seeds (greater than 7 mm) and small seeds (smaller than 7 mm) were investigated at three temperatures (15, 20, and 25 °C) in both continuous light and alternating light/dark photoperiods to determine seed propagation requirements. Photoperiod significantly affected seed germination and early seedling growth. Germination and seedling growth at a 12:12-h photoperiod performed better than in continuous light. Temperature had a significant effect on germination index (GI), vigor index (VI), germination velocity (GV), mean germination time (MGT), shoot biomass (SB), root biomass (RB), and taproot length (TL), but no significant effect on final germination percentage (FGP). A temperature of 20 °C was the optimum temperature for seed germination and early seedling growth. Average growth height (AGH) and relative growth rate (RGR) of shoots at 15 °C were greater than that at 20 °C. Large seeds had better germination and seedling performance than small seeds. However, small-seeded seedlings had greater biomass allocated to roots (BAR) and root-to-seedling ratio (RSR) than seedlings from large seeds. Small seeds of C. bungei could be more competent in unfavorable soil and light conditions than large seeds.
As a rare, endemic, important, and salt-sensitive medicinal plant species in China, Cynanchum bungei Decne seeds were treated to germinate with distilled water (control) or NaCl solutions in the presence or absence of nitric oxide (NO) donor sodium nitroprusside (SNP) to investigate the effects of exogenous NO on seed germination, seedling growth, and antioxidant enzyme activities under salt stress. Sixty mm NaCl significantly inhibited the germination and seedling growth of C. bungei. Exogenous SNP alleviated salt stress in a dose-dependent manner, as indicated by accelerating the seed germination, increasing germination index (GI), vigor index (VI), germination velocity (GV), shoot height (SH), taproot length (TL), shoot biomass (SB), root biomass (RB) as well as shortening mean germination time (MGT), and 0.1 mm SNP was the optimal concentration. SNP at 0.1 mm greatly increased the activities of superoxide dismutase (SOD) and catalase (CAT) under salt stress, which contributed to alleviate the oxidative stress induced by salt stress in C. bungei seeds. It is concluded that NO treatment is an effective practice to improve C. bungei seed germination under saline condition.