Effects of a nitric oxide donor and nitric oxide scavengers on Sorbus pohuashanensis embryo germination

The effects of an exogenous nitric oxide donor(sodium nitroprusside, SNP), a NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxode(PTIO) and carboxy-PTIO potassium salt(c PTIO) on the embryo germination of Sorbus pohuashanensis were studied in a petri dish test. SNP at 0.5–5 mmol L-1 increased germination percentage, mean time to germination, germination index and germination energy compared with the control to different degrees. Treatment with 2 mmol L-1 SNP improved germination most significantly; embryo germination percentage for mother tree 1(91.11%) and mother tree 2(64.44%) were much higher than the control. In addition,excessive SNP levels did not enhance embryo germination.Combined treatment with SNP and an NO scavenger delayed embryo germination. Treatment with c PTIO inhibited embryo germination; germination percentage was 42.22% and was lower than that of the control. These results show that low concentrations of exogenous NO can enhance the embryo germination of S. pohuashanensis,providing a simple, effective way for promoting germination of S. pohuashanensis.

Interaction between reactive oxygen species and hormones during the breaking of embryo dormancy in Sorbus pohuashanensis by exogenous nitric oxide

The breaking of dormancy mediated by reac-tive nitrogen species(RNS)is related to the accumulation of reactive oxygen species(ROS)in germinating embryos but the underlying mechanism is unclear.The objectives of this study were:(1)to explore the relationship between RNS-mediated dormancy release and ROS accumulation in germinating embryos of Sorbus pohuashanensis;and,(2)to investigate the relationships among germination time,ROS metabolism,and endogenous hormone synthesis.We studied the effects of exogenous nitric oxide(NO)donor sodium nitroprusside(SNP),the NO scavenger(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide(PTIO),abscisic acid(ABA),the exogenous ethylene donor ethrel,and the ethylene receptor inhibitor 2,5-norbornadien(NBD)on embryo germination and seedling growth.Embryos were released from dormancy by pretreatment with NO or ethylene, which was related to increased ethylene biosyn-thesis and decreased ABA levels. Breaking of dormancy by SNP was related to increased levels of ethylene, hydrogen peroxide, and glutathione, increased activities of superoxide dismutase and glutathione peroxidase, and decreased levels of ABA, superoxide anions, and malondialdehyde. These effects of nitric oxide were especially significant in seedling hypocotyls and radicles. These results demonstrate that NO can break S. pohuashanensis embryo dormancy by induc-ing ethylene biosynthesis, and that this signalling pathway is closely related to ROS accumulation and the antioxidant defence response.