Contrasting effects of ethylene perception and biosynthesis inhibitors on germination and seedling growth of barley (Hordeum vulgare L.)

The effects of the plant growth regulator ethylene, and of ethylene inhibit ors, on barley (Hordeum vulgare L.) germination and seedling growth were in vestigated. Exogenous 1-aminocyclopropane-1-carboxylic acid (ACC) at 100 mu M enhanced ethylene production by barley seedlings and stimulated shoot gro wth, whereas both germination and seedling growth were inhibited by antagon ists of ethylene perception (75 muM silver ions, 100 muM 2,5-norbornadiene (NBD)). in contrast, germination was unaffected by, and root and shoot grow th of seedlings was strongly stimulated by inhibitors of ethylene biosynthe sis (10 muM cobalt chloride, 10 muM aminoethoxyvinylglycine (AVG)). Since t he ethylene and polyamine biosynthetic pathways are linked through S-adenos ylmethionine, this prompted further explorations into the role of polyamine s in germination and seedling growth. Exogenous polyamines (putrescine, spe rmidine and spermine) at 1 muM concentration stimulated barley seedling gro wth in a similar fashion to the ethylene biosynthetic inhibitors. Both poly amines and ethylene biosynthetic inhibitors reversed the inhibitory effects of ethylene perception inhibitors on germination and seedling growth. Bloc king endogenous ethylene production with aminoethoxyvinylglycine enhanced t he free putrescine and spermidine content of germinating barley grains. Thu s endogenous polyamines may play a complementary, growth-promotive, role to ethylene in the normal course of barley germination. Further, experiments that have been carried out using inhibitors of ethylene biosynthesis may ha ve to be re-evaluated to take the possible effect of polyamines into accoun t.