Comparative Requirement for Endogenous Ethylene during Seed Germination

Abstract

Requirement for endogenous ethylene during seed germination of the following ten species was determined: Lycopersicon esculentum Mill. (tomato), Allium cepa L. (onion), Arena fatua L., dormant pure line AN-51 (wild oats), Cucumis sativus L. (cucumber), Sinapis arvenis L. (wild mustard), Tagetes erecta L. (marigold), Raphanus sativus L. (radish), Triticum aestivum L. (wheat), Catharanthus roseus L. (periwinkle), and Phaseolus aureus L. (mung bean). Experiments were done under controlled conditions suited for the germination of each species. Criteria used to determine the need for endogenous ethylene were: (i) temporal relationship between ethylene production and seed germination; (ii) parallel inhibition of ethylene synthesis and seed germination by L-alpha-(2-aminoethoxyvinyl)-glycine or CoCl2; (iii) inhibition of seed germination by 2.5-norbornadiene, a competitive inhibitor of ethylene action; and (iv) prevention by exogenous ethylene of the effects of each inhibitor on germination. All the species produced ethylene in amounts that increased concomitantly with germination. According to all the criteria used, ethylene synthesis and action were found to be necessary for the germination of T. erecta. Norbornadiene inhibited the germination of R. sativus, T. aestivum and C. roseus, and exogenous ethylene overcame this inhibition. However, inhibitors of ethylene synthesis generally did not affect the germination of these species. One exception was the inhibition of R. sativus germination by CoCl2, but this was not overcome by exogenous ethylene, indicating that CoCl2, did not act specifically by blocking ethylene synthesis. In all other species, ethylene produced by seeds appears to play no role in germination. The results show that there is no general requirement for endogenous ethylene during germination, even though all species studied so far produce ethylene. This requirement is also not linked specifically to dormancy breakage.