Cyanide-sensitive and Cyanide-resistant Respiration in the Germination of Cocklebur Seeds

Abstract

Interrelation between the CN-sensitive cytochrome path and the CN-resistant, benzohydroxamic acid (BHM)-sensitive or n-propylgallate (nPG) sensitive alternative pathway in seed respiration during germination was examined using the nondormant upper and lower seeds of X. pensylvanicum Wallr. The operation of both pathways was required for normal germination of the lower seed and for KCN- or NaN3-induced germination of both. From the sensitivity to BHM [benzohydroxamic acid] of the germination response, the alternative pathway exerts its physiological activity as soon as it develops during the early period of H2O imbibition. Pretreatments with KCN and NaN3 for promoting germination strikingly decreased only the engagement of the cytochrome pathway in the subsequent respiration without affecting that of the alternative pathway. No germination occurred without the operation of the cytochrome pathway. Excess operation of the cytochrome pathway is detrimental to germination, being maximal following the BHM-sensitive phase. The alternative and cytochrome pathways operated in a proportion of 1:5 in a period just before the lower seeds started to germinate. There was little difference between the upper seeds of relatively low germination potential and the lower seeds of relatively high potential with respect to both the developmental pattern of the alternative path and the balance of the alternative and cytochrome paths. The higher germination potential of the lower seeds may be related to their high capacities for the alternative pathway.