CO₂Enhancement of Aerobic and Hypoxic C₂H₄ Production in the Tissues of Cocklebur Seeds at Different Dormant States

Abstract

CO2 stimulated C2H4 production in the axial and cotyledonary tissues of cocklebur (Xanthium pensylvanicum Wallr.) seeds regardless of their dormant states. Axial tissues were more responsive to CO2 than cotyledonary ones, and the tissues of upper seeds were more responsive than those of lower ones. Responsiveness of upper seed tissues to CO2 increased in the following order: primarily dormant (PD), non-dormant (ND) and secondarily dormant (SD) and also with increasing the period of presoaking. The CO2 stimulation of C2H4 production occurred not only in air but also under hypoxic conditions. The pronounced C2H4 production at hypoxia in the axes of PD seeds, as compared with those of ND ones, was a result of more active CO2 evolution in PD axes than in ND ones. A lag period of 2-3 h was required for the CO2 enhancement of C2H4 production to occur, and the CO2-enhanced C2H4 production was completely inhibited by aminoethoxyvinylglycine. It was thus suggested that CO2 may promote C2H4 production by stimulating the biogenesis of 1-aminocyclopropane-1-carboxylic acid. Also, the seed-coat of cocklebur seeds produced C2H4 and its C2H4 production was enhanced by CO2. It thus became obvious that the enhancement of C2H4 production by CO2 is independent of the growth stimulation of seed tissues by CO2, since the seed-coat itself has no growth potential.