Effects of C2H4 and CO2 on respiration of pre-soaked upper cocklebur (Xanthium pennsylvanicum Wallr.) seeds during a pre-germination period were examined in relation to effects of the two gases on germination. At 33°C, cocklebur seed germination was greatly stimulated. This high temperature-stimulated germination was severely inhibited by C2H4, but not by CO2, although both gases stimulated germination at 23°C. C2H4 promoted seed respiration at 23°C, but its promotive effect decreases with increasing temperature and disappeared at about 35°C, while CO2 stimulated respiration regardless of temperature. CO2 augmented the operation of the CN-sensitive, cytochrome path (CP) regardless of temperature, resulting in an increase in the ratio of the CP flux to a CN-resistant, alternative path (AP) flux. On the other hand, C2H4 augmented the operation of both paths, particularly of the AP, at 23°C, where it promoted germination. However, at 33°C where germination is suppressed by C2H4, C2H4 preferentially stimulated respiration via the AP, thus leading to an extremely high ratio of AP to CP. The inhibitory effect of C2H4 on germination at 33°C disappeared completely in enriched O2, under which conditions CP is known to be augmented. At 23°C, CO2 and C2H4 acted independently in controlling seed respiration, but they were antagonistic at 33°C. The independent action appeared when the AP flux was very low relative to the CP flux, while the antagonism appeared when the AP flux had risen. This differential action of the two gases at different temperatures was also observed in the ATP level, adenylate pool size and energy charge of the axial tissues. These results suggest that the germination-controlling actions of both CO2 and C2H4 are fundamentally manifested through the modification of respiratory systems. However, the germination-inhibiting effect of C2H4 at 33 °C was not removed by inhibitors of AP, and there was little difference in the adenylate compounds between the C2H4-treated and non-treated seeds at 33°C. Therefore, the physiological action of C2H4 can not be explained only in terms of regulation of the respiratory system.
|Number of pages||10|
|Journal||Plant and Cell Physiology|
|Publication status||Published - 1987 Jan|
- Carbon dioxide
- Cocklebur (Xanthium pennsylvanicum)
- Energy charge
- Respiration (seed germination)