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Abstract At 23°C, both C2H4 and CO2 stimulated the germination of freshly imbibed upper cocklebur (Xanthium pennsylvanicum Wallr.) seeds, but C2H4, unlike CO2, changed to an inhibitor of germination under some soaking conditions. However, when seeds were pre-soaked for more than several hours at 23 °C prior to treatment, C2H4 strongly inhibited their germination at 33 °C, the degree of inhibition increasing with the duration of pre-soaking. Maximum inhibition occurred at 1–3 cm3 m?3 C2H4 when seeds were pre-soaked for 1 week; further increases of C2H4 concentration and pre-soaking period decreased the inhibitory effect. C2H4 was synergistic with CO2 when C2H4 promoted germination, whereas it was antagonistic when inhibitory. Such a transition of the C2H4 action occurred at ca. 27 °C. Also 1-andnocyclopropane-1-carboxylic acid, a C2H4 precursor, inhibited the germination of pre-soaked seeds at 33 °C, although it promoted the germination at 23 °C. When pre-soaked seeds were prepared for germination by chilling at 8 °C for 3 d, the inhibitory effect of C2H4 on the subsequent germination was manifested even at 23 °C. The reversal of the C2H4 action from promotion to inhibition in cocklebur seed germination is discussed in relation to the engagement of two respiratory pathways in the imbibed seeds.  相似文献   
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Abstract. Elongation responses of intact coleoptiles of rice (Oryza sativa L. ev. Sasanishiki) explants to various gases were examined under submerged conditions in continuously flowing gas-saturated incubation media. Reduced O2 tension (hypoxia). CO2 and especially C2H4 significantly stimulated coleoptile elongation; the optimal concentrations of O2, CO2 and C2H4 when applied singly were 0.07 m3 m-3, 0.10 m3 m-3, and 3 cm3, respectively. However, in addition to these gases other as yet unknown factors were involved in the enhanced elongation of rice coleoptiles under water. The actions of CO2 and C2H4, unlike that of hypoxia, were accompanied by increases in dry weight of the coleoptiles. The effect of C2H4 occurred independently of O2 concentrations, whereas that of CO2 occurred above 0.08 m3 m-3O2. Maximum elongation of rice coleoptiles under submerged conditions was obtained when the flowing medium was saturated with a gas mixture containing 0.10 m3 m-3 O2, 0.10 m3 m-3 CO2 and 10 cm3 m-3 C2H4, greatly surpassing elongation in static media. However, elongation in static media was greater than that in a closed atmosphere. The intercellular C2H4 concentration in explants growing in static media was higher than that in a closed atmosphere. These results showed that the coleoptile elongation of rice seedlings under water may be regulated by the accumulation of CO2 and C2H4 in and around the seedlings under hypoxic conditions.  相似文献   
3.
Elongation of coleoptile segments, having or not having a tip,excised from rice (Oryza sativa L. cv. Sasanishiki) seedlingswas promoted by exogenous ethylene above 0.3 µl l–1as well as by IAA above 0.1 µM. Ethylene production ofdecapitated segments was stimulated by IAA above 1.0µM,and this was strongly inhibited by 1.0 µM AVG. AVG inhibitedthe IAA-stimulated elongation of the decapitated segment witha 4 h lag period, and this was completely recovered by ethyleneapplied at the concentration of 0.03 µl l–1, whichhad no effect on elongation without exogenous IAA. The effectsof IAA and ethylene on elongation were additive. These factsshow that ethylene produced in response to IAA promotes ricecoleoptile elongation in concert with IAA, probably by prolongingthe possible duration of the IAA-stimulated elongation, butthat they act independently of each other. Moreover, AVG stronglyinhibited the endogenous growth of coleoptile segments withtips and this effect was nullified by the exogenous applicationof 0.03 µl l–1 ethylene. These data imply that theelongation of intact rice coleoptiles may be regulated cooperativelyby endogenous ethylene and auxin in the same manner as foundin the IAA-stimulated elongation of the decapitated coleoptilesegments. Key words: oryza sativa, Ethylene, Auxin, Coleoptile growth  相似文献   
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