Germination of nondormant but impotent small cocklebur seeds (Xanthium pennsylvanicum Walr.) was promoted profoundly with thiourea or benzyladenine, and slightly with gibbereUlic acid. GibbereUic acid was ineffective in causing the germination of dormant cocklebur seeds, although thiourea and benzyladenine were effective. Experiments with excised seed pieces showed that the promotive effects of thiourea, benzyladenine, and gibbereUlic acid on cocklebur seed germination were associated with the enhancement of growth of seed parts; thiourea stimulated predominantly the axial growth, whereas benzyladenine stimulated predominantly the cotyledonary growth.Potassium nitrate or indoleacetic acid had little effect on the initial growth of either axes or cotyledons. Except for gibberellic acid, all of the compounds employed enhanced ethylene production, but in general, the ethylene production seemed more likely to be a consequence of growth rather than a cause of it. We conduded that the chemical regulation of seed germination may be a consequence of the alteration of growth capabilities in either the axes or cotyledons, or both.In a previous paper (10), we observed that cocklebur seeds respond in different manners to various germination stimulators: seeds treated with TU' or CO2 exhibited normal germination, but 02 enrichment caused germination in which the seed coat was mostly broken at the cotyledonary side rather than at the axial end. On the other hand, the seeds germinated with BA, C2H4, and GA3 exhibited an intermediate pattern in which approximately half of the germinations were normal. Granting that seed germination in dicot plants is a phenomenon occurring when the axis and the cotyledons generate enough thrust to overcome the restraint by the seed coat (8), these diverse response patterns might result from the differential growth responsiveness of the axis and cotyledon: for example, TU could preferentially enhance growth of the embryonic axis proper, whereas BA could more greatly enhance growth of the cotyledons and hence the abnormal lateral breaking of the seed coat. We have previously presented some evidence that C2H4, unlike CO2, strongly stimulates both the axial and cotyledonary growth (7).These findings caused us to examine the relative effectiveness of various known germination stimulators (15), such as TU, KNO3, BA, GA3, and IAA, in stimulating the growth of axial and cotyledonary seed pieces. Experiments were also directed toward a comparison between the dormant and nondormant seeds in response to these stimulators.' Abbreviation: TU: thiourea. MATERIALS AND METHODSSeeds of cocklebur (Xanthium pennsylvanicum Wallr.) were used in this experiment. For germination tests, dormant small seeds newly harvested in 1973, and the nondormant but impotent small seeds fully after-ripened since 1972 were exposed to various drugs on two filter paper discs in 5-cm Petri dishes with 2 ml water. For growth tests, the embryonic axis and cotyledon segments were excised from large seeds according to the procedur...
The germination response of small, upper seeds of cocklebur (Xanthium pensylvanicum Wallr.) was examined with respect to the germination stimulants oxygen, CO2, ethylene, gibberellic acid, benzyladenine, thiourea and KNO3. Thiourea, benzyladenine, ethylene and oxygen-enriched air (50% O2) stimulated germination, but gibberellic acid was only slightly effective and KNO3 had little effect. In contact with thiourea or CO2, seeds usually germinated by extrusion of the radicle without any change of germination pattern, but while in O2-enriched air the seed coat was predominantly ruptured at the cotyledon end. In about half of the seeds germinated with ethylene, benzyladenine and gibberellic acid, the seed coat split at the cotyledon side. Trapping of endogenously evolved ethylene and CO2 from the ambient atmosphere did not affect the actions of benzyladenine and gibberellic acid, but the action of thiourea was significantly reduced by trapping CO2. Except for thiourea, with which the CO2 production was enhanced, benzyladenine, gibberellic acid and KNO3 did not increase CO2 and ethylene production from the seed in the germination period. The maximum germination percentage was obtained by a combi- nation of CO2, ethylene, gibberellic acid and benzyladenine, but the interaction of gibberellic acid and benzyladenine was not significant. In contrast, the interaction of gibberellic acid and ethylene was very effective, and further addition of CO2 to this combination hastened the germination in air and also facilitated it under the semi-anaerobiosis assumed to exist in a natural underground habitat, although the effect of benzyladenine alone was nearly completely suppressed by semi- anaerobiosis. Thus the particular importance of CO2, ethylene and gibberellic acid in the normal germination regulation of this seed is suggested.
Growth responses to exogenous CO2 or ethylene and the production of CO2 or ethylene in embryonic axes excised from dormant or non-dormant seeds of cocklebur (Xanthium pensylvanicum Wallr.) were examined in relation to oxygen tension. There were two ethylene-producing systems in the axes, one anaerobic and one aerobic. The former was active in dormant seeds and the latter was active in non-dormant seeds. The axes from non-dormant but impotent small seeds, incapable of germinating under ordinary conditions, showed higher activities for both systems. However, there was no qualitative difference in the oxygen response as to CO2 output between the dormant and non-dormant axes, but CO2 output under aerobic conditions was greater with non-dormant seeds. Regardless of dormancy status, growth stimulation of axes by CO2 occurred when it was applied during the beginning of incubation and in atmospheres with oxygen concentrations insufficient to permit normal axial growth. Nevertheless, the stimulation of ethylene production by CO2 was parallel with the increase of oxygen tension, suggesting that the CO2-stimulated ethylene production could not be the result of CO2-stimulated axial growth. The growth response was most sensitive to ethylene after the CO2-sensitive period and before an oxygen-requiring period. Similarly to the action of CO2, the most striking effect of ethylene on the growth of non-dormant axes was obtained in oxygen-deficient atmospheres. However, the synergistic interaction between CO*2 and ethylene occurred only in aerobic conditions. Unlike the non-dormant axes, the dormant ones, whose aerobic ethylene productivity was very small, responded to ethylene with increased growth in proportion to increasing oxygen tension.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.