Dormancy and impotency of cocklebur seeds III. CO_2- and C_2H_4-dependent growth of the embryonic axis and cotyledon segments

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Growth of segments of embryonic axes and cotyledons excised from dormant or nondormant cocklebur (Xanthium pennsylvanicum Wallr.) seeds and CO_2 and C_2H_4 production in these segments were examined in relation to the effects of temperature, CO_2 and C_2H_4. Both the nondormant axes and cotyledons grew even at low temperatures below 23℃, but the dormant ones failed to grow. There was only little difference in the CO_2 evolution between the nondormant and dormant ones, but both the axis and cotyledon segments from the dormant seeds exhibited little or no C_2H_4 productivity, unlike the nondormant ones, at low temperatures. However, a high temperature of 33℃ caused rapid extension growth and C_2H_4 production even in dormant axes and cotyledons. The inability of dormant axes and cotyledons to grow disappeared completely in the presence of C_2H_4 at fairly low concentrations. Removal of endogenous CO_2 and C_2H_4 reduced the growth in both axes and cotyledons, while exogenous CO_2 mainly enhaced axial growth although exogenous C_2H_4 strongly stimulated the growth of both organs. Regardless of the dormant status, however, maximum growth of these organs occurred when C_2H_4 was given together with CO_2. We suggest that dormancy in cocklebur seeds is due to the lack of growing ability in both organs, caused by the lack of C_2H_4 productivity in both dormant axes and cotyledons, particularly in the former.
日本植物生理学会の論文