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E. J. Wolterin and A. H. Halevy

Placing cut snapdragon (Antirrhinum majus L.) spikes horizontally induced elevated ethylene production rates. The imposition of curvature was preceded (2 h after gravistimulation) by an asymmetrical distribution of ethylene between lower and upper longitudinally halved stem sections, in favor of the lower halves. A corresponding gradient of free IAA could be detected only 30 min after gravistimulation. This IAA gradient was rapidly reversed after 1–24 h of gravistimulation, showing higher IAA levels in the upper stem halves. Additionally, one ACC synthase (ACS) gene, isolated from the bending zone of horizontal spikes, was apparently not expressed in IAA-treated stems. Thus, the gravity-induced ethylene asymmetry does not reflect an asymmetrical distribution of free IAA, but rather possibly exhibits a stress response imposed by change of stem orientation. Abolishing the ethylene gradient across the stem by applying various ethylene inhibitors [CoCl2, aminoethoxyvinyl-glycine (AVG), silver thiosulfate (STS), 2,5-norbornadiene (NBD), or 1-methylcyclopropene (1-MCP)], by exposure to ethylene (1-10 μl l-1), or by using Ca2+ antagonists [LaCl3, EGTA, 1,2-bis (2-aminophenoxy)ethane-N,N,N’,N’-tetraacetic acid (BAPTA) or trans-1,2-cyclohexane dinitro-N,N,N’,N’-tetraacetic acid (CDTA)], significantly inhibited curvature. This indicates that the ethylene gradient is correlated with bending. The results therefore suggest a role for ethylene in mediating the progress of the gravitropic response.

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Involvement of Ethylene Biosynthesis and Action in Regulation of the Gravitropic Response of Cut Flowers

E. J. Wolterin and A. H. Halevy

Involvement of Ethylene Biosynthesis and Action in Regulation of the Gravitropic Response of Cut Flowers

Placing cut snapdragon (Antirrhinum majus L.) spikes horizontally induced elevated ethylene production rates. The imposition of curvature was preceded (2 h after gravistimulation) by an asymmetrical distribution of ethylene between lower and upper longitudinally halved stem sections, in favor of the lower halves. A corresponding gradient of free IAA could be detected only 30 min after gravistimulation. This IAA gradient was rapidly reversed after 1–24 h of gravistimulation, showing higher IAA levels in the upper stem halves. Additionally, one ACC synthase (ACS) gene, isolated from the bending zone of horizontal spikes, was apparently not expressed in IAA-treated stems. Thus, the gravity-induced ethylene asymmetry does not reflect an asymmetrical distribution of free IAA, but rather possibly exhibits a stress response imposed by change of stem orientation. Abolishing the ethylene gradient across the stem by applying various ethylene inhibitors [CoCl2, aminoethoxyvinyl-glycine (AVG), silver thiosulfate (STS), 2,5-norbornadiene (NBD), or 1-methylcyclopropene (1-MCP)], by exposure to ethylene (1-10 μl l-1), or by using Ca2+ antagonists [LaCl3, EGTA, 1,2-bis (2-aminophenoxy)ethane-N,N,N’,N’-tetraacetic acid (BAPTA) or trans-1,2-cyclohexane dinitro-N,N,N’,N’-tetraacetic acid (CDTA)], significantly inhibited curvature. This indicates that the ethylene gradient is correlated with bending. The results therefore suggest a role for ethylene in mediating the progress of the gravitropic response.

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