Role of Leaves in Ethylene-induced Femaleness of Cucumber Plants

SAITO Takashi, TAKAHASHI Hideyuki

doi:10.2503/jjshs.55.445

To understand the mechanism of action of ethylene in pistillate flower induction in cucumber plants, the effects of Ethrel, an ethylene releasing reagent, and gaseous ethylene were studied. The present investigation was aimed at clarifying the site of action of ethylene in inducing pistillate flowers and the role of leaves in expression of the effect.<br>Localized treatment of either the 1st, 2nd or 3rd leaf, or shoot tip with Ethrel stimulated the production of pistillate flowers as much as when the whole plant or both 2nd leaf and shoot tip were treated. Better yields were obtained when the shoot tip or physiologically most active leaf were subjected to the treatment. Ethrel treatment of the shoot tip or roots was effective in inducing pistillate flowers in the presence but not the absence of mature leaves. When the expanded leaves were removed from the plant, leaving only the 2nd leaf to apply Ethrel to, the subsequent time of its removal gave an indication of the time needed for the required amount of Ethrel to be translocated to the shoot tip for the production of pistillate flowers. When the 2nd leaf was removed after 6 hours, no pistillate flowers were produced, while some flowers appeared when the leaf was removed 12 to 24 hours after the treatment. As the time of removal of the leaf was delayed, the number of pistillate flowers due to Ethrel increased, when the leaf was removed 10 days after treatment almost the same number of pistillate flowers were obtained as in non-defoliated plants. Application of ethylene gas to the shoot tip alone could induce pistillate flowers, but not when all expanded leaves were detached from the plant. Also, ethylene treatment of a mature leaf failed to induce pistillate flowers. Ethrel treatment of a single leaf stimulated abundant ethylene evolution not only from the treated region, but also from the shoot tip. When Ethrel was applied to the shoot tip, ethylene evolution from the treated region was much higher in defoliated than in nondefoliated plants. This may be due to the absence of expanded leaves which act as a sink, thus causing accumulation of Ethrel in the shoot tip.<br>These results imply that the differentiation of pistillate flower is not only controlled by ethylene but that some factor which is produced in mature leaves and migrates into the shoot tip has to be coupled with a high level of ethylene for the formation of pistillate flowers. Furthermore, the results suggest that the site of action of ethylene is the floral bud itself in a certain developmental stage.

Role of Leaves in Ethylene-induced Femaleness of Cucumber Plants

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