Application of Silver Nitrate Induces Functional Bisexual Flowers in Gynoecious Cucumber Plants (Cucumis sativus L.)

The most common cucumber plants (Cucumis sativus L.) show monoecious sex expression and produce both male and female flowers on the same plant, whereas plants of the gynoecious type produce only female flowers under natural conditions. Ethylene is a plant hormone that affects sex differentiation in cucumber plants. In the gynoecious cucumber, application of the ethylene biosynthesis inhibitor aminoethoxyvinyl glycine (AVG) induced only male flowers, whereas application of the ethylene action inhibitor silver nitrate (AgNO3) induced male and morphologically bisexual flowers. To investigate whether the morphologically bisexual flowers that were induced by AgNO3 in gynoecious cucumber plants have functional sexual organs, we analyzed the function of pistils and stamens. Seeds were produced by cross-fertilization and the pollen tubes were elongated on sucrose medium in eight of the twenty-five morphologically bisexual flowers. These results show that the application of AgNO3 to gynoecious cucumber plants produces functional bisexual flowers. In functional bisexual flowers, the length of pistils was similar to that of the female flowers of gynoecious cucumber plants and the length of stamens was similar to that of male and bisexual flowers of andromonoecious cucumber plants. In contrast, stamen length was inversely proportional to pistil length in the group of morphologically bisexual flowers that were induced by AgNO3. These results suggest that the morphology of the sexual organs is different in morphologically bisexual flowers and in functional bisexual flowers. It is possible that the functional bisexual flowers that were induced by AgNO3 in gynoecious cucumber plants are the result of exclusive blockade of ethylene signals that inhibit stamen development.