Interaction between Kinetin and Light on Germination of Grand Rapids Lettuce Seeds

At 260 Grand Rapids lettuce seeds require an exposure to white or red (6500A-6800A) light in order to germinate. This stimulating effect is reversed if this illumination is followed immediately by a brief exposure to far-red light (7000A-7500A). This phenomenon, discovered by Flint and McAllister (4), has been widely studied (3, 8). Many factors, such as lowering the temperature to 160 (1), can lessen the light requirement of these seeds or even cause it to disappear completely. Miller (6) reported that kinetin permitted Grand Rapids lettuce seeds to germinate in darkness, thereby replacing their light requirement. He revised this conclusion when he observed that the high germination percentage was due to an accidental penetration of light during the experiments and its synergistic interaction with kinetin (7). In contrast, Haber and Tolbert (5) came to the conclusion that kinetin only stimulated germination in darkness and presented no interaction with light. The purpose of this study was to make a detailed investigation of the action of kinetin on lettuce seed germination, and to propose a possible explanation of the contradictory results previously obtained. The terminology used and the definition of germination are those given by Evenari (3).