Is the Diageotropic Tomato Ethylene Deficient?

The production of ethylene by a mutant form of tomato ( Lycopersicon esculentum Mill. cv. Ailsa Craig) with diageotropic shoot growth was compared with that from non‐mutant, upright plants. No difference in the rate of production by segments of petiole or stem apex was observed. The amounts of ethylene produced by excised segments of petiole from diageotropic and upright plants in response to wounding were also comparable. When the roots of either kind of plant were exposed to anaerobic conditions, the production of ethylene increased in the petioles; in ordinary plants this was associated with epinastic curvature, while in diageotropic plants the direction of shoot extension became reorientated from the horizontal to a more upright position. Exogenous ethylene gas had similar effects. These results support the view that the mutant has a modified response mechanism to gravity and to ethylene rather than an abnormally slow rate of ethylene production in the shoot. Since applying inhibitors of ethylene action to non‐mutant, upright plants did not induce diageotropism, endogenous ethylene seems unlikely to play a significant role in maintaining their upright orientation. The roots of both kinds of plant produced large amounts of ethylene, although the rate for diageotropic roots was about 37% less than that of roots from normal plants. Application of indol‐3‐ylacetic acid increased the production of ethylene by all roots but those from mutant plants were less responsive.