TOMATO ROOT-GROWTH, GRAVITROPISM, AND LATERAL DEVELOPMENT - CORRELATION WITH AUXIN TRANSPORT

Tomato (Lycopersicon esculentum, Mill.) roots were analyzed during gro wth on agar plates. Growth of these roots was inhibited by the auxin t ransport inhibitors naphthylphthalamic acid (NPA) and semicarbazone de rivative I. (SCB-1). The effect of auxin transport inhibitors on root gravitropism was analyzed by measurement of the angle of gravitropic c urvature after the roots were reoriented 90 degrees from the vertical. NPA and SCB-1 abolished both the response of these roots to gravity a nd the formation of lateral roots, with SCB-1 being the more effective at inhibition. Auxins also inhibited root growth. Both auxins tested has a slight effect on the gravity response, but this effect is probab ly indirect, since auxins reduced the growth rate. Auxins also stimula ted lateral root growth at concentration where primary root growth was inhibited. When roots were treated with both IIA and NPA simultaneous ly, a cumulative inhibition of root growth was found. When both compou nds were applied together, analysis of gravitropism and lateral root f ormation indicated that the dominant effect was exerted by auxin trans port inhibitors. Together, these data suggest a model for the role of auxin transport in controlling both primary and lateral root growth.