Kinetics of upward bending response of gravistimulated snapdragon shoots
Recording of the gravitropic response

Angular Position Transducer

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Picture 2. The way in which the gravitropic curvature (degrees)
was obtained is as follows: the angle (starting with 0^o)
was measured by means of an inverted protractor lined up with the
top part of the shoot. A thin wire, attached to the basis of
the protractor, which was held down by a small weight, marked the angle
on the curved side of the protractor.

It has been shown that the effect of inhibitors mainly occurs during the early phases of the gravitropic response and that the final curvature was often similar to that of the control shoot (Wheeler et al., 1986). In an attempt to gain more information about the initial gravitropic response, the gravitropic response was measured by means of an Angular Position Transducer (APT) (Gould Instruments Inc., Cleveland, OH). The principle of an APT is the conversion of the upward bending of the shoot into an electrical signal which can be visualized with a thermal strip chart recorder. The shoot, which was placed in a large test tube containing tap water or preservative solution (Floralife, Burr Ridge, IL), was attached to the APT with a thin copper wire. To prevent leakage of water and movement of the shoot during upward bending, the shoot was placed in a rubber seal (obtained from the University Flower Shop, Ann Arbor, MI) and made lead proof with sealant (Qubit systems Inc., Kingston, ONT, Canada). The appartus setup and its mutual connections are depicted in fig. 4. The thermal pen was set ca. 8 cm above the bottom line of the strip chart so that negative angles could be measured. When using small and tender shoots from the MBG, it was observed that the APT had a restraining influence on the gravitropic response. This was probably due to the weight and friction of the lever. In an attempt to solve this problem, a counter-balancing weight was attached in such a way that the lever was in a balance. This solution was an improvement although still not perfect. With the larger commercial shoots the influence was less obvious.