Kinetics of upward bending response of gravistimulated snapdragon
shoots
Abstract
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During gravitropism the top of snapdragon (Antirrhinum majus)
stalks re-orientes by bending upward. This research is devoted to enhance
the knowledge of upward bending kinetics and to develop new methods for
studying the gravitropic curvature. The snapdragon shoot was held in a
horizontal position in the light at room temperature and color slides ware
taken at intervals of 15 minutes during the upward bending response. With
imaging processing software, the scanned slides were put on top of each
other to create a time-lapse photograph of the whole bending process. By
projecting the slides, gravitropic curvatures were measured with a
protractor. Bending the tip occurs at a zone just before the first open
flower and starts after a lag phase of around 30-60 minutes. The
gravitropic response can be divided into two clear phases. During the
first one, a linear bending rate was abserved of 28 degrees/h until a
maximum angle of 140 degrees was reached. In the second phase, the tip of
the shoot bent back to its vertical position. This 'overshoot' correction
was considerably slower and took around 30 hours to complete. When the
shoot was re-orientated to its original vertical position, the tip bent
again, but this time at a different place. This means that the bending
zone moves along the rapidly elongation shoot. The morphological and
physiological state of the bending zone could therefore be of great
importance to our understanding of the mechanism of gravitropic response
in flowering snapdragon shoots.