Other Real-Time Movement
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In the case of root movement, a very interesting phenomenon was found using the Super-HARP camera, which enabled the visualization of root movement in the dark.
Although the first data on plants show that the harmful effect is growth inhibition, the first effect of the toxicity was to stop the rotation movement of the roots before growth inhibition occurred.
When there was a chemical change in the environment, although the circumnutation of the root tip ceased, the root was able to elongate, and it was interesting that after a while the root movement resumed. In the case of a rice root, one round of movement of the rice root tip showed a constant time of approximately 50 minutes. However, this movement ceased when Al ion was supplied. The time needed for resuming the movement of the root tip was dependent on the Al ion concentration. It is not known what triggers the resumption of the movement of the root tip.
KeywordsHARP camera Circumnutation Root movement Moving angle Movement cycle Al
8.1 Root Movement During Growth (HARP Camera Images in the Dark)
Circumnutation is a rotating movement of a growing plant organ that is considered to result from endogenous rhythmic processes. The regular autonomous rotating movement of a root is due to different growth on the sides of the root, based on oscillators at the cellular or tissue level. However, the mechanisms responsible for circumnutation are still unclear. In particular, because of the lack of imaging tools, it has not been possible to acquire rotating images of roots under dark conditions. Since light has an influence on the physiological activity of the root, such as inducing photosynthesis, the development of devices that enable seeing the root under dark conditions is needed. Since we could use a super-HARP camera developed by the NHK broadcasting technology institute in Japan, we could visualize root circumnutation in the dark.
It is known that Al ions induce callose production, as an earliest reaction, damaging plasma membranes and inhibiting root elongation. Our study suggested that the inhibition of root tip circumnutation occurred before callose production, followed by the inhibition of root elongation.
Whole root movement is controlled by the balance of plant hormones, and auxin probably plays a central role in root development because of its cell extension effect. Since auxin extends root cells, it has been supposed that the localization of auxin generates circumnutation. As an alternative, some environmental conditions have been discussed, including the possibility that certain metal ions induce circumnutation.
Circumnutation plays an important role in the effective development of roots in soil structures containing inhomogeneous nutrients. With a rotating root tip, roots are able to select the appropriate direction to extend smoothly. Because of the lack of tools, it was extremely difficult to study root movement in the dark. The Super-HARP camera used in this study allowed the acquisition of images in dark conditions, approximately 300 pmol/m2/s, under which no other optical devices could obtain images. Thus, the observation of root growth using the Super-HARP camera is better than any other method to study root activity in the dark.
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