Plants circling in outer space
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چکیده
Plants do not grow in a strict linear manner, rather they circumnutate. That is, they exhibit an oscillatory or helical growth pattern around an axis. Circumnutation is readily apparent in vines such as morning glory or grape (Fig. 1), but in fact it is nearly ubiquitous in plants. Circumnutation occurs in almost all plant organs throughout all stages of development (Johnsson, 1997; Larson, 2000). In the late 19th century, plant scientists noted that plant organs, including roots, shoots, stems, hypocotyls, branches, leaves and flower stalks, did not grow exactly in a linear direction. The mean growth direction may be maintained for long periods of time, but the organ’s instantaneous growth direction usually rotates or oscillates slowly around a mean. Circumnutation is best visualized using time-lapse photography (Fig. 2), and numerous examples, including sunflower seedlings, Arabidopsis stems and morning glory stems, are illustrated in movies found at the Plants-inMotion website (http://plantsinmotion.bio.indiana.edu/). The paper by Johnsson et al. (pp. 621–629) in this issue of New Phytologist uses microgravity as a tool to study this interesting phenomenon in plants.
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