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Physiol Plant. 2018 Jan;162(1):135-144. doi: 10.1111/ppl.12640. Epub 2017 Oct 18.

Modification of growth anisotropy and cortical microtubule dynamics in Arabidopsis hypocotyls grown under microgravity conditions in space.

Author information

Graduate School of Science, Osaka City University, Osaka, 558-8585, Japan.
Japan Space Forum, Tokyo, 101-0062, Japan.
Advanced Engineering Services Co., Ltd, Tsukuba, 305-0032, Japan.
Chiyoda Corporation, Yokohama, 221-0022, Japan.
Japan Manned Space Systems Corporation, Tokyo, 100-0004, Japan.
Japan Aerospace Exploration Agency, Tsukuba, 305-8505, Japan.
Graduate School of Science and Technology, Sophia University, Tokyo, 102-8554, Japan.
Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, 277-8561, Japan.
LPixel Inc, Tokyo, 113-0033, Japan.
Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, 630-0192, Japan.
Graduate School of Science and Engineering, Saitama University, Saitama, 338-8570, Japan.


We carried out a space experiment, denoted as Aniso Tubule, to examine the effects of microgravity on the growth anisotropy and cortical microtubule dynamics in Arabidopsis hypocotyls, using lines in which microtubules are visualized by labeling tubulin or microtubule-associated proteins (MAPs) with green fluorescent protein (GFP). In all lines, GFP-tubulin6 (TUB6)-, basic proline-rich protein1 (BPP1)-GFP- and spira1-like3 (SP1L3)-GFP-expressing using a constitutive promoter, and spiral2 (SPR2)-GFP- and GFP-65 kDa MAP-1 (MAP65-1)-expressing using a native promoter, the length of hypocotyls grown under microgravity conditions in space was longer than that grown at 1 g conditions on the ground. In contrast, the diameter of hypocotyls grown under microgravity conditions was smaller than that of the hypocotyls grown at 1 g. The percentage of cells with transverse microtubules was increased under microgravity conditions, irrespective of the lines. Also, the average angle of the microtubules with respect to the transverse cell axis was decreased in hypocotyls grown under microgravity conditions. When GFP fluorescence was quantified in hypocotyls of GFP-MAP65-1 and SPR2-GFP lines, microgravity increased the levels of MAP65-1, which appears to be involved in the maintenance of transverse microtubule orientation. However, the levels of SPR2 under microgravity conditions were comparable to those at 1 g. These results suggest that the microgravity-induced increase in the levels of MAP65-1 is involved in increase in the transverse microtubules, which may lead to modification of growth anisotropy, thereby developing longer and thinner hypocotyls under microgravity conditions in space.

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