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Space experiment reveals the mechanisms of how PIN proteins direct one of the plant hormones "auxin" to form a seedling of a cucumber

Last Updated: December 28, 2016

Tohoku University Graduate School of Life Sciences

Professor Hideyuki Takahashi's group at Tohoku University Graduate School of Life Sciences elucidated that the transfer of auxin, one of the plant hormones, in plants is seen differently between under the gravity environment on the ground and under the microgravity environment in space.

The past space experiment revealed that plants grow differently in space than plants grown on the ground. The experiment conducted this time clarified the detailed movement of plant hormones in plants by observing cucumber seedlings. The results suggest that plants on the ground may have evolved by acquiring a sense of gravity direction and transferring auxin downward to control growth.

"PIN proteins" that play a role in transporting auxin out of plant cells direct the transfer of auxin in plants.

Through collaborative research with JAXA, Professor Takahashi's group clarified that the plant seedlings emerged differently on the ground than in space depending on the level of gravity, and that PIN proteins which transfer auxin play an important role in forming the shape of plants.

The past space experiment revealed that plants grow differently in space than plants grown on the ground. This time the research reveals that PIN proteins move in cells as induced by gravitational stimulation, and cells having PIN proteins cooperate to create previously unknown paths (such as the endodermal cell layer becoming a canal through which auxin is laterally transported from the upper to lower flank). Auxins on the upper side of cucumber seedlings transfer the pathway downward to form an ideal shape for growth.

The results also suggest that this growth mechanism may easily collapse under a microgravity environment, therefore, future food cropping in space may require artificial gravity or alternative means.

The experiment was conducted by Astronaut Satoshi Furukawa while onboard the ISS and Kibo's Payload Flight Control Team (PL FCT) on the ground.

The results were published in npj Microgravity, part of the Nature Partner Journals on September 15, 2016.

Published research
Title: The gravity-induced re-localization of auxin efflux carrier CsPIN1 in cucumber seedlings: spaceflight experiments for immunohistochemical microscopy
Authors: Chiaki Yamazaki, Nobuharu Fujii, Yutaka Miyazawa, Motoshi Kamada, Haruo Kasahara, Ikuko Osada, Toru Shimazu, Yasuo Fusejima, Akira Higashibata, Takashi Yamazaki, Noriaki Ishioka, Hideyuki Takahashi
Journal: npj Microgravity Volume Page: npj Microgravity 2, Article number: 16030 (2016) DOI:10.1038/npjmgrav.2016.30

Read more about Prof. Takahashi's research at:
How Do Plants Grow in Microgravity?

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