The gravity-induced re-localization of auxin efflux carrier CsPIN1 in cucumber seedlings: spaceflight experiments for immunohistochemical microscopy

• Published in: NPJ microgravity 2016-09, Vol.2 (1), p.16030-16030, Article 16030
• Main Authors: Yamazaki, Chiaki, Fujii, Nobuharu, Miyazawa, Yutaka, Kamada, Motoshi, Kasahara, Haruo, Osada, Ikuko, Shimazu, Toru, Fusejima, Yasuo, Higashibata, Akira, Yamazaki, Takashi, Ishioka, Noriaki, Takahashi, Hideyuki
• Format: Article
• Language: English
• Subjects: 631/136; 631/449; Applied Microbiology; Biomedical and Life Sciences; Biotechnology; Classical and Continuum Physics; Immunology; Life Sciences; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics
• ISSN: 2373-8065; 2373-8065
• DOI: 10.1038/npjmgrav.2016.30

Reorientation of cucumber seedlings induces re-localization of CsPIN1 auxin efflux carriers in endodermal cells of the transition zone between hypocotyl and roots. This study examined whether the re-localization of CsPIN1 was due to the graviresponse. Immunohistochemical analysis indicated that, when cucumber seedlings were grown entirely under microgravity conditions in space, CsPIN1 in endodermal cells was mainly localized to the cell side parallel to the minor axis of the elliptic cross-section of the transition zone. However, when cucumber seeds were germinated in microgravity for 24 h and then exposed to 1 g centrifugation in a direction crosswise to the seedling axis for 2 h in space, CsPIN1 was re-localized to the bottom of endodermal cells of the transition zone. These results reveal that the localization of CsPIN1 in endodermal cells changes in response to gravity. Furthermore, our results suggest that the endodermal cell layer becomes a canal by which auxin is laterally transported from the upper to the lower flank in response to gravity. The graviresponse-regulated re-localization of CsPIN1 could be responsible for the decrease in auxin level, and thus for the suppression of peg formation, on the upper side of the transition zone in horizontally placed seedlings of cucumber. Botany: Gravity needed for proper cucumber development Simulated gravity may help to enable proper growth of food crops in space, say Japanese researchers. Cucumbers normally develop a small, specialized protuberance at the transition between the plant’s root and stem, with gravity acting as an important environmental cue for the formation of this so-called “peg”. Hideyuki Takahashi from Tohoku University, with colleagues across Japan, investigated the morphology and distribution of a protein called CsPIN1, which is involved in mediating peg development through the plant hormone auxin. The team looked at cucumber seedlings grown on the International Space Station under either microgravity or simulated gravity via centrifugation. Centrifugation directed crosswise to the axis of the seedling led to the correct localization of CsPIN1 in the plant's cells, which could facilitate proper peg formation. The findings could help future astronauts grow food in space.