Nakajima Yusuke, Nara Yoshitaka, Kobayashi Akie, Sugita Tomoki, Miyazawa Yutaka, Fujii Nobuharu, Takahashi Hideyuki
Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
Faculty of Science, Yamagata University, 1-4-12 Kojirakawa-machi, Yamagata 990-8560, Japan.
J Exp Bot. 2017 Jun 15;68(13):3441-3456. doi: 10.1093/jxb/erx193.
The direction of auxin transport changes in gravistimulated roots, causing auxin accumulation in the lower side of horizontally reoriented roots. This study found that auxin was similarly involved in hydrotropism and gravitropism in rice and pea roots, but hydrotropism in Lotus japonicus roots was independent of both auxin transport and response. Application of either auxin transport inhibitors or an auxin response inhibitor decreased both hydrotropism and gravitropism in rice roots, and reduced hydrotropism in pea roots. However, Lotus roots treated with these inhibitors showed reduced gravitropism but an unaltered or an enhanced hydrotropic response. Inhibiting auxin biosynthesis substantially reduced both tropisms in rice and Lotus roots. Removing the final 0.2 mm (including the root cap) from the root tip inhibited gravitropism but not hydrotropism in rice seedling roots. These results suggested that modes of auxin involvement in hydrotropism differed between plant species. In rice roots, although auxin transport and responses were required for both gravitropism and hydrotropism, the root cap was involved in the auxin regulation of gravitropism but not hydrotropism. Hydrotropism in Lotus roots, however, may be regulated by a novel mechanism that is independent of both auxin transport and the TIR1/AFBs auxin response pathway.
在受到重力刺激的根中，生长素运输方向发生改变，导致水平重新定向的根的下侧生长素积累。本研究发现，生长素同样参与水稻和豌豆根的向水性和向重力性，但百脉根根的向水性与生长素运输和反应均无关。施用生长素运输抑制剂或生长素反应抑制剂均降低了水稻根的向水性和向重力性，并降低了豌豆根的向水性。然而，用这些抑制剂处理的百脉根根表现出向重力性降低，但向水反应未改变或增强。抑制生长素生物合成显著降低了水稻和百脉根根的两种向性。从根尖去除最后的0.2毫米（包括根冠）抑制了水稻幼苗根的向重力性，但不影响向水性。这些结果表明，生长素参与向水性的模式在不同植物物种间存在差异。在水稻根中，虽然向重力性和向水性都需要生长素运输和反应，但根冠参与生长素对向重力性的调节，而不参与向水性的调节。然而，百脉根根的向水性可能受一种独立于生长素运输和TIR1/AFB生长素反应途径的新机制调控。
