In the International Space Station experiment ‘Auxin Transport’, polar auxin transport (PAT) in shoots of etiolated maize (Zea mays L. cv. Golden Cross Bantam) grown under microgravity in space was substantially enhanced compared with those grown on Earth. To clarify the mechanism, the effects of microgravity on expression of ZmPIN1a encoding essential auxin efflux carrier and cellular localisation of its products were investigated. The amounts of ZmPIN1a mRNA in the coleoptiles and the mesocotyls in space-grown seedlings were almost the same as those in 1 g-grown seedlings, but its products were not. Immunohistochemical analysis with anti-ZmPIN1a antibody revealed a majority of ZmPIN1a localised in the basal side of plasma membranes of endodermal cells in the coleoptiles and the mesocotyls, and in the basal and lateral sides of plasma membranes in coleoptile parenchymatous cells, in which it directed towards the radial direction, but not towards the vascular bundle direction. Microgravity dramatically altered ZmPIN1a localisation in plasma membranes in coleoptile parenchymatous cells, shifting mainly towards the vascular bundle direction. These results suggest that mechanism of microgravity-enhanced PAT in maize shoots is more likely to be due to the enhanced ZmPIN1a accumulation and the altered ZmPIN1a localisation in parenchymatous cells of the coleoptiles.

在国际空间站实验“生长素运输”中，与在地球上生长的相比，在太空微重力下生长的黄化玉米（ Zea mays L. cv. Golden Cross Bantam）芽中的极性生长素运输（PAT）显着增强。为了阐明其机制，研究了微重力对编码必需生长素外排载体的ZmPIN1a表达及其产物的细胞定位的影响。太空育苗的胚芽鞘和中胚轴中ZmPIN1a mRNA的含量与1 g幼苗几乎相同，但其产物却不同。使用抗 ZmPIN1a 抗体进行的免疫组织化学分析显示，大部分 ZmPIN1a 位于胚芽鞘和中胚轴内胚层细胞质膜的基底侧，以及胚芽鞘薄壁细胞质膜的基底侧和外侧，其中它针对径向方向，但不朝向维管束方向。微重力极大地改变了ZmPIN1a在胚芽鞘薄壁细胞质膜中的定位，主要向维管束方向移动。这些结果表明，微重力增强玉米芽中 PAT 的机制更可能是由于 ZmPIN1a 积累的增强和 ZmPIN1a 在胚芽鞘薄壁细胞中定位的改变。