铵减弱拟南芥主根向地性及其相关作用途径

向地性是决定植物根系空间构型的主要因素之一，对植物锚定和水分养分吸收至关重要。除了重力，根系向地性还受土壤环境因子影响。本文采用琼脂培养方法，研究了铵对拟南芥主根向地性反应的影响及相关作用途径。结果表明：短期内，不同浓度（NH4）2SO4均显著抑制主根向地性弯曲，但随着时间的延长，根尖向地性角度逐渐变小。而等（NH4）2SO4浓度的NaCl对主根向地性抑制效应较小，不同浓度的甘露醇不阻碍主根向地性弯曲。纽织化学染色结果显示铵处理12h以内，Col-0根尖没有淀粉体的快速降解过程，并且铵对淀粉体缺失突变体pgm—1主根向地性的影响同Col-0相似。铵处理部分恢复生长素转运载体突变体auxl-22和eir1-1主根向地性缺失。这些结果表明，铵对拟南芥主根向地性的影响独立于根尖淀粉体参与的重力感应途径。

High Ammonium Reduces Root Gravitropism in Arabidopsis and Its Corresponding Mechanism

Gravitropism is one of the important factors in determining the spatial architecture of root system and thus has a great effect on the capacity of plants to anchorage and take up water and nutrients in the soil. Besides controlled by gravity, root gravitropism is also affected by various environmental stimuli. The effects and corresponding mechanism of ammonium on root gravitropism in Arabidopsis were studied with agar medium. The results showed that all concentrations of （NH4）2SO4 used significantly inhibited root gravitropic curvature at earlier time, but the gravitropic angles became smaller along with treatment prolonging. Equal concentrations of NaCl had less inhibitory effect on root gravitropism than that of （NH4）2SO4 and various concentrations of mannitol did not inhibit root gravitropism. Histochemical staining showed that there was no rapid degradation of amyloplast in root columella cells of Col-0 under ammonium stress within 12 h period, and the starchless mutant pgm-1 displayed similar root gravitropic change pattern as that of Col-0 when treated with ammonium. However, the agravitropism of auxin transporter mutants auxl-22 and eirl-1 can be partially rescued by ammonium treatment. These results indicated that the effect of ammonium on root gravitropism might be independent of the amyloplast in gravity sensing cells.