The flowers of angiosperm species typically contain specialized conical cells. Although substantial progress has been achieved regarding the mechanisms underlying flower development, little is known about how petal cells achieve final conical shape. Here, we use 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) as a fluorescent pH indicator for analyzing the apoplastic pH of conical cells in Arabidopsis and show that normal conical cell expansion requires auxin signaling and apoplastic pH changes. By combining imaging analysis and genetic and pharmacological experiments, we demonstrate that apoplastic acidification and alkalization correlate with an increase and decrease in tip sharpening of conical cells, respectively. Initial expansion of conical cells is accompanied by decreased apoplastic pH, which is associated with increased auxin signaling. Decreased auxin levels, transport, or signaling abolishes cell wall acidification and causes reduced tip sharpening and heights of conical cells. These findings provide an insight into apoplastic pH regulation of conical cell expansion.

被子植物的花朵通常含有特殊的圆锥形细胞。尽管在花发育的基本机制方面已经取得了实质性进展，但人们对花瓣细胞如何达到最终圆锥形的了解却很少。在这里，我们使用8-羟基py-1,3,6-三磺酸三钠盐（HPTS）作为荧光pH指示剂，用于分析拟南芥圆锥形细胞的质外性pH值并表明正常的圆锥形细胞扩增需要生长素信号传导和质外性pH变化。通过结合成像分析以及遗传和药理实验，我们证明了质外体酸化和碱化分别与锥形细胞尖端锐化的增加和减少相关。锥形细胞的初始扩增伴随着质外体pH降低，这与生长素信号传导增强有关。生长素水平，运输或信号传导的减少消除了细胞壁的酸化，并导致尖端锐化和圆锥形细胞高度降低。这些发现提供了对锥形细胞扩增的质外pH调节的见解。