Cotton fiber is a single-celled seed trichrome that arises from the epidermis of the ovule’s outer integument. The fiber cell displays high polar expansion and thickens but not is disrupted by cell division. Therefore, it is an ideal model for studying the growth and development of plant cells. Sphingolipids are important components of membranes and are also active molecules in cells. However, the sphingolipid profile during fiber growth and the differences in sphingolipid metabolism at different developmental stages are still unclear. In this study, we detected that there were 6 classes and 95 molecular species of sphingolipids in cotton fibers by ultrahigh performance liquid chromatography-MS/MS (UHPLC-MS/MS). Among these, the phytoceramides (PhytoCer) contained the most molecular species, and the PhytoCer content was highest, while that of sphingosine-1-phosphate (S1P) was the lowest. The content of PhytoCer, phytoceramides with hydroxylated fatty acyls (PhytoCer-OHFA), phyto-glucosylceramides (Phyto-GluCer), and glycosyl-inositol-phospho-ceramides (GIPC) was higher than that of other classes in fiber cells. With the development of fiber cells, phytosphingosine-1-phosphate (t-S1P) and PhytoCer changed greatly. The sphingolipid molecular species Ceramide (Cer) d18:1/26:1, PhytoCer t18:1/26:0, PhytoCer t18:0/26:0, PhytoCer t18:1/h20:0, PhytoCer t18:1/h26:0, PhytoCer t18:0/h26:0, and GIPC t18:0/h16:0 were significantly enriched in 10-DPA fiber cells while Cer d18:1/20:0, Cer d18:1/22:0, and GIPC t18:0/h18:0 were significantly enriched in 20-DPA fiber cells, indicating that unsaturated PhytoCer containing hydroxylated and saturated very long chain fatty acids (VLCFA) play some role in fiber cell elongation. Consistent with the content analysis results, the related genes involved in long chain base (LCB) hydroxylation and unsaturation as well as VLCFA synthesis and hydroxylation were highly expressed in rapidly elongating fiber cells. Furthermore, the exogenous application of a potent inhibitor of serine palmitoyltransferase, myriocin, severely blocked fiber cell elongation, and the exogenous application of sphingosine antagonized the inhibition of myriocin for fiber elongation. Taking these points together, we concluded that sphingolipids play crucial roles in fiber cell elongation and SCW deposition. This provides a new perspective for further studies on the regulatory mechanism of the growth and development of cotton fiber cells.

中文翻译：

---

棉纤维生长过程中的鞘脂分布表明，含有羟基化和饱和 VLCFA 的植物神经酰胺对纤维细胞伸长很重要

棉纤维是从胚珠外珠被的表皮产生的单细胞种子三色。纤维细胞表现出高极性膨胀和增厚，但不会被细胞分裂破坏。因此，它是研究植物细胞生长发育的理想模型。鞘脂是细胞膜的重要成分，也是细胞中的活性分子。然而，纤维生长过程中的鞘脂分布以及不同发育阶段鞘脂代谢的差异仍不清楚。本研究通过超高效液相色谱-MS/MS（UHPLC-MS/MS）检测棉纤维中的鞘脂类物质6大类95个分子种类。其中，植物神经酰胺（PhytoCer）分子种类最多，PhytoCer含量最高，而1-磷酸鞘氨醇（S1P）最低。PhytoCer、具有羟基化脂肪酰基的植物神经酰胺（PhytoCer-OHFA）、植物葡萄糖神经酰胺（Phyto-GluCer）和糖基肌醇磷酸神经酰胺（GIPC）在纤维细胞中的含量高于其他类别。随着纤维细胞的发育，1-磷酸植物鞘氨醇（t-S1P）和PhytoCer发生了很大变化。鞘脂分子种类神经酰胺 (Cer) d18:1/26:1、PhytoCer t18:1/26:0、PhytoCer t18:0/26:0、PhytoCer t18:1/h20:0、PhytoCer t18:1/h26： 0、PhytoCer t18:0/h26:0 和 GIPC t18:0/h16:0 在 10-DPA 纤维细胞中显着富集，而 Cer d18:1/20:0、Cer d18:1/22:0 和 GIPC t18:0/h18:0 在 20-DPA 纤维细胞中显着富集，表明含有羟基化和饱和的超长链脂肪酸 (VLCFA) 的不饱和 PhytoCer 在纤维细胞伸长中起一定作用。与含量分析结果一致，参与长链碱基（LCB）羟基化和不饱和以及VLCFA合成和羟基化的相关基因在快速伸长的纤维细胞中高表达。此外，丝氨酸棕榈酰转移酶的强效抑制剂多球菌素的外源性应用严重阻断了纤维细胞的伸长，而鞘氨醇的外源性应用拮抗了多球菌素对纤维伸长的抑制作用。综合这些观点，我们得出结论，鞘脂在纤维细胞伸长和 SCW 沉积中起着至关重要的作用。