Chloroplasts contain high amounts of monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) and low levels of the anionic lipids sulfoquinovosyldiacylglycerol (SQDG), phosphatidylglycerol (PG), and glucuronosyldiacylglycerol (GlcADG). The mostly extraplastidial lipid phosphatidylcholine is found only in the outer envelope. Chloroplasts are the major site for fatty acid synthesis. In Arabidopsis, a certain proportion of glycerolipids is entirely synthesized in the chloroplast (prokaryotic lipids). Fatty acids are also exported to the endoplasmic reticulum and incorporated into lipids that are redistributed to the chloroplast (eukaryotic lipids). MGDG, DGDG, SQDG, and PG establish the thylakoid membranes and are integral constituents of the photosynthetic complexes. Phosphate deprivation induces phospholipid degradation accompanied by the increase in DGDG, SQDG, and GlcADG. During freezing and drought stress, envelope membranes are stabilized by the conversion of MGDG into oligogalactolipids. Senescence and chlorotic stress lead to lipid and chlorophyll degradation and the deposition of acyl and phytyl moieties as fatty acid phytyl esters.

中文翻译：

---

叶绿体脂质及其生物合成

叶绿体含有大量的单半乳糖二酰基甘油 (MGDG) 和二半乳糖二酰基甘油 (DGDG)，以及少量的阴离子脂质磺基奎诺糖基二酰基甘油 (SQDG)、磷脂酰甘油 (PG) 和葡萄糖醛酸二酰基甘油 (Glc)。大多数质外脂质磷脂酰胆碱仅存在于外膜中。叶绿体是脂肪酸合成的主要场所。在拟南芥中，一定比例的甘油脂完全在叶绿体（原核脂质）中合成。脂肪酸也被输出到内质网并结合到脂质中，然后再分配到叶绿体（真核脂质）。MGDG、DGDG、SQDG 和 PG 建立类囊体膜，是光合复合物的组成部分。磷酸盐缺乏诱导磷脂降解，伴随着 DGDG、SQDG 和 GlcADG 的增加。在冷冻和干旱胁迫期间，通过将 MGDG 转化为寡聚半乳糖脂来稳定包膜。衰老和褪绿应激导致脂质和叶绿素降解以及酰基和植基部分作为脂肪酸植酯的沉积。