Inoue Yuko, Moriyasu Yuji
Graduate School of Nutritional and Environmental Sciences, University of Shizuoka, 52-1 Yada, Shizuoka, 422-8526 Japan.
Plant Cell Physiol. 2006 Apr;47(4):471-80. doi: 10.1093/pcp/pcj013. Epub 2006 Jan 31.
Net degradation of cellular components occurs in plant cells cultured under starvation conditions, and autophagy contributes to the degradation of intracellular proteins. In this study, we investigated the degradation of membrane phospholipids by autophagy in cultured tobacco (Nicotiana tabacum) cells. The amounts of total phospholipids and a major phospholipid, phosphatidylcholine (PC), decreased, whereas phosphorylcholine, a degradation product of PC, increased in response to deprivation of sucrose. The addition of glycerol to the culture medium inhibited both the degradation of phospholipids and the concomitant increase of phosphorylcholine. Glycerol, however, did not block autophagy, which was assessed by the accumulation of autolysosomes in the presence of a cysteine protease inhibitor. On the other hand, 3-methyladenine, an inhibitor of autophagy, did not affect the net degradation of PC. We labeled intracellular phospholipids by loading cells with a fluorochrome-labeled fatty acid and chased it under sucrose-free conditions. Glycerol slowed down the decrease in the amount of fluorochrome-labeled PC, suggesting that it inhibits the degradation process of PC. These results show that phospholipids are degraded by mechanisms different from autophagy in tobacco cells cultured under sucrose-free conditions.
在饥饿条件下培养的植物细胞中会发生细胞成分的净降解，自噬有助于细胞内蛋白质的降解。在本研究中，我们研究了培养的烟草（Nicotiana tabacum）细胞中自噬对膜磷脂的降解作用。总磷脂和一种主要磷脂磷脂酰胆碱（PC）的量减少，而PC的降解产物磷酸胆碱则随着蔗糖的剥夺而增加。向培养基中添加甘油可抑制磷脂的降解以及磷酸胆碱的相应增加。然而，甘油并不阻断自噬，自噬通过在半胱氨酸蛋白酶抑制剂存在下自溶酶体的积累来评估。另一方面，自噬抑制剂3-甲基腺嘌呤并不影响PC的净降解。我们通过用荧光染料标记的脂肪酸加载细胞来标记细胞内磷脂，并在无蔗糖条件下追踪它。甘油减缓了荧光染料标记的PC量的减少，表明它抑制了PC的降解过程。这些结果表明，在无蔗糖条件下培养的烟草细胞中，磷脂通过与自噬不同的机制被降解。
