Plant and Cell Physiology Advance Access originally published online on January 31, 2006
Plant and Cell Physiology 2006 47(4):471-480; doi:10.1093/pcp/pcj013
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Autophagy is not a Main Contributor to the Degradation of Phospholipids in Tobacco Cells Cultured under Sucrose Starvation Conditions
1 Graduate School of Nutritional and Environmental Sciences, University of Shizuoka, 52-1 Yada, Shizuoka, 422-8526 Japan
2 School of Food and Nutritional Sciences, University of Shizuoka, 52-1 Yada, Shizuoka, 422-8526 Japan
* Corresponding author: E-mail, moriyasu{at}u-shizuoka-ken.ac.jp; Fax, +81-54 264 5099.
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.
(Received July 19, 2005; Accepted January 19, 2006)
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