Studies on autophagy in tobacco cultured cells

植物中央液泡被认为是动物溶酶体的同源细胞器，它是酸性的，含有各种水解酶。然而，我们不知道它是否像动物溶酶体那样发挥蛋白水解室的功能。为了研究这一问题，我们利用异养生长的烟草悬浮培养细胞，研究了蔗糖饥饿诱导自噬的机制。当细胞在无蔗糖的培养基中孵育时，诱导胞内蛋白质的大量降解。这种蛋白质降解的诱导被半胱氨酸蛋白酶抑制剂如E-抑制，半胱氨酸蛋白酶抑制剂也导致许多膜结合的小泡在核周细胞质中积累。这些小泡的直径为1到6微米，其中有几个嗜奥米粒。这些结果表明，这些小泡是植物的自溶体，它们参与了蔗糖饥饿诱导的细胞蛋白质降解。因此，植物细胞可能具有与中央液泡分离的裂解细胞器。

The plant central vacuole has been thought to be an organelle homologous to animal lysosomes ; it is acidic and contains various kinds of hydrolytic enzymes. However, we do not know if it functions as a proteolytic compartment as animal lysosomes do. To investigate this question, we have studied the mechanism of autophagy induced upon sucrose starvation, using heterotrophically growing tobacco suspension culture cells.When the cells are incubated in sucrose-free culture medium, bulk degradation of intracellular protein is induced. This induction of protein degradation is inhibited by cysteine protease inhibitors such as E-64, which also cause accumulation of many membrane-bound vesicles in the perinuclear cytoplasm. These vesicles are 1 to 6 micrometers in diameter and have several osmiophilic particles within them. They are acidic compartments and contain acid phosphatase.These results suggest that the vesicles are plant autolysosomes and that they contribute to cellular protein degradation which is induced by sucrose starvation. Thus plant cells are likely to possess a lytic organelle separate from the central vacuole.