Affenzeller Matthias Josef, Darehshouri Anza, Andosch Ancuela, Lütz Cornelius, Lütz-Meindl Ursula
Plant Physiology Division, Cell Biology Department, University of Salzburg, Hellbrunnerstrasse 34, 5020 Salzburg, Austria.
J Exp Bot. 2009;60(3):939-54. doi: 10.1093/jxb/ern348. Epub 2009 Feb 12.
Programmed cell death (PCD) is a key element in normal plant growth and development which may also be induced by various abiotic and biotic stress factors including salt stress. In the present study, morphological, biochemical, and physiological responses of the theoretically immortal unicellular freshwater green alga Micrasterias denticulata were examined after salt (200 mM NaCl or 200 mM KCl) and osmotic stress induced by iso-osmotic sorbitol. KCl caused morphological changes such as cytoplasmic vacuolization, extreme deformation of mitochondria, and ultrastructural changes of Golgi and ER. However, prolonged salt stress (24 h) led to the degradation of organelles by autophagy, a special form of PCD, both in NaCl- and KCl-treated cells. This was indicated by the enclosure of organelles by ER-derived double membranes. DNA of NaCl- and KCl-stressed cells but not of sorbitol-treated cells showed a ladder-like pattern on agarose gel, which means that the ionic rather than the osmotic component of salt stress leads to the activation of the responsible endonuclease. DNA laddering during salt stress could be abrogated by addition of Zn(2+). Neither cytochrome c release from mitochondria nor increase in caspase-3-like activity occurred after salt stress. Reactive oxygen species could be detected within 5 min after the onset of salt and osmotic stress. Respiration, photosynthetic activity, and pigment composition indicated an active metabolism which supports programmed rather than necrotic cell death in Micrasterias after salt stress.
程序性细胞死亡（PCD）是植物正常生长发育的关键因素，它也可能由各种非生物和生物胁迫因素诱导，包括盐胁迫。在本研究中，检测了理论上永生的单细胞淡水绿藻齿缘微口藻在盐胁迫（200 mM NaCl或200 mM KCl）和等渗山梨醇诱导的渗透胁迫后的形态、生化和生理反应。KCl导致了形态变化，如细胞质空泡化、线粒体极度变形以及高尔基体和内质网的超微结构变化。然而，长时间的盐胁迫（24小时）导致了通过自噬（一种特殊形式的PCD）对细胞器的降解，在NaCl和KCl处理的细胞中均如此。这通过内质网衍生的双膜包裹细胞器得以表明。NaCl和KCl胁迫细胞的DNA而非山梨醇处理细胞的DNA在琼脂糖凝胶上呈现出梯状模式，这意味着盐胁迫的离子成分而非渗透成分导致了负责的核酸内切酶的激活。盐胁迫期间的DNA梯状条带可通过添加Zn(2+)消除。盐胁迫后，线粒体中细胞色素c未释放，caspase-3样活性也未增加。在盐胁迫和渗透胁迫开始后5分钟内即可检测到活性氧。呼吸作用、光合活性和色素组成表明存在活跃的代谢，这支持了齿缘微口藻在盐胁迫后发生程序性而非坏死性细胞死亡。
