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 Zn2+. 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.
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机译:程序性细胞死亡(PCD)是正常植物生长发育的关键因素,也可能由多种非生物和生物胁迫因素(包括盐胁迫)诱导。在本研究中,研究了盐(200 mM NaCl或200 mM KCl)和等渗山梨糖醇引起的渗透胁迫后,对理论上永生的单细胞淡水绿藻Micrasterias denticulata的形态,生化和生理反应进行了研究。氯化钾引起形态变化,例如细胞质空泡化,线粒体的极端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NaCl和KCl处理的细胞中细胞吞噬细胞通过自噬(一种PCD的特殊形式)降解。 ER衍生的双膜包裹细胞器表明了这一点。 NaCl和KCl胁迫细胞的DNA在琼脂糖凝胶上未显示梯形图案,这意味着盐胁迫的离子而非渗透成分会导致负责的核酸内切酶活化。 Zn 2 + sup>可以消除盐胁迫下的DNA阶梯化。盐胁迫后,细胞色素c从线粒体释放或caspase-3样活性均未发生。在盐和渗透胁迫开始后的5分钟内可以检测到活性氧。盐胁迫后,呼吸,光合作用和色素组成表明活跃的新陈代谢能够支持微囊藻的程序性死亡而不是坏死性细胞死亡。
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