Salt stress-induced cell death in the unicellular green alga Micrasterias denticulata

Abstract

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.

Inhibition of Target of Rapamycin Signaling and Stress Activate Autophagy in Chlamydomonas reinhardtii

“…In agreement with this hypothesis, it has been recently shown that autophagosome-like structures are generated as a response to prolonged salt stress in the unicellular green alga Micrasterias denticulata (Affenzeller et al, 2009). However, the molecular features of autophagy have never been characterized in green algae.…”

Sensitivity of Antarctic freshwater algae to salt stress assessed by fast chlorophyll fluorescence transient

“…3). It is well established for microalgae that a slight decrease in F V /F M values during salt and osmotic stress does not bring substantial limitation to photosynthetic processes within the first few hours of salinity stress (Affenzeller et al 2009). Prolonged salt stress, however, may decrease photosynthetic efficiency as shown for salt-stressed green alga Scenedesmus (Demetriou et al 2007).…”

Cajal bodies and their role in plant stress and disease responses

“…Indeed, different types of stress such as UV irradiation, osmotic stress, transcriptional inhibition, heat shock and starvation, alter structure of CBs and redistribute coilin and other CB components. 18 It has previously been reported that plant cells exposed to high salt (NaCl), can induce osmotic shock, imbalance in the cellular ion concentration and oxidative stress, 92 which are manifested by increased H 2 O 2 production, accumulation of programmed cell death (PCD) markers, cytosolic cytochrome c leakage and bleaching. 93,94 In order to determine whether coilin and/or CBs can influence such responses to abiotic stress, coilin silenced K D transgenic or non-transgenic tobacco leaf discs were treated with increased concentrations of NaCl.…”