Formation of cytoplasmic heat shock granules in tomato cell cultures and leaves.

Abstract

Biochemical and electron microscopic analyses of heat-shocked suspension cultures of Peruvian tomato (Lycopersicon peruvianum) revealed that a considerable part of the dominant small heat shock proteins (hsps) with an Mr of -17,000 are structural proteins of newly forming granular aggregates in the cytoplasm (heat shock granules), whose formation strictly depends on heat shock conditions (37 to 40°C) and the presence or simultaneous synthesis of hsps. However, under certain conditions, e.g., in preinduced cultures maintained at 25°C, hsps also accumulate as soluble proteins without concomitant assembly of heat shock granules. Similar heat shock-induced cytoplasmic aggregates were also observed in other cell cultures and heat-shocked tomato leaves and corn coleoptiles.All types of eucaryotic organisms respond to supraoptimal temperatures by synthesis of heat shock proteins (hsps) (1,5,23,24), which are evidently essential for heat shock survival and recovery (2,14,16,20,23

Evidence That Ternary Complex (eIF2-GTP-tRNAiMet)–Deficient Preinitiation Complexes Are Core Constituents of Mammalian Stress Granules

“…By sequestering untranslated mRNA from the translational machinery, SGs have been proposed to determine the duration of stress-induced translational arrest (Kedersha et al, 1999). Because heat-shock transcripts are excluded from the SGs found in heat-shocked plant cells (Nover et al, 1983), this mechanism might explain, in part, the preferential translation of heat-shock transcripts in stressed cells.…”

“…Stress granules (SGs) are discrete cytoplasmic foci at which untranslated mRNAs accumulate in cells subjected to environmental stress (Nover et al, 1983(Nover et al, , 1989Scharf et al, 1998;Kedersha et al, 1999Kedersha et al, , 2000. In mammalian cells, the assembly of SGs is initiated by the phosphorylation of eIF2␣ (Kedersha et al, 1999), a translation initiation factor that loads the initiator tRNA onto the small ribosomal subunit (reviewed by Berlanga et al, 1998;Gray and Wickens, 1998).…”

Heat shock proteins: the search for functions.

“…(d) HSP70 changes from a "soluble" cytosolic to a nuclear-cytoskeletal fraction after a heat shock, and this insoluble form is solubilized by an ATP-dependent reaction (11,41). (e) The small HSPs form large insoluble aggregates in a perinuclear region of the cell after prolonged heat shock (11,55), but these aggregates dissociate during cell recovery.…”

The Identification of a Heat-Shock Protein Complex in Chloroplasts of Barley Leaves

“…Despite the high degree of sequence homology between RBP and HSP60 proteins, however, it has yet to be shown that the synthesis of RBP increases significantly during heat shock. In plant cells experiencing heat stress, many of the induced cytoplasmic HSPs aggregate into morphologically unique structures known as HSGs (21,22,[25][26][27]. HSGs appear in the cytoplasm as dense granular complexes under the electron microscope (21, 27) but exist as smaller-sized precursor particles under normal conditions.…”

“…In plant cells experiencing heat stress, many of the induced cytoplasmic HSPs aggregate into morphologically unique structures known as HSGs (21,22,(25)(26)(27). HSGs appear in the cytoplasm as dense granular complexes under the electron microscope (21,27) but exist as smaller-sized precursor particles under normal conditions.…”