title: Salicylic acid-mediated potentiation of Hsp70 induction correlates with reduced apoptosis in tobacco protoplasts.
abstract: BACKGROUND
  Elevated temperatures jeopardize plant disease resistance, as mediated by salicylic acid (SA). SA potentiates heat-induced expression of the 70-kDa heat shock protein (Hsp70) in tomato cells. In mammalian cells, Hsp70 suppresses apoptosis. We hypothesized that potentiation of heat-induced Hsp70 by SA contributes to a reduction in apoptosis in tobacco protoplasts.
  
  
  METHODS
  Tobacco protoplasts (Nicotiana tabacum) were exposed to SA (70 microM) at normal temperatures or in combination with heat shock. Hsp70/Hsc70 accumulation and phosphatidylserine (PS) exposure, DNA fragmentation, as well as loss of mitochondrial membrane potential were quantified by flow cytometry.
  
  
  CONCLUSIONS
  SA at normal temperatures did not influence Hsp70/Hsc70 accumulation, but were found to induce apoptosis. In contrast, SA in combination with HS potentiated heat-induced Hsp70/Hsc70 accumulation in tobacco protoplasts that correlated negatively with apoptosis, illustrated by decreased PS exposure and DNA fragmentation and enhanced mitochondrial membrane potential. We propose that this correlation supports a possible role for apoptosis suppression by Hsp70 under elevated temperatures during pathogen infection.
authors.affiliation: Biochemistry Division, Department of Chemistry and Biochemistry, Rand Afrikaans University, Auckland Park, South Africa.
authors.forename: Marianne J
authors.initials: MJ
authors.lastname: Cronjé
authors.forename: Iona E
authors.initials: IE
authors.lastname: Weir
authors.forename: Liza
authors.initials: L
authors.lastname: Bornman
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D053938:DNA Fragmentation; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006358:Hot Temperature; D008564:Membrane Potentials / Q000502:physiology; D008928:Mitochondria / Q000378:metabolism; D010718:Phosphatidylserines / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D011523:Protoplasts / Q000187:drug effects* / Q000378:metabolism; D020156:Salicylic Acid / Q000378:metabolism* / Q000494:pharmacology*; D014026:Nicotiana / Q000166:cytology / Q000502:physiology*
chemical_list: D018840:HSP70 Heat-Shock Proteins; D010718:Phosphatidylserines; D010940:Plant Proteins; D020156:Salicylic Acid