title: Comparative studies of thermotolerance: different modes of heat acclimation between tolerant and intolerant aquatic plants of the genus Potamogeton.
abstract: OBJECTIVE
  Molecular-based studies of thermotolerance have rarely been performed on wild plants, although this trait is critical for summer survival. Here, we focused on thermotolerance and expression of heat shock transcription factor A2 (HSFA2) and its putative target gene (chloroplast-localized small heat shock protein, CP-sHSP) in two allied aquatic species of the genus Potamogeton (pondweeds) that differ in survival on land.
  
  
  METHODS
  The degree of thermotolerance was examined using a chlorophyll bioassay to assess heat injury in plants cultivated under non- and heat-acclimation conditions. Potamogeton HSFA2 and CP-sHSP genes were identified and their heat-induction was quantified by real-time PCR.
  
  
  RESULTS
  The inhibition of chlorophyll accumulation after heat stress showed that Potamogeton malaianus had a higher basal thermotolerance and developed acquired thermotolerance, whereas Potamogeton perfoliatus was heat sensitive and unable to acquire thermotolerance. We found two duplicated HSFA2 and CP-sHSP genes in each species. These genes were induced by heat shock in P. malaianus, while one HSFA2a gene was not induced in P. perfoliatus. In non-heat-acclimated plants, transcript levels of HSFA2 and CP-sHSP were transiently elevated after heat shock. In heat-acclimated plants, transcripts were continuously induced during sublethal heat shock in P. malaianus, but not in P. perfoliatus. Instead, the minimum threshold temperature for heat induction of the CP-sHSP genes was elevated in P. perfoliatus.
  
  
  CONCLUSIONS
  Our comparative study of thermotolerance showed that heat acclimation leads to species-specific changes in heat response. The development of acquired thermotolerance is beneficial for survival at extreme temperatures. However, the loss of acquired thermotolerance and plasticity in the minimum threshold temperature of heat response may be favourable for plants growing in moderate habitats with limited daily and seasonal temperature fluctuations.
authors.affiliation: Department of Biology, Graduate School of Science, Kobe University, Rokkodai, Nada, Japan.
authors.forename: Momoe
authors.initials: M
authors.lastname: Amano
authors.forename: Satoko
authors.initials: S
authors.lastname: Iida
authors.forename: Keiko
authors.initials: K
authors.lastname: Kosuge
mesh_terms: D000064:Acclimatization / Q000502:physiology; D002736:Chloroplasts / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D006360:Heat-Shock Proteins / Q000096:biosynthesis* / Q000235:genetics; D018869:Heat-Shock Response / Q000235:genetics / Q000502:physiology*; D006358:Hot Temperature; D007564:Japan; D031821:Potamogetonaceae / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014157:Transcription Factors
chemical_list: D006360:Heat-Shock Proteins; D014157:Transcription Factors