Investigation of tolerance mechanism against extremely high temperature of endemic and thermophyl heliotropium thermophilum plant

In order to elucidate the tolerance mechanism of the endemic and thermophil Heliotropium thermophilum to extremely high temperatures, the soil temperature was gradually increased in the laboratory conditions and the growth of plants lived at 20±5, 40±5, 60±5 and 80±5°C was observed for 10 weeks. It was seen that shoot length, shoot fresh and dry weight of plant groups living at 40±5oC were higher than other groups. Root lengths decreased with increasing temperature. Leaf water potential and stomatal conductivity decreased, thiobarbituric acid-reactive substances (TBARS), hydrogen peroxide (H2O2), superoxide (O2.-), methylglyoxal (MG) contents were insignificantly increased in plants living at 80±5oC. It was found that superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR), dehydroasorbate reductase (DHAR) activities, ascorbate (AsA) and glutathione (GSH) contents, osmolite level, ABA content and heat shock factors (HSF) gene expression also extremely increased in plants. In addition, according to western blot analysis results, it was determined that the protein contents of FeSOD, CAT, GPX, GR were parallel with enzymes activities. In line with the findings obtained, it was concluded that H. thermophilum grown in laboratory conditions is a thermophile model plant which can tolerate excessive soil temperature (80±5ºC) by stimulating the antioxidant and glyoxalase system, ABA synthesis, HSF expression levels and osmolite accumulation. Keywords: Heliotropium thermophilum, Extremely high temperature, Thermophile, Abscisic acid, Osmolite, Heat shock factor