THE INFLUENCE OF HIGH TEMPERATURES ON SOME PHYSIOLOGICAL INDICES AND THE CONTENT OF HSP70, BiP, IRE1 GENES mRNA IN WHEAT LEAVES
The effect of high temperatures on the growth of leaves, their water content, heat tolerance and dynamics of HSP70, BiP, IRE1 genes transcription was investigated in 7-day-old seedlings of winter wheat (Triticum aestivum L.) variety Moskowskaya 39. It was found that a temperature of 33 °C causes a slight inhibition of leaf growth and some increase in the heat tolerance of their cells, but does not affect the water content of the leaf tissues, i. e. acts as a “mild” stress for the plants. The temperature of 37 °C led to a greater inhibition of leaf growth and a faster increase in the heat resistance of the plants, but did not affect the water content of leaf tissues either, i. e. acted as a “moderate” stress. Exposure to the temperature of 43 °С caused “severe” stress, which terminated leaf growth altogether, reduced the water content of leaf tissues and heat tolerance, and after 3 days resulted in the plant death. All the treatments (exposures to 33, 37 and 43 °C temperatures) led to changes in the transcription of the genes HSP70, BiP, IRE1, which encode the proteins involved in the folding of protein molecules, in the leaves of the seedlings. The nature of the change in the BiP and IRE1 mRNA levels depended on the absolute values of the temperatures used in the experiment. The analysis of changes in the transcription levels of the BiP and IRE1 genes, which are considered to be markers of endoplasmic reticulum stress (ER stress), has demonstrated that their transcription at 33 °С declined, proving the absence of ER stress. Intensification of the high-temperature exposure to 37 °C, on the contrary, leads to an accumulation of transcripts of these genes, obviously reflecting the onset of ER-stress. The temperature of 43 °С apparently also caused the development of ER-stress, since in this case the accumulation of BiP gene transcripts was initially observed, but the absence of an integral component of IRE1 probably prevented the protein quality control system from functioning properly. Based on the data obtained, it was concluded that changes in the content of HSP70, BiP and IRE1 mRNA play an important role in the development of the heat resistance of wheat plants and the protection of cells from ER stress in response to high temperatures.