Additive effects of combined heat and salt stress is manifested in an enhanced sodium ions accumulation and increased membrane damage in wheat seedlings

Suchawadee Shunkao1, Maysaya Thitisaksakul2, Paweena Pongdontri2, and Piyada Theerakulpisut1*
Domestication of wheat (Triticum aestivum L.) in some tropical and subtropical regions may encounter both high temperature and soil salinity problems. This research aims to investigate how salt and heat stress combination affects growth and physiological characteristics of wheat seedlings to unravel their response mechanisms. The 14-d-old wheat seedlings of three cultivars were treated with salt stress (150 mM NaCl), heat stress (42 °C for 4 h) and combined stress (150 mM NaCl at 42 °C for 4 h). Growth and physiological parameters were monitored at 0 h, 24 h, 5 d and 10 d after stress exposure except for ion concentration, which was analyzed at 5 d post stress exposure. The combined stress inhibited shoot growth and compromised physiological parameters (e.g., relative water content [RWC], malondialdehyde [MDA], electrolyte leakage [EL], Na+ content and Na+/K+ ratio) to a greater extent than a single salt or heat stress, demonstrating additive effects particularly on plant water status and membrane stability. After 10 d exposure to the combined stress, the most sensitive cultivar 'Fahng 60' exhibited the highest reduction in shoot dry weight (34%). Moreover, 'Fhang 60' showed the lowest RWC (36%) and the highest EL (75%) while 'Samerng 2' and 'Phrae 60' had RWC of 70% and 64%, and EL of 54% and 60%, respectively. The effect was remarkably evidenced after 5 d of stress exposure, suggesting a late onset of stress injury. Together, the results demonstrated that the effect of salt and heat stress combination was additive, which could be manifested in an enhanced Na+ accumulation and membrane damage.
Keywords: Heat stress, membrane stability, salt stress, stress combination, Triticum aestivum, wheat.
1Khon Kaen University, Faculty of Science, Department of Biology, Khon Kaen 40002, Thailand.*Corresponding author (piythe@kku.ac.th).2Khon Kaen University, Faculty of Science, Department of Biochemistry, Khon Kaen 40002, Thailand.