ABSTRACT.
Membrane stability and antioxidant enzyme activity of rice seedlings in response to short-term high temperature treatments

Anoma Dongsansuk1*, Warunya Paethaisong2, and Piyada Theerakulpisut2
 
The impact of temperature on plants varies depending on the temperature level and the time of exposure.The aim of this study was evaluating different short-term temperatures to stimulate rice (Oryza sativa L.) seedling growth indicated by some physiological functions. Thus, oxidative stress, membrane stability and antioxidant activity in 'Dular', 'IR64' and 'KDML105' rice seedlings were evaluated in response to 25, 35 and 45 ºC for 30 min. At 25 ºC, 'IR64' showed higher electrolyte leakage (EL) percentages, protein contents and peroxidase (POX) activity but lower hydrogen peroxide (H2O2) content. At 35 ºC, the highest H2O2 content was found in 'KDML105' followed by 'IR64' and 'Dular'. In all rice seedlings the lowest EL was after 35 ºC exposure and activities of catalase (CAT) in 'IR64' and 'KDML105', ascorbate peroxidase (APX) in 'Dular', 'IR64' and 'KDML105' and glutathione reductase (GR) in 'Dular', 'IR64' and 'KDML105', and superoxide dismutase (SOD) in 'Dular' and 'KDML105' were stimulated by higher H2O2 production. At 45 ºC, all rice seedlings showed pronounced EL increase but reduced H2O2 production, protein content and all antioxidant enzyme activities.These results suggested that short-term temperature at 35 ºC was an optimum condition for all rice seedlings as indicated by the least membrane damage (EL ≈ 45.04%) and induction of most antioxidant enzymes (CAT, APX, GR and SOD ≈ 48.29 nmol min-1 μg-1 protein, 247.49 ng ascorbic acid min-1 μg-1 protein, 0.16 μMmin-1 μg-1 protein and 0.078 unit min-1 μg-1 protein, respectively). This temperature induced higher H2O2 production which plays a significant role in signaling molecules to stimulate protein function and antioxidant enzyme activities. While short-term 45 ºC proved to be damaging temperature for all rice seedlings because of membrane damage and decreased reactive oxygen species defense mechanism.
Keywords: Antioxidant enzyme, electrolyte leakage, heat stress, hydrogen peroxide, Oryza sativa.
1Khon Kaen University, Faculty of Agriculture, Mittraphap Road Muang, 40002, Khon Kaen, Thailand.*Corresponding author (danoma@kku.ac.th).2Khon Kaen University, Faculty of Science, Mittraphap Road Muang, 40002, Khon Kaen, Thailand.