Effects of Heat Stress after Anthesis on PSII Photochemical Efficiency and the Antioxidant Activity of Wheat Cultivars

Mahroo Mojtabaie Zmani,Mousa Meskarbashee,Majid Nabipour

doi:10.15832/ankutbd.446391

Abstract

This study was conducted to investigate the effects of heat stress after anthesis on the performance of Photosystem II (PSII) and the enzymatic activity of catalase and ascorbate peroxidase. Two treatments-normal and heat stress-were conducted on four bread wheat cultivars from 7 days after anthesis until maturity. Heat stress led to an acceleration of chlorosis, reduced the efficiency of electron transfer and increased concentrations of malondialdehyde; however, the level of susceptibility varied depending on the cultivars. On the 10th day of heat stress, reductions in fluorescence parameters, depending on the cultivar, were 6.9 to 18.9% for Fv/Fm, 9 to 21% for ΦPSII and 8.3 to 19.4% for F’v/F’m compared to normal conditions. Catalase activity increased after initial exposure to heat stress. However, after 10 days of treatment, catalase activity increased in the Chamran and Aflak cultivars by 32% and 45%, respectively, but it did not change in the Dez cultivar and decreased 22% in Darab2. Ascorbate peroxidase activity decreased in two treatments, while the amount of reduction in heat stress treatment was more than the normal treatment. The highest levels of enzymatic activity were observed in Chamran under heat stress conditions, whereas Darab2 and Dez showed the lowest activity of the enzymes. Chlorophyll fluorescence parameters and chlorophyll index had a significant negative correlation with the levels of malondialdehyde; however, they had a significant positive correlation with the antioxidant activity.

Highlights

Heat stress during the grain filling period is one of the most important abiotic factors limiting wheat yields (Triticum aestivum L.)
Several studies have shown that the inhibition of Rubisco activity directly leads to the inhibition of CO2 assimilation under moderate heat stress (Salvucci & Crafts-Brander 2004), while under severe heat stress, the dissociation of the oxygen evolving complex, inhibition of electron transfer from quinone A to quinone B and general damage to the reaction centres of Photosystem II (PSII) lead to the inhibition of photosynthesis (Harding et al 1990; Allakhverdiev et al 2008)
Maximum reductions in grain yield were observed in the Darab2 and Aflak cultivars, while the least amount of reductions in yields was observed in Dez and Chamran (Table 1)

Summary

Introduction

Heat stress during the grain filling period is one of the most important abiotic factors limiting wheat yields (Triticum aestivum L.). Decrease in photosynthetic activity leads to reductions in wheat growth (Harding et al 1990). Reduction of photosynthesis at high temperatures occurs due to the impairment of the structure and function of chloroplasts and decrease in chlorophyll content (Xu et al 1995). Degradation of proteins and membranes caused by heat stress leads to an increase in the production of reactive oxygen species (ROS) and this is followed by oxidative stress (Sairam et al 2000). Heat stress can disrupt this balance (either by increasing the production of activated oxygen species or reducing the quenching ability of ROS in the cell) and reinforce lipid peroxidation of cell membranes (Liu & Huang 2000; Allakhverdiev et al 2008)

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Results

Conclusion