Investigating the effects of flooding stress in different developmental stages on the content of antioxidant enzymes, photosynthetic pigments and grain yield of wheat

Environmental stresses are always one of the most important factors in reducing the crops yield and production. When plants encountered with flooding stress, the concentration of active oxygen species increases. Increasing these compounds can damage to several cellular metabolic responses, such as Membrane integrity, photosynthesis and photosystem II efficacy. Following these events, early leaf aging and leaf area reduction may result in the loss of carbon fixation in the plant. Plants, in order to Confront with activated oxygen species, produce antioxidants, which reduces the effects of stress. Accordingly, this research was carried out to investigate the effects of flooding stress during tillering and stem elongation in two Koohdasht and Morvarid wheat cultivars on the content of antioxidant enzymes, photosynthetic pigments and their relationship with grain yield.

To conduct this research, a factorial experiment was conducted in a completely randomized design at Gorgan University of Agricultural Sciences and Natural Resources in two years, 1394 and 1395. The experimental treatments consisted of the length of the stress period at five levels (0, 7, 14, 21 and 28 days) as the first factor, the time of flooding based on the development stage of wheat (tillering and stem elongation) as the second factor and cultivar (Koohdasht and Morvarid) were considered as the third factor. In order to apply flood stress, the pots for each treatment were somehow placed in a water-filled pond that plants stem at a height of 2 cm was below the water. After applying stress treatments, traits such as content of catalase and superoxide dismutase enzymes, ascorbic acid, chlorophyll a, chlorophyll b, cartenoied and grain yield were measured. Also, linear models were used to describe the relationships between measured traits and flooding duration.

The results of this study showed that the damages of flooding stress in wheat depend on the time of plant placement under stress, the developing stage that stress associated with it, and the type of cultivar. In general, in this study, with increasing flooding duration, traits such as content of catalase and superoxide dismutase enzymes as well as ascorbic acid content increased significantly (linearly), but the amount of photosynthetic pigments (linearly) decreased significantly. On the other hand, the rate of increase of catalase and superoxide dismutase enzymes in Koohdasht was more than Morvarid. Also, the reduction of chlorophyll a and chlorophyll b in Morvarid was higher than in Koohdasht, but the reduction of cartenoied in Koohdasht was higher than in Morvarid cultivars. Finally, with increasing the duration of flooding period, the grain yield of Koohdasht and Morvarid cultivars decreased by 3.67 and 3.20 percent per day, respectively. In both cultivars, flood stress during stem elongation stage decreased seed yield significantly more than the tillering stage.

Flooding stress has a very important role in reducing wheat grain yield. In this regard, the duration of the stress period was the most important factor affecting the yield, and then the developmental stage where the stress occurred during it and the cultivar were ranked second and third, respectively. Increased content of catalase and superoxide dismutase enzymes was associated with reducing the grain yield, as the production of these enzymes occured in response to increased active oxygen species (oxidative stress) during the flooding. Reduce the content of photosynthetic pigments also means a reduction in plant photosynthetic capacity during flooding stress. The total of these changes led to a linear decrease in grain yield in both cultivars and both developmental stages. The more severe reduction in grain yield, when flooding occurred at the stem elongation stage, indicates the greater sensitivity of this developmental stage to stress.