The effect of drought stress on antioxidant enzyme activity and chlorophyll content of some advanced genotypes of lentil (Lens culinaris Medik)

Introduction Drought is one of the most important environmental stresses that influence various growth steps of the plant including germination, plantlet establishment, and production all over the world (Bacilar et al., 2007; Ben Ahmad et al., 2009). Drought stress has significantly increased in recent years because of changes in climate and increasing CO2 levels. Therefore, identification of the resistant plant varieties against drought stress in a necessity. Investigation the enabling mechanisms of plants to adapt to drought stress and protect their growth in that condition can help to select the resistant plants against drought stress to be cultivated in dry and semi-dry regions. Identification of the physiological mechanisms Lentil with the scientific name of Lens culinaris is from leguminous, one-year, long-day, self- pollinated, and diploid family (2n=14) with mean 5.28% protein. Lens culinaris is resistant to drought. Materials and methods 12 Lens culinaris genotypes (Table 1) were examined in rainfed and deficit irrigation conditions in 2015-2016 agricultural years as the split spots based on randomized complete block designs with three repetitions whose main irrigation factor was in 2 levels (rainfed and deficit) and the secondary factor of genotypes in two individual Ardabil agriculture research stations and central part of Germi city in different conditions and climates to evaluate the genetic varieties of Lens culinaris cultivars, screening the quantitative indexes of resistance against drought, and identification of the resistant cultivars against drought. All plots were simultaneously irrigated in two steps of flowering and pot filling in 10ml in deficit irrigation treatment in each region and weren’t irrigated in stress treatment or rainfed and just raining was used up to the end of harvest. Each test unit was made of 4 cultivation line with 4m length, 30cm row distance, and 133 bushes in each row. Hand weeding was done in several steps to fight with weeds. Each genotype is harvested in proportion to its physiological consideration. In this step, two edge lines and 0.5m of two middle lines end were omitted to remove edge effect. Harvest was with hand. Seed performance was determined after threshing and separating the seeds from the straw based on seed weight (gr). Physiological characteristics were measured after the plant sheathing in both rainfed and deficit irrigation types Results and discussion Table of the combined variance analysis (Table 1) showed that the significant difference was observed among proline, chlorophyll a and chlorophyll b and peroxidase enzyme values of two cultivation methods, the comparison of the mean chlorophyll a and chlorophyll b (ml/gr) of wet weight in Germi region was 0.22 and 0.079 with the significant difference from Ardabil region. The reaction of chlorophyll a and chlorophyll b to drought stress may be resulted by the plant metabolism tolerance in addition to the genetic differences against drought, and lack of the significant reaction between chlorophyll to stress can be attributed to the growth reduction in leaf. There was a significant difference in proline (μm/gr of wet weight) in Germi and Ardabil, but the amount of enzyme peroxidase (μgr of enzyme/gr of leaf) was higher in Ardabil. Proline accumulation is a popular physiological response of plants to the extensive range of bio and non-bio stresses (Geravandi et al., 2011). The maximum imposed damage by drought stress was for proline of Germi; as though, stress increased 23% of proline than Ardebil condition. In Gunes et al. (2008) research, drought stress after pollination significantly increased proline. There was a significant difference between rainfed and deficit irrigation conditions based on variance analysis. Bilesavar cultivar was considered as a control sample with the maximum peroxidase enzyme. Conclusions The results of this test show that in rainfed cultivation (drought stress) enzyme activity of the antioxidant and peroxidase, ascorbate peroxidas, proline and some characteristics for resistance plant against drought stress are increase.