Tuz stresi altındaki bazı buğday (Triticum aestivum L.) genotiplerinde potasyum nitrat uygulamalarının etkisinin fizyolojik olarak araştırılması = Investigation of the physiological effect of potassium nitrate applications on the some wheat (Triticum aestivium L.) genotypes under salt stress

Abstract

In this study, a possible ameliorative effect of KNO3 (3 mM) on metabolic disorders in some wheat (Triticum aestivum L.) genotypes (Bayındır, Bozkır, Buhara, Meke, Selçuklu, Şehzade, Taner ve Yavuz) under salt stress (80 mM NaCl) was investigated at both germination and early seedling stage through the changes in some physiological growth parameters and activities of some antioxidant enzymes. Seeds that are used in this study were obtained from the Republic of Türkiye Ministry of Agriculture and Forestry Bahri Dagdas International Agricultural Research Institute, Konya, Türkiye. After sterilized in 5% sodium hypochlorite for 10 minutes, wheat seeds were placed between wet filter papers in plastic bags and allowed to germinate in climate chamber at 25 C under 40-45% relative humidity in a dark environment for 7 days. Filter papers were wetted with bidistilled water (control), sodium chloride solution (80 mM), potassium nitrate solution (3 mM) or 80 mM NaCl + 3 mM KNO3. On the 7th day of experiment, plants were harvested. The root and coleoptile length of barley plants were measured with a milimetric ruler. The fresh weight of roots and coleoptiles were separately weighted and plant materials were kept in an oven at 70 C for 3 days until the constant weight was reached. After that the dry weight of root and shoot of barley plants were determined. The dry weight of seeds and seed remains were weighted before the establishment and on the 7th day of the experiment, respectively. The amount of consumed seed reserves, conversion coefficient, and reserve comsumption (%) were calcılated. Total superoxide dismutase, ascorbate peroxidase, glutathione reductase, and guaiacol peroxidase activities were measured after extraction in liqiuid nitrogen of coleoptiles and centrifugation under cold (4 C) conditions. Experiments were a randomized complete block design with different independent replicates. Analysis of variance (ANOVA) was performed using SPSS 20.0 statistical software for Windows. To separate significant differences between means, LSD (least significant difference) test was used at P = 0.05 Salt stress caused significant decreases in root lenght, coleoptile lenght and total lenght in all wheat genotypes used in this study compared to the respective controls, probably due to inhibition of the mitotic activity in the apical meristems in wheat genotypes. Salt stress most negatively affected the genotype Buhara regarding root growth but the genotype Şehzade was least affected by salinity. Similarly, the genotype most negatively affected by salt stress in terms of coleoptile growth was Bayındır, and the genotype least affected was Şehzade. These results clearly showed that the wheat genotypes used in this study represented significant variations based on the genotype and organ type regarding salt tolerance. The results of this study also showed that KNO3 application did not mitigate the inhibitory effect of salt stress on root growth. However, it can be said that the genotype that responds best to KNO3 application under salinity in terms of root growth is Meke, and the genotype that gives the weakest response is Yavuz. However, it was observed that KNO3 application eliminated the inhibitory effect of salt stress on coleoptile growth in all genotypes used in this study. Accordingly, compared to roots, it can be said that coleoptiles have the capacity to respond better metabolically to KNO3 application in ameliorating the negative effects of salt stress on growth. In addition, the genotype that responded best to KNO3 application under salt stress in terms of coleoptile growth was Şehzade, while the weakest response was created by the Yavuz genotype. These results also show that the Yavuz genotype has a relatively low capacity to take up potassium ions from the growth medium through the roots and transport them to the above-ground organs. In the study, root fresh weight was not affected by salt application in Buhara and Selçuk genotypes compared to controls, but decreased in other genotypes. When evaluated in terms of root dry weight, salt stress did not affect Selçuklu and Yavuz genotypes, but caused a decrease in root dry weight in other genotypes compared to the controls. In the study, KNO3 applied to Bayındır and Bozkır genotypes under salt stress caused a significant increase in root fresh weights, which decreased due to salt stress. KNO3 application did not affect root dry weights in wheat genotypes under salt stress. Accordingly, it can be said that the KNO3 application is very effective in regulating the water relations between the Bayındır and Bozkır genotypes and the growth environment and providing salt tolerance. In addition, this effect of KNO3 differed according to organ type in wheat genotypes. The results obtained from the study showed that salt stress significantly reduced the coleoptile fresh and dry weights compared to the relevant controls, except for the coleoptile dry weight of the Yavuz genotype. Compared to roots, the improving effect of KNO3 application is more evident in terms of coleoptile fresh and dry weight in most of the genotypes subjected to salt stress. Accordingly, the applied KNO3 positively affects both water status and biomass production of coleoptiles in wheat genotypes under salt stress. As a result of salt application, the amount of reserves used in the seeds of all wheat genotypes used in the study and the rate of reserve usage decreased significantly compared to the controls. The conversion coefficient decreased in all genotypes except the Buhara and Yavuz genotypes. These results may indicate that proteolytic and glycolytic reactions in the seeds of wheat genotypes under salt stress slow down. This may be due to the decrease in the activities of the enzymes responsible for catalyzing the relevant reactions. KNO3 application to wheat genotypes under salt stress caused the conversion coefficient to increase in many genotypes but did not significantly affect the usage rate and amount of storage materials. These results show that the reactions required to catabolize storage substances into building blocks in salt-stressed seeds are accelerated by KNO3 application. Still, the use rate of these building blocks in biosynthetic reactions cannot be significantly increased by KNO3 application. APOD activity was increased by salinity in the genotypes of Bozkır and Selçuklu, whereas it was not affected in the remaining genotypes. These results showed that the rate of hydrogen peroxide accumulation in coleoptile tissues in the genotypes Bozkır and Selçuklu increased as a result of salinity. In addition, the induced APOD activity in the genotypes Bozkır and Selçuklu under salinity may indicate the accelerated rate of hydrogen peroxide detoxification. KNO3 application did not dramatically change the APOD activity in wheat genotypes under salinity except the genotypes Bayındır and Bozkır. Especially in the genotype Bozkır, the KNO3 application ameliorated the destructive effect of salinity, probably by decreasing hydrogen peroxide accumulation. GR activity was significantly increased in the genotypes Bayındır, Meke, Selçuklu, and Taner under salt stress compared to the relevant controls; but it remained unchanged in the rest of the wheat genotypes. The higher GR activity in the genotypes Bayındır, Meke, Selçuklu, and Taner under salt stress indicated that production rate of the reduced glutathione is increased. KNO3 significantly reduced GR activity in the genotypes Bayındır and Meke under salt stress. However, KNO3 did not affect GR activity in other genotypes. The reduced activity of GR in the genotypes Bayındır and Meke under salinity asa result of KNO3 application may show ameliorative effect of KNO3 on hydrogen peroxide production. GPOD activity increased significantly in the genotypes Bayındır, Bozkır, Buhara, Meke, and Selçuklu in response to salinity compared to the relevant controls. However, it remained unaffected in the rest of the genotypes. KNO3 decreased GPOD activity in the genotypes Bayındır, Bozkır, Meke and Selçuklu under salt stress; but other genotypes were not affected. These results may indicate that salt stress caused hudrogen peroxide-induced oxidative stress in some wheat genotypes. In conclusion, the results of the study showed that salt stress negatively affected physiological growth parameters in most of the wheat genotypes used in the study. It has been demonstrated that KNO3 application eliminates the growth inhibition caused by salt stress to a certain extent, especially in coleoptiles It has been shown that the rate of degradation of macromolecules increases as a result of KNO3 applications. Still, the rate of use of the resulting building blocks in biosynthetic reactions is not affected. In addition, it may be concluded that KNO3 application reduced the effects of oxidative stress and accumulation of radicals because of the decreased and/or uncahnged activities of some antioxidant enzymes.