Investigation of physiologic effects of exogenous nitric oxide (NO) application on wheat exposed to boron stress

Turkey, especially West Anatolia Region, has 61% of the boron (B) reserves of the world and B toxicity in this region is a major problem for cultivated areas. Wheat which is an important crop product in Turkey grows in this area and affected from B toxicity. Nitric oxide (NO) is an important signal molecule which plays a role in plant growth, development and various intracellular processes. In this thesis study, ameliorative effect of NO in Bezostoya (B sensitive) and Kutluk 94 (B tolerant) wheat cultivars exposed to 10 mM B stress by addition of different concentrations of a NO donor, Sodium nitroprusside (SNP). For this aim, shoot and root lengths, % electrolyte leakage (EL%), malondialdehyde (MDA), proline, hydrogen peroxide (H2O2), Glutathione peroxidase (GPX), Glutathione reductase (GR), Glutathione S-transferase (GST), Nitrate reductase (NR), low molecular weight organic acid (LMWOA), polyamine (PA), cysteine, GSH, GSSG and phytochelatine (PC2) contents and NR gene expression levels were investigated in both wheat cultivars. Reductions in shoot and root weights were determined in both wheat cultivars exposed to B stress. When 0.2 mM SNP was added to 10 mM boron concentration, shoot weight levels of Bezostoya and Kutluk 94 wheats were increased by %64 and %103 respectively. By 10 mM boron stress, H2O2 content of wheat shoots of Bezostoya and Kutluk 94 plants was increased by %102 and %70 respectively, as compared to control group. H2O2 levels of Bezostoya and Kutluk 94 wheat plants were reduced by %13 and %23 respectively, when 0.2 mM SNP was added to 10 mM boron concentration. 10 mM boron concentration caused decreased GPX activity in Bezostoya and Kutluk 94 wheat shoots by %33 and %14 respectively as compared to the control group. Enzyme activity levels were increased by %32 and %9.8 when 0.2 mM SNP was added to boron stress. NR enzyme activity levels of Bezostoya and Kutluk 94 wheat shoots were decreased by %57.43 and %25.76 respectively, under the 10 mM boron stress when compared to control group. When 0.2 mM SNP was added to 10 mM boron concentration, NR enzyme activity levels of Bezostoya and Kutluk 94 wheat shoots were increased by %220.67 and %70.33 respectively. When 10 mM boron was applied; benzoic, malic and oxalic acid levels of Bezostoya shoots decreased by %49, %36, %40 and these acid levels of Kutluk 94 shoots decreased by %19, %16, %23 respectively. Addition of 0.2 mM SNP concentration increased the benzoic, malic and oxalic acid levels of Bezostoya shoots by %118, %42, %90 and increased the acid levels by %22, %54, %39 of Kutluk 94 shoots respectively. Boron levels of the roots and shoots of Bezostoya and Kutluk 94 wheat cultivars increased after 10 mM boron addition. 0.1, 0.2 ve 0.5 mM addition of SNP to 10 mM boron stress caused reduction of boron levels of Kutluk 94 wheat shoots by %12, %40 and %32.5. Putrescine, spermidine and spermine contents of Bezostoya wheat cultivars were increased by %60.47, %27.24 and %68.57 respectively, however, in Kutluk 94 wheat cultivars there were %46.94, %24.27 and %37.39 increases in polyamine contents by 10 mM boron stress as compared to control group. Addition of SNP to boron stress environment decreased the polyamine levels which caused by stress. However, best response obtained by 0.2 mM SNP concentration. Cysteine, GSH and GSSG levels of Kutluk 94 roots exposed to 10 mM boron concentration, decreased by %38.80, %31.06 and %52.87; while these levels in Bezostoya wheat plant roots decreased by %39.60, %41.87 and %56.89. By 10 mM boron stress, PC2 levels of Bezostoya wheat shoots increased by %94.49 as compared to the control group. This increase was %80.44 in Kutluk 94 wheat shoots. When 0.1, 0.2 and 0.5 mM SNP applied to 10 mM boron stress, PC2 levels of Bezostoya wheat plant decreased by %19.02, %36.42 and %51.60; while these levels were %22.98, %39.35 and %45.08 in Kutluk 94. RT-PCR results of NR enzyme expression levels were decreased by 4.5 fold in Bezostoya wheat plant and 2.6 fold in Kutluk 94 by the addition of 10 mM boron. By 0.2 mM SNP addition, NR expressions were increased by 10.57, 6.65 fold in Bezostoya and Kutluk 94 shoots, respectively, as compared to 10 mM boron stress. These results show that NO ameliorated many metabolic processes having vital importance in wheat growth and development. Thus, exogenous NO may be used as an amendatory in wheat cultivation areas having B toxicity problem.