Determination of chromium tolerance of barley (Hordeum vulgare L.) cultivars to hexavalent chromium stress

In this research, hexavalent chromium [Cr(VI)] tolerance of some barley (Hordeum vulgare L.) cultivars grown in Turkey was investigated at early seedling stage in hydroponic culture.In the first stage of this research, the effect of different Cr(VI) concentrations (0, 75, 150 and 225 µM) on shoot and root growth of eight barley cultivars (Angora, Avcı-2002, Aydanhanım, Başgül, Bülbül-89, Orza-96, Tarm-92, Zeynelağa) was examined. In general, the lengths, fresh and dry weights of shoots and roots of barley cultivars were significantly decreased with increasing Cr(VI) concentration. To determine differences in Cr(VI) tolerance of barley cultivars, the tolerance index (%), which is a function of shoot and root dry weights, was evaluated. As a result, the most Cr-tolerant barley cultivar, Zeynelağa, and the most Cr-sensitive barley cultivar, Orza-96, were determined.In the second stage of this research, the effect of Cr(VI) stress on Cr accumulation, photosynthetic pigments content, ? -aminolevulinic acid dehydratase (ALAD) activity, proline content, malondialdehyde (MDA) content, activities of some antioxidant enzymes [superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidase (POD) and catalase (CAT)] and two-dimensional (2-D) electrophoretic profiles of total soluble proteins in Cr-tolerant Zeynelağa and Cr-sensitive Orza-96 barley cultivars.1)Chromium was more accumulated in roots than shoots tissues of barley cultivars. Cr accumulation in shoot tissue of Cr-tolerant Zeynelağa was relatively higher than in Cr-sensitive Orza-96, while inverse pattern was determined in root tissue.2)The total chlorophyll (chlorophyll a + b) content of Cr-tolerant Zeynelağa was significantly increased at 75 µM Cr(VI), while it was significantly decreased at 225 µM Cr(VI) compared to control. The total chlorophyll content of Cr-sensitive Orza-96 decreased significantly with an increase in Cr(VI) concentration. The carotenoid content of Orza-96 was more affected by Cr(VI) stress compared to Zeynelağa barley cultivar. Although Cr(VI) stress reduced significantly the ALAD activity compared to control, there was no consistent difference between ALAD activities of two barley cultivars.3)Proline and MDA contents in leaf tissues of Cr-tolerant Zeynelağa and Cr-sensitive Orza-96 barley cultivars were significantly increased with an increasing Cr(VI) concentration. This effect was found more pronounced in Orza-96 than Zeynelağa.4)Cr(VI) stress caused an increase in the activities of SOD, APX, POD and CAT antioxidant enzymes in leaf tissues of Cr-tolerant Zeynelağa and Cr-sensitive Orza-96 barley cultivars. The SOD activity was found 2 times higher in Zeynelağa, while it was found 3 times higher in Orza-96 at 225 µM Cr(VI) compared to their control. The APX activity was more increased in Cr-sensitive Orza-96 than Cr-tolerant Zeynelağa cultivar. The POD activity of Cr-tolerant Zeynelağa was more induced than that of the Cr-sensitive Orza-96. However, Zeynelağa had significantly higher CAT activity than Orza-96 grown at 75 and 150 µM Cr(VI).5)In protein analysis, the total soluble proteins extracted from leaf tissues of Cr-tolerant Zeynelağa and Cr-sensitive Orza-96 subjected to control and 225 µM Cr(VI) concentration were analyzed by two-dimensional (2­D) electrophoresis (IEF/SDS­PAGE) followed by silver staining. As a result of Cr(VI) stress, low molecular weight proteins (<31.5 kDa) in leaf tissues of barley cultivars were evaluated. Two proteins (22.0 kDa, pI 6.6 ve 22.5 kDa, pI 6.9) in Zeynelağa and Orza-96 barley cultivars were newly synthesized at 225 µM Cr(VI) compared to control. The synthesis of 5 proteins (21.0-23.9 kDa, pI 6.1-7.5) were markedly increased under Cr(VI) stress in Zeynelağa barley cultivar, while synthesis of 6 proteins (21.0-23.9 kDa, pI 6.2-7.5) were markedly increased in Orza-96. However, the amounts of 15 and 16 proteins (15.6-30.1 kDa, pI 5.7-7.0) were markedly decreased in Zeynelağa and Orza-96, respectively.