Ewa Gajewska

Antioxidative responses and proline level in leaves and roots of pea plants subjected to nickel stress

The activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), glutathione S-transferase (GST) as well as proline content were studied in leaves and roots of 14 day-old pea plants treated with NiSO4 (10, 100, 200 µm) for 1, 3, 6 and 9 days. Exposure of pea plants to nickel (Ni) resulted in the decrease in CuZnSOD as well as total SOD activities in both leaves and roots. The activity of APX in leaves of plants treated with 100 and 200 µm Ni increased following the 3rd day after metal application, while in roots at the end of the experiment the activity of this enzyme was significantly reduced. In both organs CAT activity generally did not change in response to Ni treatment. The activity of GST in plants exposed to high concentrations of Ni increased, more markedly in roots. In both leaves and roots after Ni application accumulation of free proline was observed, but in the case of leaves concentration of this amino acid increased earlier and to a greater extent than in roots. The results indicate that stimulation of GST activity and accumulation of proline in the tissues rather than antioxidative enzymes are involved in response of pea plants to Ni stress.

Nickel-induced changes in nitrogen metabolism in wheat shoots

The influences of 50 and 100muM Ni on growth, tissue Ni accumulation, concentrations of nitrate, ammonium, glutamate, and proline as well as the activities of nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthase (GOGAT), glutamate dehydrogenase (GDH), alanine aminotransferase (AlaAT), and aspartate aminotransferase (AspAT) were examined in the shoots of wheat seedlings cv. Zyta. Exposure of the seedlings to Ni resulted in a rapid accumulation of this metal in the shoots, which was accompanied by significant reduction in fresh weight of these organs. Tissue nitrate content decreased in response to Ni stress, while ammonium concentration increased substantially. Glutamate concentration was slightly lowered up to the 4th day of the metal exposure. In contrast, proline content increased significantly, starting from the first day after Ni treatment. NR activity showed a decline of up to 40% below the control level after Ni application; however, its activation state remained unaltered. Heavy metal treatment also resulted in a marked decrease in NiR activity, which after 7d of exposure to 100muM Ni was almost 80% lower than in the control. GS activity in wheat shoots was not influenced by Ni application. Contrary to Fd-GOGAT exhibiting reduced activity in the shoots of Ni-treated wheat seedlings, NADH-GOGAT activity was considerably enhanced, exceeding the control value even by 165%. After 7d of exposure to Ni, both NADH-GDH and NAD-GDH activities in wheat shoots were markedly induced; however, NAD-GDH activity showed a significant decrease at the early stage of the experiment. Both AlaAT and AspAT glutamate-producing activities were considerably stimulated by Ni treatment. Our results suggest that induction of NADH-GOGAT, NADH-GDH, AlaAT, and AspAT activities may compensate for the reduced Fd-GOGAT activity and serve as an alternative means of glutamate synthesis in wheat shoots under Ni stress.

Tributyltin (TBT) induces oxidative stress and modifies lipid profile in the filamentous fungus Cunninghamella elegans

To investigate the response of the tributyltin-degrading fungal strain Cunninghamella elegans to the organotin, a comparative lipidomics strategy was employed using an LC/MS-MS technique. A total of 49 lipid species were identified. Individual phospholipids were then quantified using a multiple reaction monitoring method. Tributyltin (TBT) caused a decline in the amounts of many molecular species of phosphatidylethanolamine or phosphatidylserine and an increase in the levels of phosphatidic acid, phosphatidylinositol and phosphatidylcholine. In the presence of TBT, it was observed that overall unsaturation was lower than in the control. Lipidome data were analyzed using principal component analysis, which confirmed the compositional changes in membrane lipids in response to TBT. Additionally, treatment of fungal biomass with butyltin led to a significant increase in lipid peroxidation. It is suggested that modification of the phospholipids profile and lipids peroxidation may reflect damage to mycelium caused by TBT.

Nickel-induced changes in carbon metabolism in wheat shoots.

In this study, we analyzed the toxic effect of Ni during the development of wheat shoots. Typical developmental alterations in carbon metabolism-related parameters reflecting changes associated with the transition of the seedlings from heterotrophic to autotrophic metabolism were observed in the control shoots between the 1st and the 4th days. Adverse effects of 50 and 100 μM Ni became evident starting from the 4th day of growth on the metal-containing media. We found that Ni-induced stimulation of phosphoenolpyruvate carboxylase (PEPC) activity coincided with decrease in the ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) level and with declines in net photosynthetic rate (P(N)) and stomatal conductance (g(s)). Application of Ni resulted in increased activities of several dehydrogenases: glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH), isocitrate dehydrogenase (NADP-ICDH) and malate dehydrogenase (NADH-MDH). In contrast, the activities of malic enzymes (NADP-ME and NAD-ME) decreased due to Ni stress. Treatment with Ni led to accumulation of glucose and declined concentration of sucrose as well as considerable increases in concentrations of malic and citric acids. Our results indicate that Ni stress redirects the carbon metabolism of developing wheat shoots to provide carbon skeletons for synthesis of amino acids and organic acids as well as to supply reducing power to sustain normal metabolic processes and to support defense mechanisms against oxidative stress.

Alleviation of nickel toxicity in wheat (Triticum aestivum L.) seedlings by selenium supplementation

Abstract Hydroponically grown wheat seedlings were treated with 50 μM N i and/or 15 μM Se. After a 7-day culture period, their growth parameters, N i, Se, F e, and M g contents, electrolyte leakage, photosynthetic pigment concentrations, and photochemical activity of photosystem II were determined. Exposure of wheat seedlings to N i alone resulted in reduction in the total shoot and root lengths, by 22% and 50%, respectively. Addition of Se to the N i-containing medium significantly improved the growth of these organs, compared to the seedlings subjected to N i alone. Application of Se decreased the accumulation of N i in shoots and roots and partially alleviated the N i-induced decrease in F e and M g concentations in shoots. Electrolyte leakage increased in response to N i stress, but in shoots it was diminished by Se supplementation. Exposure to N i led to a decrease in chlorophyll a and b contents and enhancement of chlorophyll a/b ratio, but did not influence the concentration of carotenoids. Enrichment of the N i-containing medium with Se significantly increased chlorophyll b content, compared to the seedlings treated with N i alone. Photochemical activity, estimated in terms of the maximum quantum yield of photosystem II , decreased in response to N i treatment but was significantly improved by simultaneous addition of Se. Results of our study suggest that alleviation of N i toxicity in wheat seedlings by Se supplementation may be related to limitation of N i uptake.

An automatic segmentation method for scanned images of wheat root systems with dark discolourations

An automatic segmentation method for scanned images of wheat root systems with dark discolourations The analysis of plant root system images plays an important role in the diagnosis of plant health state, the detection of possible diseases and growth distortions. This paper describes an initial stage of automatic analysis—the segmentation method for scanned images of Ni-treated wheat roots from hydroponic culture. The main roots of a wheat fibrous system are placed separately in the scanner view area on a high chroma background (blue or red). The first stage of the method includes the transformation of a scanned RGB image into the HCI (Hue-Chroma-Intensity) colour space and then local thresholding of the chroma component to extract a binary root image. Possible chromatic discolourations, different from background colour, are added to the roots from blue or red chroma subcomponent images after thresholding. At the second stage, dark discolourations are extracted by local fuzzy c-means clustering of an HCI intensity image within the binary root mask. Fuzzy clustering is applied in local windows around the series of sample points on roots medial axes (skeleton). The performance of the proposed method is compared with hand-labelled segmentation for a series of several root systems.

A Method for Thiarubrine Canals Extraction in Optical Coherence Tomography Images of Schkuhria Pinnata Roots

Abstract This paper presents a method of automatic recognition of thiarubrine canals in images obtained with Optical Coherence Tomography technique. The plant material was the Ri-transformed root culture of South American herb Schkuhria pinnata. The series of highresolution OCT B-scans for the study were collected using custom made experimental system operating light of 800 nm central wavelength. The method reduces significant artefacts and uses region growing approach adapted to specific features of OCT images. Results of the identification have been compared with data obtained by specialist for selected B-scans. The algorithm accuracy was also verified using a simple numeric phantom.

Trichoderma harzianum diminished oxidative stress caused by 2,4- dichlorophenoxyacetic acid (2,4-D) in wheat, with insights from lipidomics

2,4-dichlorophenoxyacetic acid (2,4-D) is among the most commonly used herbicides applied for weed control during wheat cultivation. However, its application could affect wheat growth. The present study investigates the effect of the ascomycetous fungus Trichoderma harzianum on lipid peroxidation, phospholipids, signaling lipids and phospholipase D in the seedlings of wheat (Triticum aestivum L.) treated with 2,4-D (2.5 mg L-1). In the group of 4-day-old seedlings exposed to the herbicide, increased lipid peroxidation and inhibition of growth were observed in shoots and roots. Moreover, elevated levels of oxylipins were noted. Among them, the amount of 13-HOTrE oxygenated from linolenic acid (18:3) increased the most significantly. Concurrently, in the seedlings inoculated with T. harzianum, growth was stimulated when the level of phosphatidylcholine (PC) increased. Moreover, in wheat seedlings treated with 2,4-D and T. harzianum, the level of lipid peroxidation was similar to that in the control and there was no increase observed in oxylipins and phospholipase D activity. T. harzianum might have partly alleviated the toxic effect of 2,4-D on wheat seedlings.