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  • Author: Elżbieta Kuźniak x
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Open access

Joanna Chojak, Elżbieta Kuźniak, Urszula Świercz, Joanna Sekulska-Nalewajko and Jarosław Gocławski

Summary

We studied the effects of sequentially applied salt stress and Pseudomonas syringae pv lachrymans (Psl) infection in cucumber (Cucumis sativus L.). Infection development, shoot and root growth potential, the concentrations of chlorophyll and proline as well as electrolyte leakage, lipid peroxidation and H2O2 production were determined. Cucumber plants were first exposed to salt stress and irrigated for seven days with 50 or 100 mM NaCl and thereafter inoculated by Psl. Abiotic stress compromised the defence response to pathogen and disease severity was the highest in 100 mM NaCl-treated plants. The reduced performance of salinized plants under biotic stress could be related to salt stressinduced plant growth inhibition with leaf expansion being the most sensitive to salinity, decreased chlorophyll content, increased electrolyte leakage and prolonged H2O2 accumulation in leaves implying perturbations in redox homeostasis. The response of NaCl-treated and control plants to bacterial infection differed in terms of H2O2 generation and lipid peroxidation. This study confirmed that proline is an important component of local and systemic responses to salt stress and infection. The results contribute to our knowledge of the nature of plant response to a combination of abiotic and biotic stresses

Open access

Katarzyna Bergier, Elżbieta Kuźniak, Marzena Wielanek, Aleksandra Królicka and Maria Skłodowska

We compared the biochemical profiles of Physalis ixocarpa hairy roots transformed with Agrobacterium rhizogenes ATCC and A4 strains with non-transformed root cultures. The studied clones of A4- and ATCC-induced hairy roots differed significantly; the latter showed greater growth potential and greater ability to produce secondary metabolites (tropane alkaloids) and to biotransform hydroquinone to arbutin. We compared glucose content, alanine and aspartate aminotransferase activity, and L-phenylalanine ammonia-lyase activity. We analyzed markers of prooxidant/antioxidant homeostasis: catalase, ascorbate peroxidase, oxidase, glutathione peroxidase and transferase activity, and the levels of ascorbate, glutathione, tocopherol and lipid peroxidation. We found that transformation induced strain-specific regulation, including regulation based on redox signals, determining the rate of allocation of carbon and nitrogen resources to secondary metabolism pathways. Our results provide evidence that A. rhizogenes strain-specific modification of primary metabolites contributed to regulation of secondary metabolism and could determine the ability of P. ixocarpa hairy root clones to produce tropane alkaloids and to convert exogenously applied hydroquinone to pharmaceutically valuable arbutin. Of the studied parameters, glucose content, L-phenylalanine ammonia-lyase activity and alanine aminotransferases activity may be indicators of the secondary metabolite-producing potential of different P. ixocarpa hairy root clones.

Open access

Jarosław Gocławski, Joanna Sekulska-Nalewajko and Elżbieta Kuźniak

Abstract

The increased production of Reactive Oxygen Species (ROS) in plant leaf tissues is a hallmark of a plant’s reaction to various environmental stresses. This paper describes an automatic segmentation method for scanned images of cucurbits leaves stained to visualise ROS accumulation sites featured by specific colour hues and intensities. The leaves placed separately in the scanner view field on a colour background are extracted by thresholding in the RGB colour space, then cleaned from petioles to obtain a leaf blade mask. The second stage of the method consists in the classification of within mask pixels in a hue-saturation plane using two classes, determined by leaf regions with and without colour products of the ROS reaction. At this stage a two-layer, hybrid artificial neural network is applied with the first layer as a self-organising Kohonen type network and a linear perceptron output layer (counter propagation network type). The WTA-based, fast competitive learning of the first layer was improved to increase clustering reliability. Widrow–Hoff supervised training used at the output layer utilises manually labelled patterns prepared from training images. The generalisation ability of the network model has been verified by K-fold cross-validation. The method significantly accelerates the measurement of leaf regions containing the ROS reaction colour products and improves measurement accuracy.