Abstract
Antioxidant systems of maize root cell walls grown on different nitrogen sources were evaluated. Plants were grown on a medium containing only NO3- or the mixture of NO3-+NH4+, in a 2:1 ratio. Eleven-day old plants, two days after the initiation of lateral roots, were used for the experiments. Cell walls were isolated from lateral roots and primary root segments, 2-7 cm from tip to base, representing zones of intense or decreased growth rates, respectively. Protein content and the activity of enzymes peroxidase, malate dehydrogenase and ascorbate oxidase ionically or covalently bound to the walls, as well as cell wall phenolic content and antioxidant capacity, were determined. Cell walls of plants grown on mixed N possess more developed enzymatic antioxidant systems and lower non-enzymatic antioxidant defenses than cell walls grown on NO3-. Irrespective of N treatment, the activities of all studied enzymes and protein content were higher in cell walls of lateral compared to primary roots. Phenolic content of cell walls isolated from lateral roots was higher in NO3--grown than in mixed N grown plants. No significant differences could be observed in the isozyme patterns of cell wall peroxidases isolated from plants grown on different nutrient solution. Our results indicate that different N treatments modify the antioxidant systems of root cell walls. Treatment with NO3- resulted in an increase of constitutive phenolic content, while the combination of NO3-+NH4+ elevated the redox enzyme activities in root cell walls.
Highlights
The plant cell is enclosed by the apoplast that consists of the cell wall fibrillar structure and the intercellular liquid and gas spaces
Our results indicate that different N treatments modify the antioxidant systems of root cell walls
Plants grown on mixed N had higher protein content in comparison with nitrate grown plants in all fractions, except the ionic fraction isolated from primary roots
Summary
The plant cell is enclosed by the apoplast that consists of the cell wall fibrillar structure and the intercellular liquid and gas spaces. Apoplast, especially the root apoplast, as the exposed compartment of the plant cell, is important for all of the plant’s interactions with its environment (Zhou et al, 2011) It can detect environmental changes and stress signals and transfer them into the cell interior to trigger a whole cell response (Zhou et al, 2011). At high concentration ROS cause damage to biomolecules, whereas at low/moderate concentration they act as secondary messengers in intracellular signaling cascades that elicit various cellular responses. Cell wall enzymes, such as class III peroxidases (PODs) in their oxidative cycle, malate dehydrogenase (MDH), oxalate- and amine oxidases are related to H2O2-production necessary for polymerization pro-
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