Abstract
Canavanine (CAN) is a nonproteinogenic amino acid, and its toxicity comes from its utilization instead of arginine in many cellular processes. As presented in previous experiments, supplementation of tomato (Solanum lycopersicum L.) with CAN led to decreased nitric oxide (NO) level and induced secondary oxidative stress. CAN improved total antioxidant capacity in roots, with parallel inhibition of enzymatic antioxidants. The aim of this work was to determine how CAN-dependent limitation of NO emission and reactive oxygen species overproduction impact content, localization, and metabolism of phenolic compounds (PCs) in tomato roots. Tomato seedlings were fed with CAN (10 and 50 µM) for 24 or 72 h. Inhibition of root growth due to CAN supplementation correlated with increased concentration of total PCs; CAN (50 µM) led to the homogeneous accumulation of PCs all over the roots. CAN increased also flavonoids content in root tips. The activity of polyphenol oxidases and phenylalanine ammonia-lyase increased only after prolonged treatment with 50 µM CAN, while expressions of genes encoding these enzymes were modified variously, irrespectively of CAN dosage and duration of the culture. PCs act as the important elements of the cellular antioxidant system under oxidative stress induced by CAN.
Highlights
Reactive oxygen species (ROS), as products of incomplete reduction of oxygen, are formed in every cell of living organisms
There are some data that show that nonproteinogenic amino acids (NPAAs) act in the plant defense reaction as key mediators or effectors in response to abiotic stresses [32] or biotic stresses due to their ability to modify ROS or reactive nitrogen species (RNS) production
Induction of oxidative stress exhibited by overaccumulation of ROS and RNS in plants exposed to various NPAAs was demonstrated [24,25,33,34], the involvement of phenolic compounds (PCs) in ROS scavenging or production was not investigated
Summary
Reactive oxygen species (ROS), as products of incomplete reduction of oxygen, are formed in every cell of living organisms. In the last decades, more and more has been understood about their signaling role, pointing at an important function in modeling the plant response to environmental conditions. The induction of oxidative stress due to the overproduction of ROS is considered as a common response of plants to various stress factors [1]. The cellular antioxidant system could counteract oxidative stress by scavenging ROS. Among the enzymes controlling the concentration of ROS, the enzymes of the Halliwell-Asada cycle (glutathione reductase (GR), monodehydroascorbate reductase, dehydroascorbate reductase, ascorbate peroxidase), which determine the appropriate redox state of low-molecular antioxidants, are important. For proper action of the antioxidant system, low-molecular nonenzymatic antioxidants such as glutathione, ascorbate, tocopherols, and carotenoids are necessary [2]
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