Effect of Spermine Treatment on the Functioning of Thellungiella salsuginea Antioxidant System

The effect of spermine (Spm) treatment on the content of polyamines (PAs) and activities of anti oxidant enzymes in the roots and leaves of Thellungiella salsuginea (Pall.) O.E. Schulz plants grown under optimal conditions were studied. The genes encoding three forms of ascorbate peroxidase (APX; APX1, APX2, and APX4) and genes of key enzymes of proline metabolism (Pro, P5CS1, 1P5CD) were identified, and their expression intensity was measured. Sixdayold plants were treated with Spm (1 and 2 mM) and with the inhibitor of polyamine oxidase (PAO) activity, N,N(2hydroxyethyl)hydrazine (HEH, 1 and 2 mM) sep arately or in combination by adding these compounds to nutrient medium. Roots and leaves responded dif ferently to Spm treatment. In the leaves, the content of PAs reduced due to a decreased in the spermidine (Spd) content, whereas in the roots the total pool of PAs increased due to putrescine (Put) and Spd accumu lation. Treatment with Spm activated PAO in the roots but not in the leaves; HEH removed this increase, but the intercellular Spm concentration was not substantially changed. It was suggested that treatment with Spm suppressed the biosynthesis of intracellular Spm and, on the other hand, stimulated the reverse conversion of Spm into Spd and further into Put due to the activation of one of the PAO isoforms. Plant treatment with Spm was not accompanied by a noticeable activation enzymes degrading hydrogen peroxide in the roots: APX, (except of peroxidase II), and catalase. However, the activity of Cu/ZnSOD doubled and the activity of MnSOD reduced. In the leaves, slight activation of peroxidases I and III, the inhibition of Cu/Zn and MnSOD, differential changes in the timecoursed of gene expression of three APX isoforms, and acti vated gene expression of key enzymes of Pro metabolism were observed. At the same time, the level of MDA did not increase either in the leaves or in the roots. This indicates that treatment of Th. salsuginea plants with Spm under optimal growing conditions did not enhance ROS generation and did not manifest prooxidant properties.