Ascorbate Peroxidase of Moss Dicranum scoparium: Gene Identification and Enzyme Activity.

In the present work, the APX gene encoding ascorbate peroxidase in the moss Dicranum scoparium was for the first time cloned and sequenced, and a high homology of APX with ascorbate peroxidase genes of the mosses Grimmia pilifera and Physcomitrella patens was shown. The structure of the protein was characterized using bioinfomatics approach, and the activity of the enzyme under abiotic stresses was studied. An increase in the activity of ascorbate peroxidase was detected during desiccation of D. scoparium shoots. When exposed to heat shock, a decrease in the activity of ascorbate peroxidase correlated with a decrease in the expression of APX. Conserved elements, which were found in the structure of ascorbate peroxidase gene and protein, indicate that these sequences are conserved in the plant genome during evolution, in support of the importance of this enzyme in maintaining cellular redox status.

Nitrate reductase from Triticum aestivum leaves: regulation of activity and possible role in production of nitric oxide.

Nitrate reductase (NR) and peroxidase (POX) are important enzymes involved in the metabolism of reactive oxygen (ROS) and nitrogen species in leaves of wheat (Triticum aestivum L.) seedlings. It has been confirmed that NR activity in wheat leaves depends on the light conditions and the presence of nitrates during the cultivation of the seedlings, and it is regulated by the molybdenum cofactor and phosphorylation. In the present study, confocal microscopy and EPR spectroscopy studies showed that the addition of nitrite, a product of NR, increased the level of nitric oxide (NO). This increase was prevented by the addition of sodium azide, an inhibitor of NR. The results suggest that in wheat leaves one of the key functions of NR is the formation of the signaling NO molecule. Cultivation of green plants under conditions of prolonged (4 days) darkness, a strong stress factor for photosynthesizing cells, decreased the activity of NR. Moreover, darkness induced significant elevation of the POX activity that was prevented by the addition of nitrate to the growth medium. It is proposed that the changes in light conditions result in the competition between nitrate- and ROS-metabolizing activities of POX in leaves, and a possible interaction between NR and POX controls the levels of NO and ROS in the leaf tissue.

Production of hydrogen peroxide and nitric oxide following introduction of nitrate and nitrite into wheat leaf apoplast.

Infiltration of wheat (Triticum aestivum L.) seedling leaves with excess of nitrate, nitrite, or the NO donor sodium nitroprusside leads to increase both in content of hydroperoxide and activity of peroxidase and decrease in superoxide dismutase (SOD) activity in the leaf apoplast. Polymorphism of extracellular peroxidases and the presence of Cu/Zn-SOD have been shown in apoplast. Using an ESR assay, a considerable increase in the level of NO following infiltration of leaf tissues with nitrite has been demonstrated. These data suggest development of both oxidative and nitrosative stresses in leaves exposed to high levels of nitrate or nitrite. A possible interplay of NO and reactive oxygen species in plant cells is discussed.

[Activity of lectins of winter wheat seedlings infected with mycoplasma and treated with salicylic acid].

Changes in activity of soluble and cell wall lectins have been revealed in seedlings of winter wheat Triticum aestivum L. cultivar Mironovskaya 808 after infection with mycoplasma Acholeplasma laidlawii 118. The protective effect of salicylic acid was manifested as negating the bursts of lectin activity induced by mycoplasma infection.

[Change in lectin specificity of winter wheat seedlings in the course of infection with mycoplasms]. / Izmenenie lektinovoi aktivnosti prorostkov ozimoi pshenitsy pri infitsirovanii mikoplazmami.

The activity of soluble lectins in leaves and roots of seedlings of winter wheat (Triticum aestivum L.) cultivar Mironovskaya 808 increased 1 day and 2 days, respectively, after infection with the mycoplasma Acholeplasma laidlawii 118. Analysis of acid-soluble proteins of wheat leaves by PAGE revealed the appearance of 22- and 20-kDa polypeptides, the disappearance of a 14-kDa polypeptide, and an increase in the content of polypeptides with molecular weights of 76, 48, 25, and 18 kDa. The 18-kDa polypeptide is a subunit of wheat germ agglutinin. A change in the activity of lectins may be a nonspecific response of plants to infection with the pathogen.