[Dynamics of ultrastructure changes in sheet plate fiber flax with braking transport assimilate by nitrate-anion]

Changes in leaf mesophyll cell ultrastructure under nitrate feeding into the apoplast of common flax (Linum usitatissimum L.) in the form of 50 mM KNO3 solution were studied. In 30 min after the beginning of nitrate feeding through the transpiration water stream, swelling of mitochondrial and microbodies, clarification of their matrices, and curling of dictyosome discs into annular structures were observed. These events characterized symplastic domain formed by mesophyll, bundle sheath and phloem parenchyma cells, and were not found in companion cell-sieve element complex. Simultaneously, formation of large central vacuoles in companion cells was noted. Restoration of organelle structures in assimilating cells and phloem parenchyma in 1-2 h after treatment was accompanied by enhancement of morphological changes in phloem elements and companion cells and signs of plasmolysis in the mesophyll cells. It was supposed that the two-phase character of changes in leaf organelle ultrastructure and photosynthesis might reflect duality of leaf cell response to nitrate ion. The rapid alterations of the structure can be coupled with direct influence of the anion on cell metabolism and(or) with signal-regulatory functions of oxidized nitrogen forms, while the slower ones reflect the result of suppression of photoassimilate export from leaves by the anion.