NITRATE ION BARS ASSIMILATE TRANSLOCATION FROM LEAVES

Solution of potassium nitrate (0.5%) was fed under the pressure of 104 Pa to detached shoots of common flax (Linum usitatissimum L.). One hour after the beginning of nitrate feeding a photosynthetic chamber was put on the middle shoot part, through which ¹⁴CO₂ (0.03%) was blown for 3 min.
The investigation of ¹⁴C distribution throughout the shoot in 3 h after exposure of the shoot middle part to ¹⁴CO₂ showed that nitrate introduction into the apoplast led to inhibition of assimilate export.
Concurrently ¹⁴C-sucrose accumulated in the leaves, whereas in leaves of control shoots (water feeding) the relative content of ¹⁴C-sucrose after the initial increase decreased with time.
Study of leaf minor vein ultrastructure revealed that in 30 min after the beginning of nitrate feeding through the transpiration water stream swelling and clarification of mitochondria in phloem parenchyma cells were observed.
These effects were not found in companion cell-sieve element complex.
Parallel to this, in companion cells, formation of large central vacuoles was remarked.
Retrieval of organelle structures in phloem parenchyma in 1-2 h occurred on the background of enhancing morphological changes in phloem elements and companion cells.
It was supposed that the two-phase character of changes in leaf organelle ultrastructure may reflect duality of leaf cell response to nitrate ion.
Possible mechanisms of nitrate influence on sucrose transport and leaf cell ultrastructure are discussed.

International Symposium on Source-Sink Relationships in Plants

S.N. Batasheva, F.A. Abdrakhimov, G.G. Bakirova , V.I. Chikov

flax, apoplast, nitrogen nutrition, carbon metabolism, source-sink relationships, ultrastructure, phloem

https://doi.org/10.17660/ActaHortic.2009.835.8