The shoots of fireweed (Chamerion angustifolium (L.) Holub) and common flax (Linum usitatissimum L.) were infused with 50 mM KNO3 solution to compare the influence of nitrate on photosynthesis and assimilate export from leaves in plants with the symplastic and apoplastic phloem loading, respectively. The infusion of nitrate in the shoots of both plant species lowered 14CO2 fixation and enhanced the assimilate transport in the upward direction. Irrespective of the phloem loading type, the incorporation of 14C into sucrose decreased in nitrate-treated seedlings exposed to assimilation for short (3 min) periods. However, when shoots were sampled 3 h after 14CO2 fixation, the content of 14C-labeled sucrose was higher in treated plants than in control seedlings infused with water. In fireweed, in contrast to flax, a similar temporal pattern was also characteristic for 14C incorporation into oligosaccharides. Within 3 h after nitrate infusion into the fireweed apoplast, the mitochondria and the cell vacuolar system underwent ultrastructural changes indicative of the increase in cytosolic osmotic pressure. At the same time, we observed accumulation of fibrillar inclusions in cell vacuoles of vascular bundles. It is concluded that the mechanisms of nitrate influence on photosynthesis and sugar export in leaves of symplastic and apoplastic plants are similar to a certain extent and involve the blocking of pores in phloem tubes, initiated by the NO-signaling system.
Russian Journal of Plant Physiology – Springer Journals
Published: May 3, 2011
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