Journal Article

Nitric Oxide Generation in Vicia faba Phloem Cells Reveals Them to Be Sensitive Detectors as Well as Possible Systemic Transducers of Stress Signals

Furch, Alexandra C. U., Kogel, Karl-Heinz, Gaupels, Frank, Mur, Luis A. J., Will, Torsten, van Bel, Aart J. E.

2008

Overview

Vascular tissue was recently shown to be capable of producing nitric oxide (NO), but the production sites and sources were not precisely determined. Here, NO synthesis was analysed in the phloem of Vicia faba in response to stress-and pathogen defence-related compounds. The chemical stimuli were added to shallow paradermal cortical cuts in the main veins of leaves attached to intact plants. NO production in the bare-lying phloem area was visualized by real-time confocal laser scanning microscopy using the NO-specific fluorochrome 4,5-diaminofluorescein diacetate (DAF-2 DA). Abundant NO generation in companion cells was induced by 500 pm salicylic acid (SA) and 10 μm hydrogen peroxide (H₂O₂), but the fungal elicitor chitooctaose was much less effective. Phloem NO production was found to be dependent on Ca²⁺ and mitochondrial electron transport and pharmacological approaches found evidence for activity of a plant NO synthase but not a nitrate reductase. DAF fluorescence increased most strongly in companion cells and was occasionally observed in phloem parenchyma cells. Significantly, accumulation of NO in sieve elements could be demonstrated. These findings suggest that the phloem perceives and produces stress-related signals and that one mechanism of distal signalling involves the production and transport of NO in the phloem.

• Publisher: Blackwell Publishing,Blackwell Publishing Ltd
• Subject: biosynthesis / calcium / confocal laser scanning microscopy / cytology / detectors / Dose-Response Relationship, Drug / drug effects / electron transfer / elicitors / Fluorescence / fluorescent dyes / fungi / Hydrogen / hydrogen peroxide / hydrogen peroxide (H2O2) / Hydrogen Peroxide - pharmacology / leaves / metabolism / nitrate reductase / nitric oxide / nitric oxide (NO) / Nitric Oxide - biosynthesis / nitric oxide synthase / Nitric Oxide Synthase - metabolism / Oligosaccharides / Oligosaccharides - pharmacology / Oxidative stress / Oxides / parenchyma (plant tissue) / pathogen resistance / pathogens / Peroxides / pharmacology / Phloem / Phloem - cytology / Phloem - metabolism / Plant physiology / Plant tissues / Plants / salicylic acid / Salicylic Acid - pharmacology / sieve elements / Sieve tubes / Signal Transduction / stress / systemic signalling / Vicia faba / Vicia faba - cytology / Vicia faba - drug effects / Vicia faba - metabolism