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1.  Involvement of nitric oxide and auxin in signal transduction of copper-induced morphological responses in Arabidopsis seedlings 
Annals of Botany  2011;108(3):449-457.
Background and Aims
Plants are able to adapt to the environment dynamically through regulation of their growth and development. Excess copper (Cu2+), a toxic heavy metal, induces morphological alterations in plant organs; however, the underlying mechanisms are still unclear. With this in mind, the multiple signalling functions of nitric oxide (NO) in plant cells and its possible regulatory role and relationship with auxin were examined during Cu2+-induced morphological responses.
Methods
Endogenous auxin distribution was determined by microscopic observation of X-Gluc-stained DR5::GUS arabidopsis, and the levels of NO, superoxide and peroxynitrite were detected by fluorescence microscopy. As well as wild-type, NO-overproducer (nox1) and -deficient (nia1nia2 and nia1nia2noa1-2) arabidopsis plants were used.
Key Results
Cu2+ at a concentration of 50 µm resulted in a large reduction in cotyledon area and hypocotyl and primary root lengths, accompanied by an increase in auxin levels. In cotyledons, a low Cu2+ concentration promoted NO accumulation, which was arrested by nitric oxide synthase or nitrate reductase inhibitors. The 5-μm Cu2+-induced NO synthesis was not detectable in nia1nia2 or nia1nia2noa1-2 plants. In roots, Cu2+ caused a decrease of the NO level which was not associated with superoxide and peroxynitrite formation. Inhibition of auxin transport resulted in an increase in NO levels, while exogenous application of an NO donor reduced DR5::GUS expression. The elongation processes of nox1 were not sensitive to Cu2+, but NO-deficient plants showed diverse growth responses.
Conclusions
In plant organs, Cu2+ excess results in severe morphological responses during which the endogenous hormonal balance and signal transduction are affected. Auxin and NO negatively regulate each other's level and NO intensifies the metal-induced cotyledon expansion, but mitigates elongation processes under Cu2+ exposure.
doi:10.1093/aob/mcr176
PMCID: PMC3158692  PMID: 21856638
Arabidopsis thaliana; auxin; copper; morphological responses; nitric oxide
2.  Involvement of nitrate reductase in auxin-induced NO synthesis 
Plant Signaling & Behavior  2008;3(11):972-973.
It is well known for a long time, that nitric oxide (NO) functions in variable physiological and developmental processes in plants, however the source of this signaling molecule in the diverse plant responses is very obscure.1 Although existance of nitric oxide sythase (NOS) in plants is still questionable, LNMMA (NG-monomethyl-L-arginine)-sensitive NO generation was observed in different plant species.2,3 In addition, nitrate reductase (NR) is confirmed to have a major role as source of NO.4,5 This multifaced molecule acts also in auxin-induced lateral root (LR) formation, since exogenous auxin enhanced NO levels in regions of Arabidopsis LR initiatives. Our results pointed out the involvement of nitrate reductase enzyme in auxin-induced NO formation. In this addendum, we speculate on auxin-induced NO production in lateral root primordial formation.
PMCID: PMC2633746  PMID: 19704423
atnoa1; indole-3-butyric acid; nia1; nia2 double mutant; nitric oxide

Results 1-2 (2)