Long-term copper (Cu2+) exposure impacts on auxin, nitric oxide (NO) metabolism and morphology of Arabidopsis thaliana L.

Plants are able to dynamically adapt to their environment by reprogramming of their growth and development. Copper (Cu²⁺) excess modifies shoot and root architecture of plants by a lesser known mechanism, therefore the involvement of a major hormone component (auxin) and a signal molecule (nitric oxide) in Cu²⁺-induced morphological responses were studied in Arabidopsis using microscopic methods. Auxin-inducible gene expression was visualized in DR5::GUS Arabidopsis and nitric oxide (NO) levels were detected by DAF-FM fluorophore in the stem and root system. Copper excess caused the inhibition of stem and root growth of Arabidopsis, during which cell elongation, division and expansion were also affected. The symptoms of stress-induced morphogenic response were found in the root system of 25???M Cu²⁺-treated plants. In both organs, the decrease of auxin-dependent gene expression was found, which can partly explain the growth inhibitions. Besides hormonal system, nitric oxide metabolism was also affected by Cu²⁺. In root tips, copper excess induced NO generation, while NO content in lateral roots was not affected by the treatments. Using nia1nia2 mutants, nitrate reductase enzyme as a putative source of Cu²⁺-induced NO was identified in Arabidopsis primary roots.