Nitric Oxide Biosynthesis in White Poplar (Populus alba L.) Suspension Cultures Challenged with Heavy Metals

摘要

The present work reports on the generation of nitric oxide (NO) in white poplar (Populus alba L., cv.' Villafranca') cell suspension cultures exposed to copper (150 muM CUCI_2), zinc (2 mM ZnSO_4) and cadmium (200 (muM CdSO_4). Since it is currently believed that at least two distinct enzymatic pathways are responsible for NO production in plants, the response of 'Villafranca' cells to heavy metals was monitored using specific inhibitors of the nitrate-dependent pathway and a mammalian inhibitor of the L-arginine-dependent pathway. Production of nitrite (NO_2~-), as a measure of NO released in the culture medium, was quantified using the Griess reaction. Copper treatment resulted into a 3.2-fold enhancement of NO production in white poplar cell cultures. A lower increase (2-fold) was observed with the cadmium treatment. In contrast, NO production did not change in the zinc-treated cells. The use of 100 muM sodium azide and 200 muM sodium tungstate resulted into complete inhibition of NO productionwhile in cells exposed to 500 muM N~G-monomethyl-L-arginine the rate of NO generation was only partially affected. The white poplar cultures exposed to heavy metals showed the morphological hallmarks of both Programmed Cell Death and necrosis, as evidenced by Evans Blue staining. The nuclear morphology was also investigated.