Nitric oxide is involved in the regulation of melatonin-induced antioxidant responses in Catharanthus roseus roots under cadmium stress

Nitric oxide (NO) and melatonin are two biostimulant molecules in plants that not only modulate the growth and development of plants but also confer enhanced tolerance to abiotic stresses. Therefore, in this study, the interactive effects of melatonin and nitric oxide (NO) on seedlings of Catharanthus roseus (L.) G. Don was evaluated under both control and conditions of stress due to Cd. Our results show that both melatonin and sodium nitroprusside (SNP, as an NO donor) significantly improved seedling growth, which was associated with the enhanced concentration of photosynthetic pigments in both the control plants and under Cd-stress conditions. Impacts of both melatonin and SNP were more pronounced in the Cd-stressed plants than control seedlings. The Cd stress increased [H.sub.2][O.sub.2] and lipid peroxidation levels in roots. Melatonin, as well as SNP, increased endogenous NO concentration in roots. Both melatonin and SNP enhanced the concentration of proline and the activities of antioxidant enzymes (SOD, POD, APX, CAT) and lowered [H.sub.2][O.sub.2] and lipid peroxidation levels in roots of C. roseus plants under Cd stress. These melatonin-induced responses in the roots were suppressed by 4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO; a specific scavenger of NO), but inhibition of melatonin biosynthesis by p--chlorophenylalanine, could not reverse the protective effects conferred by NO. These outcomes suggest that NO, as a downstream signaling molecule, is implicated in the melatonin-promoted antioxidant responses in roots of C. roseus plants. Key words: antioxidative defense, cadmium, Catharanthus roseus, melatonin, nitric oxide. L'oxyde nitrique (NO) et la melatonine sont deux molecules biostimulantes chez les vegetaux qui, non seulement, modulent la croissance et le developpement des plantes, mais leur conferent aussi une tolerance accrue aux stress abiotiques. Ainsi, dans cette etude, l'effet interactif de la melatonine et du NO sur des semis de Catharanthus roseus (L.) G. Don a ete evalue sous des conditions contrôle et de stress provoque par le Cd. Les resultats ont montre que la melatonine et le nitroprussiate de sodium (NPS comme donneur de NO) amelioraient significativement la croissance des semis qui etait associee a une concentration accrue de pigments photosynthetiques tant en condition contrôle que sous un stress provoque par le Cd. Les impacts de la melatonine et du NPS etaient plus prononces sur les plants stresses par le Cd que les semis contrôles. Le stress provoque par le Cd augmentait les niveaux de [H.sub.2][O.sub.2] et de peroxydation lipidique dans les racines. La melatonine de meme que le NPS augmentaient la concentration de NO endogene dans les racines. La melatonine et le NPS augmentaient la concentration de proline et l'activite d'enzymes antioxydantes (SOD, POD, APX et CAT) et diminuaient les niveaux de [H.sub.2][O.sub.2] et de peroxydation lipidique dans les racines des plants de C. roseus en condition de stress provoque par le Cd. Ces reponses induites par la melatonine dans les racines etaient supprimees par le 4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxyde (cPTIO, un piegeur specifique de NO), mais l'inhibition de la biosynthese de melatonine par la p-chlorophenylalanine ne pouvait renverser les effets protecteurs conferes par le NO. Ces resultats montrent que le NO, en tant que signal en aval, est implique dans les reponses antioxydantes favorisees par la melatonine dans les racines de plants de C. roseus. [Traduit par la Redaction] Mots-cles: defense antioxydante, cadmium, Catharanthus roseus, melatonine, oxyde nitrique.
Introduction Cadmium is an extremely toxic heavy metal that enters agricultural soils, especially in developing countries, via the application of urban composts, phosphate fertilizers, metal-based pesticides, ripening agents, and waste-water [...]