Nitric oxide counteracts cytotoxic processes mediated by reactive oxygen species in plant tissues

BELIGNI, MV; LAMATTINA, L

PLANTA

Año: 1999 vol. 208 p. 337 - 344

0032-0935

Abstract. Many environmental conditions subjectplants to oxidative stress, in which reactive oxygenspecies (ROS) are overproduced. These ROS act astransduction signals in plant defense responses, but alsocause e€ects that result in cellular damage. Since nitricoxide (NO) is a bioactive molecule able to scavengeROS, we analyzed its e€ect on some cytotoxic processesproduced by ROS in potato (Solanum tuberosum L. cv.Pampeana) leaves. Two NO donors: (i) sodiumnitroprusside and (ii) a mixed solution of ascorbic acidand NaNO2, were able to prevent chlorophyll lossmediated by the methyl viologen herbicide diquat (aROS generator), with e€ective concentrations fallingbetween 10 and 100 lM of the donors. This protectionwas mimicked by thiourea and penicillamine, twoantioxidant compounds. Residual products from NOgeneration and decomposition failed to prevent chloro-phyll decline. A speciRc NO scavenger, the potassium saltof 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO), arrested NO-mediatedchlorophyll protection. In addition, some eventsmediated by ROS during infection of potato leaves withPhytophthora infestans (race 1, 4, 7, 8, 10, 11, matingtype A2) were also examined. In this sense, NO provedto markedly decrease ion leakage and the number oflesions, indicative of cell death, produced upon infectionin potato leaves. The NO-mediated decrease in ionleakage was also inhibited by carboxy-PTIO. Fragmen-tation of DNA diminished when P. infestans-infectedpotato leaves were treated with 100 lM SNP. Theseresults suggest that, acting as an antioxidant, NO canstrongly counteract many ROS-mediated cytotoxicprocesses in plants. Moreover, the evidence of NO functionality in the plant kingdom is strengthened bythis work.