Nitric Oxide and Reactive Oxygen Species Do Not Elicit Hypersensitive Cell Death but Induce Apoptosis in the Adjacent Cells During the Defense Response of Oat

Abstract

Nitric oxide (NO) acts as a signaling molecule in many cellular responses in plants and animals. Oat plants (Avena sativa L.) evoke the hypersensitive response (HR), which shares morphological and biochemical features with mammalian apoptosis, such as DNA laddering and heterochromatin condensation, in response to the avirulent crown rust fungus (Puccinia coronata f. sp. avenae). We examined the role of NO and reactive oxygen species (ROS) in the initiation of hypersensitive cell death, which is induced by direct contact with the pathogen, and apoptotic cell death in the adjacent cells. Cytofluorimetric analysis using the fluorescent NO probe DAF and the H2O2 probe DCF demonstrated that NO and H2O2 were generated simultaneously in primary leaves at an early stage of the defense response. The NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) markedly enhanced H2O2 accumulation detected by 3,3-diaminobenzidine staining and DCF, whereas treatment with the NO donor S-nitroso-N-acetylpenicillamine (SNAP) strongly suppressed it. Superoxide dismutase (SOD) increased NO accumulation, suggesting that endogenous NO may modulate the level of H2O2 by interacting with O2- in the HR lesion. Cytological observation showed that administration of cPTIO, SNAP, or SOD had no effect on elicitation of hypersensitive cell death, but clearly reduced heterochromatin condensation in the nearby cells and DNA laddering. These findings indicate that NO and ROS are not essential mediators for the initiation of hypersensitive cell death. However, NO and O2- but not H2O2 are required for the onset of apoptotic cell death in the adjacent cells, where excess NO may exert its anti-apoptotic function by regulating cellular redox state.

Reactive oxygen species and plant resistance to fungal pathogens

“…They consist in non-fluorescent molecules that become fluorescent when oxidised by ROS, and the emitted fluorescence can be observed by fluorimetry and/or by fluorescent microscopy, an advantage of such probes (Benikhlef et al, 2013;Bulgakov et al, 2012;Fester and Hause, 2005;Guo et al, 2010;Kolla et al, 2007;L'Haridon et al, 2011;Li et al, 2007;Liu et al, 2010;Ma et al, 2013;Peleg-Grossman et al, 2012;Plancot et al, 2013;Tada et al, 2004;Wen et al, 2008;Ye et al, 2013). Luminol or luminol analogues are sensitive chemiluminescent probes used to quantify a relative intensity of ROS by counting the emitted light with a luminometer, CDD camera or a scintillation counter (Dubreuil-Maurizi et al, 2010;Flury et al, 2013;Kunz et al, 2006;L'Haridon et al, 2011;Mersmann et al, 2010).…”

Plant defense response against Fusarium oxysporum and strategies to develop tolerant genotypes in banana

“…ROS in association with salicylic acid are proposed to mediate the establishment of systemic defenses (Durrant and Dong 2004). The cytological studies have revealed that ROS and NO are associated with cell death adjacent to infected cells and so that both signals modulate each other's accumulation (Tada et al 2004). Upregulation of NADPH oxidases was reported in the resistant banana cultivar in response to Foc (TR4) infection (Li et al 2012).…”

Resistance mechanisms of wild tomato germplasm to infection of Oidium neolycopersici

“…The key role of NO as a signal molecule and in defence processes of plants was documented in the relationships of plants to wound reaction (Orozco-Cardenas and Ryan 2002) and interactions with viruses, bacteria, oomycetes (e.g. Sedlářová et al 2011) and fungi (Tada et al 2004;Prats et al 2005;Piterková et al 2009). NO is vital for initiation and development of a hypersensitive response in plants, modification of gene expression and synthesis of PR (pathogenesis related) proteins (Wendehenne et al 2004;Zeier et al 2004;Mur et al 2006;Zaninotto et al 2006).…”