Nitric oxide is an upstream signal involved in the multisignalling network during the Russian wheat aphid resistance response and its application enhances resistance

The Russian wheat aphid (RWA) is serious pest of wheat in South Africa since its discovery in 1978. Nitric oxide (NO) plays an essential role in the RWA resistance response of wheat. This study was conducted to establish whether NO acts upstream or downstream of salicylic acid (SA) during the RWA defence response and also to investigate the effect of NO application on RWA control. In addition, the involvement of peroxynitrite in the RWA resistance response of wheat was studied. Resistant and/or susceptible plants grown under controlled conditions (25 ± 2°C) were used. Using a NO donor, sodium nitroprusside (SNP), and a NO production inhibitor, sodium tungstate (NaWO4), it was proved that NO acts upstream of SA during the RWA resistance response of wheat. Furthermore, a significant decrease in RWA intrinsic increase rate (rm) and disease symptom development after SNP application emphasized the role of NO in the RWA resistance responses. High levels of peroxynitrite (by-product of NO) content in the RWA infested resistant plants and inhibition of secondary defence enzymes (β-1,3-glucanase and peroxidase) after urate (inhibitor of peroxynitrite production) application proposed the involvement of this molecule in the signalling events of the RWA resistance

Involvement of Nitric Oxide in the Russian Wheat Aphid Resistance Response of Wheat

The involvement of nitric oxide (NO) in the Russian wheat aphid (RWA), Diuraphis noxia (Kurdjumov), resistance response of wheat (Triticum aestivum L.) was investigated. Resistant (cv. Tugela DN) and near isogenic susceptible (cv. Tugela) wheat plants grown under green-house conditions were used. Russian wheat aphid infestation induced an early accumulation of NO to a higher level in the resistant than susceptible plants. Nitric oxide accumulation corresponded with increased nitrate reductase (NR, EC 1.6.6.1) and nitrite reductase (NiR, EC 1.7.7.1) activities, suggesting a possible association with NO production. Inhibition studies confirmed the involvement of NR in NO production during the RWA resistance response. The use of a NO donor or NR inhibitor revealed that NO could act as another early signal for induction of the secondary defence enzymes, intercellular β-1,3-glucanase and peroxidase

Differential generation of hydrogen peroxide upon exposure to zinc and cadmium in the hyperaccumulating plant specie (Sedum alfredii Hance)*

Sedum alfredii Hance has been identified as zinc (Zn) and cadmium (Cd) co-hyperaccumulator. In this paper the relationships of Zn or Cd hyperaccumulation to the generation and the role of H2O2 in Sedum alfredii H. were examined. The results show that Zn and Cd contents in the shoots of Sedum alfredii H. treated with 1000 μmol/L Zn2+ and/or 200 μmol/L Cd2+ increased linearly within 15 d. Contents of total S, glutathione (GSH) and H2O2 in shoots also increased within 15 d, and then decreased. Total S and GSH contents in shoots were higher under Cd2+ treatment than under Zn2+ treatment. However, reverse trends of H2O2 content in shoots were obtained, in which much higher H2O2 content was observed in Zn2+-treated shoots than in Cd2+-treated shoots. Similarly, the microscopic imaging of H2O2 accumulation in leaves using H2O2 probe technique showed that much higher H2O2 accumulation was observed in the Zn2+-treated leaf than in the Cd2+-treated one. These results suggest that there are different responses in the generation of H2O2 upon exposure to Zn2+ and Cd2+ for the hyperaccumulator Sedum alfredii H. And this is the first report that the generation of H2O2 may play an important role in Zn hyperaccumulation in the leaves. Our results also imply that GSH may play an important role in the detoxification of dissociated Zn/Cd and the generation of H2O2