Plant Sciences

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Browsing Plant Sciences by Subject "3-glucanase"

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    ItemOpen Access
    Involvement of reactive nitrogen species in the Russian wheat: aphid resistance response of wheat
    (University of the Free State, 2010-05-31) Moloi, Makoena Joyce; Van der Westhuizen, Amie J.
    English: A recent accumulating body of evidence points to the importance of nitric oxide (NO) as a signal molecule involved in the regulation of many physiological and biochemical processes in plants. This study was aimed at investigating the involvement of reactive nitrogen species (RNS), in particular NO and peroxynitrite (ONOO-), in the Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), resistance response of wheat (Triticum aestivum L.). Resistant (cv. Tugela DN) and near isogenic susceptible (cv. Tugela) wheat plants were grown under the greenhouse conditions in trays at 24 oC (± 2 oC) and were infested at an early three leaf stage with approximately 20 RWAs (biotype RWASA1) per plant. RWA infestation induced an early accumulation (3-9 hours post infestation) of NO to a higher level in the resistant than susceptible plants. A corresponding increase in the activity of nitrate reductase (NR, EC 1.6.6.1) and inhibition studies using sodium tungstate (NR inhibitor) confirmed its involvement in NO production during the RWA resistance response. In addition, results indicated that the reduction of nitrate (NO3-) to nitrite (NO2-) involves NR and subsequently, nitrite reductase (NiR, EC 1.7.7.1) is responsible for the direct production of NO from NO2-. Inhibition studies using a nitric oxide synthase (NOS, EC 1.14.13.39) inhibitor, N-nitrilo-L-arginine-methyl ester (L-NAME), further proved that NOS has no significant effect on NO production during the RWA resistance response. In an experimental approach using sodium nitroprusside (SNP, NO donor) and / or sodium tungstate (NR inhibitor), it was discovered that NO acts as a signal for the induction of activities of secondary defense related enzymes such as the intercellular β-1,3-glucanase and peroxidase. Higher β-1,3-glucanase transcript accumulation after SNP treatment in resistant plants further supported the involvement of NO as signal molecule during the RWA defense response. In addition, results revealed that NO acts upstream of salicylic acid (SA) during the signaling events. High production of ONOO- [a product of an interaction between superoxide anion (O2-) and NO] in resistant plants after RWA infestation, suggests its involvement in the RWA resistance response. Inhibition of β-1,3-glucanase and peroxidase activities by urate (a specific inhibitor of ONOO- production), further suggests the involvement of ONOO- in the induction of the secondary RWA defense response. Furthermore, it was found that SNP root application of wheat plants resulted in transient resistance only. However, in contrast to root treatments, application of SNP as a seed dressing was more effective and has indeed a great potential of alleviating RWA damage in the susceptible plants by reducing aphid attraction as well as the intrinsic rate of aphid increase.
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    ItemOpen Access
    Isolation and eliciting activity of the Russian wheat aphid saliva in the resistance response of wheat
    (University of the Free State, 2011) Taiwe, Bernice; Mohase, L.
    The comparative effect of elicitors in Russian wheat aphid (Diuraphis noxia, Kurdjumov, RWA) saliva on the inducible defence related responses in different wheat (Triticum aestivum L.) cultivars was investigated. The elicitors emanated from the South African RWA biotype 1 (RWASA1) and biotype 2 (RWASA2) saliva. Elicitors from RWASA1 and RWASA2 salivary material were intercellularly injected into wheat cultivars, Tugela (lacks resistance genes), Tugela Dn1 (Dn1 resistance gene) and PAN 3144 (Dn5 resistance gene) and the induced defence responses were measured. The accumulation of pathogenesis related (PR) proteins, peroxidase (PR9) and β-1,3-glucanase (PR2) involved in RWA resistance in wheat were used as indicators of the resistance response. Additionally, lipoxygenase (LOX) involved in the synthesis of lipid signals, jasmonates and other oxylipins, was also employed as a marker of resistance. Peroxidase, β-1,3-glucanase and LOX activities were determined spectrophometrically. The elicitors in RWASA1 saliva induced higher levels of peroxidase, β-1,3-glucanse and LOX activities in both Dn1 and Dn5 containing cultivars. However, the induced level of defence related enzyme activities was quantitatively higher in Dn1 than Dn5 containing cultivars. The purified elicitor active fractions from RWASA1 saliva also induced enhanced defense responses that were significantly higher in Dn1 than Dn5 containing cultivars. This differential induction of defence responses suggests a stronger recognition of RWASA1 elicitors by the Dn1 gene products. In contrast, elicitors in RWASA2 saliva interacted with the receptors in Dn5-containing wheat cultivars in a highly specific manner. The elicitors from crude saliva induced defence responses only in the Dn5, but not the Dn1 containing cultivar. The purer eliciting fractions, collected from the various chromatographic separations, also induced selective defence responses that were evident only in PAN 3144 (Dn5) Even though we suspect elicitors in the saliva of RWASA1 and RWASA2 to be distinct, they induced similar levels of defence related enzyme activities in the Dn5 containing cultivar. The elicitor active fractions purified from RWASA2 saliva induced similar responses in PAN 3144 (Dn5) as elicitors from crude saliva. This implies a strong capacity conferred by the Dn5 mediated resistance, to recognize distinct elicitors from the saliva of the two aphid biotypes. Polypeptide profiles of RWASA1 and RWASA2 crude and purified fractions of the salivary material, revealed expression of similar as well as distinct protein bands. These differences probably contributed to the disparity in the expression of defence related enzyme activities by saliva of RWASA1 and RWASA2 in wheat cultivars. Boiling of these fractions abolished the induced defence related activities, suggesting their proteinaceous character. Furthermore, the differential presence of carbohydrates and amino acids in elicitor active fractions originating from RWASA1 and RWASA2 saliva implies that in addition to proteins, carbohydrates or at least glycoproteins, could be one of active components in these inducing fractions. The findings from this study confirm that the defence related enzymes (peroxidase, β-1,3-glucanase and lipoxygenase) associated with RWA resistance in wheat, are induced by elicitors in RWA saliva. The study has further indicated differential effects of elicitors in RWASA1 and RWASA2 saliva in wheat cultivars expressing different resistance genes. Elicitors in RWASA2 saliva have overcome the resistance conferred by the Dn1 resistance gene, but are avirulent to cultivars containing the Dn5 gene. Furthermore, this Dn5 resistance gene, not only confers resistance after treatment with elicitors in RWASA2 saliva, but also in RWASA1 saliva.