ABSTRACT
Stripe rust, caused by Puccinia striiformis f. sp. tritici, is a serious disease of wheat. The spring wheat cultivar Kariega expresses complete adult plant resistance to stripe rust, whereas Avocet S is susceptible. In former studies, quantitative trait loci (QTL) analysis of doubled haploid lines derived from a Kariega x Avocet S cross revealed two major QTL (QYr.sgi-7D and QYr.sgi-2B.1) and two minor QTL (QYr.sgi-1A and QYr.sgi-4A.1) responsible for the adult resistance of Kariega in the field. Avocet S contains none of these QTL. In the present study, stripe rust development was compared, by means of fluorescence and confocal laser scanning microscopy, in flag leaves of Kariega, Avocet S and six doubled haploid (DH) lines, containing all four, none or one QTL. Depending on the QTL present, the infection types of the DH lines ranged from resistant to fully susceptible. No differences in fungal growth were observed during the first 5 days post inoculation (dpi), whereas the mean length of the fungal colonies started to differ at 6 dpi. Interestingly, MP 51 carrying QYr.sgi-7D responded with lignification to the fungal growth without restricting it, whereas MP 35 containing QYr.sgi-2B.1 did not show lignified host tissue, but fungal growth was restricted. RT PCR experiments with sequences of pathogenesis-related (PR) proteins resulted in a slightly stronger induction of PR 1, 2 and 5, known markers for the hypersensitive reaction, and peroxidases in MP 51, whereas a second band for chitinases was detected in MP 35 only.
Subject(s)
Basidiomycota/growth & development , Plant Diseases/microbiology , Triticum/microbiology , Haploidy , Immunity, Innate/genetics , Microscopy, Confocal , Plant Diseases/genetics , Quantitative Trait Loci/genetics , Reverse Transcriptase Polymerase Chain Reaction , Triticum/geneticsABSTRACT
The effect of Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), infestation on the hydrogen peroxide (H(2)O(2)) content and NADPH oxidase (EC 1.6.3.1) activity was studied in the resistant (cv. Tugela DN) and near-isogenic susceptible (cv. Tugela) wheat (Triticum aestivum L.). The objective of this study was to investigate the involvement of the reactive oxygen species (ROS) during the resistance responses against the RWA. Infestation significantly induced an early accumulation of the H(2)O(2) and increase of NADPH oxidase activity to higher levels in the resistant than susceptible plants. Results of inhibitory studies using diphenylene iodonium (DPI), a suicide inhibitor of NADPH oxidase, strongly suggested a possible signalling role for H(2)O(2) during RWA resistance response by activation of downstream defence enzymes [intercellular peroxidase (EC 1.11.1.7) and beta-1,3-glucanase (EC 3.2.1.39)].
Subject(s)
Aphids , Plant Diseases , Reactive Oxygen Species/metabolism , Triticum/metabolism , Triticum/parasitology , Animals , Hydrogen Peroxide/metabolism , Immunity, Innate/drug effects , NADPH Oxidases/antagonists & inhibitors , NADPH Oxidases/metabolism , Onium Compounds/pharmacology , Signal TransductionABSTRACT
Evidence for the presence of a polygalacturonase-inhibiting protein (PGIP) from a monocotyledonous cereal is presented. A 40.3-kDa PGIP that was closely associated with the cell wall was acetone-extracted and purified from wheat (Triticum aestivum L.) leaves and stems. Wheat PGIP exhibited a highly selective inhibitory activity against endopolygalacturonase (EPG) from various fungi. Of nine EPG tested, wheat PGIP only inhibited EPG from Cochliobolus sativus, a pathogen of the tribe Poaceae. A short N-terminal amino acid sequence of wheat PGIP shows no similarity to any other characterized PGIP.
Subject(s)
Antifungal Agents/isolation & purification , Enzyme Inhibitors/isolation & purification , Fungi/drug effects , Plant Proteins/isolation & purification , Polygalacturonase/antagonists & inhibitors , Triticum/physiology , Antifungal Agents/pharmacology , Fungi/classification , Immunoblotting , Luminescent Measurements , Microbial Sensitivity Tests , Plant Proteins/chemistry , Plant Proteins/pharmacology , Spectrometry, Mass, Matrix-Assisted Laser Desorption-IonizationABSTRACT
Elicitors are molecules which can induce the activation of plant defence responses. Elicitor activity of intercellular wash fluid from Russian wheat aphid, Diuraphis noxia (Mordvilko) infested resistant (cv Tugela DN), and susceptible (cv Tugela), wheat (Triticum aestivum L.), was investigated. Known Russian wheat aphid resistance related responses such as peroxidase and beta-1,3-glucanase activities were used as parameters of elicitor activity. The intercellular wash fluid from infested resistant plants contains high elicitor activity while that from infested susceptible plants contains no or very little elicitor activity. After applying C-18 reverse phase and concanavalin A Sepharose chromatography, elicitor active glycoproteins were isolated from the intercellular wash fluid of Russian wheat aphid infested resistant wheat. The elicitor-active glycoproteins separated into three polypeptides during sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The isolated glycoproteins elicited peroxidase activity to higher levels in resistant than in susceptible cultivars. It was evident that the glycoproteins were probably a general elicitor of plant origin. Information gained from these studies is valuable for the development of plant activators to enhance the defence responses of plants.
