Increased Lipoxygenase Activity is Involved in the Hypersensitive Response of Wheat Leaf Cells Infected with A virulent Rust Fungi or Treated with Fungal Elicitor

Abstract

Puccinia coronata avenae, Puccinia gram inis tritici, L ipoxygenase, Elicitor, H ypersensitive R eac tionThe hypersensitive reaction in incom patible wheat-rust interactions is characterized by an increase in lipoxygenase activity detectable as early as 28 h after penetration o f the pathogen. In contrast, lipoxygenase activity in the com patible interaction did not increase until the onset o f sporulation.Lipoxygenase activity also increased follow ing treatm ent o f wheat leaves with an elicitor frac tion from germ tubes o f Puccinia gram inis tritici. In trod u ctionH ost cell necrosis is recognized as one of the most prom inent defense mechanisms against biotrophic parasites such as the rust fungi. Light and electron microscopic studies have dem onstrated that in some incom patible interactions rapid localized host cell death accom panies this type of response to the inva sion of an avirulent pathogen [1][2][3][4].A lterations in m em brane structure resulting in leakage of electrolytes and serious disorder to cellu lar control mechanisms would be expected to occur concom itantly with cell death [see review 5]. M em brane disorganization may result from lipoxygenasecatalyzed peroxidation of membrane lipids; this in cludes the peroxidation of the ds,ds-l,4 -p en tad ien e systems commonly found in unsaturated fatty acids to the corresponding conjugated hydroperoxides. We therefore investigated the activity of lipoxygen ase in susceptible and resistant wheat cultivars inocu lated with Puccinia graminis tritici or, alternatively, with a nonpathogenic organism, Puccini coronata avenae. In addition, results are presented concerning the effect of an elicitor fraction isolated from germ tubes of w heat stem rust uredospores on the activity of lipoxygenase. A bbreviation s: Pgt, Puccinia gram inis tritici; Pea, Puccinia coronata avenae. Reprint requests to Prof. Dr. H. J. Grambow. Verlag der Zeitschrift für Naturforschung, D -7400 Tübingen 0 3 4 1 -0 3 8 2 /8 6 /0 5 0 0 -0 5 5 9 $ 01.30/0 M aterials and M eth o d s H ost and pathogenW heat plants were grown in a growth cham ber at 20 °C, 50-60% relative humidity, 16 h light regime and 15 klux. Primary leaves of 7 day-old plants were inoculated with uredospores or treated with elicitor. The following wheat cultivars were used throughout the experiments; cv. M arquis, which is susceptible to Puccinia gram inis tritici (Pgt), race 32, and which exhibits hypersensitivity to the non-pathogen Puc cinia coronata avenae (Pea); the corresponding, nearly isogenic line of cv. M arquis which carries the Sr5 gene for resistance against Pgt; cv. 417/65 which is highly resistant to Pgt, race 32.U redospores of Pgt, race 32, were collected from infected leaves of wheat cv. Little Club, and stored either at 4 °C for a few days or frozen in liquid nitro gen at -192 °C where they m aintained their infectivity over long periods. U redospores of Pea were col lected from oat cv. Pc40 and stored under the same conditions as Pgt.Plants were infected by spraying them with a sus pension of ur...

Oxylipin Profiling Reveals the Preferential Stimulation of the 9-Lipoxygenase Pathway in Elicitor-treated Potato Cells

“…in rice (35), wheat (36,37), or broad bean (38)), accumulation of transcripts corresponding to 9-LOX-encoding cDNAs has so far only been reported to take place in the solanaceous plants tobacco and potato in response to infection with oomycetes or to treatment with oomycetederived elicitors (39,40,20). Here, we show further that, concomitant with the accumulation of transcripts corresponding to the 9-LOX-encoding cDNA stlox1, higher 9-LOX activity and increased levels of 9-LOX products can be measured after elicitor treatment in potato cells.…”

Oxidation of fatty acids are associated with Russian wheat aphid resistance in wheat

“…The assay was done according to the methods of Grossmann and Zakut (1979) and Ocampo et al (1986). The LOX reaction mixture consisted of 1 mL 0.1 M sodium citrate phosphate buffer (pH 6.2), 50 µL of enzyme extract and 150 µL of 2.5 mM linoleic acid.…”

Mechanosensitive Expression of a Lipoxygenase Gene in Wheat

“…The homogenates were shaken for 15 min on a Eppendorf shaker and centrifuged at 12,OOOg for 20 min. LOX enzyme activity of the resulting supernatant was measured at 30°C with linoleic acid as a substrate (Ocampo et al, 1986). The molar extinction coefficient of the reaction product, 2.5 X 107 cm-' mol-I, was used for the calculation of the enzyme activity.…”

“…LOXs (EC 1.13.11.12) are a family of enzymes that catalyze the introduction of molecular oxygen into the cis,cis-1,4-pentadiene structure of polyunsaturated fatty acids (Vick and Zimmermann, 1987;Siedow, 1991). LOXs have been implicated in plant growth and development, mobilization of lipid reserves, senescence, ABA biosynthesis, wound responses, and resistance against pathogens and pests (Ocampo et al, 1986;Vick and Zimmerman, 1987;Creelman et al, 1992;Croft et al, 1993). The primary products of LOX-catalyzed reactions, fatty acid hydroperoxides, are often metabolized into molecules with known or suspected regulatory activity, such as jasmonic acid and traumatic acid (Vick and Zimmermann, 1987;Vick, 1991;Hamberg, 1993).…”