Treatment of the first leaves of barley (Hordeum vulgare L. cv. Golden Promise) seedlings with methyl jasmonate (MJ) led to small, but significant increases in levels of free putrescine and spermine 1 d later and to significant increases in levels of free putrescine, spermidine and spermine by 4 d following treatment. MJ-treated first leaves also exhibited significant increases in the amounts of soluble conjugates of putrescine and spermidine 1, 2 and 4 d after treatment. In second leaves of plants where the first leaves had been treated with MJ, no significant changes in levels of free polyamines were observed, but significant increases in levels of soluble conjugates of putrescine and spermidine were detected. These changes were accompanied by increased activities of soluble ornithine decarboxylase (ODC), soluble and particulate arginine decarboxylase (ADC), and S-adenosylmethionine decarboxylase (AdoMetDC), in first and second leaves following treatment of the first leaves with MJ. Activities of soluble and particulate diamine oxidase (DAO) were also higher in first and second leaves following treatment of the first leaves with MJ. Treatment of the first leaves with MJ led to a significant reduction in powdery mildew (Blumeria graminis f. sp. hordei) infection on the second leaves and also resulted in significant increases in activities of the plant defence-related enzymes, phenylalanine ammonia lyase (PAL) and peroxidase.
Polyamine levels and activities of enzymes of polyamine biosynthesis and catabolism were examined in the barley cultivar Delibes (Ml1al + Ml(Ab)) reacting hypersensitively to the powdery mildew fungus, Blumeria graminis f. sp. hordei (race CC220). Levels of free putrescine and spermine and of conjugated forms of putrescine, spermidine and spermine were greatly increased 1-4 d following inoculation of barley with the powdery mildew. These changes in polyamine levels were accompanied by elevated activities of the polyamine biosynthetic enzymes ornithine decarboxylase (ODC), arginine decarboxylase (ADC) and S -adenosylmethionine decarboxylase (AdoMetDC) and the polyamine catabolic enzymes diamine oxidase (DAO) and polyamine oxidase (PAO). Activities of two enzymes involved in conjugating polyamines to hydroxycinnamic acids, putrescine hydroxycinnamoyl transferase (PHT) and tyramine feruloyl-CoA transferase (TFT) were also examined and were found to increase significantly 1-4 d after inoculation. The possibility that the increased levels of free spermine, increased polyamine conjugates, and increased DAO and PAO activities are involved in development of the hypersensitive response of Delibes to powdery mildew infection is discussed.
These results demonstrate the rapidity with which resistance to pathogen infection can be induced following wounding and provides a possible mechanism by which pathogen infection might be halted.
In the incompatible interaction between the barley cultivar Hart (mlo allele) and the powdery mildew fungus Blumeria graminis DC. Speer f. sp. hordei Marchal, free spermidine and conjugated forms of putrescine and spermidine were found to accumulate 1–3 days following inoculation. The increase in free spermidine could be accounted for by increased activities of the biosynthetic enzymes ornithine decarboxylase (EC 4.1.1.17) and S‐adenosylmethionine decarboxylase (EC 4.1.1.50). Activities of the transferase enzymes putrescine hydroxycinnamoyl transferase (EC 2.3.1.‐) and tyramine feruloyl‐CoA transferase (EC 2.3.1.‐) were also increased in leaves of Hart inoculated with powdery mildew, as were activities of the polyamine catabolic enzymes diamine oxidase (DAO, EC 1.4.3.6) and polyamine oxidase (PAO, EC 1.4.3.4). The possible role of conjugated polyamines, and increases in DAO and PAO, in penetration based resistance to powdery mildew infection is discussed.
Treatment of the first leaves of barley seedlings with the oxylipin colneleic acid, or the two trihydroxy oxylipins 9,12,13-trihydroxy-11(E)-octadecenoic acid and 9,12,13-trihydroxy-10(E)-octadecenoic acid, reduced infection of that leaf by the powdery mildew fungus Blumeria graminis Speer f sp hordei Marchal. When applied to first leaves, etheroleic acid and colneleic acid, as well as the trihydroxy oxylipin 9,12,13-trihydroxy-10(E),15(Z)-octadecadienoic acid, also reduced mildew infection in second leaves. In all cases where local and systemic effects against mildew were observed, activity of the defence-related enzyme phenylalanine ammonia lyase (PAL) was increased, but only following challenge inoculation with powdery mildew. Peroxidase activity was not affected by oxylipin treatment or mildew inoculation. Whether the effects observed were due to the oxylipins or to breakdown products is not known, since no information is available on the stability of these particular oxylipins on leaf surfaces. Nevertheless, these data represent the first report of systemic effects against pathogen infection following pre-treatment with oxylipins.
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