The Creation and Physiological Relevance of Divergent Hydroxylation Patterns in the Flavonoid Pathway

Flavonoids and biochemically-related chalcones are important secondary metabolites, which are ubiquitously present in plants and therefore also in human food. They fulfill a broad range of physiological functions in planta and there are numerous reports about their physiological relevance for humans. Flavonoids have in common a basic C6-C3-C6 skeleton structure consisting of two aromatic rings (A and B) and a heterocyclic ring (C) containing one oxygen atom, whereas chalcones, as the intermediates in the formation of flavonoids, have not yet established the heterocyclic C-ring. Flavonoids are grouped into eight different classes, according to the oxidative status of the C-ring. The large number of divergent chalcones and flavonoid structures is from the extensive modification of the basic molecules. The hydroxylation pattern influences physiological properties such as light absorption and antioxidative activity, which is the base for many beneficial health effects of flavonoids. In some cases antiinfective properties are also effected

Pyrenophora teres: Profile of an increasingly damaging barley pathogen

Pyrenophora teres, causal agent of net blotch of barley, exists in two forms, designated P. teres f. teres and P. teres f. maculata, which induce net form net blotch (NFNB) and spot form net blotch (SFNB), respectively. Significantly more work has been performed on the net form than on the spot form although recent activity in spot form research has increased because of epidemics of SFNB in barley‐producing regions. Genetic studies have demonstrated that NFNB resistance in barley is present in both dominant and recessive forms, and that resistance/susceptibility to both forms can be conferred by major genes, although minor quantitative trait loci have also been identified. Early work on the virulence of the pathogen showed toxin effector production to be important in disease induction by both forms of pathogen. Since then, several laboratories have investigated effectors of virulence and avirulence, and both forms are complex in their interaction with the host. Here, we assemble recent information from the literature that describes both forms of this important pathogen and includes reports describing the host–pathogen interaction with barley. We also include preliminary findings from a genome sequence survey

Phytoalexin accumulation in sorghum: Identification of a methyl ether of luteolinidin

A method of HPLC analysis of 3-deoxyanthocyanidins was developed which allowed the detection of these phytoalexins by plasma desorption mass spectrometry (PDMS). In addition, the times at which samples were taken were increased to 60 h post-inoculation. As a result of the changes in protocol, a new deoxyanthocyanidin was detected. The compound was isolated and purified and found by PDMS to have a molecular weight of 285. In addition to the PDMS data, bathochromic shift analyses indicated that the structure of the compound is consistent with that of a 5-methyl ether of luteolinidin. Fungitoxicity assays demonstrated that the compound is a phytoalexin as it prevented germination by, and kiled conidia of Colletotrichum sublineolum, the sorghum anthracnose pathogen, at a concentration of 3 μM. The 5- methoxyluteolinidin exhibited greater fungitoxicity than luteolinidin, a non- methoxylated phytoalexin.link_to_subscribed_fulltex

Growth of Pyrenophora teres in planta during barley net blotch disease

The two forms of barley net blotch disease, spot form and net form, are caused by Pyrenophora teres f. maculata (Ptm) and P. teres f. teres (Ptt) respectively. While Ptm and Ptt are genetically very similar, their disease pathophysiologies are different. Ptm causes circular or elliptical brown lesions whereas Ptt causes distinctive dark-brown, longitudinal lesions. In this study, we have demonstrated that these distinct disease symptoms may be explained by differences in fungal growth. Ptm appeared to initially grow as a biotroph forming intracellular vesicles within epidermal cells before switching to necrotrophic (intercellular) growth in the mesophyll. In contrast, Ptt appeared to avoid the biotrophic stage and established itself within the mesophyll more quickly. Symptom development was considerably lessened during seedling and adult plant resistance to Ptt, even though growth of the pathogen was still quite similar to that seen on a susceptible cultivar (albeit not as extensively). In a detached leaf system, net blotch symptoms did not develop and extensive Ptt growth occurred on leaves of a resistant barley line, suggesting in planta studies are more reliable. The greater knowledge of both forms of P. teres contributed by this study may enable development of resistance strategies to these pathogens.Damien J. Lightfoot and Amanda J. Abl