Mycorrhizas are the most important mutualistic symbioses on earth. The most prevalent type are the arbuscular mycorrhizas (AMs) that develop between roots of most terrestrial plants and fungal species of the Zygomycota. The AM fungi are able to grow into the root cortex forming intercellular hyphae from which highly branched structures, arbuscules, originate within cortex cells. The arbuscules are responsible for nutrient exchange between the host and the symbiont, transporting carbohydrates from the plant to the fungus and mineral nutrients, especially phosphate, and water from the fungus to the plant. Plants adapt their phosphate uptake to the interaction with the AM fungus by synthesis of specific phosphate transporters. Colonization of root cells induces dramatic changes in the cytoplasmic organization: vacuole fragmentation, transformation of the plasma membrane to a periarbuscular membrane covering the arbuscule, increase of the cytoplasm volume and numbers of cell organelles, as well as movement of the nucleus into a central position. The plastids form a dense network covering the symbiotic interface. In some of these changes, microtubules are most likely involved. With regard to the molecular crosstalk between the two organisms, a number of phytohormones (cytokinins, abscisic acid, jasmonate) as well as various secondary metabolites have been examined: (i) Jasmonates occur at elevated level, which is accompanied by cell-specific expression of genes involved in jasmonate biosynthesis that might be linked to strong carbohydrate sink function of AM roots and induced defense reactions; (ii) apocarotenoids (derivatives of mycorradicin and glycosylated cyclohexenones) accumulate in most mycorrhizal roots examined so far. Their biosynthesis via the nonmevalonate methylerythritol phosphate (MEP) pathway has been studied resulting in new insights into AM-specific gene expression and biosynthesis of secondary isoprenoids.

In biosynthesis of octadecanoids and jasmonate (JA), the naturally occurring enantiomer is established in a step catalysed by the gene cloned recently from tomato as a single-copy gene (Ziegler et al., 2000). Based on sequence homology, four full-length cDNAs were isolated from Arabidopsis thaliana ecotype Columbia coding for proteins with AOC activity. The expression of AOCgenes was transiently and differentially up-regulated upon wounding both locally and systemically and was induced by JA treatment. In contrast, AOC protein appeared at constitutively high basal levels and was slightly increased by the treatments. Immunohistochemical analyses revealed abundant occurrence of AOC protein as well as of the preceding enzymes in octadecanoid biosynthesis, lipoxygenase (LOX) and allene oxide synthase (AOS), in fully developed tissues, but much less so in 7-day old leaf tissues. Metabolic profiling data of free and esterified polyunsaturated fatty acids and lipid peroxidation products including JA and octadecanoids in wild-type leaves and the jasmonate-deficient mutant OPDA reductase 3 (opr3) revealed preferential activity of the AOS branch within the LOX pathway. 13-LOX products occurred predominantly as esterified derivatives, and all 13-hydroperoxy derivatives were below the detection limits. There was a constitutive high level of free 12-oxo-phytodienoic acid (OPDA) in untreated wild-type and opr3 leaves, but an undetectable expression of AOC. Upon wounding opr3 leaves exhibited only low expression of AOC, wounded wild-type leaves, however, accumulated JA and AOC mRNA. These and further data suggest regulation of JA biosynthesis by OPDA compartmentalization and a positive feedback by JA during leaf development.

In this study, we report the cloning of the three‐member LePS2 gene family of acid phosphatases via subtractive screening of a cDNA library of Pi‐starved cultivated tomato cells (Lycopersicon esculentum Mill. cv. Lukullus). As members of the plant Pi‐starvation response, LePS2 genes were tightly regulated in cultivated cells and tomato seedlings by Pi availability. The LePS2 enzymes which are most likely expressed in the cytoplasma could be involved in processes that are accompanied by degradation of phosphorylated organic substrates. Independently from exogenous phosphate supply LePS2 expression was detected in tomato endosperm during germination. LePS2 genes were differentially induced after infection with the bacterial pathogen Pseudomonas syringae and in the early stages of flower development. Using RT–PCR it was found that the gene LePS2B was the most abundant transcript in phosphate‐depleted cells, but a reduced expression was determined in floral buds and it was not found during pathogen interaction. In this respect, it is interesting that the promoter sequences of the LePS2 genes are also divergent. LePS2 gene products may have functions in developmental processes which are restricted to distinct plant tissues or cell types.

The allene oxide cyclase (AOC)‐catalyzed step in jasmonate (JA) biosynthesis is important in the wound response of tomato. As shown by treatments with systemin and its inactive analog, and by analysis of 35S::prosysteminsense and 35S::prosysteminantisense plants, the AOC seems to be activated by systemin (and JA) leading to elevated formation of JA. Data are presented on the local wound response following activation of AOC and generation of JA, both in vascular bundles. The tissue‐specific occurrence of AOC protein and generation of JA is kept upon wounding or other stresses, but is compromised in 35S::AOCsense plants, whereas 35S::AOCantisense plants exhibited residual AOC expression, a less than 10% rise in JA, and no detectable expression of wound response genes. The (i) activation of systemin‐dependent AOC and JA biosynthesis occurring only upon substrate generation, (ii) the tissue‐specific occurrence of AOC in vascular bundles, where the prosystemin gene is expressed, and (iii) the tissue‐specific generation of JA suggest an amplification in the wound response of tomato leaves allowing local and rapid defense responses.

Expression of defense-associated genes was analyzed in leaf tissues of near-isogenic resistant and susceptible barley cultivars upon infection by Rhynchosporium secalis. The genes encoding pathogenesis-related (PR) proteins PR-1, PR-5, and PR-9 are specifically expressed in the mesophyll of resistant plants, whereas a germin-like protein (OxOLP) is synthesized in the epidermis irrespective of the resistance genotype. Restriction-mediated differential display was employed to identify additional epidermis-specific genes. This resulted in the detection of another PR gene, PR-10, along with a lipoxygenase gene, LoxA, and a gene of unknown function, pI2-4, which are specifically induced in the epidermis of resistant plants. The gene encoding a putative protease inhibitor, SD10, is preferentially but not exclusively expressed in the epidermis. The fungal avirulence gene product NIP1 triggers the induction of the four PR genes only. At least two additional elicitors, therefore, must be postulated, one for the unspecific induction of OxOLP and one for the resistance-specific induction of LoxA, pI2-4, and SD10. PR-10 expression can be assumed to be the consequence of NIP1 perception by epidermis cells. In contrast, gene expression in the mesophyll is likely to be triggered by an as yet unknown signal that appears to originate in the epidermis and that is strongly amplified in the mesophyll.

A red pigment, lilacinone (1), was isolated from fruit bodies of the toadstool Lactarius lilacinus. Its structure was established by 2D NMR and APCIMS methods. Compound 1 is a novel type of fungal aminobenzoquinone pigment and may be biosynthetically derived from three molecules of anthranilic acid.

The novel morphinans 13 –18 , which carry amino acid substituents at C(6), with potentially limited access to the central nervous system were prepared in two steps from 14‐O‐methyloxymorphone (5 ). Reductive amination with amino acid tert‐butyl esters gave compounds 7 –12 , which were hydrolyzed with tetrafluoroboric acid. Structure elucidation (including X‐ray analysis), preliminary μ‐opioid receptor binding studies, and calculations of pharmacokinetic parameters were carried out.

Hypersensitive cell death is an important defense reaction of plants to pathogen infection and is accompanied by lipid peroxidation processes. These may occur non-enzymatically by the action of reactive oxygen species or may be catalyzed by enzymes such as α-dioxygenases, lipoxygenases, or peroxidases. Correlative data showing increases in 9-lipoxygenase products in hyper-sensitively reacting cells have so far suggested that a large part of lipid peroxidation is mediated by a specific set of 9-lipoxygenases. To address the significance of 9-lipoxygenases for this type of pathogen response in potato, RNA interference constructs of a specific pathogen-induced potato 9-lipoxygenase were transferred to potato plants. Significantly reduced 9-lipoxygenase transcript levels were observed in transgenic plants after pathogen treatment. In addition, 9-lipoxygenase activity was hardly detectable, and levels of 9-lipoxygenase-derived oxylipins were reduced up to 12-fold after pathogen infection. In contrast to wild type plants, high levels of non-enzymatically as well as 13-lipoxygenase-derived oxylipins were present in 9-lipoxygenase-deficient plants. From this we conclude that during the normal hypersensitive response in potato, lipid peroxidation may occur as a controlled and directed process that is facilitated by the action of a specific 9-lipoxygenase. If 9-lipoxygenase-mediated formation of hydroperoxides is repressed, autoxidative lipid peroxidation processes and 13-lipoxygenase-mediated oxylipins synthesis become prominent. The unaltered timing and extent of necrosis formation suggests that the origin of lipid hydroperoxides does not influence pathogen-induced cell death in potato.

12-Hydroxyjasmonate, also known as tuberonic acid, was first isolated from Solanum tuberosum and was shown to have tuber-inducing properties. It is derived from the ubiquitously occurring jasmonic acid, an important signaling molecule mediating diverse developmental processes and plant defense responses. We report here that the gene AtST2a from Arabidopsis thaliana encodes a hydroxyjasmonate sulfotransferase. The recombinant AtST2a protein was found to exhibit strict specificity for 11- and 12-hydroxyjasmonate with Km values of 50 and 10 μm, respectively. Furthermore, 12-hydroxyjasmonate and its sulfonated derivative are shown to be naturally occurring inA. thaliana. The exogenous application of methyljasmonate to A. thaliana plants led to increased levels of both metabolites, whereas treatment with 12-hydroxyjasmonate led to increased level of 12-hydroxyjasmonate sulfate without affecting the endogenous level of jasmonic acid. AtST2a expression was found to be induced following treatment with methyljasmonate and 12-hydroxyjasmonate. In contrast, the expression of the methyljasmonate-responsive gene Thi2.1, a marker gene in plant defense responses, is not induced upon treatment with 12-hydroxyjasmonate indicating the existence of independent signaling pathways responding to jasmonic acid and 12-hydroxyjasmonic acid. Taken together, the results suggest that the hydroxylation and sulfonation reactions might be components of a pathway that inactivates excess jasmonic acid in plants. Alternatively, the function of AtST2a might be to control the biological activity of 12-hydroxyjasmonic acid.

The F2 progeny of a third backcross(BC3) line, BC line 240, derived from a Turkish accession of wild barley (Hordeum vulgare ssp. spontaneum),segregated for resistance to scald (Rhynchosporium secalis) in a manner indicating the presence of a single dominant resistance gene. Two SCAR marker slinked to this resistance were developed from AFLP markers. Screens of disomic and ditelosomic wheat-barley addition lines with the SCAR markers demonstrated that the scald resistance gene is located in the centromeric region of barley chromosome 3H,a region previously reported to contain a major scald resistance locus, Rrs1. Markers that flank the Rrs1 locus were used to screen the wild barley-derivedBC3F2 population. These markers also flank the wild barley-derived scald resistance, indicating that it maps to the same locus as Rrs1; it may beallelic, or a separate gene within a complex locus. However, BC line 240 does not respond to treatment with the Rhynchosporium secalis avirulence factorNIP1 in the same way as the Rrs1-carrying cultivar Atlas46. This suggests that the scald resistance gene derived from wild barley confers a different specificity of response to theRrs1 allele in Atlas46.In order to increase the durability of scald resistance in the field, we suggest that at least two scald resistances should be combined into barley cultivars before release. The scald resistance gene described here will be of value in the Australian environment, and the several markers linked to it will facilitate pyramiding.