Phytochemical investigations of Aloe sabaea afforded a new chlorinated amide, N-4′-chlorobutylbutyramide, and the toxic piperidine alkaloids coniine, γ-coniceine and the quarternary N,N-dimethylconiine. This is the first report of the occurrence of a chlorinated compound in the Aloeaceae family.

Neither the molecular mechanism by which plant microtubules nucleate in the cytoplasm nor the organization of plant mitotic spindles, which lack centrosomes, is well understood. Here, using immunolocalization and cell fractionation techniques, we provide evidence that γ-tubulin, a universal component of microtubule organizing centers, is present in both the cytoplasm and the nucleus of plant cells. The amount of γ-tubulin in nuclei increased during the G2 phase, when cells are synchronized or sorted for particular phases of the cell cycle. γ-Tubulin appeared on prekinetochores before preprophase arrest caused by inhibition of the cyclin-dependent kinase and before prekinetochore labeling of the mitosis-specific phosphoepitope MPM2. The association of nuclear γ-tubulin with chromatin displayed moderately strong affinity, as shown by its release after DNase treatment and by using extraction experiments. Subcellular compartmentalization of γ-tubulin might be an important factor in the organization of plant-specific microtubule arrays and acentriolar mitotic spindles.

From the acetone extract of the North American toadstool Lepiota americana 2-aminophenoxazin-3-one (1) and a novel amino-1,4-benzoquinone derivative, lepiotaquinone (2), were isolated. The structure of 2 was confirmed by its preparation from 2-aminophenol and amino-1,4-benzoquinone.

During growth under conditions of phosphate limitation, suspension-cultured cells of tomato (Lycopersicon esculentum Mill.) secrete phosphodiesterase activity in a similar fashion to phosphate starvation-inducible ribonuclease (RNase LE), a cyclizing endoribonuclease that generates 2′:3′-cyclic nucleoside monophosphates (NMP) as its major monomeric products (T. Nürnberger, S. Abel, W. Jost, K. Glund [1990] Plant Physiol 92: 970–976). Tomato extracellular phosphodiesterase was purified to homogeneity from the spent culture medium of phosphate-starved cells and was characterized as a cyclic nucleotide phosphodiesterase. The purified enzyme has a molecular mass of 70 kD, a pH optimum of 6.2, and an isoelectric point of 8.1. The phosphodiesterase preparation is free of any detectable deoxyribonuclease, ribonuclease, and nucleotidase activity. Tomato extracellular phosphodiesterase is insensitive to EDTA and hydrolyzes with no apparent base specificity 2′:3′-cyclic NMP to 3′-NMP and the 3′:5′-cyclic isomers to a mixture of 3′-NMP and 5′-NMP. Specific activities of the enzyme are 2-fold higher for 2′:3′-cyclic NMP than for 3′:5′-cyclic isomers. Analysis of monomeric products of sequential RNA hydrolysis with purified RNase LE, purified extracellular phosphodiesterase, and cleared −Pi culture medium as a source of 3′-nucleotidase activity indicates that cyclic nucleotide phosphodiesterase functions as an accessory ribonucleolytic activity that effectively hydrolyzes primary products of RNase LE to substrates for phosphate-starvation-inducible phosphomonoesterases. Biosynthetical labeling of cyclic nucleotide phopshodiesterase upon phosphate starvation suggests de novo synthesis and secretion of a set of nucleolytic enzymes for scavenging phosphate from extracellular RNA substrates.

Natural products cover a diversity space not yet available from synthetic libraries, with an unrivalled success rate as drug leads. The combinatorial synthesis of non-oligomeric natural-product-based libraries, however, is still limited to few examples because access to easily modified units strongly depends on the availability of a core structure either from a natural source, or through a suitable synthetic route. Only a few resourceful groups have managed the latter approach for more demanding multifunctional natural drug leads, such as epothilones.

In barley leaves 13-lipoxygenases are induced by jasmonates. This leads to induction of lipid peroxidation. Here we show by in vitro studies that these processes may further lead to autoxidative formation of (2E)-4-hydroxy-2-hexenal from (3Z)-hexenal.

Chemische Signale wurden bereits im 19.Jahrhundert als Regulatoren von Wachstum und Entwicklung der Pflanzen postuliert.In den letzten 70 Jahren wurde die Wirkungsweise der klassischen Pflanzenhormone wie der Auxine, Gibberelline, Cytokinine, Ethylen und Abscisinsäure aufgeklärt. Doch erst im letzten Jahrzehnt entdeckte man die Bedeutung der Brassinosteroide, der Peptidhormone und der Jasmonate.

Plants and certain bacteria use a non‐mevalonate alternative route for the biosynthesis of many isoprenoids, including carotenoids. This route has been discovered only recently and has been designated the deoxyxylulose phosphate pathway or methylerythritol phosphate (MEP) pathway. We report here that colonisation of roots from wheat, maize, rice and barley by the arbuscular mycorrhizal fungal symbiont Glomus intraradices involves strong induction of transcript levels of two of the pivotal enzymes of the MEP pathway, 1‐deoxy‐D‐xylulose 5‐phosphate synthase (DXS) and 1‐deoxy‐D‐xylulose 5‐phosphate reductoisomerase (DXR). This induction is temporarily and spatially correlated with specific and concomitant accumulation of two classes of apocarotenoids, namely glycosylated C13 cyclohexenone derivatives and mycorradicin (C14) conjugates, the latter being a major component of the long‐known ‘yellow pigment’. A total of six cyclohexenone derivatives were characterised from mycorrhizal wheat and maize roots. Furthermore, the acyclic structure of mycorradicin described previously only from maize has been identified from mycorrhizal wheat roots after alkaline treatment of an ‘apocarotenoid complex’ of yellow root constituents. We propose a hypothetical scheme for biogenesis of both types of apocarotenoids from a common oxocarotenoid (xanthophyll) precursor. This is the first report demonstrating (i) that the plastidic MEP pathway is active in plant roots and (ii) that it can be induced by a fungus.

Glycosyltransferases of plant secondary metabolism transfer nucleotide-diphosphate-activated sugars to low molecular weight substrates. Until recently, glycosyltransferases were thought to have only limited influence on the basic physiology of the plant. This view has changed. Glycosyltransferases might in fact have an important role in plant defense and stress tolerance. Recent results obtained with several recombinant enzymes indicate that many glycosyltransferases are regioselective or regiospecific rather than highly substrate specific. This might indicate how plants evolve novel secondary products, placing enzymes with broad substrate specificities downstream of the conserved, early, pivotal enzymes of plant secondary metabolism.

In a split-root system root colonization by the arbuscular mycorrhizal fungus Glomus mosseae on one side is reduced when roots on the other side are already colonized by G. mosseae. Root colonization by arbuscular mycorrhizal fungi enhances the P-status of plants, thus the observed suppressional effect on further root colonization in precolonized barley plants could be P-level regulated. Split-root systems allow to separate plant mediated P-effects on root colonization by arbuscular mycorrhizal fungi from direct P-effects on arbuscular mycorrhizal fungi. By adding a KH2PO4-solution to one side of the split-root system of non-mycorrhizal control plants, higher P-levels were obtained as in split-root systems of G. mosseae precolonized plants. Subsequent inoculation with G. mosseae of the P-supplied and the precolonized plants resulted in an inhibition of root colonization in the precolonized plants, but not in the P-supplied plants, discarding the enhanced P-level as the responsible factor for the observed suppression. Cyclohexenone derivatives are secondary plant compounds only found in roots of mycorrhizal plants. Analysis of cyclohexenone derivatives in mycorrhizal and non-mycorrhizal roots in split-root systems revealed that cyclohexenone derivatives can be detected in mycorrhizal roots, but not in non-mycorrhizal roots of mycorrhizal plants. The presented results show clearly that cyclohexenone derivatives are not systemically accumulated and that the P-levels are not the responsible factors for the observed systemic suppression of mycorrhization in roots of precolonized barley plants.