The patterns of secondary metabolites in leaves of yeast invertase-transgenic tobacco plants (Nicotiana tabacum L. cv. Samsun NN) were analyzed. Plants expressing cytosolic yeast-derived invertase (cytInv) or apoplastic (cell wall associated) yeast invertase (cwInv) showed a characteristic phytochemical phenotype compared to untransformed controls (wild-type plants). The level of phenylpropanoids decreased in the cytInv plants but increased in the cwInv plants, which showed an induced de novo synthesis of a caffeic acid amide, i.e. N-caffeoylputrescine. In addition, the level of the coumarin glucoside scopolin was markedly enhanced. Increased accumulation of scopolin in the cwInv plants is possibly correlated with the induction of defense reactions and the appearance of necrotic lesions similar to the hypersensitive response caused by avirulent pathogens. This is consistent with results from potato virus Y-infected plants. Whereas there was no additional increase in the coumarins in leaves following infection in cwInv plants, wild-type plants showed a slight increase and cytInc a marked increase.

Hydroxycinnamoyl-CoA : tyramine N-(hydroxycinnamoyl) transferase (THT) is a pivotal enzyme in the synthesis of N-(hydroxycinnamoyl)-amines, which are associated with cell wall fortification in plants. The cDNA encoding THT was cloned from the leaves of UV-C treated Capsicum annuum (hot pepper) using a differential screening strategy. The predicted protein encoded by the THT cDNA is 250 amino acids in length and has a relative molecular mass of 28,221. The protein sequence derived from the cDNA shares 76% and 67% identity with the potato and tobacco THT protein sequences, respectively. The recombinant pepper THT enzyme was purified using a bacterial overexpression system. The purified enzyme has a broad substrate specificity including acyl donors such as cinnamoyl-, sinapoyl-, feruloyl-, caffeoyl-, and 4-coumaroyl-CoA and acceptors such as tyramine and octopamine. In UV-C treated plants, the THT mRNA was strongly induced in leaves, and the elevated level of expression was stable for up to 36 h. THT mRNA also increased in leaves that were detached from the plant but not treated with UV-C. THT expression was measured in different plant tissues, and was constitutive at a similar level in leaf, root, stem, flower and fruit. Induction of THT mRNA was correlated with an increase in THT protein.

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Crude aqueous extracts from Arabidopsis leaves were subjected to chromatographic separations, after which the different fractions were monitored for antimicrobial activity using the fungus Neurospora crassa as a test organism. Two major fractions were obtained that appeared to have the same abundance in leaves from untreated plants versus leaves from plants challenge inoculated with the fungusAlternaria brassicicola. One of both major antimicrobial fractions was purified to homogeneity and identified by 1H nuclear magnetic resonance, gas chromatography/electron impact mass spectrometry, and gas chromatography/chemical ionization mass spectrometry as 4-methylsulphinylbutyl isothiocyanate (ITC). This compound has previously been described as a product of myrosinase-mediated breakdown of glucoraphanin, the predominant glucosinolate in Arabidopsis leaves. 4-Methylsulphinylbutyl ITC was found to be inhibitory to a wide range of fungi and bacteria, producing 50% growth inhibition in vitro at concentrations of 28 μm for the most sensitive organism tested (Pseudomonas syringae). A previously identified glucosinolate biosynthesis mutant, gsm1-1, was found to be largely deficient in either of the two major antimicrobial compounds, including 4-methylsulphinylbutyl ITC. The resistance ofgsm1-1 was compared with that of wild-type plants after challenge with the fungi A. brassicicola,Plectosphaerella cucumerina, Botrytis cinerea, Fusarium oxysporum, orPeronospora parasitica, or the bacteria Erwinia carotovora or P. syringae. Of the tested pathogens, only F. oxysporum was found to be significantly more aggressive on gsm1-1 than on wild-type plants. Taken together, our data suggest that glucosinolate-derived antimicrobial ITCs can play a role in the protection of Arabidopsis against particular pathogens.

When inorganic phosphate is limiting, Arabidopsis has the facultative ability to metabolize exogenous nucleic acid substrates, which we utilized previously to identify insensitive phosphate starvation response mutants in a conditional genetic screen. In this study, we examined the effect of the phosphate analog, phosphite (Phi), on molecular and morphological responses to phosphate starvation. Phi significantly inhibited plant growth on phosphate-sufficient (2 mm) and nucleic acid-containing (2 mmphosphorus) media at concentrations higher than 2.5 mm. However, with respect to suppressing typical responses to phosphate limitation, Phi effects were very similar to those of phosphate. Phosphate starvation responses, which we examined and found to be almost identically affected by both anions, included changes in: (a) the root-to-shoot ratio; (b) root hair formation; (c) anthocyanin accumulation; (d) the activities of phosphate starvation-inducible nucleolytic enzymes, including ribonuclease, phosphodiesterase, and acid phosphatase; and (e) steady-state mRNA levels of phosphate starvation-inducible genes. It is important that induction of primary auxin response genes by indole-3-acetic acid in the presence of growth-inhibitory Phi concentrations suggests that Phi selectively inhibits phosphate starvation responses. Thus, the use of Phi may allow further dissection of phosphate signaling by genetic selection for constitutive phosphate starvation response mutants on media containing organophosphates as the only source of phosphorus.

In elicitor-treated potato cells, 9-lipoxygenase-derived oxylipins accumulate with the divinyl ether colneleic acid as the major metabolite. Here, the identification of a potato cDNA is described, whose predicted amino acid sequence corresponds to divinyl ether synthases, belonging to the recently identified new P450 subfamily CYP74D. The recombinant protein was expressed in Escherichia coli and shown to metabolize 9-hydroperoxy linoleic acid to colneleic acid at pH 6.5. This fatty acid derivative has been implicated in functioning as a plant antimicrobial compound. RNA blot analyses revealed accumulation of divinyl ether synthase transcripts both upon infiltration of potato leaves with Pseudomonas syringae and after infection with Phytophthora infestans.

Pflanzen und bestimmte Pilze haben im Laufe ihrer Entwicklungsgeschichte „gelernt”︁, in einer engen Assoziation im Boden, der Mykorrhiza, eine äußerst erfolgreiche Symbiose miteinander einzugehen. Arbuskuläre Mykorrhizapilze helfen Pflanzen sich auf nährstoffarmen Böden ausreichend mit Wasser, Nährsalzen und Spurenelementen zu versorgen und fördern entscheidend Diversität und Produktivität von Pflanzengesellschaften. Darüber hinaus zeigen mykorrhizierte Pflanzen eine erhöhte Widerstandsfähigkeit gegen Pathogenbefall. Im Gegenzug „bezahlt”︁ die Pflanze den Pilz für diesen Gewinn mit Kohlenhydraten in Form einfacher Zucker (Glucose, Fructose). Durch manche Erfolge in der Erforschung der Mykorrhiza auf Metaboliten‐ und Genebene beginnen wir allmählich zu erahnen, wie komplex die molekularen Interaktionen dieser Symbiose sind. Es ist zu erwarten, dass das steigende Interesse an der Mykorrhizaforschung zu neuen Einsichten in die Strategien von Pflanzen und Pilzen in der Entwicklung mutualistisch‐symbiontischer Assoziationen führen wird.

Bisher war die Funktion der Polyphenoloxidasen (PPO) unklar. Inzwischen konnte aber gezeigt werden, dass eine Tyrosinase an der Betacyan‐Biosynthese des Portulakröschens (siehe Bild) und der Roten Rübe sowie eine Chalkon‐spezifische PPO an der Auronbildung in gelben Löwenmaulblüten beteiligt ist.

Enzymes in search of a function, for polyphenol oxidases (PPOs), described as such, this situation has changed recently. A tyrosinase is involved in betacyanin biosynthesis in common portulaca (see picture) and red beet, and a chalcone‐specific PPO is responsible for the formation of aurones in yellow snapdragon flowers.

R,R-Bis­[(3-benzyl­oxazolan-4-yl)-methyl] di­sulfide, C22H28N2O2S2, is a chiral di­sulfide which is a highly effective catalyst for the enantioselective addition of diethyl­zinc to aldehydes, including aliphatic ones. The mol­ecule has crystallographic twofold rotation symmetry.