Certain plant species and genotypes are able to accumulate large quantities of heavy metals in their shoots. Based on this trait the concept of phytoremediation was developed, i.e. the use of metal hyperaccumulating plants for the cleansing of contaminated soils and water. In order to more efficiently use this capacity, an engineering of plants might be needed. However, very little is known about the underlying molecular mechanisms. Our work is focussing on the identification and characterization of plant genes involved in plant metal uptake, tolerance and accumulation. Phytochelatins are small glutathione-derived metal-binding peptides which are part of the plant metal detoxification system. Genes encoding phytochelatin synthases have been cloned and are now being studied with regard to their regulation, biochemistry and biotechnological potential. Another project aimes at the dissection of metal responses in the metallophyte Arabidopsis halleri. This plant, a close relative to the model plant Arabidopsis thaliana, is Cd hypertolerant and Zn hyperaccumulating. It grows,for instance, on medieval mining sites in the Harz mountains in Germany and in many other metal-contaminated sites in Central Europe. We have isolated metal-regulated genes from A.halleri and molecularly analyzed interesting candidate genes with regard to their function and involvement in metal accumulation and tolerance.

The formation of phytochelatins, small metal‐binding glutathione‐derived peptides, is one of the well‐studied responses of plants to toxic metal exposure. Phytochelatins have also been detected in some fungi and some marine diatoms. Genes encoding phytochelatin synthases (PCS) have recently been cloned from Arabidopsis , wheat and Schizosaccharomyces pombe . Surprisingly, database searches revealed the presence of a homologous gene in the Caenorhabditis elegans genome, DDBJ/EMBL/GenBank accession no. 266513. Here we show that C. elegans indeed expresses a gene coding for a functional phytochelatin synthase. CePCS complements the Cd2+ sensitivity of a Schizosaccharomyces pombe PCS knock‐out strain and confers phytochelatin synthase activity to these cells. Thus, phytochelatins may play a role for metal homeostasis also in certain animals.

Phytochelatins represent a major detoxifying pathway for heavy metals in plants and many other organisms. The Arabidopsis thaliana CAD1 (=AtPCS1 ) gene encodes a phytochelatin synthase and cad1 mutants are phytochelatin deficient and cadmium hypersensitive. The Arabidopsis genome contains a highly homologous gene, AtPCS2 , of which expression and function were studied in order to understand the apparent non‐redundancy of the two genes. Low constitutive AtPCS2 expression is detected in all plant organs analyzed. The AtPCS2 gene encodes a functional phytochelatin synthase as shown by expression in Saccharomyces cerevisiae and the complementation of a Schizosaccharomyces pombe phytochelatin synthase knockout strain.

The chemical stability and colorant properties of three betaxanthins recently identified from Celosia argentea varieties were evaluated. Lyophilized betaxanthin powders from yellow inflorescences of Celosia exhibited bright yellow color and high color purity with strong hygroscopicity. The aqueous solutions containing these betaxanthins were bright yellow in the pH range 2.2−7.0, and they were most stable at pH 5.5. The betaxanthins in a model system (buffer) were susceptible to heat, and found to be as unstable as red betacyanins (betanin and amaranthine) at high temperatures (>40 °C), but more stable at 40 °C with the exclusion of light and air. The three betaxanthins had slightly higher pigment retention than amaranthine/isoamaranthine in crude extracts at 22 °C, as verified by HPLC analysis. Lyophilized betaxanthins had much better storage stability (mean 95.0% pigment retention) than corresponding aqueous solutions (14.8%) at 22 °C after 20 weeks. Refrigeration (4 °C) significantly increased pigment retention of aqueous betaxanthins to 75.5%.

Two novel alkaloidal glucosides derived from the recently discovered antidesmone (1 ), together with four known megastigmane and three lignan glucosides, two of which had not previously been described, were isolated from 1‐butanol extracts of Antidesma membranaceum (Euphorbiaceae). The structural elucidation of (17RS )‐17‐(β‐D ‐glucopyranosyloxy)antidesmone (2 ) and (17RS )‐8‐deoxo‐17‐(β‐D ‐glucopyranosyloxy)antidesmone (3 ) is based on 1H, 13C, COSY, NOESY, HMQC and HMBC NMR spectra, together with LC/ESI‐CIDMS and CD data. Determination of the absolute configuration at C‐17 was accomplished by comparison with 1H NMR spectroscopic data for alk‐2‐yl β‐D ‐glucopyranosides, an approach that also proved useful for the megastigmane glucosides blumenyl C β‐D ‐glucopyranoside (4 ), 3‐oxo‐α‐ionyl β‐D ‐glucopyranoside (5 ), blumenyl B β‐D ‐glucopyranoside (6 ) and blumenyl A β‐D ‐glucopyranoside (7 ). The lignan glucosides lyoniresin‐4‐yl β‐D ‐glucopyranoside (8 ), 4′‐O‐methyllyoniresin‐4‐yl β‐D ‐glucopyranoside (9 ) and secoisolariciresin‐4‐yl β‐D ‐glucopyranoside (10 ), featuring an unusual glucosylation position, were investigated with the aid of 1H and 2D NMR, CD and MS data.

Several sulfur-containing optically active C2-symmetrical ligands have been synthesized from (R)-cysteine and applied successfully as chiral catalysts in the asymmetric addition of diethylzinc to aldehydes. The resulting secondary alcohols could be obtained in good yields and excellent enantiomeric excess.

The isolation of three C-glycosyl chromones, four anthraquinones and a mixture of phytosterols from the leaves of Aloe rubroviolacea was reported.

A new 5-methylchromone glycoside, named 7-O-methylaloeresin A (2-acetonyl-8-C-β-D[2′-O-(E)-4-hydroxycinnamoyl]glucopyranosyl-7-methoxy-5-methylchromone, 1), was isolated from Commiphora socotrana (Burseraceae). Its structure was elucidated by spectroscopic data (MS, UV, 1H- and 13C-NMR).

Enzymatic and non-enzymatic lipid peroxidation has been implicated in programmed cell death, which is a major process of leaf senescence. To test this hypothesis we developed a high-performance liquid chromatography (HPLC) method for a simultaneous analysis of the major hydro(pero)xy polyenoic fatty acids. Quantities of lipid peroxidation products in leaves of different stages of development including natural senescence indicated a strong increase in the level of oxygenated polyenoic fatty acids (PUFAs) during the late stages of leaf senescence. Comprehensive structural elucidation of the oxygenation products by means of HPLC, gas chromatography/mass spectrometry and 1H nuclear magnetic resonance suggested a non-enzymatic origin. However, in some cases a small share of specifically oxidized PUFAs was identified suggesting involvement of lipid peroxidizing enzymes. To inspect the possible role of enzymatic lipid peroxidation in leaf senescence, we analyzed the abundance of lipoxygenases (LOXs) in rosette leaves of Arabidopsis. LOXs and their product (9Z,11E,13S,15Z)-13-hydroperoxy-9,11,15-octadecatrienoic acid were exclusively detected in young green leaves. In contrast, in senescing leaves the specific LOX products were overlaid by large amounts of stereo-random lipid peroxidation products originating from non-enzymatic oxidation. These data indicate a limited contribution of LOXs to total lipid peroxidation, and a dominant role of non-enzymatic lipid peroxidation in late stages of leaf development.

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.