Silicon and heavy metal tolerance of higher plants.

The heavy metal tolerant Cardaminopsis halleri, grown on Zn and Cu polluted soil, showed electron dense metal containing precipitates (Zn, Cu, Sn, Fe, Al) on the leaf surface, in the intercellular spaces (Zn, Cu, Sn), the cell walls and the cell wall thickenings of the xylem vessels (Zn, traces of Cu and Fe). Large amounts of Zn were measured in the vacuoles, the main storage compartment for this metal in Cardarminopsis. The cytoplasm and nuclei contained small precipitates, including mainly Zn and Si. As shown by ESI Zn was co-localized with Si in these structures. The EEL-spectra of the cytoplasmic precipitates corresponded with the spectra of Zn-silicate. Besides Zn-silicate, electron translucent structures in the cytoplasm were identified as SiO2 by their EEL spectra. It was concluded that in the cytoplasm of Cardaminopsis Zn is transiently accumulated as silicate, being slowly degraded to SiO2. Zn is translocated into the vacuole and accumulated in an unknown form. A second Si and Zn-uptake mechanism was found, excluding a membrane and cytoplasm passage. Pinocytotic vesicles, formed by the plasmamembrane and the tonoplast, enable a direct translocation of Si and Zn from extracellular compartments into the vacuole. The formation of Zn-silicate is part of the heavy metal tolerance mechanism and may be responsible for the amelioration of the Zn toxicity in Cardaminopsis.

Receptor-mediated activation of a MAP kinase in pathogen defense of plants.

Parsley cells recognize the fungal plant pathogen Phytophthora sojae through a plasma membrane receptor. A pathogen-derived oligopeptide elicitor binds to this receptor and thereby stimulates a multicomponent defense response through sequential activation of ion channels and an oxidative burst. An elicitor-responsive mitogen-activated protein (MAP) kinase was identified that acts downstream of the ion channels but independently or upstream of the oxidative burst. Upon receptor-mediated activation, the MAP kinase is translocated to the nucleus where it might interact with transcription factors that induce expression of defense genes.

Expression of a single-chain Fv antibody against abscisic acid creates a wilty phenotype in transgenic tobacco.

The plant hormone abscisic acid (ABA) participates in the control of several important physiological processes in plants such as stomata regulation, seed dormancy and stress tolerance. A new strategy was developed to study these phenomena by blocking abscisic acid with intracellularly expressed specific single-chain variable fragment (scFv) antibodies. Here evidence is presented that the expression of single-chain Fv antibodies against abscisic acid in the endoplasmic reticulum of transgenic tobacco cells leads to a wilty phenotype. Stomatal conductance is increased at high CO2 concentrations dependent on the level of antibody expression in leaves. Symptoms of abscisic acid deficiency were generated in the transformants although they have even higher levels of abscisic acid than wild-type plants.

HSP68--a DnaK-like heat-stress protein of plant mitochondria.

A 68-kDa heat-stress protein (HSP68) has been purified from cell-suspension cultures of tomato (Lycopersicon peruvianum L.). Antibodies raised against HSP68 cross-react with the Escherichia coli heat-stress protein DnaK. HSP68 was found to be a hydrophilic, ATP-binding protein. Immunological analysis of subcellular fractions and immunogold-labelling of ultrathin sections showed consistently that HSP68 is localized in the mitochondrial matrix. In-vitro translation experiments indicated that HSP68 is synthesized as a precursor protein. Immunoscreening of cDNA libraries from tomato and potato (Solanum tuberosum L.) led to the isolation of corresponding cDNA clones. The deduced amino-acid sequences show strong relationships to the DnaK-like proteins from bacteria and organelles of eukaryotic cells. The protein HSP68 is constitutively expressed, but its synthesis is increased during heat stress in all cells of higher plants investigated so far.

[Double-labeling with gold particles]. / Doppelmarkierungen mit Goldpartikeln.

The peculiarities of different methods of multiple marking by gold granules are summarized. Especially the application to thin sections is taken in consideration. The GLAD-technique, the direct immunolabeling and the indirect methods employing immunogoldmarkers respectively protein A-gold are discussed.

Dictyosomes participate in the intracellular pathway of storage proteins in developing Vicia faba cotyledons.

The main storage globulins of Vicia faba seeds, vicilin and legumin, were localized in ultrathin sections of developing cotyledons employing the protein A/colloidal gold-technique. Double labelling experiments with monospecific immunoglobulins directed against vicilin or legumin using different size classes of protein A-colloidal gold showed that both globulins are associated with protein lumps in the vacuoles of early developmental stages of the seeds and with the rough endoplasmic reticulum, the site of storage protein biosynthesis. Furthermore, vicilin and legumin have been detected in protein-containing vesicles in the cytoplasm as well as in dictyosomes and the dictyosome-derived vesicles. The association of storage globulins with the dictyosomes was also indicated by cell fractionation and immunoblotting of organelle contents derived from microsome, enriched dictyosome and protein body preparations. Protein blotting analyses employing a Concanavalin A/peroxidase technique showed that certain vicilin polypeptides were already glycosylated in the rough endoplasmic reticulum. Another part of the vicilin fraction as well as legumin polypeptides did not show any affinity to Concanavalin A. These data provide a direct evidence for a transient involvement of dictyosomes in the intracellular pathway of legume storage globulins from the rough endoplasmic reticulum to their accumulation site in the protein bodies.

Electron microscopic immunocytochemical localization of storage proteins in Vicia faba seeds.

The main storage proteins legumin and vicilin were located by immuno-labeling with protein A-gold in formaldehyde fixed tissues of Vicia faba seeds at different developmental stages. Both proteins were found to be accumulated together in the same protein bodies. Besides these organelles only the rough endoplasmic reticulum (ER) is labeled in particular developmental stages of the cotyledons. A fraction of proteins accumulated in the vacuoles at earlier stages of development also represents storage proteins. Besides the formation of protein bodies by the ER a second route of origination from vacuoles is proposed for Vicia faba seeds at early developmental stages.