Showing papers by "Leibniz Association published in 1992"

Jasmonates: Metabolism, Biological Activities, and Modes of Action in Senescence and Stress Responses

Abstract: First detected as fragrant constituents of the essential oils ofJasminum(Demoleet al.1962) andRosmarinum(Crabalona, 1967), (—)-jasmonic acid (JA) and its methyl ester (JA-Me) became of interest for plant physiologists after the first observations on growth inhibition (Yamaneet al.1980) and leaf senescence promotion (Ueda and Kato, 1980). In recent years many more physiological processes were found to be influenced by these cyclopentanone compounds. Thus, in combination with the ubiquitous occurrence in plants and a low dose — activity relationship, it seems justified to coordinate jasmonates to the “classical” five phytohormone groups, distinguished by the conception of being natural regulators in plant growth and development.

Secondary metabolites produced by callus cultures of various Ruta species

Abstract: Callus cultures were established from hypocotyl explants of R. bracteosa, R. chalepensis and R. macrophylla. Calli were maintained for more than three years on MS-medium supplemented with 1 mg l-1 of each 2,4-D and kinetin. Acridone and furoquinoline alkaloids and coumarins have been isolated from four week old calli grown on a hormone containing and hormone-free medium. A new chlorinated acridone alkaloid has been detected.

LEA electron accelerators for radiation processing

Abstract: A diode-type electron processor equipped with a linear cathode is described. The design of the low-energy accelerator LEA and some results of its operation as part of different pilot units for electron beam curing of coatings and printing inks are discussed.

Liquid chromatography/atmospheric pressure chemical ionization mass spectrometry of gibberellin conjugates

Abstract: The analysis of gibberellins (GAs) usually deals with those of free form. Gibberellins of conjugate form are not as extensively investigated because: (i) the conjugate form is presumed to be inactive per se, and (ii) procedures for purification are troublesome, as is definitive analysis. However, in any study of how hormone levels are regulated, quantitation of GA-conjugates cannot be ignored. Conjugation of GAs may well be as important a step in GA deactivation as is the C-2β-hydroxylation step. Some GA-conjugates (e.g. glucosyl esters) may also be useful storage forms in buds, seeds, bulbs, or other overwintering organs.

Identification of native gibberellin-O-glucosides in Zea mays L. and Hordeum vulgare L.

Abstract: In cereals the induction of a-amylase during germination is claimed to depend on gibberellins (GAs), e.g. GA3. Nowadays, this view is disputed, because of the low level of endogenous GAs within the caryopses and because of a-amylase induction in the presence of inhibitors of GA biosynthesis (Grosselindemann et al., 1988; Lenton and Appleford, 1991). However, endogenous GA conjugates, which are known to accumulate e.g. in legume seeds during maturation, might serve as a pool of GAs during germination, provided they are present in cereals too, and are hydrolysed during germination to yield free GAs.

Biologically active microbial compounds as useful agents in agriculture.

Abstract: Among natural products the so-called secondary metabolites comprise a very large group of substances showing a remarkable diversity of chemical structures, complexity and bioactive properties. The variety of secondary metabolites that are synthesized by microorganisms seems to be no less than those synthesized by higher plants. The occurrence of secondary metabolites is not common to all microorganisms but restricted to certain taxa or even strains. These metabolites are often synthesized only in a certain period of the life cycle of a given organism mostly after cessation of vegetative growth. There are many sometimes conflicting discussions about the function of secondary metabolites. Secondary metabolism is an aspect of cellular differentiation. Since the discovery of penicillin in 1928 by Alexander Fleming the search for useful therapeutic agents after the Second World War has greatly stimulated research activities in the field of microbial biochemistry. Several thousands of antibiotics have been isolated mostly from streptomycetes and fungi. This goal was achieved with the aid of traditional screening methods. To explore the wealth of microbial secondary metabolites depends inter alia on non-classical test methods. Hans Z/ihner is one of the pioneers who has emphasized the importance of unconventional screening techniques for the discovery of new bioactive compounds. The gaining importance of microbial metabolites for use in agriculture will be illustrated below (Figure 1).

In vitro plant regeneration from leaf explants of C3 and C3-C4-intermediate Flaveria species

Abstract: A procedure is described for the invitro regeneration of whole plants of Flaveria cronquistii (C3 species) F. pubescens and F. chloraefolia (both C3-C4 intermediate species) using different concentrations of 6-benzylaminopurine and alpha-napnthalenic acid.