J. R. Hillman

Plant cell walls as dietary fibre : range, structure, processing and function

The ingestion of dietary fibre has been correlated with the prevention of many health-threatening diseases and cancers. Plant cell walls are the major source of dietary fibre and this review investigates the relationship between the structure of different types of plant cell walls and their beneficial effects. The effects of processing and cooking on dietary fibre are also examined. Structure-function relationships between individual cell wall components and the beneficial effects of dietary fibre are not well defined and it may be that the physical, physiochemical and topochemical properties of plant cell walls and their components are also important.

Abscisic Acid and Ion Fluxes Through Photosynthetic and Artificial Membranes

Summary The effects of abscisic acid on transmembrane ion flux were investigated using osmotically shocked pea chloroplasts, chromatophores from the photosynthetic bacterium Rhodopseudomonas capsulata, and artificial membrane vesicles. ABA did not significantly enhance the ionic permeability of chloroplastic or chromatophore membranes. In addition, ABA did not accelerate proton efflux from acid-loaded phospholipid vesicles.

Endogenous abscisic acid in lettuce fruits

Summary Abscisic acid has been extracted from lettuce fruits of two varieties, «Great Lakes« and «Arctic King«, and identified by a combination of methods including partitioning, chromatography, spectropolarimetry and gas chromatography-mass spectrometry. The abscisic acid present in the dry fruits of the two varieties has been determined quantitatively and in “Great Lakes” the levels decreased during germination.

Apical Dominance and Correlations by Hormones

Correlative control systems provide most of the rationale and impetus for research on plant growth substances, elevating the research beyond natural product chemistry. The phenomenon of apical dominance is widely assumed to be a classical and exemplary example of hormonally integrated growth in plants, principally brought about by indole-3-acetic acid (IAA). This may be a correct assumption, but the available evidence in favour of the hypotheses based on the dogma is equivocal. Some of the major deficiencies encountered in devising working hypotheses to explain merely one aspect of apical dominance - the correlative inhibition of lateral buds by the apical region of the shoot - are the subject of this chapter. Several general reviews of correlative inhibition have been published [1, 3, 9, 16, 22–24].

Endogenous Estradiol-17 β in Phaseolus vulgaris

Summary Evidence based on chromatographic (TLC, Lipidex, GLC), mass spectrometric (GC-MS, selective current ion monitoring) and radioimmunoassay procedures is presented for the occurrence of estradiol-17β (E 2 ) in the dwarf French bean Phaseolus vulgaris . Methods for the isolation of such compounds from plant extracts are detailed and problems of the quantification of E 2 in phenolic extracts are discussed.

The Metabolism of Estrogens in vivo and in vitro by Phaseolus vulgaris

Summary Seedlings of Phaseolus vulgaris cv. Canadian Wonder were incubated with 4-14C-estrone, 4-14C-estradiol-17β and 6,7-3H-estrone sulphate. Evidence from TLC, column chromatography on Lipidex, radio-GLC and crystallisation to constant specific activity suggests that estrone and estradiol-17β are interconvertible in plant tissues. Evidence was also obtained that a tissue homogenate supplemented with cofactors can metabolise estrone. Analysis by gas chromatography as well as combined gas chromatography- mass spectrometry demonstrated unequivocally that the major product was estradiol. These data represent the first evidence from full mass spectrometry that estrogens can be metabolised by plant tissues.

Derivatives of Indole-3-acetic Acid for SIM GC-MS Studies

Summary The preparatory yield and mass spectrometric properties of three derivatives of indole-3-acetic acid (IAA) were examined with regard to their suitability for SIM GC-MS studies of the endogenous compound. The bis -TMSi and methyl derivatives showed high yields and limited fragmentation whereas anomalous results were obtained in assessing the yield of HFB-IAA-Me.

Opportunities and problems in plant biotechnology – an overview

In Chapter 11 of Our Mutual Friend , Dickens noted that “Mr Podsnap had even acquired a peculiar flourish of his right arm in often clearing the world of its most difficult problems, by sweeping them behind him”. With a surname redolent of a kitchen botanist, Mr Podsnap no doubt realised that problems are mere opportunities for the theatrically dextrous. Perhaps the act of sweeping provides forward momentum to capitalise on yet more problems. In plant biotechnology, many of the problems confronting mankind are opportunities to employ exciting science.

Distribution of indole-3-acetic acid in shoots of Phaseolus vulgaris L.

Summary The quantitative distribution of indole-3-acetic acid in the shoots of Phaseolus seedlings has been examined using a gas chromatography-mass spectrometry procedure. The levels of IAA in the leaves and internode sections did not vary significantly with physiological maturity although the level of IAA in the leaves was consistently lower than that of the apex.

Plant Growth Substances and the Ionic Permeability of Membranes

The concept that plant growth substances might exert their primary effects by altering membrane properties was proposed by Veldstra [20]. In reviewing the effects of growth substances on ion transport Van Steveninck [19] posed a series of questions on their mode of action with respect to ion transport, including (1) whether growth substances directly affect membrane permeability or conductance through interaction with the membrane structure, and (2) whether growth substances affect metabolic processes which involve the establishment of ion gradients. A number of authors have attempted to answer these questions, in particular for ABA [21] and IAA [16,18]. In searching for a simpler experimental system for ABA, Lea and Collins [11] abandoned biological membranes and used artificial phospholipid membranes. They found transient fluctuations in conductance which they associated with the formation of multimeric channels. Their data, therefore, suggest that ABA has an effect on membrane conductance which is independent of receptor molecules, indicating that ABA has a mode of action analogous to uncouplers (compounds which make membranes permeable to H+) or ionophores (compounds which increase membrane permeability to certain ions or groups of ions). The evidence from biological systems on whether ABA has ionophoretic properties is conflicting. It has previously been suggested that ABA was an uncoupler [3] or might have properties like those of an uncoupler [13]. However, Boyer [11 found no evidence for uncoupling of chloroplasts by ABA.