Showing papers in "Plant Biology in 1992"

Metal tolerance in plants

Abstract: Nearly 60 years ago, Prat (1934) initiated the research of heavy metal resistance in plants when he was analysing the growth performance of two populations of Silene dioica (Melandrium sylvestre), one from a copper mine and one from a non-mine soil. He was able to demonstrate a heritable copper resistance in the mine population, relative to the non-mine population, which he explained as a result of evolution by natural selection. Nearly 20 years later Bradshaw (1952) and Baumeister (1954) started further research on ecological and physiological differentiation between plants from metal-enriched and noncontaminated habitats. The species chosen for study were predominantly Agrostis capillaris in the Bradshaw group (Jowett 1959; Gregory 1965; McNeilly 1965; Antonovics 1966) and Silene vulgaris in the Baumeister group (Broker 1962; Ernst 1964; Gries 1965; Riither 1966). In the late 1950s Duvigneaud (1958), while studying the vegetation on metalliferous soils in Central Africa, added to the above approaches a phytogeographic one and introduced the study of speciation processes in metallophytes. In the 1950s, the study of evolutionary and physiological aspects of metal resistance was hampered by the absence of convenient techniques for measuring metal concentrations in small plant samples. The techniques available for metal analysis were either timeconsuming, such as phase separation (Ernst 1964), or costly and only applicable for laboratory-raised plant material, i.e. radiolabelling (Turner & Gregory 1967; Peterson 1969). Only after applying atomic absorption spectrophotometry on wet-ashed plant material (Reilly 1967) did time and cost-effective metal analyses become possible.

Cadmium tolerance and toxicity, oxygen radical processes and molecular damage in cadmium‐tolerant and cadmium‐sensitive clones of Holcus lanatus L.

Abstract: SUMMARY Two clones of the grass Holcus lanatus from a metal-contaminated (Hallen Wood, Avonmouth, UK) and an uncontaminated site (Totley, Sheffield, UK) accumulated cadmium from Cd-amended hydroponic cultures, the Totley material to two-fold higher concentrations than the Hallen Wood. The Totley clone showed impaired growth at relatively low Cd concentrations; the reduction in parallel tolerance indices (TIs) to 50% occurred at an external Cd concentration of 53 μM compared with 94 μM in the Cd-tolerant Hallen Wood material. In both clones Cd was transported to the shoots; in the non-tolerant (Cd-sensitive) Totley tissues the two-fold greater Cd accumulation was accompanied by a two-fold rise in lipid peroxidation, indicative of membrane damage by reactive oxygen species in the shoot, though not in the roots. Evidence for the involvement of activated forms of oxygen was also seen in the highly significant correlations between Cd uptake into the shoot and the activities of superoxide dismutase (r = 0·95) and guaiacol peroxidase (r = 0·96), but confined to the sensitive Totley material. It was concluded that one potentially highly-damaging effect of Cd was to promote the generation of partly-reduced and highly-reactive forms of oxygen in the Cd-sensitive clone and that the site of activated oxygen formation was the shoot rather than the root.

Meta-population dynamics of biennial plants: how to exploit temporary habitats

Abstract: SUMMARY Extinction of local populations of plants of many biennial plant species has been frequently reported. Survival of these species on the meta-population level implies a balance between extinction and regeneration, either through seed dispersal or from the seedbank. We distinguish between three types of biennials (transient, fugitive and persistent) and review the relation between dynamics of local populations and habitat characteristics, such as disturbance. Some species are safe-site limited whereas other species demonstrate a combination of safe-site and seed limitation. Meta-population dynamics are illustrated with two examples (Senecio jacobaea and Cynoglossum officinale). We distinguish between patch dynamics (loss and genesis of sites that are suitable for population development) and meta-population dynamics of biennials (population behaviour within and between sites, and dispersal). A hypothesis is developed on the regulation of patch dynamics. Finally we discuss the question: what makes biennials suited for exploiting temporary habitats?

Cyanobacterial Picoplankton from Lake Constance

Abstract: Four types of unicellular cyanobacteria were classified by pigment composition and cell size. These originated from the picoplankton fraction of Lake Constance, Germany. β-Carotene and zeaxanthin were found to be the main carotenoids of three Synechococcus isolates. In this group, coccoid forms with phycocyanin-rich phycobilisomes also produce caloxanthin and nostoxanthin, which are xanthophylls with 3 and 4 hydroxy groups, respectively. In addition, these rare carotenoids are observed in rod-forming Synechococcus isolates which contain phycoerythrin-rich phycobilisomes, but they are very low or absent in the coccoid phycoerythrin-rich isolates. Due to size and pigment content the coccoid forms are similar to Synechococcus leopoliensis (SAUG B 1402-1, formerly Anacystis nidulans) and S. rubescens (SAUG B 3.81) while the rod-forming isolates differ from S. elongatus (PCC 6716) in phycobilisome composition. The isolate BO 8402 was tentatively assigned to Synechocystis but differs in pigment composition from all strains described as yet. The green cultures exhibited a faint red glow due to an unusual high in vivo autofluorescence from phycocyanin. Neither were phycobilisomes found in a standard preparation nor was allophycocyanin present. The most abundant carotenoids are β-carotene and caloxanthin, while zeaxanthin, with 12 % of all colored carotenoids, is low. All forms described in this paper lack complementary chromatic adaptation, indicating that the pigment composition is a reliable parameter to identify these freshwater isolates.

Enzymatic Characteristics of UDP‐sulfoquinovose: Diacylglycerol Sulfoquinovosyltransferase from Chloroplast Envelopes

Abstract: Envelope membranes from chloroplasts contain UDP-sulfoquinovose: diacylglycerol sulfoquinovosyltransferase which catalyses the final step in sulfolipid assembly. In situ produced diacylglycerol served as radioactive acceptor to measure enzymatic activity. With this assay, several enzymatic parameters were investigated. The enzyme, which has maximal activity at pH 7.5, was stimulated by magnesium ions due to a decrease of the Km for uridine 5′-diphospho-sulfoquinovose from 80 pM (no magnesium) to 10 μM (5 mM magnesium). This stimulation had a Km of 0.7 mM magnesium and may be relevant in light/dark modulation of the enzymatic activity. The lower efficiency of guanosine 5′-diphospho-sulfoquinovose observed before can be ascribed to a higher Km of this sugar nucleotide (400 μM). Under optimized and linearized conditions the sulfoquinovosyltransferase displayed about 10% of the activity of the UDP-galactose: diacylglycerol galactosyltransferase which competes in the same membrane system for diacylglycerols. Addition of acidic lipids, such as sulfolipid and phosphatidylglycerol, to envelope membranes resulted in an inhibition of the sulfoquinovosyltransferase, whereas the galactosyltransferase was not affected. In vivo this may contribute to an adjustment of the sulfolipid proportion in plastid membranes. In contrast to the galactosyltransferase the sulfoquinovosyltransferase did not discriminate against the dipalmitoyl molecular species of diacylglycerol when offered together with the oleoyl-palmitoyl species. Under conditions when oleoyl-palmitoyl-and dipalmitoyl-diacylglycerols were synthesized with concurrent conversion to monogalactosyl and sulfoquinovosyl diacylglycerol, the sulfolipid was highly enriched in the fully saturated species. This may explain the occurrence of dipalmitoyl species in sulfolipids, as found in many plants.

Continuing range extension of Halophila stipulacea (Forssk.) Aschers. (Hydrocharitaceae) in the Mediterranean—now found at Kefallinia and Ithaki (Ionian Sea)

Abstract: SUMMARY A stand of the seagrass Halophila stipulacea (Forssk.) Aschers. has been discovered at the Ionian Island of Kefallinia. Detached floating plants have been observed in various harbours on Kefallinia and Ithaki, indicating a further range extension in the Mediterranean.

Ecological and physiological aspects of tissue‐cultured plants

Abstract: Tissue-cultured plants are different from normal plants because of the environmental conditions in a tissue-culture container. Together with the water retention capacity (WRC) of the headspace in a container, the gas composition is responsible for n divergent physiological behaviour. By controlling the WRC of the headspace the physiology and anatomy of tissue-cultured plants can be improved to resemble normal plants. During culture in vitro under our conditions, the CO 2 -level showed a typical circadian shift depending upon illumination, but was always higher than the normal atmospheric concentration

Influences of blue and red light on the photosynthetic apparatus of Chlorella kessleri : alterations in pigment-protein complexes

Abstract: In white light of 332-mu-mol m-2 s-1 oxygen evolution of Chlorella kessleri is about 30 % higher after growth in blue light than after growth in red light of the same quantum fluence rate When determined by the light-induced absorbance change at lambda-820 nm, blue light-adapted cells possess about 60 % more reaction centres per total chlorophyll in photosystem II Correspondingly, the cells exhibit about 30 % more Hill activity of PS II Conversely, red light-adapted cells contain relatively more reaction centres and higher electron flow capacities of photosystem I The distribution of total chlorophyll among the pigment-protein complexes, CPI, CPIa, CPa, and LHC II, corresponds to these data There is more chlorophyll associated with the light-harvesting complex of PS II, LHC II, in cells under blue light conditions, but more chlorophyll bound to both complexes of PS I, CPI and CPIa, in cells under red light conditions The respective ratios of chlorophyll a/chlorophyll b of all complexes are identical for blue and red light-adapted cells This results in a higher relative amount of chlorophyll b in blue light-adapted cells Total carotenoids per total chlorophyll are increased by 20 % in red light-adapted cells Their distribution among the pigment-protein complexes is unknown, however the ratios of lutein, neoxanthin and violaxanthin extractable from LHC II are different in blue (321: 359: 320) and in red (514: 267: 219) light-adapted cells