Vegetation study as a generator for population biological and physiological research on salt marshes

The paper deals with some views on the phytocoenose in relation to the functioning of vegetation and its plant-species populations in space and time. From these viewpoints the study of vegetation is seen as a field of tension between the organismic and reductionistic approaches. Both have their value, provided any dogmatism is avoided and either can be applied to the other.In the field of vegetation structure characteristic features of life-form spectra and species distribution, inversion phenomena in zonation, and community architecture in relation to production and decomposition are discussed. In this connection some remarks are made on habitat and niche differentiation with respect to the phytocoenose concept.Vegetation dynamics are discussed in relation to the introduction of Spartina anglica, the frequency of flooding by the tides, different environmental disturbances caused by heavy winter frost, rainfall and hot and dry periods, as well as to human interferences for agricultural and civil-technical purposes.It is suggested that salt-marsh plants may have found refuge areas in inland habitats as well as on more southerly coastal sites during glaciations.Nomenclature follows Tutin et al. (1964–1980).The author wishes to thank his collaborators Messrs B. P. Koutstaal and W. de Munck for much fieldwork, and Mrs M. J. van Leerdam-de Dreu and Messrs A. A. Bolsius and J. A. van den Ende for the preparation of text and figures.Communication No. 302 of the Delta Institute for Hydrobiological Research.     

Sulphide tolerance in coastal halophytes

The effect of sulphide on the growth of several species of salt-marsh plants was investigated. Relative growth rates were significantly reduced in two upper-marsh species, Festuca rubra and Atriplex patula, and in the lower-marsh species Puccinellia maritima. However the growth of Salicornia europaea, a species frequently associated with sulphide-containing sediments, was unaffected. In a separate experiment the wide ranging halophyte Aster tripolium, also appeared to be tolerant of sulphide at a concentration frequently encountered in salt marshes. Sulphide pretreatment inhibited the activity of two metallo-enzymes, polyphenol oxidase and external phosphatase, in plants from the upper marsh, but had no effect on enzymes from P. maritima or S. europaea. The rate of respiration by root tissue was significantly reduced in all of the species investigated but whereas the uptake of ⁸⁶rubidium was markedly inhibited in the other three species, uptake by S. europaea showed a significant stimulation. Similarly, whereas sulphide-grown plants of F. rubra, A. patula and P. maritima had a considerably reduced tissue iron content, the total iron concentration in S. europaea tissues was comparable to that of the controls. When the sulphide-tolerant species A. tripolium was grown in sulphide-containing media there was no significant effect on the tissue concentration of any of the elements investigated. These results are discussed in relation to possible mechanisms of sulphide toxicity and resistance.     

Environmental structures and variation in coastal vegetation of the Golfe du Lion (France)

On the French Mediterranean seashore, the essential environmental factors are: salinity, humidity, human activity, instability, and nature of the soil. Each of these factors presents a large range of variation. According to the values and the rhythm of changes presented by each of them a hierarchy of impacts has been established. As a consequence one ecological impact or another may be the result of the occurrence of mosaìcs in the plant cover. Thus, to explain the structures observed, it is necessary to distinguish between homogeneous systems in the landscape characterized by a similar hierarchy of impacts of the master factors. Analyses prove that vegetation units are either independent of each other (they are the reflection of a geomorphological structure, of climatic differences or of human influences), or organized into more or less complex phytoecological systems in which the mosaic of plant associations is governed by the activity of plant interactions. Some examples from salt ponds and sand dune systems explain these conclusions.     

The impact of grazing on plant communities,plant populations and soil conditions on salt marshes

Grazing an abandoned salt marsh causes retrogressive succession, since mid salt-marsh communities change into lower salt-marsh communities. Grazing and mowing are compared in detail. Both management practices enhance species diversity in an abandoned salt marsh. This can be attributed to the removal of litter. The finding that lower salt-marsh species appear more with grazing than with mowing or abandoning is not related to a higher soil salinity as compared to mowing or abandoning, but probably to locally baring of the soil by grazing animals. Only species of pioneer or unstable environments seem to have a persistent seed bank, for other species seed dispersal seems to be a limiting factor for their establishment.Nomenclature follows Heukels & van Ooststroom (1977) for species; Westhoff & den Held (1969) for syntaxa.Mrs R. Rusthoven analyzed the soil samples, Mr E. Leeuwinga drawed the figures, and Mrs J. O'Brien corrected the English text.     

The influence of food plant dispersion on caterpillar searching success

Abstract. 1. Collards (Brassica oleracea L.) grown in clumps were more difficult for unstarved, early instar cabbage white caterpillars (Pieris rapae L.) to find than collards spaced at regular intervals, although total plant densities were identical.
2. Early instar, unstarved larvae are less mobile than later instar larvae (our data) or starved larvae (Jones' 1977 data).
3. Starved larvae and late instar larvae tend to find plants more readily than do unstarved or younger larvae.
4. We contend that larval mobility governs the success of searching caterpillars and their sensitivity to variations in plant dispersion.
5. Our results show that the dispersion of targets can influence searching success even though target density is constant. This means that the degree of clumping in host plants is capable of influencing their availability to herbivores.     

Forward mutation assay of V79 cells to 6-thioguanine resistance in a soft agar technique that eliminates effects of metabolic co-operation

A technique involving culture in soft agar was used for the assay of forward mutation of V79 cells to 6-thioguanine (6TG) resistance. The main reason for the use of soft agar was to prevent reduction in recovery of mutants depending on the cell density plated for mutation selection, which is the chief problem in the liquid method, and which results mainly from metabolic co-operation due to cell-to-cell contact.V79 cells grew well in fortified soft agar medium (DMEM + 20% FBS) showing cloning efficiencies (>80%) as high as in liquid culture. Therefore, V79/HGPRT mutagenesis could be assayed quantitatively in soft agar culture.The frequency of 6TG-resistant colonies in agar selective medium increased linearly with increase in concentration of EMS. Toxicity and mutagenic responses were greater in soft agar than in liquid culture.In cultures of untreated and EMS-treated cells, more than 95% of the 6TG-resistant colonies isolated were aminopterin-sensitive.Use of soft agar for selection prevented the reduction in the number of mutants with increase in the size of incula on plating up to 1?2 × 10⁶ cells per 9-cm dish: in liquid culture, even with a lower plating number (2 × 10⁵ cells per 9-cm dish), a notable reduction in numbers of mutants was observed. This character was re-examined in a reconstruction experiment. The results show that, when up to 2 × 10⁶ cells were plated per 9-cm dish, 6TG-resistant cells were almost completely recovered from the soft agar medium, whereas only 10% were recovered from liquid culture.     

Persistence of Bacillus thuringiensis parasporal crystal insecticidal activity in soil

Spores and parasporal crystals of a Bacillus thuringiensis var. aizawai (H-serotype 7), strain HD137, streptomycin-resistant mutant were added to acidic (pH 5.0) natural and autoclaved soil and incubated at ?0.10 MPa, 25°C. Populations of B. thuringiensis in both soil treatments showed exponential rates of mortality which were represented by linear regression, the loss of viability being greater in natural than autoclaved soil. In natural soil, parasporal crystal insecticidal activity was lost at a complex, nonexponential rate. The initial, rapid decrease of activity gradually slowed, and the level of activity stabilized at 10% of the original inoculum level after 250 days incubation, until the cessation of sampling at >2 years. In autoclaved soil no significant (P > 0.2) loss of parasporal crystal insecticidal activity was detected over the same period, which suggested that soil microorganisms were responsible for the loss of crystal insecticidal activity in the natural, nonsterilized soil. The rate of loss of crystal activity in natural soil correlated well with assay data reported in the literature using Galleria mellonella, which measures the combined activity of spore and crystal. In autoclaved soil correlation was poor, probably due to variability in the bioassay data.     

Bluelight-induced,flavin-mediated transport of redox equivalents across artificial bilayer membranes

Summary This paper continues our studies of physico-chemical properties of vesicle-bound flavins. Based on previous results, an advanced model system was designed in order to study the mechanisms underlying bluelight-induced redox transport across artificial membranes. The lumen of single-shelled vesicles was charged with cytochromec, and amphiphilic flavin (AF1 3, AF1 10) was bound to the membrane. Upon bluelight irradiation redox equivalents are translocated from exogeneous 1e ^–(EDTA)-and 2e ^–(BH₃CN^–) donors across the membrane finally reducing the trapped cytochromec both under aerobic and anaerobic conditions. The mechanisms involved are explored and evidence for the involvement of various redox states of oxygen, dihydroflavin and flavosemiquinone is presented.     

Effect of Phospholipase Digestion and Lysophosphatidylcholine on Dopamine Receptor Binding

[3H]Spiperone specific binding by microsomal membranes isolated from sheep caudate nucleus is decreased by trypsin and phospholipase A2 (Vipera russeli), but is insensitive to neuraminidase. The inhibitory effect of phospholipase A2 is correlated with phospholipid hydrolysis. After 15 min of phospholipase (5 micrograms/mg protein) treatment, a maximal effect is observed; the maximal lipid hydrolysis is about 56% and produces 82% reduction in [3H]spiperone binding. Equilibrium binding studies in nontreated and treated membranes showed a reduction in Bmax from a value of 388 +/- 9.2 fmol/mg protein before phospholipase treatment to a value of 52 +/- 7.8 fmol/mg protein after treatment, but no change in affinity (KD = 0.24 +/- 0.042 nM) was observed. Albumin washing of treated membranes removes 47% of lysophosphatidylcholine produced by phospholipid hydrolysis without recovering [3H]spiperone binding activity. However, the presence of 2.5% albumin during phospholipase A2 action (1.5 micrograms/mg protein) prevents the inhibitory effect of phospholipase on [3H]spiperone binding to the membranes, although 28% of the total membrane phospholipid is hydrolysed. Lysophosphatidylcholine, a product of phospholipid hydrolysis, mimics the phospholipase A2 effect on receptor activity, but the [3H]spiperone binding inhibition can be reversed by washing with 2.5% defatted serum albumin. Addition of microsomal lipids to microsomal membranes pretreated with phospholipase does not restore [3H]spiperone stereospecific binding. It is concluded that the phospholipase-mediated inhibition of [3H]spiperone binding activity results not only from hydrolysis of membrane phospholipids, but also from an alteration of the lipid environment by the end products of phospholipid hydrolysis.     

In vitro characterization of salt stress effects and the selection of salt tolerant plants in rice (Oryza sativa L.)

Summary The response of plant cells to salt stress was studied on embryo derived calli of rice (Oryza sativa L.) in order to identify cellular phenotypes associated with the stress. The feasability of selecting salt tolerant callus and its subsequent regeneration to plants was also studied. Callus was grown on agar-solidified media containing 0%, 1% and 2% (w/v) NaCl for 24 days. Parameters such as fresh weight, dry weight, soluble protein and proline content were measured. The callus growth decreased markedly with increasing NaCl concentration in the medium. The proline content was enhanced several fold in salt stressed calli. A prolonged exposure of callus to the salt environment led to discolouration and arrested growth in the majority of the calli and only a small number of callus cells maintained healthy and stable growth. These variants were subcultured every three weeks for a period of four months onto medium containing 1% NaCl to identify tolerant lines. At the end of the third cell passage, the tolerant calli were transferred to regeneration medium to regenerate plants. The regeneration frequency in the salt-selected lines was enhanced when compared to unselected lines.