Searching for a model for use in vegetation analysis

Summary Indirect gradient analysis methods require an explicit vegetation model which must be based on direct gradient analysis studies. Various vegetation models are reviewed. Field evidence for the models is discussed. Experimental studies of species response to environmental gradients are reviewed and discussed. Three types of gradient are recognized as important for development of models: indirect environmental gradients where the environmental factor has no direct physiological influence on plant growth e.g. elevation; direct environmental gradients where the factor has a direct physiological effect on growth but is not an essential resource, e.g. pH; resource gradients where the factor is an essential resource for plant growth. The behaviour of the ecological carrying capacity and the role of competition along such gradients are shown to be important for developing vegetation models.     

Local immunity and the uterine cervix: Implications for cancer-associated viruses

Summary Studies of cervical secretions as well as cells composing the endocervix have provided evidence for a functional and potentially important immunological system in the mucosa of that organ. The availability of the tools of cell biology as well as three agents that may be used as probes to infect cervical mucosa experimentally has made possible a detailed approach to define the structural and functional characteristics of local cervical immunity. A long-term goal of these studies is to determine how the cervical immune response may be regulated to reduce local viral replication and virus-associated diseases. With Langerhans cells for antigen presentation, cervical immune responses generally remain detectable for more than 30 days, are predominantly of the IgA isotype, can be influenced by estrogen or progesterone, and are best elicited by local rather than systemic exposure to antigen. Cervical immune responses to the human papillomaviruses (HPV) are of particular importance in this regard because this virus is associated with cervical neoplasia. While responses in serum to HPV-16 proteins L1, E4, and E7 has been found in up to 78% of persons with HPV-associated cervical neoplasms, data showing that a local response of comparable frequency consistently occurs have yet to be confirmed. The current status of local HPV-16-specific immunoglobulin as a potentially useful indicator of HPV-16-related infection or pre-cancer is controversial, and is confounded by several potentially important factors, including patient age, estrogen/progesterone level, smoking status, and sample admixture with serum immunoglobulin.     

Reproduction and development of the weakly electric fish,Pollimyrus isidori (Mormyridae,Teleostei) in captivity

Synopsis No clear sexual dimorphism occurs in Pollimyrus isidori. Females usually grew slightly larger than males. The anal-fin reflex, however, makes it easy to discriminate between males and females. Spawning took place during the first six hours of the dark phase, in the territory of the male. During each spawning act 2–4 eggs were laid. The male put the eggs into a well-hidden nest previously constructed from plant material. The eggs, free embryos, and larvae of several spawnings were guarded by the male for several weeks. The females laid on average 120 eggs per fractional spawning. The eggs were 2 mm in diameter, not adhesive and very yolky. There was a relationship between pH and viability (% embryos hatched). Hatching occurred on the third day after spawning. The respiratory network of segmental origin in the median fin fold was well developed in the free embryos. Transition to exogenous feeding occurred on day 14. The larval period ended when the fish were 15 mm long and 40–50 days old. First gonadal recrudescence occurred at a total length of 6 cm (about 200 days old). The environmental factors decreasing conductivity and pH, increasing water level, and imitation of rain led to gonadal recrudescence, but pH did not act as a cue. Recrudescence was triggered by a decrease of conductivity, but absolute values or ionic composition of the water were not important. Maturation was completed after about fifty days. Mature and spawning fish no longer required any variation of these environmental factors to maintain mature gonads. A steady and considerable increase in conductivity led to gonadal regression. The fish did not show postbreeding refractoriness.     

Seasonal environmental predictability and homing in riverine fishes

Synopsis A recent paper by L'Abée-Lund & Vøllestad (1985) discussed the importance of environmental predictability in the evolution of natal stream homing in fishes. While we agree that there is a relationship between predictability and homing, we dispute the authors' contention that fall spawning fishes home more frequently than spring spawners. We also challenge the generalization that riverine environments are more predictable in fall than in spring, and present flow data from several salmonid spawning rivers in British Columbia, Canada to bolster our argument.     

Analysis of vegetation-environment relationships using a simultaneous equations model

The simultaneous equations model based on regression analysis was adopted to analyse relations between vegetation and environment in a forest reserve in the eastern part of Poland. It allowed a direct analysis of the vegetational variation caused by both environmental factors and interactions between species. In the system sampled several significant interrelations were found, and the ecological importance of particular factors and species was determined. Similar analysis performed by reciprocal averaging did not yield such satisfactory results, because of the equivocal correlation pattern between ecological variables and ordination axes, the dominance of the first axis and the exclusion of interspecific relations.     

Variation in kafirin and alcohol-soluble glutelin chromatograms of sorghum inbred lines revealed by reversed-phase high-performance liquid chromatography

Summary Separations of kafirin and alcohol soluble glutelin proteins by reversed-phase high-performance liquid chromatography (RP-HPLC) from 7 inbreds and one hybrid of sorghum [Sorghum bicolor (L.) Moench] and one source of Johnsongrass [Sorghum halapense (L.) Pers.] were compared. Objectives were to assess the stability of protein profiles for seed sources produced at different locations and in different environments to examine the potential of RP-HPLC to provide genotypic profiles for sorghum. Analyses of variance data showed that levels of variation due to environments and locations were small; the majority of variation (93%) was among genotypes. Associations among inbreds revealed by multivariate and cluster analysis showed similarity with those that would be expected on the basis of pedigree. A chi-square analysis showed no deviation in the hybrid profile from the expected 21 ratio of peaks from the female and male inbred parents, respectively. Improvements in the ability to correctly assign common peaks are necessary before associations among numerous sorghum genotypes can be reliably demonstrated by analysis of data from reversed-phase high-performance liquid chromatography (RP-HPLC).     

Changes in the chemical composition of carbohydrates and proteins in surface water during a bloom ofMicrocystis in Lake Suwa

Carbohydrates and proteins in surface water during a bloom ofMictrocystis, which is the dominant summer phytoplankton in Lake Suwa, were analyzed in order to evaluate the function ofMicrocystis in organic matter metabolism. Glucose was the predominant sugar constituent of the cellular carbohydrate fraction and decreased in quantity from inside towards the outside of the cell through the slime layer. Other constituent sugars, on the other hand, were present in larger proportions in the lake water. Although the sugar composition of the cells did not change in July and August, during the first period of theMicrocystis bloom, it changed appreciably in September when the water temperature decreased below 20°C accompanied by the decrease in solar radiation and a marked change in nutrient concentration. It appears that the sugar composition of the cells may change in response to some environmental stresses. In addition, a temporal change in the sugar composition was found, particularly in the fraction containing the slime extracted by shaking. Among the constituent amino acids of the cells, the percentage of arginine, aspartic acid and leucine decreased from inside toward the outside of the cell, while glutamic acid, threonine, serine and glycine showed an opposite trend. In contrast to the carbohydrates, the percentage composition of each amino acid varied little throughout the period of the bloom.     

Auxin production by plant associated bacteria: impact on endogenous IAA content and growth of Triticum aestivum L.

Aims:  The aim of this study was to investigate the potential of bacterial strains of Bacillus, Pseudomonas, Escherichia, Micrococcus and Staphylococcus genera associated with wild herbaceous flora to enhance endogenous indole-3-acetic acid (IAA) content and growth of Triticum aestivum var. Inqalab-91.
Methods and Results:  Gas chromatography and mass spectrometric (GC–MS) analysis revealed that bacterial strains produced 0·6–8·22 μg IAA ml⁻¹ in the presence of L-tryptophan. Plant microbe experiments showed a significant positive correlation between auxin production by bacterial strains and endogenous IAA content of T. aestivum for GC–MS ( r  = 0·618; P  = 0.05) and colorimetric analysis ( r  = 0·693; P  = 0.01). Similarly, highly significant positive correlation for shoot length ( r  = 0·627; P  = 0.01) and shoot fresh weight ( r  = 0·626; P  = 0.01) was observed with auxin production under axenic conditions. Bacterial inoculations also enhanced shoot length (up to 29·16%), number of tillers (up to 97·35%), spike length (up to 25·20%) and seed weight (up to 13·70%) at final harvest.
Conclusions:  Bacterial strains have the ability to increase the endogenous IAA content and growth of T. aestivum var. Inqalab-91.
Significance and Impact of the Study:  Microbial strains of wild herbaceous flora can be effectively used to enhance the growth and yield of agronomically important crops.     

Life-history variation in agricultural and wild populations of Erucastrum nasturtiifolium (Brassicaceae)

In the present study we relate the variability in life-history traits (such as flowering time and lifespan) of the herbaceous biennial–perennial Erucastrum nasturtiifolium (Brassicaceae) to habitat type. We studied plant populations from arable fields and from eroded mountain habitats, such as badlands and rocky slopes. Collection sites ranged from low basin to sub-alpine regions in the NE Iberian Peninsula. Plants were grown under common garden conditions to evaluate genetic variation among and within populations. Plants were also subjected to a resource gradient to detect genetic variation in phenotypic plasticity. The populations exhibited differentiation across a number of life-history traits (mainly flowering time and lifespan) and morphological traits related to growth (basal stem diameter, plant height and number of branches). This suggests that life-history differences among populations are genetically based. Moreover, our results show that variation in flowering time and lifespan are affected by habitat type independent of other abiotic factors such as altitude or continentality. Thus, populations from arable fields started flowering in their first year and displayed annual cycles, whereas those from wild habitats generally flowered in their second year and showed biennial or even perennial cycles. Intra-population differences in flowering time were observed in only one population, and were related to nutrient availability. We suggest that early-flowering and shorter lifespan populations of E. nasturtiifolium may have been selected from late-flowering and longer lifespan populations as part of a selective process ensuring survival and future offspring amidst unpredictable and frequently disturbed environments such as exist in many agricultural habitats.