Environment factors influence in vitro interspecific interactions between A. ochraceus and other maize spoilage fungi,growth and ochratoxin production

The effect of water availability (water activity,a_w; 0.995–0.90) and temperature (18–30 °) on in vitro interactions between an ochratoxin producing strain of Aspergillus ochraceus and six other spoilage fungi was assessed in dual culture experiments on a maize meal-based agar medium. Inprimary resource capture of nutrient substrate, A. ochraceus was dominant against many of the interacting species, being able to overgrow and replace A. candidus, and sometimes A. flavus and the Eurotium spp. regardless of a_w or temperature. However, with freely available water (0.995 a_w) A. alternata and A. niger were dominant, with mutual antagonism between A. ochraceus and A. flavus at 25–30 °C. In the driest conditions tested (0.90 a_w) there was also mutual antagonism between A. ochraceus and the two Eurotium spp. Overall, under allconditions tested the Index of Dominance for A. ochraceus was much higher than for other competing species combined suggesting that A. ochraceus wasa good competitive colonist able to replace a numberof other species. However, the growth rate ofA. ochraceus was modified and decreased by the interaction with competitors. Interaction between A. ochraceus and species such as A. alternata (18°C/0.995) and Eurotium spp. (0.995–0.95 and 25–30 °C) resulted in a significant stimulation of ochratoxin production. Theresults are discussed in relation to the effect that environmental factors have on the possible competitiveness of A. ochraceus in the maizegrain ecosystem and the role of ochratoxin in nicheexclusion of competitors. This revised version was published online in June 2006 with corrections to the Cover Date.     

Role of the cocoon ofAcrolepiopsis assectella (Lep., Hyponomeutoidae) in host recognition by the parasitoidDiadromus pulchellus (Hym., Ichneumonidae)

The study of various behavioural criteria of femaleDiadromus pulchellus parasitoids in the presence of theirAcrolepiopsis assectella hosts has shown the essentially chemical nature of the stimulant determining host recognition. The physical stimuli of the cocoon seem not to be implicated. Thus cocoons whose original texture has been completely altered, either mechanically or chemically, as well as the silk excreted by the host caterpillars significantly stimulates the female parasitoids. The cocoon contact kairomones are detected in testing the aqueous extracts ofA. assectella which provoke a positive behavioural response from the females in a threshold concentration of 1 cocoon-equivalent. The comparison of aqueous extracts ofA. assectella host cocoons, and of non-host species:Bombyx mori, Ephestia kuehniella andCacoecimorpha pronubana demonstrate the kairomone specificity of the silk, the extracts of non-host cocoons being ignored by the parasitoid, as were the silk threads left byE. kuehniella caterpillars. Finally the contact kairomones linked to the silk seem to be independent of the host plant and of the nutrient diet of the host caterpillars. The cocoons spun by the caterpillars reared on leeks or on artificial diets with or without powdered leek provoke similar responses in the parasitoids.     

A new relationship for rarefaction

All diversity indices are functions of the vector of the numbers of individuals in different species in a statistical population. So they are also functions of the number of species. It is well known, from the species-area curve and from collector's curves, that the number of species is a function of sampling effort. The rarefaction and Coleman functions are both functions that allow comparisons to be made at the same number of individuals, but have different mathematical forms. We show that the numerical difference between them, in the samples we have studied, is negligibly small. We show how to modify the Coleman function to allow for sampling without replacement, and show that the modified function is identical to the hypergeometric rarefaction function. Rarefaction should always be used, with any index, when comparing diversity in different size samples, but the number of species is the preferred index. Suggestions for comparing rarefaction curves from different samples are made.     

Mycorrhizal promotion of host stomatal conductance in relation to irradiance and temperature

Colonization of roots and soil by arbuscular mycorrhizal (AM) fungi sometimes promotes stomatal conductance (g _s) of the host plant, but scientists have had difficulty predicting or manipulating the response. Our objective was to test whether the magnitude of AM influence on g _s is related to environmental conditions: irradiance, air temperature or leaf temperature. Stomatal conductances of two groups of uncolonized sorghum plants were compared to g _s of plants colonized by Glomus intraradices (Gi) or Gigaspora margarita (Gm) in 31 morning and afternoon periods under naturally varying greenhouse conditions. Stomatal conductance of Gi and Gm plants was often markedly higher than g _s of similarly sized nonAM plants. AM promotion of g _s was minimal at the lowest irradiances and lowest air and leaf temperatures, but was substantial at intermediate irradiance and temperatures. AM promotion was again low or absent at the highest irradiances and temperatures. Magnitude of AM promotion of g _s was not a function of absolute g _s. Promotion of g _s by Gi and Gm was remarkably similar. Differing phosphorus fertilization did not affect g _s.     

Advances in functional regulation mechanisms of plant aquaporins: Their diversity,gene expression,localization, structure and roles in plant soil-water relations (Review)

Aquaporins are important molecules that control the moisture level of cells and water flow in plants. Plant aquaporins are present in various tissues, and play roles in water transport, cell differentiation and cell enlargement involved in plant growth and water relations. The insights into aquaporins’ diversity, structure, expression, post-translational modification, permeability properties, subcellular location, etc., from considerable studies, can lead to an understanding of basic features of the water transport mechanism and increased illumination into plant water relations. Recent important advances in determining the structure and activity of different aquaporins give further details on the mechanism of functional regulation. Therefore, the current paper mainly focuses on aquaporin structure-function relationships, in order to understand the function and regulation of aquaporins at the cellular level and in the whole plant subjected to various environmental conditions. As a result, the straightforward view is that most aquaporins in plants are to regulate water flow mainly at cellular scale, which is the most widespread general interpretation of the physiological and functional assays in plants.     

Seasonal variation of leaf tissue elasticity in four forest tree species

Measures of leaf tissue elasticity were determined by analyzing the turgor pressure-water content relation developed from pressure-volume experiments, in four naturally occurring forest tree species. The relation between the bulk tissue elastic modulus and tissue turgor pressure varied by species and varied with state of leaf maturation through the growing season. Although the values of the elastic modulus reported here agree in magnitude with values reported in general for higher plant tissue, the functional dependency of the apparent elasticity on tissue water status was more complex in this study than can be accounted for by current models.     

Evolution and expression of class III peroxidases

Class III peroxidases are members of a large multigenic family, only detected in the plant kingdom and absent from green algae sensu stricto (chlorophyte algae or Chlorophyta). Their evolution is thought to be related to the emergence of the land plants. However class III peroxidases are present in a lower copy number in some basal Streptophytes (Charapyceae), which predate land colonization. Gene structures are variable among organisms and within species with respect to the number of introns, but their positions are highly conserved. Their high copy number, as well as their conservation could be related to plant complexity and adaptation to increasing stresses. No specific function has been assigned to respective isoforms, but in large multigenic families, particular structure-function relations can be expected. Plant peroxidase sequences contain highly conserved residues and motifs, variable domains surrounded by conserved residues and present a low identity level among their promoter regions, further suggesting the existence of sub-functionalization of the different isoforms.     

Transpiration efficiency of the grapevine cv. Semillon is tied to VPD in warm climates

Water‐use efficiency in grapevines is dependent on the aerial and below‐ground environment of the plant. Specifically, transpiration efficiency, the ratio of net carbon fixation to water loss, may be influenced by soil moisture and the leaf‐to‐air vapour pressure deficit (VPD) in the soil–plant–atmosphere continuum. The interactive effect of these abiotic parameters, however, has not been suitably investigated in field‐grown grapevines. Accordingly, gas exchange of an anisohydric variety, Semillon, was assessed across a number of vineyards in two warm grape‐growing regions of New South Wales (NSW) to ascertain how soil moisture and VPD interact to affect transpiration efficiency at the leaf level. Leaf gas exchange measurements demonstrated that the rate of transpiration (E) was driven by VPD, particularly under high soil moisture. Both high VPD and low soil moisture decreased photosynthesis (A) and instantaneous leaf transpiration efficiency (A/E). Increased intrinsic leaf transpiration efficiency (A/g) in response to drying soil was limited to vines growing in a non‐irrigated vineyard. In this site, A/g was negatively related to vine water status. VPD did not have a substantial influence on A/g in any vineyard. While VPD is the main driver for A/E, soil moisture is an important determinant of A/g. Under high VPD, stomatal closure in Semillon leaves was not substantial enough to suitably curtail transpiration, and as a consequence A/E declined. These data indicate that in warm climates, irrigation scheduling of anisohydric varieties must take into account both VPD and soil moisture so that vine water status can be maintained.