Effects of Culture Conditions on Poly(beta-Hydroxybutyric Acid) Production by Haloferax mediterranei

The halobacterium Haloferax mediterranei accumulates poly(beta-hydroxybutyrate) (PHB) as intracellular granules. The conditions for PHB production in batch and continuous cultures have been studied and optimized. Phosphate limitation is essential for PHB accumulation in large quantities. Glucose and starch are the best carbon sources. With 2% starch, 0.00375% KH(2)PO(4), and 0.2% NH(4)Cl in batch culture, a production of ca. 6 g of PHB per liter was reached, being 60% of the total biomass dry weight, and giving a yield over the carbon source of 0.33 g/g. The PHB production in continuous cultures was stable over a 3-month period. Our results demonstrate that H. mediterranei is an interesting candidate for industrial production of biological polyesters.     

‘Salivary secretions’ of eriophyoids (Acari: Eriophyoidea): first results of an experimental model

This paper concerns an approach to direct collection of eriophyoid salivary secretions, and reports preliminary results on biological assays providing evidence for the presence of plant growth promoting substances in these secretions. Eleven species belonging to the Phytoptidae, Eriophyidae and Diptilomiopidae, characterized by different host–plant interactions, were studied by immersing mites into the following oils: condensate of cedar oil, oil for immersion lenses, two kinds of olive oil, -terpineol, hystolemon, vaseline oil, and soybean oil. Some species secreted small droplets of lipophobic substances at the tip of their mouthparts when they were immersed in objective lens oil. Mite mortality and percentage of secreting specimens depended on the species and the medium used. Aceria caulobia (Nalepa) was selected as the candidate for subsequent study, because this species displayed a higher percentage of secreting mites than the other species and numerous specimens were easily collected by means of an airflow and filtering device. The induced secretions were studied from January to June of 2000, 2001 and 2002. Rapid salivary bioassays were performed during the period of maximum induced secretion in 2001. They were evaluated using a wheat-coleoptile and an excised-radish-cotyledon growth test, respectively, for indole-3-acetic acid-like and cytokinin-like activity. The bioassays suggested the presence of chemicals with plant growth regulatory effects. A brief account of eriophyoid mortality in the oils was also given.     

Sedimentation equilibrium in a solution containing an arbitrary number of solute species at arbitrary concentrations: theory and application to concentrated solutions of ribonuclease

Simple expressions are derived describing the equilibrium concentration gradient of each species in a solution containing an arbitrary number of solute species at arbitrary concentration, as a function of the concentration of all species. Quantitative relationships between the species gradients and experimentally observable signal gradients are presented. The expressions are model-free and take into account both attractive and repulsive interactions between all species. In order to analyze data obtained from strongly nonideal solutions, a statistical thermodynamic model for repulsive solute-solute interactions is required. The relations obtained are utilized to analyze the dependence of the equilibrium gradient of ribonuclease A in phosphate-buffered saline, pH 7.4, upon total protein concentration. Experimental results are interpreted in the context of a model for weak self-association leading to the formation of significant amounts of oligomers at total protein concentrations exceeding 25 g/l.     

Carboxypeptidase E is required for normal synaptic transmission from photoreceptors to the inner retina

Defects in the gene encoding carboxypeptidase E (CPE) in either mouse or human lead to multiple endocrine disorders, including obesity and diabetes. Recent studies on Cpe-/- mice indicated neurological deficits in these animals. As a model system to study the potential role of CPE in neurophysiology, we carried out electroretinography (ERG) and retinal morphological studies on Cpe-/- and Cpe fat/fat mutant mice. Normal retinal morphology was observed by light microscopy in both Cpe-/- and Cpe(fat/fat) mice. However, with increasing age, abnormal retinal function was revealed by ERG. Both Cpe-/- and Cpe fat/fat animals had progressively reduced ERG response sensitivity, decreased b-wave amplitude and delayed implicit time with age, while maintaining a normal a-wave amplitude. Immunohistochemical staining showed specific localization of CPE in photoreceptor synaptic terminals in wild-type (WT) mice, but in both Cpe-/- and Cpe fat/fat mice, CPE was absent in this layer. Bipolar cell morphology and distribution were normal in these mutant mice. Electron microscopy of retinas from Cpe fat/fat mice revealed significantly reduced spherule size, but normal synaptic ribbons and synaptic vesicle density, implicating a reduction in total number of vesicles per synapse in the photoreceptors of these animals. These results suggest that CPE is required for normal-sized photoreceptor synaptic terminal and normal signal transmission to the inner retina.     

Leaf movements and photoinhibition in relation to water stress in field-grown beans

Photoinhibition in plants depends on the extent of light energy being absorbed in excess of what can be used in photochemistry and is expected to increase as environmental constraints limit CO2 assimilation. Water stress induces the closure of stomata, limiting carbon availability at the carboxylation sites in the chloroplasts and, therefore, resulting in an excessive excitation of the photosynthetic apparatus, particularly photosystem II (PSII). Mechanisms have evolved in plants in order to protect against photoinhibition, such as non-photochemical energy dissipation, chlorophyll concentration changes, chloroplast movements, increases in the capacity for scavenging the active oxygen species, and leaf movement or paraheliotropism, avoiding direct exposure to sun. In beans (Phaseolus vulgaris L.), paraheliotropism seems to be an important feature of the plant to avoid photoinhibition. The extent of the leaf movement is increased as the water potential drops, reducing light interception and maintaining a high proportion of open PSII reaction centres. Photoinhibition in water-stressed beans, measured as the capacity to recover F(v)/F(m), is not higher than in well-watered plants and leaf temperature is maintained below the ambient, despite the closure of stomata. Bean leaves restrained from moving, increase leaf temperature and reduce qP, the content of D1 protein and the capacity to recover F(v)/F(m) after dark adaptation, the extent of such changes being higher in water-stressed plants. Data are presented suggesting that even though protective under water stress, paraheliotropism, by reducing light interception, affects the capacity to maintain high CO2 assimilation rates throughout the day in well-watered plants.     

Evidence for increased proton dissociation in low-activity forms of dephosphorylated squash-leaf nitrate reductase

The pH dependence of squash-leaf nitrate reductase has been studied. It has been found that high- and low-activity forms of purified nitrate reductase (both forms dephosphorylated) have different optimum pH values. A high-activity form has always a higher pH optimum compared with a low-activity form. Model computations show that the decrease in activity and the corresponding change of the pH optimum is apparently due to a conformation-dependent increase of proton dissociation of the enzyme. As previously shown, this behavior is also observed in leaf extracts during the conversion (and probably phosphorylation of nitrate reductase) from a high-active form to a low-active form when plants are transferred from light to darkness.     

From signal transduction to autophagy of plant cell organelles: lessons from yeast and mammals and plant-specific features

Autophagy is an evolutionarily conserved intracellular process for the vacuolar degradation of cytoplasmic constituents. The central structures of this pathway are newly formed double-membrane vesicles (autophagosomes) that deliver excess or damaged cell components into the vacuole or lysosome for proteolytic degradation and monomer recycling. Cellular remodeling by autophagy allows organisms to survive extensive phases of nutrient starvation and exposure to abiotic and biotic stress. Autophagy was initially studied by electron microscopy in diverse organisms, followed by molecular and genetic analyses first in yeast and subsequently in mammals and plants. Experimental data demonstrate that the basic principles, mechanisms, and components characterized in yeast are conserved in mammals and plants to a large extent. However, distinct autophagy pathways appear to differ between kingdoms. Even though direct information remains scarce particularly for plants, the picture is emerging that the signal transduction cascades triggering autophagy and the mechanisms of organelle turnover evolved further in higher eukaryotes for optimization of nutrient recycling. Here, we summarize new research data on nitrogen starvation-induced signal transduction and organelle autophagy and integrate this knowledge into plant physiology.     

Field assessment of host plant specificity and potential effectiveness of a prospective biological control agent, Aceria salsolae, of Russian thistle, Salsola tragus

The eriophyid mite, Aceria salsolae de Lillo and Sobhian, is being evaluated as a prospective classical biological control agent of invasive alien tumbleweeds, including Salsola tragus, S. collina, S. paulsenii and S. australis, in North America. Previous laboratory experiments to determine the host specificity of the mite indicated that it could sometimes persist and multiply on some nontarget plants, including Bassia hyssopifolia and B. scoparia. These are both European plants whose geographic range overlaps that of the mite, but the mite has never been observed on them in the field. A field experiment was conducted in Italy to determine if the mite would infest and damage these plants under natural outdoor conditions. The results indicate that this mite does not attain significant populations on these nontarget plants nor does it significantly damage them. Salsola tragus was heavily infested by A. salsolae, and plant size was negatively correlated to the level of infestation. Although S. kali plants were also infested, their size did not appear to be affected by the mites. The other nontarget plants were not as suitable for the mite in the field as in previous laboratory experiments. We conclude that there would be no significant risk to nontarget plants as a result of using A. salsolae as a biological agent to control Salsola species in North America.     

Effectiveness of eriophyid mites for biological control of weedy plants and challenges for future research

Eriophyid mites have been considered to have a high potential for use as classical biological control agents of weeds. We reviewed known examples of the use of eriophyid mites to control weedy plants to learn how effective they have been. In the past 13 years, since Rosenthal’s 1996 review, 13 species have undergone some degree of pre-release evaluation (Aceria genistae, A. lantanae, Aceria sp. [boneseed leaf buckle mite (BLBM)], A. salsolae, A. sobhiani, A. solstitialis, A. tamaricis, A. thalgi, A. thessalonicae, Cecidophyes rouhollahi, Floracarus perrepae, Leipothrix dipsacivagus and L. knautiae), but only four (A. genistae, Aceria sp. [BLBM], C. rouhollahi and F. perrepae) have been authorized for introduction. Prior to this, three species (Aceria chondrillae, A. malherbae and Aculus hyperici) were introduced and have become established. Although these three species impact the fitness of their host plant, it is not clear how much they have contributed to reduction of the population of the target weed. In some cases, natural enemies, resistant plant genotypes, and adverse abiotic conditions have reduced the ability of eriophyid mites to control target weed populations. Some eriophyid mites that are highly coevolved with their host plant may be poor prospects for biological control because of host plant resistance or tolerance of the plant to the mite. Susceptibility of eriophyids to predators and pathogens may also prevent them from achieving population densities necessary to reduce host plant populations. Short generation time, high intrinsic rate of increase and high mobility by aerial dispersal imply that eriophyids should have rapid rates of evolution. This raises concerns that eriophyids may be more likely to lose efficacy over time due to coevolution with the target weed or that they may be more likely to adapt to nontarget host plants compared to insects, which have a longer generation time and slower population growth rate. Critical areas for future research include life history, foraging and dispersal behavior, mechanisms controlling host plant specificity, and evolutionary stability of eriophyid mites. This knowledge is critical for designing and interpreting laboratory and field experiments to measure host plant specificity and potential impact on target and nontarget plants, which must be known before they can be approved for release. One of the more successful examples of an eriophyid mite controlling an invasive alien weed is Phyllocoptes fructiphilus, whose impact is primarily due to transmission of a virus pathogenic to the target, Rosa multiflora. Neither the mite nor the virus originated from the target weed, which suggests that using “novel enemies” may sometimes be an effective strategy for using eriophyid mites.     

What’s “cool” on eriophyoid mites?

Fundamental knowledge on the morphology, biology, ecology, and economic importance of Eriophyoidea has been exhaustively compiled by Lindquist et al. (Eriophyoid mites—their biology, natural enemies and control; Elsevier, 1996). Since that time, the number of recognized species and the economic importance of the taxon have increased substantially. The aim of this paper is to analyze and briefly review new findings from eriophyoid mites’ literature after Lindquist et al. book, stressing persistent gaps and needs. Much recent attention has been given to sampling and detection, taxonomy and systematics, faunistic surveys, internal morphology, rearing techniques, biological and ecological aspects, biomolecular studies, and virus vectoring. Recommendations are made for integrating research and promoting broader dissemination of data among specialists and non-specialists.