Relative importance of osmotic-stress and ion-specific effects on ABA-mediated inhibition of leaf expansion growth in Phaseolus vulgaris

The osmotic and ion-specific components of salt-induced inhibition of leaf expansion growth were investigated in beans grown from 12 h to several days in either NaCl-containing solution cultures, an isosmotic concentrated macronutrient solution, or a vermiculite–compost mixture with low Na⁺ but high Cl^– availability. Inhibition of leaf expansion and leaf ABA increase was more intense in the NaCl than in the isosmotic macronutrient treatment. Root Na⁺ was highly correlated to inhibition of leaf expansion and leaf or xylem sap ABA. When Na⁺ was sequestered in soil, salinized plants showed no reduction in leaf expansion or ABA increase, regardless of the presence of high leaf Cl^– concentrations. Stomatal conductance exhibited an exponential relationship with the reciprocal value of xylem sap ABA. Our results indicate that an ion-specific effect caused by Na⁺ in roots may account for an ABA-mediated reponse of both stomatal closure and leaf expansion inhibition.     

Evolution of spore release mechanisms in the saprolegniaceae (Oomycetes): evidence from a phylogenetic analysis of internal transcribed spacer sequences

Classical studies on spore release within the Saprolegniaceae (Oomycetes) led to the proposition that different mechanisms of sporangial emptying represent steps in an evolutionary transition series. We have reevaluated this idea in a phylogenetic framework using internal transcribed spacer sequences of four genera. These data were compared with the response to osmotic stress exhibited by each taxon. Saprolegnia emerges as the most basal genus, sister to Achlya, Thraustotheca, and Dictyuchus. Achlya and Thraustotheca are most closely related, while Dictyuchus appears to have evolved along a separate evolutionary lineage. The resulting phylogenetic framework is consistent with the idea that the mechanism of sporangial emptying exhibited by Saprolegnia represents the plesiomorphic condition from which the other mechanisms were derived independently. These alternative mechanisms of spore release may have resulted from a small number of mutations that inhibited axonemal development and altered the temporal and spatial expression of lytic enzymes that degrade the sporangial wall. Copyright 1998 Academic Press.     

Hepatopancreas but not ovary is the site of vitellogenin synthesis in female fresh water crab, Oziothelphusa senex senex

The objective of the present study was to explore the site of synthesis of vitellogenin (Vtg) in fresh water edible crab, Oziothelphusa senex senex. Vtg cDNA fragments were isolated from the hepatopancreas of female crabs using RT-PCR method, and the deduced amino acid sequence of O. senex senex showed more than 60% identity with other brachyuran Vtg sequences. RT-PCR analysis showed that Vtg mRNA can be detected only in hepatopancreas of female Oziothelphusa but not in other tissues including eyestalks, Y-organs, mandibular organs, thoracic ganglion, hypodermis and ovary. Antibodies were raised against vitellin purified from the ovary of O. senex senex. Immunoprecipitation analysis revealed the presence of Vtg in the hepatopancreas of vitellogenic stage I females and in the hemolymph, hepatopancreas and ovary extracts from vitellogenic stage II females but absent in hemolymph and hepatopancreas extract of males. These results suggest that Vtg is synthesized only in hepatopancreas but not in the ovaries of O. senex senex. In addition, Vtg synthesized in hepatopancreas is transported to ovary through hemolymph.     

Indirect Effects of Temperature on Stink Bug Fitness,via Maintenance of Gut-Associated Symbionts

Impacts of climate change on organisms are already apparent, with effects ranging from the individual to ecosystem scales. For organisms engaged in mutualisms, climate may affect population performance directly or indirectly through mediated effects on their mutualists. We tested this hypothesis for two stink bugs, Acrosternum hilare and Murgantia histrionica, and their gut-associated symbionts. We reared these species at two constant temperatures, 25 and 30°C, and monitored population demographic parameters and the presence of gut-associated symbionts with diagnostic PCR primer sets. Both stink bugs lost their respective gut symbionts within two generations at 30°C. In addition, the insect survivorship and reproductive rates of both A. hilare and M. histrionica at 30°C were lower than at 25°C. Other demographic parameters also indicated a decrease in overall insect fitness at the high temperature. Collectively our data showed that the decrease in host fitness was coupled with, and potentially mediated by, symbiont loss at 30°C. This work illustrates the need to better understand the biology of animal-symbiont associations and the consequences of local climate for the dynamics of these interactions.The effect of climate on organisms, communities, and the environment at large has become a pressing issue for biologists and environmental scientists. Recent studies indicate that previous forecasts were conservative in their predictions for the magnitude of global warming (29). Up-to-date models suggest that the global mean surface temperature will increase by 1.8 to 4°C by the year 2100 (11). The ecological impact of such warming is already apparent (35) in the effects seen on species fitness (24), range shifts (22), species interactions (10), and community structure (32).It is important to note that many macroorganisms live in symbiosis with microbes and that host fitness may be affected indirectly by higher temperatures due to the disruption of mutualistic relationships. Some corals, for example, have symbiotic relationships with photosynthesizing dinoflagellates (zoothanxellae) that provide them with nutrients (31). Higher water temperatures in reef ecosystems, among other factors, induce the expulsion of microbial symbionts by the host, resulting in coral bleaching (15). Therefore, it is plausible that observed effects of climate on species distribution or performance might stem from disruption of symbiotic interactions as much as from direct effects on host biology.Despite the current interest in insect-microbe symbioses, the vast majority of such systems have been poorly studied. A group of insects that has recently received some attention are the true bugs (Hemiptera, Pentatomomorpha). Studies in the early 1900s suggested that mutualistic bacteria colonized a portion of the gut of insects in different pentatomomorphan families (9). More specifically, monocultures of bacteria were present in high densities in the crypt- (or cecum-) bearing organ preceding the hindgut of hosts, with different bacterial taxa associated with different true bug families. Furthermore, studies have shown that these symbionts are mutualistic (1, 8, 13, 14, 26). Among these bug families, the stink bugs (Pentatomidae) have been shown to depend on their gut symbionts (1). Pentatomid symbionts are polyphyletic and closely related to plant-associated bacteria in the genera Erwinia and Pantoea (25). Although the mechanism of symbiont vertical transmission is poorly understood, females seem to smear the surface of eggs with bacteria while ovipositing (3). Aposymbiotic first instars hatch but remain on the surface of eggs and acquire the symbiont by probing on the egg surface, as evidenced by the fact that surface sterilization of egg masses generates aposymbiotic individuals (1, 26, 28).Climate change has already affected stink bug performance and geographic range (19, 20). In Japan, populations of two pentatomid species, Nezara viridula and N. antennata, have shifted northwards and to higher elevations, respectively, over the last 50 years (33). However, we found previously that for one of these species high temperature eliminated gut symbionts, without any clear decrease in host fitness (27). Thus, it remains unclear whether temperature change played a role, either directly or indirectly, in these geographic shifts. To better understand the extent to which temperature mediates stink bug ecology and prevalence of their gut bacteria, we conducted laboratory studies with two pentatomid species, Acrosternum hilare and Murgantia histrionica. We show that high temperature affects the symbiotic relationship, with concomitant reduction in insect fitness.     

Trophic supplements to intraguild predation

Intraguild predation (IGP) is a dominant community module in terrestrial food webs that occurs when multiple consumers feed both on each other and on a shared prey. This specific form of omnivory is common in terrestrial communities and is of particular interest for conservation biology and biological control given its potential to disrupt management of threatened or pest species. Extensive theory exists to describe the dynamics of three-species IGP, but these models have largely overlooked the potential for other, exterior interactions, to alter the dynamics within the IGP module. We investigated how three forms of feeding outside of the IGP module by intraguild predators (i.e. trophic supplementation) affect the dynamics of the predators (both IG predator and IG prey) and their shared resource. Specifically, we examined how the provision of a constant donor-controlled resource, the availability of an alternative prey species, and predator plant-feeding affect the dynamics of IGP models. All three forms of trophic supplements modified the basic expectations of IGP theory in two important ways, and their effects were similar. First, coexistence was possible without the IG prey being a superior competitor for the original shared resource if the IG prey could effectively exploit one of the types of trophic supplements. However, supplements to the IG predator restricted the potential for coexistence. Second, supplements to the IG prey ameliorated the disruptive effects of the IG predator on the suppression of the shared resource, promoting effective control of the resource in the presence of both predators. Consideration of these three forms of trophic supplementation, all well documented in natural communities, adds substantial realism and predictive power to intraguild predation theory.     

Angiotensin II increases adipose angiotensinogen expression

In addition to the well-defined contribution of the liver, adipose tissue has been recognized as an important source of angiotensinogen (AGT). The purpose of this study was to define the angiotensin II (ANG II) receptors involved in regulation of adipose AGT and the relationship of this control to systemic AGT and/or angiotensin peptide concentrations. In LDL receptor-deficient (LDLR(-/-)) male mice, adipose mRNA abundance of AGT was 68% of that in liver, and adipose mRNA abundance of the angiotensin type 1a (AT(1a)) receptor (AT(1a)R) was 38% of that in liver, whereas mRNA abundance of the angiotensin type 2 (AT(2)) receptor (AT(2)R) was 57% greater in adipose tissue than in liver. AGT and angiotensin peptide concentrations were decreased in plasma of AT(1a)R-deficient (AT(1a)R(-/-)) mice and were paralleled by reductions in AGT expression in liver. In contrast, adipose AGT mRNA abundance was unaltered in AT(1a)R(-/-) mice. AT(2)R(-/-) mice exhibited elevated plasma angiotensin peptide concentrations and marked elevations in adipose AGT and AT(1a)R mRNA abundance. Increases in adipose AGT mRNA abundance in AT(2)R(-/-) mice were abolished by losartan. In contrast, liver AGT and AT(1a)R mRNA abundance were unaltered in AT(2)R(-/-) mice. Infusion of ANG II for 28 days into LDLR(-/-) mice markedly increased adipose AGT and AT(1a)R mRNA but did not alter liver AGT and AT(1a)R mRNA. These results demonstrate that differential mRNA abundance of AT(1a)/AT(2) receptors in adipose tissue vs. liver contributes to tissue-specific ANG II-mediated regulation of AGT. Chronic infusion of ANG II robustly stimulated AT(1a)R and AGT mRNA abundance in adipose tissue, suggesting that adipose tissue serves as a primary contributor to the activated systemic renin-angiotensin system.