Microbodies in fungi: a review

Summary Microbodies are ubiquitous organelles in fungal cells, occurring in both vegetative hyphae and spores. They are bounded by a single membrane and may contain a crystalloid inclusion with subunits spaced at regular intervals. Typically, they contain catalase which reacts with the cytochemical stain 3,3-diaminobenzidine to yield an electron-opaque product, urate oxidase,l--hydroxy acid oxidase andd-amino acid oxidase. Their fragility and the necessity to disrupt the tough fungal cell wall before isolating them make them difficult to isolate. Analysis of enzymes in purified or partially purified microbodies from fungi indicates that they participate in fatty acid degradation, the glyoxylate cycle, purine metabolism, methanol oxidation, assimilation of nitrogenous compounds, amine metabolism and oxalate synthesis. In organisms where microbodies are known to contain enzymes of the glyoxylate cycle, they are known as glyoxysomes; where they are known to contain peroxidatic activity, they are known as peroxisomes. In some cases microbodies contain enzymes for only a portion of a pathway or cycle. Thus, they must be involved in metabolic cooperation with other organelles, particularly mitochondria. The number, size and shape of microbodies in cells, their buoyant density and their enzyme contents may vary with the composition of the medium; their proliferation in cells is regulated by the growth environment. The isolation from the same organism of microbodies with different buoyant densities and different enzymes suggests strongly that more than one type of microbody can be formed by fungi.     

Arabidopsis: Sensitivity of growth to high temperature

Arabidopsis thaliana seedlings as measured by an electrolyte leakage assay, have been found to be extremely sensitive to high temperature stress as compared to a high temperature tolerant variety (Tracy) of soybean. Over 50% ion leakage occurred in Arabidopsis leaves during a 15-minute exposure to 50°C, indicating a heat killing time of less than 15 minutes. In contrast, the heat killing time for soybean at 50°C was over five times longer. When soybean or Arabidopsis seedlings in culture plates were exposed to 37°C for 2 hours and then returned to 23°C, they suffered no apparent short-term or long-term damage. Soybean seedlings given a 42°C, treatment for 2 hours also showed no damage. Arabidopsis seedlings after a 42°C treatment for 2 hours showed no apparent immediate damage, but 48 hours after return to 23°C severe damage symptoms were visible and after 96 hours all the seedlings were dead. Both soybean and Arabidopsis seedlings synthesize heat shock proteins (hsps) when exposed to 42°C for 2 hours. The hsps synthesized are of similar molecular weights, although the relative abundances of the different size classes are very different in the two plants. Even though hsps are produced in Arabidopsis seedlings after a 2 hour exposure to 42°C their presence is not sufficient for the seedlings to recover from the effects of rhe heat shock when returned to 23°C. Our results show that Arabidopsis has a heat sensitive genotype. This along with its other characteristics should make it a good model system in which to assay in transgenic plants, the functions of homologous and heterologous genes that might be candidates for determining heat tolerance in plants.     

Time-Dependent Increase in Protein Phosphorylation Following One-Trial Enhancement in Hermissenda

Abstract: One-trial conditioning of the nudibranch mollusk Hermissenda produces short- and long-term changes in excitability (enhancement) of identified sensory neurons. To investigate the biochemical mechanisms underlying this example of plasticity, we have examined changes in protein phosphorylation at different times following the in vitro conditioning trial. Changes in the incorporation of ³²PO₄ into proteins were determined using two-dimensional polyacrylamide gel electrophoresis, autoradiography, and densitometry. Conditioning resulted in increases in levels of several phosphoproteins, five of which, ranging in apparent molecular mass from 22 to 55 kDa, were chosen for analysis. The increased phosphorylation of the 46- and 55-kDa phosphoproteins detected 2 h postconditioning was significantly greater than the level of phosphorylation detected in an unpaired control group, indicating that long-term enhancement is pairing specific. Statistically significant increases in phosphorylation as compared with the control group that received only light were detected immediately after conditioning (5 min) for the 55-, 46-, and 22-kDa phosphoproteins, at 1 h for the 55- and 46-kDa phosphoproteins, and at 2 h for the 55-, 46-, and 22-kDa phosphoproteins. The 46- and 55-kDa phosphoproteins are putative structural proteins, and the 22-kDa phosphoprotein is proposed to be a protein kinase C substrate previously identified in Hermissenda following multitrial classical conditioning. Time-dependent increases in protein phosphorylation may contribute to the induction and maintenance of different memory stages expressed in sensory neurons after one-trial conditioning.     

Influence of galls of Phanacis taraxaci on carbon partitioning within common dandelion, Taraxacum officinale

We examined how leaf galls, induced by the cynipid wasp Phanacis taraxaci, influence the partitioning of photoassimilates within the host, the common dandelion, Taraxacum officinale. Galled and ungalled plants were exposed to ¹⁴CO₂ and the labelled photoassimilates accumulating within galls and other parts of the host were measured. During the growth phase of the gall they were physiological sinks for photoassimilates, accumulating 9% to 70% of total carbon produced by the host, depending upon the number of galls per plant. High levels of ¹⁴C assimilation in the leaves of galled plants compared to controls, suggest that galls actively redirect carbon resources from unattacked leaves of their host plant. This represents a significant drain on the carbon resources of the host, which increases with the number and size of galls per plant. Active assimilation of ¹⁴C by the gall is greatest in the growth phase and is several orders of magnitude lower in the maturation phase. This finding is consistent with physiological and anatomical changes that occur during the two phases of gall development and represents a key developmental strategy by cynipids to ensure adequate food resources before larval growth begins.     

LACK OF CALLING SONG DISPLACEMENT BETWEEN TWO CLOSELY RELATED GROUND CRICKETS

Thorough examinations of purported cases of reproductive character displacement are critical for reaching an understanding of the role of reinforcement in the evolution of reproductive barriers between closely related species. In this paper, we report the results of an extensive investigation of male calling song variation in the ground crickets, Allonemobius fasciatus and A. socius. Contrary to the results of an earlier study, we uncovered little evidence of displacement of songs in areas of overlap. We discuss explanations for the lack of displacement as well as for the discrepancies between the results of the current study and those of the earlier study.     

Waxes enhance Plutella xylostella oviposition in response to sinigrin and cabbage homogenates

Oviposition by the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae), on substrates treated with host stimuli (cabbage homogenate or sinigrin) and/or waxes (paraffin or a mixture of 10 single chain n-alkanes) was quantified using continuous observations and endpoint bioassays. Paraffin or an n-alkane mixture applied over cabbage homogenate or sinigrin caused an increase in oviposition compared to that on any single stimulus in choice tests. Sinigrin alone at 10^–5 M to 10^–2 M is an ovipositional stimulant; addition of alkane over sinigrin made all sinigrin concentrations (10^–6 M to 10^–2 M) significantly more stimulatory than controls. Waxes alone do not stimulate oviposition. In choice tests, insect movement between sinigrin/alkane treatment combinations was random, however, once encountered, visit duration was significantly longer on sinigrin with alkane than on sites treated with either stimulus alone. Given the ubiquity of waxes on plant surfaces and the interaction between waxes and host-specific chemical stimuli, waxes should be included when considering factors that significantly influence herbivore host acceptance.     

Fetal cells in maternal blood: recovery by charge flow separation

Fetal blood cells can be recovered from the maternal circulation by charge flow separation (CFS), a method that obviates the risks associated with amniocentesis and chorionic villus sampling. By CFS, we processed blood samples from 13 women carrying male fetuses, 2 carrying fetuses with trisomy 21, and 1 who had delivered a stillborn infant with trisomy 18. On average more than 2000 fetal nucleated red blood cells were recovered per 20-ml sample of maternal blood. Recovery of fetal cells was confirmed by fluorescence in situ hybridization with probes for chromosomes Y, 18 and 21. After culturing of CFS-processed cells, amplification by the polymerase chain reaction revealed Y-chromosomal DNA in clones from four of six women bearing male fetuses, but not in clones from three women bearing female fetuses. Received: 8 January 1996 / Revised: 22 March 1996     

Detection of Tastes in Mixture with Other Tastes: Issues of Masking and Aging

When one taste (masker) is strong enough, it can completelymask another taste (target) of different quality. How strongthe masker must be to do this depends on how strong the targetis. As the target concentration is increased, the masking concentrationmust be increased, too, but in ever-increasing proportion. Toquantify the conditions for such complete masking, the target'sdetection threshold was measured as a function of the masker'sconcentration, from zero to strong. This was done for 12 binarycombinations of sucrose, sodium chloride, citric acid and quininehydrochloride. The 12 functions generated show that some tastantsmask each other much more efficiently than others. Masking givesnew insight into the role of aging in taste: older (66–90years) subjects' thresholds, regardless of masking concentration,always measured a constant factor higher than younger (18–29years) subjects' thresholds (about two to seven times higher,depending on target tastant). Thus, with increasing level ofthe masker, the thresholds of young and elderly go up in parallel.Thresholds of tastants in water alone are false predictors ofelderly persons' ability to perceive ingredients like salt andsugar condiments in foods, where, because of masking, theirthresholds can be several times higher than in water. Age manifesteditself relatively mildly in sucrose and citric acid, moderatelyin sodium chloride, and strongly in quinine hydrochloride. Chem.Senses 21: 211–221, 1996.     

Cyclic electron flow around Photosystem II in vivo

The oxygen flash yield (Y_O2) and photochemical yield of PS II (_{PS II}) were simultaneously detected in intact Chlorella cells on a bare platinum oxygen rate electrode. The two yields were measured as a function of background irradiance in the steady-state and following a transition from light to darkness. During steady-state illumination at moderate irradiance levels, Y_O2 and _{PS II} followed each other, suggesting a close coupling between the oxidation of water and Q_A reduction (Falkowski et al. (1988) Biochim. Biophys. Acta 933: 432–443). Following a light-to-dark transition, however, the relationship between Q_A reduction and the fraction of PS II reaction centers capable of evolving O₂ became temporarily uncoupled. _{PS II} recovered to the preillumination levels within 5–10 s, while the Y_O2 required up to 60 s to recover under aerobic conditions. The recovery of Y_O2 was independent of the redox state of Q_A, but was accompanied by a 30% increase in the functional absorption cross-section of PS II (_{PS II}). The hysteresis between Y_O2 and the reduction of Q_A during the light-to-dark transition was dependent upon the reduction level of the plastoquinone pool and does not appear to be due to a direct radiative charge back-reaction, but rather is a consequence of a transient cyclic electron flow around PS II. The cycle is engaged in vivo only when the plastoquinone pool is reduced. Hence, the plastoquinone pool can act as a clutch that disconnects the oxygen evolution from photochemical charge separation in PS II.Abbreviations ADRY acceleration of the deactivation reactions of the water-splitting enzyme (agents) - Chl chlorophyll - cyt cytochrome - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - F_O minimum fluorescence yield in the dark-adapted state - F_I minimum fluorescence yield under ambient irradiance or during transition from the light-adapted state - F_M maximum fluorescence yield in the dark-adapted state - F_M maximum fluorescence yield under ambient irradiance or during transition from light-adapted state - F_V, F_V variable fluorescence (F_V=F_M–F_O ; F_V=F_M–F_I) - FRR fast repetition rate (fluorometer) - _{PS II} quantum yield of Q_A reduction (_{PS II}=(F_M – F_O)/F_M or _{PS II})=(F_M= – F_I=)/F_M=) - LHCII Chl a/b light harvesting complexes of Photosystem II - OEC oxygen evolving complex of PS II - P680 reaction center chlorophyll of PS II - PQ plastoquinone - POH₂ plastoquinol - PS I Photosystem I - PS II Photosystem II - RC II reaction centers of Photosystem II - PS II the effective absorption cross-section of PHotosystem II - TL thermoluminescence - Y_O2 oxygen flash yield The US Government right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledged.