Salinity Stiffens the Epidermal Cell Walls of Salt-Stressed Maize Leaves: Is the Epidermis Growth-Restricting?

As a result of salt (NaCl)-stress, sensitive varieties of maize (Zea mays L.) respond with a strong inhibition of organ growth. The reduction of leaf elongation investigated here has several causes, including a modification of the mechanical properties of the cell wall. Among the various tissues that form the leaf, the epidermis plays a special role in controlling organ growth, because it is thought to form a rigid outer leaf coat that can restrict elongation by interacting with the inner cell layers. This study was designed to determine whether growth-related changes in the leaf epidermis and its cell wall correspond to the overall reduction in cell expansion of maize leaves during an osmotic stress-phase induced by salt treatment. Two different maize varieties contrasting in their degree of salt resistance (i.e., the hybrids Lector vs. SR03) were compared in order to identify physiological features contributing to resistance towards salinity. Wall loosening-related parameters, such as the capacity of the epidermal cell wall to expand, β-expansin abundance and apoplastic pH values, were analysed. Our data demonstrate that, in the salt-tolerant maize hybrid which maintained leaf growth under salinity, the epidermal cell wall was more extensible under salt stress. This was associated with a shift of the epidermal apoplastic pH into a range more favourable for acid growth. The more sensitive hybrid that displayed a pronounced leaf growth-reduction was shown to have stiffer epidermal cell walls under stress. This may be attributable to the reduced abundance of cell wall-loosening β-expansin proteins following a high salinity-treatment in the nutrient solution (100 mM NaCl, 8 days). This study clearly documents that salt stress impairs epidermal wall-loosening in growth-reduced maize leaves.     

Co-Ordination of Cell Division and Tissue Expansion in Sunflower, Tobacco, and Pea Leaves: Dependence or Independence of Both Processes?

Abstract Temporal analyses of cell division and tissue expansion in pea, tobacco, and sunflower leaves reveal that both processes follow similar patterns during leaf development. Relative cell division and relative tissue expansion rates are maximal and constant during early leaf development, but they decline later. In contrast, relative cell expansion rate follows a bell-shaped curve during leaf growth. Cell division and tissue expansion have common responses to temperature, intercepted radiation, and water deficit. As a consequence, final leaf area and cell number remain highly correlated throughout a large range of environmental conditions for these different plant species, indicating that cell division and tissue expansion are co-ordinated during leaf development. This co-ordination between processes has long been explained by dependence between both processes. Most studies on dicotyledonous leaf development indicate that leaf expansion rate depends on the number of cells in the leaf. We tested this hypothesis with a large range of environmental conditions and different plant species. Accordingly, we found a strong correlation between both absolute leaf expansion rate and leaf cell number. However, we showed that this relationship is not necessarily causal because it can be simulated by the hypothesis of independence between cell division and tissue expansion according to Green's theory of growth (1976). Received 23 February 2000; accepted 3 March 2000     

Drought and Oxidative Load in the Leaves of C3 Plants: a Predominant Role for Photorespiration?

Although active oxygen species are produced at high rates inboth the chloroplasts and peroxisomes of the leaves of C₃ plants,most attention has focused on the potentially damaging consequencesof enhanced chloroplastic production in stress conditions suchas drought. This article attempts to provide quantitative estimatesof the relative contributions of the chloroplast electron transportchain and the glycolate oxidase reaction to the oxidative loadplaced on the photosynthetic leaf cell. Rates of photorespiratoryH₂O₂ production were obtained from photosynthetic and photorespiratoryflux rates, derived from steady-state leaf gas exchange measurementsat varying irradiance and ambient CO₂. Assuming a 10 % allocationof photosynthetic electron flow to the Mehler reaction, photorespiratoryH₂O₂ production would account for about 70 % of total H₂O₂ formedat all irradiances measured. When chloroplastic CO₂ concentrationrates are decreased, photorespiration becomes even more predominantin H₂O₂ generation. At the increased flux through photorespirationobserved at lower ambient CO₂, the Mehler reaction would haveto account for more than 35 % of the total photosynthetic electronflow in order to match the rate of peroxisomal H₂O₂ production.The potential signalling role of H₂O₂ produced in the peroxisomesis emphasized, and it is demonstrated that photorespiratoryH₂O₂ can perturb the redox states of leaf antioxidant pools.We discuss the interactions between oxidants, antioxidants andredox changes leading to modified gene expression, particularlyin relation to drought, and call attention to the potentialsignificance of photorespiratory H₂O₂ in signalling and acclimation.     

Detection and Characterization of UDP-Glucose:Flavonoid O-Glucosyltransferases in the Leaves of Prunus ? yedoensis Matsum

A novel O-glucosyltransferase (I4'GT) which catalyzes the transferof D-glucose from UDP-D-glucose to position 4' of prunetin (4',5-dihydroxyl-7-methoxyisoflavone)was isolated from the leaves of Prunus ? yedoensis Matsum. andpurified 66-fold by precipitation with ammonium sulfate andchromatography on DEAE-cellulose. UDP-glucose:flavonol 3-O-glucosyltransferase(F3GT) was also isolated and purified 50-fold in the same manner.The molecular weights of both I4'GT and F3GT were estimatedby elution from a column of Sephadex G-100 to be about 51,000Da. The pH optima for I4'GT and F3GT activities were 8.0 and7.5, respectively. The specificities of I4'GT and F3GT for thesugar donor were quite strict, and only UDP-glucose could serveas glucosyl donor, both ADP-D-glucose and GDP-D-glucose beingineffective. The apparent K_m values for UDP-glucose and prunetinwere 10.0µM and 1.20µM, respectively, for I4'GT.The K_m values for UDP-glucose and quercetin were 9.8 µMand 1.21 µM, respectively, for F3GT. The activities ofboth I4'GT and F3GT were stimulated by 1 mM Mg*⁺ and stronglyinhibited by 1 mM Cu²⁺, 1 mM Zn²⁺ and various reagents thatreact with sulfhydryl groups. (Received May 16, 1990; Accepted September 3, 1990)     

Does the Gradualness of Leaf Shedding Govern Nutrient Resorption from Senescing Leaves in Mediterranean Woody Plants?

To reveal the environmental and substrate quality effects on decomposition process and enzyme activities, litterbag experiments containing Nuphar and Carex leaves, Nuphar rhizome, and Ranunculus shoot, were carried in five-subalpine marshes in Lake Tahoe basin, USA. Alkaline phosphatase, β-glucosidase, and β-xylosidase activities were determined by a fluorogenic method using methyumbelliferyl substrates. Carex leaves, Nuphar rhizome and leaves, and Ranunculus shoots lost, respectively, 33, 67, 82 and 93% of original dry weight over 268 days. Decay rates were different among substrates but not among marshes. Nitrogen and carbon contents increased during the first 58 days and subsequently remained stable. Phosphorus content was stable during the experimental period except for a decrease in the first 16 days in Nuphar shoots. Enzyme activities in decomposing Carex and Nuphar leaves in four marshes were not significantly affected by environmental conditions. β-glucosidase and β-xylosidase activities in decomposing Carex leaves increased with time, but in other plant tissue these enzyme activities remained stable during experimental period. Enzyme activities were significantly different among decomposing substrates. Alkaline phosphatase activity was highest in Nuphar leaves (ca. 1286 μ-mole h⁻¹ g DW −1) but lower and similar in other plant tissues (ca. 100 and 10 μ-mole h −1 g DW −1, respectively). This study showed differences in decay rates and enzyme activities rely on substrate and not the environment conditions of the study area. Decomposition rates in the early stage of decomposition were related to cumulative enzyme activities.     

Stay dormant or escape sprouting? Turion buoyancy and sprouting abilities of the submerged macrophyte Potamogeton crispus L.

The ability of asexual propagules to disperse is an important ecological determinant of the spread and establishment of many aquatic species. However, few previous studies have addressed the relationship between the asexual propagule buoyancy and sprouting abilities in submerged macrophytes. For this reason, turions of Potamogeton crispus samples were collected from Lake Liangzi, and an incubator sprouting experiment was conducted. Our results revealed that the floating turions showed higher sprouting rates than that of sinking turions, indicating the former ones are possibly with high levels of primary metabolites. The higher N and P concentrations in the floating turions caused lower C:N, C:P, and N:P ratios in these turions compared with sinking turions, which confirmed the activation of floating turions. The free amino acid and soluble carbohydrate concentrations were also higher in floating turions than those in sinking turions. Our results also revealed that turion leaf porosity rather than starch concentration may determine the density of P. crispus turions. This study makes a contribution to our understanding of how the internal characteristics of turions can (at least partly) determine dispersal outcomes and offers new insights into the dispersal and sprouting of asexual propagules of submerged macrophytes.     

Spring Wheat Leaf Appearance and Temperature: Extending the Paradigm?

Extensive research shows temperature to be the primary environmental factor controlling the phyllochron, or rate of leaf appearance, of wheat (Triticum aestivum L.). Experimental results suggest that soil temperature at crown depth, rather than air temperature above the canopy, would better predict wheat leaf appearance rates. To test this hypothesis, leaf appearance in spring wheat ('Nordic') was measured in a 2-year field experiment (Nunn clay loam soil; fine, smectitic, mesic Aridic, Argiustoll) with three planting dates and two soil temperature treatments. One temperature treatment (denoted +3C) consisted of heating the soil at crown depth to 3 degrees C above the ambient soil temperature (denoted +0C). Main stem cumulative leaf number was measured at least weekly until flag leaf emergence. Leaf appearance was essentially linear with both air and soil growing degree-days (GDD), although there was a stronger linear relationship with soil GDD in the +0C plants than in +3C plants. A weak positive relationship between planting date and the phyllochron was observed. Unexpectedly, we found that heating the soil did not increase the rate of leaf appearance, as the paradigm would predict. To explain these results, we propose extending the paradigm in two ways. First, three processes are involved in leaf appearance: (1) cell division at the shoot apex forms the primordium; (2) cell division in the intercalary meristem forms the cells that then (3) expand to produce the leaf. Cell division is predominantly controlled by temperature, but cell expansion is considerably more affected by factors other than temperature, explaining the influence of other factors on the phyllochron. Secondly, the vertical distribution of the two meristems and region of cell expansion occur over a significant distance, where temperature varies considerably, and temperature at a specific point (e.g. crown depth) does not account for the entire temperature regime under which leaves are developing.     

Cell death in Leishmania induced by stress and differentiation: programmed cell death or necrosis?

Unicellular organisms, such as the protozoan parasite Leishmania, can be stimulated to show some morphological and biochemical features characteristic of mammalian apoptosis. This study demonstrates that under a variety of stress conditions such as serum deprivation, heat shock and nitric oxide, cell death can be induced leading to genomic DNA fragmentation into oligonucleosomes. DNA fragmentation was observed, without induction, in the infectious stages of the parasite, and correlated with the presence of internucleosomal nuclease activity, visualisation of 45 to 59 kDa nucleases and detection of TUNEL-positive nuclei. DNA fragmentation was not dependent on active effector downstream caspases nor on the lysosomal cathepsin L-like enzymes CPA and CPB. These data are consistent with the presence of a caspase-independent cell death mechanism in Leishmania, induced by stress and differentiation that differs significantly from metazoa.     

Sludge Reduction by Predatory Activity of Aquatic Oligochaetes in Wastewater Treatment Plants: Science or Fiction? A Review

Biological aerobic wastewater treatment plants (WWTPs) produce a lot of excess sludge. The costs for handling this residual product are increasing, so the search for alternative techniques to reduce the amount of sludge has to be continued. Activated sludge consists of inorganic and organic substances, bacteria, protozoa and metazoa. Due to incomplete biomass conversion, sludge consumption yields less oligochaete biomass. From a technological point of view, the application of aquatic oligochaetes to reduce the sludge production offers interesting perspectives. This paper aims to review the feasibility for the reduction of activated sludge in WWTPs by means of aquatic oligochaetes. Also the current techniques concerning sludge reduction are taken into account. Several of the WWTPs relevant parameters, which may influence predatory activity of aquatic oligochaetes, are discussed: particle size, organic content of substrate, bacteria preference, life cycle and population dynamics of aquatic oligochaetes, temperature, pH, oxygen and process conditions. From the literature it appeared that most research has been performed on laboratory scale. Only a few authors mention a significant reduction of the sludge production by ‘sessile’ species such as Lumbriculus. Vermicultures for the reduction of activated sludge are rather common in developing countries. Incidentally large annelid blooms have been noticed in WWTPs. It remains obscure which factors trigger the initiation of annelid blooms in WWTPs and which are of importance to maintain a stable annelid population in WWTPs. The influence of a considerable worm bloom on the waste sludge production is still under investigation.     

Uptake of organic matter by the roots of sweet potato: Analysis of the δ14C value of plants

Summary To determine whether sweet potato (Ipomoea batatas (L.) Poir.) takes up organic matter through the roots from the medium, the concentrations of natural¹⁴C (¹⁴C) in plant organic matter, atmospheric CO₂ and compost applied to media were examined under soil and sand culture conditions. In these experiments, three kinds of composts of different ¹⁴C were used. CO₂ derived from the mineralization of compost was continuously pumped out from the pots and its direct uptake by the leaves was prevented.¹⁴C of plant parts harvested after the 43 days experimental period were affected by the ¹⁴C of the compost in the treatments where the compost of rice straw was applied, and which suggested that a significant amount of plant carbon was derived from the compost.     

Models of Electrical Activity: Calibration and Prediction Testing on?the?Same Cell

Mathematical models are increasingly important in biology, and testability is becoming a critical issue. One limitation is that one model simulation tests a parameter set representing one instance of the biological counterpart, whereas biological systems are heterogeneous in their properties and behavior, and a model often is fitted to represent an ideal average. This is also true for models of a cell’s electrical activity; even within a narrowly defined population there can be considerable variation in electrophysiological phenotype. Here, we describe a computational experimental approach for parameterizing a model of the electrical activity of a cell in real time. We combine the inexpensive parallel computational power of a programmable graphics processing unit with the flexibility of the dynamic clamp method. The approach involves 1), recording a cell’s electrical activity, 2), parameterizing a model to the recording, 3), generating predictions, and 4), testing the predictions on the same cell used for the calibration. We demonstrate the experimental feasibility of our approach using a cell line (GH4C1). These cells are electrically active, and they display tonic spiking or bursting. We use our approach to predict parameter changes that can convert one pattern to the other.     

Cell milieu significantly affects the fate of AApoAI amyloidogenic variants: predestination or serendipity?

Background

Specific apolipoprotein A-I variants are associated to severe hereditary amyloidoses. The organ distribution of AApoAI amyloidosis seems to depend on the position of the mutation, since mutations in residues from 1 to 75 are mainly associated to hepatic and renal amyloidosis, while mutations in residues from 173 to 178 are mostly responsible for cardiac, laryngeal, and cutaneous amyloidosis. Molecular bases of this tissue specificity are still poorly understood, but it is increasingly emerging that protein destabilization induced by amyloidogenic mutations is neither necessary nor sufficient for amyloidosis development.

Hyperphagia by self- and xeno-cannibalism: Cell death by indigestion? A reminiscence of the Phedrus Fabula “Rana Rupta et Bos”?

The occurrence of self- and xeno-cannibalism could be considered as two different aspects of the same well-regulated process. The formation of autophagosomes can represent a survival option for a cell in unfavorable conditions but it can also lead to cell demise. In fact, autophagy has been considered as an additional and clear-cut cell death pathway. We herein speculate that self-eating by autophagy could be paralleled by a cannibalistic behavior, e.g., by cell feeding of siblings, that can also become detrimental. This behavior in fact, once exacerbated, can also lead to cell death, probably bolstering intracellular oxidative imbalance. In this case, a survival option, such as self- and xeno-cannibalism, can be turned into a peculiar death option: cell death by feeding excess. Under this point of view, over-feeding cells are reminiscent of the frog in the Phedrus Fabula “Rana Rupta et Bos”.     

Regulation of Prostate Cancer Cell Survival by Protein Kinase C? Involves Bad Phosphorylation and Modulation of the TNFα/JNK Pathway

Protein kinase Cϵ (PKCϵ), a diacyglycerol- and phorbol ester-responsive serine-threonine kinase, has been implicated in mitogenic and survival control, and it is markedly overexpressed in human tumors, including in prostate cancer. Although prostate cancer cells undergo apoptosis in response to phorbol ester stimulation via PKCδ-mediated release of death factors, the involvement of PKCϵ in this response is not known. PKCϵ depletion by RNAi or expression of a dominant negative kinase-dead PKCϵ mutant potentiated the apoptotic response of PMA and sensitized LNCaP cells to the death receptor ligand TNFα. On the other hand, overexpression of PKCϵ by adenoviral means protected LNCaP cells against apoptotic stimuli. Interestingly, PKCϵ RNAi depletion significantly enhanced the release of TNFα in response to PMA and greatly potentiated JNK activation by this cytokine. Further mechanistic analysis revealed that PMA fails to promote phosphorylation of Bad in Ser¹¹² in PKCϵ-depleted LNCaP cells, whereas PKCϵ overexpression greatly enhanced Bad phosphorylation. This effect was independent of Akt, ERK, or p90Rsk, well established kinases for Ser¹¹² in Bad. Moreover, expression of a S112A-Bad mutant potentiated PMA-induced apoptosis. Finally, we found that upon activation PKCϵ accumulated in mitochondrial fractions in LNCaP cells and that Bad was a substrate of PKCϵ in vitro. Our results established that PKCϵ modulates survival in prostate cancer cells via multiple pathways.