The absence of molybdenum cofactor sulfuration is the primary cause of the flacca phenotype in tomato plants

The molybdenum cofactor (MoCo)-containing enzymes aldehyde oxidase (AO; EC 1.2.3.1) and xanthine dehydrogenase (XDH; EC 1.2.1.37) require for activity a sulfuration step that inserts a terminal sulfur ligand into the MoCo. The tomato flacca mutation was originally isolated as a wilty phenotype due to a lack of abscisic acid (ABA) that is related to simultaneous loss of AO and XDH activities. An expressed sequence tag candidate from tomato was selected on the basis of homology to sulfurases from animals, fungi and the recently isolated Arabidopsis genes LOS5/ABA3. The tomato homologue maps as a single gene to the bottom of chromosome 7, consistent with the genetic location of the flacca mutation. The structure of FLACCA shows a multidomain protein with an N-terminal NifS-like sulfurase domain; a mammal-specific intermediate section; and a C-terminus containing conserved motifs. Prominent among these are molybdopterin oxidoreductases and thioredoxin redox-active centre/iron-sulfur-binding region signatures which may be relevant to the specific sulfuration of MoCo. Indeed, the molecular analysis of flacca identifies the mutation in a highly conserved motif located in the C-terminus. Activity gel assays show that FLACCA is expressed throughout the plant. Transient and stable complementation of flacca and the Arabidopsis aba3 mutants with Aspergillus nidulans hxB and FLACCA yielded full, partial and tissue-specific types of Mo-hydroxylase activities. Restoration of activity in the root alone is sufficient to augment plant ABA content and rectify the wild-type phenotype. Thus the pleiotropic flacca phenotype is due to the loss of activity of enzymes requiring a sulfurated MoCo.     

Effect of isotope substitution and controlled dehydration on the photoinduced electron transport reactions of quinone acceptors and multiheme cytochrome C in bacterial photosynthetic reaction center

Isotope substitution of H₂O by ²H₂O causes an increase in the rate of dark recombination between photooxidized bacteriochlorophyll (P⁺) and reduced primary quinone acceptor in Rhodobacter sphaeroides reaction centers (RC) at room temperature. The isotopic effect declines upon decreasing the temperature. Dehydration of RC complexes of Ectothiorhodospira shaposhnikovii chromatophores containing multiheme cytochrome c causes a decrease in the efficiency of transfer of a photomobilized electron between the primary and secondary quinone acceptors and from cytochrome to P⁺. In the case of H₂O medium these effects are observed at a lower hydration than in ²H₂O-containing medium. In the E. shaposhnikovii chromatophores subjected to dehydration in H₂O, the rate of electron transfer from the nearest high-potential cytochrome heme to P⁺ is virtually independent of hydration within the P/P₀ range from 0.1 to 0.5. In samples hydrated in ²H₂O this rate is approximately 1.5 times lower than in H₂O. However, the isotopic effect of this reaction disappears upon dehydration. The intramolecular electron transfer between two high-potential hemes of cytochrome c in samples with ²H₂O is inhibited within this range of P/P₀, whereas in RC samples with H₂O there is a trend toward gradual inhibition of the interheme electron transfer with dehydration. The experimental results are discussed in terms of the effects of isotope substitution and dehydration on relaxation processes and charge state of RC on implementation of the reactive states of RC providing electron transfer control.     

Two different novel cis-acting elements of erd1, a clpA homologous Arabidopsis gene function in induction by dehydration stress and dark-induced senescence

Many plant genes have been shown to be induced by water stress and function in stress tolerance. The erd1 gene has been shown to be upregulated in response to both water stress and etiolation. Promoter studies using the erd1 promoter region fused to the luciferase (LUC) reporter gene in Arabidopsis thaliana were performed to identify the putative cis elements involved. Results indicated that the cis elements, responsible for gene expression during dehydration and etiolation, are separately located in two discrete portions of the erd1 promoter. Base substitution analysis showed that a 14-bp region from -599 to -586, and a myc recognition motif from -466 to -461 are necessary for the induction of LUC activity in dehydrated plants. On the other hand, base substitution analysis revealed that both an abscisic acid responsive element (ABRE)-like sequence (from -199 to -195) and an ACGT sequence (from -155 to -152) are required for an etiolation-induced increase in LUC activity. LUC activity measurements from etiolated transgenic plants incubated in either water, N6-benzyleadenine (BA), or a 1% sucrose solution found that while BA was able to delay the increase in LUC activity seen in water-treated plants, no increase in LUC activity was seen in plants incubated in sucrose. These results indicate that the erd1 promoter contains two different regulatory systems that are involved in upregulation by dehydration stress and dark-induced senescence.     

Water deprivation tolerance and humidity response in a larval dragonfly: a possible adaptation for survival in drying ponds

Abstract.  Water deprivation tolerance is investigated in the last larval stadium of Libellula depressa under various conditions of relative humidity (60–100% relative humidity; RH). Most of the larvae maintained at 100% RH emerge and, at lower RH levels show some resistance to dehydration because they die after a mean period ranging from 1.4 days at 60% RH up to 6.7 days at 90% RH. In dual-choice chambers with humidity gradients from 63–74% RH and from 68–84% RH, larvae spend most of the time in the moist side of the chamber. In a Y-tube olfactometer, the larvae reveal a positive hygrotaxis to two airstreams carrying different amounts of water vapour (98% vs. 50%) and spend most of their time in the 'humid' arm. The ecological significance of desiccation tolerance and hygropositive response in the last larval stadium of L. depressa is discussed in relation to the presence of hygroreceptors in dragonfly larvae.     

A simple centrifugal dehydration force method to characterize water compartments in fresh and post-mortem fish muscle

A centrifugal dehydration force (CDF) method to quantify changes in tissue hydration in fresh and in post-mortem muscular fish tail tissue is presented. The data obtained were used to assess fluid flow rate from tissues and the size of hydration compartments expressed in g water/g dry mass (DM). Curve fit analysis demonstrated that muscle tissue has three detectable water compartments. Application of the method to the fresh fish indicated the presence of a large non-bulk water compartment (3.14 g water/g DM) with a much smaller (0.11 g water/g DM) inner non-bulk water sub-compartment in addition to a comparatively small bulk water compartment (0.99 g water/g DM). At 10 min and at 4h post-mortem, no significant change in size or flow rate of the water compartments was observed. At 24h post-mortem the muscular fish tissue, stored in water, swelled with statistically significant increase in total water and in the bulk water compartment but no significant change in the size of the non-bulk water compartments. The water flow rate from the non-bulk water compartment was, however, increased significantly in the 24h dead tissue. This simple CDF method has application for quantization of bulk and non-bulk water compartments in other biological and non-biological systems.     

Best hyperspectral indices for tracing leaf water status as determined from leaf dehydration experiments

Leaf water status information is highly needed for monitoring plant physiological processes and assessing drought stress. Retrieval of leaf water status based on hyperspectral indices has been shown to be easy and rapid. However, a universal index that is applicable to various plants remains a considerable challenge, primarily due to the limited range of field-measured datasets. In this study, a leaf dehydration experiment was designed to obtain a relatively comprehensive dataset with ranges that are difficult to obtain in field measurements. The relative water content (RWC) and equivalent water thickness (EWT) were chosen as the surrogates of leaf water status. Moreover, five common types of hyperspectral indices including: single reflectance (R), wavelength difference (D), simple ratio (SR), normalized ratio (ND) and double difference (DDn) were applied to determine the best indices. The results indicate that values of original reflectance, reflectance difference and reflectance sensitivity increased significantly, particularly within the 350–700 nm and 1300–2500 nm domains, with a decrease in leaf water. The identified best indices for RWC and EWT, when all the species were considered together, were the first derivative reflectance based ND type index of dND (1415, 1530) and SR type index of dSR (1530, 1895), with R² values of 0.95 (p < 0.001) and 0.97 (p < 0.001), respectively, better than previously published indices. Even so, different best indices for different species were identified, most probably due to the differences in leaf anatomy and physiological processes during leaf dehydration. Although more plant species and field-measured datasets are still needed in future studies, the recommend indices based on derivative spectra provide a means to monitor drought-induced plant mortality in temperate climate regions.     

Performance of down-flow hanging sponge (DHS) reactor coupled with up-flow anaerobic sludge blanket (UASB) reactor for treatment of onion dehydration wastewater

In this study, a promising system consisting of up-flow anaerobic sludge blanket (UASB) reactor followed by down-flow hanging sponge (DHS) reactor was investigated for onion dehydration wastewater treatment. Laboratory experiments were conducted at two different phases, i.e., phase (1) at overall hydraulic retention time (HRT) of 11 h (UASB reactor: 6 h and DHS reactor: 5 h) and phase (2) at overall HRT of 9.4 h (UASB reactor: 5.2 h and DHS reactor: 4.2 h). Long-term operation results of the proposed system showed that its overall TCOD, TBOD, TSS, TKN and NH₄N removal efficiencies were 92 ± 5, 95 ± 2, 95 ± 2, 72 ± 6 and 99 ± 1.3%, respectively (phase 1). Corresponding values for the 2nd phase were 85.4 ± 5, 86 ± 3, 87 ± 6, 65 ± 8 and 95 ± 2.8%. Based on the available results, the proposed system could be more viable option for treatment of wastewater generated from onion dehydration industry in regions with tropical or sub-tropical climates and with stringent discharge standards.     

Furfural production from xylose using sulfonic ion-exchange resins (Amberlyst) and simultaneous stripping with nitrogen

The aim of this work deals with the development of new approaches to the production of furfural from xylose. It combines relatively cheap heterogeneous catalysts (Amberlyst 70) with simultaneous furfural stripping using nitrogen under semi-batch conditions. Nitrogen, compared to steam, does not dilute the vapor phase stream when condensed. This system allowed stripping 65% of the furfural converted from xylose and almost 100% of selectivity in the condensate. Moreover, high initial xylose loadings led to the formation of two water-furfural phases, which could reduce further purification costs. Constant liquid-vapor equilibrium along stripping could be maintained for different xylose loadings. The modeling of the experimental data was carried out in order to obtain a liquid-vapor mass-transfer coefficient. This value could be used for future studies under steady-state continuous conditions in similar reaction-systems.     

Physical changes of β-sitosterol crystals in oily suspensions during heating

The aim of this research was to describe the thermal behavior of β-sitosterol crystals in oil-suspensions with a focus on the role of water during heating. The suspensions were prepared by recrystallization in order to achieve a microcrystalline particle size. The structural changes together with the mechanical properties of the suspensions during heating were studied by using variable temperature X-ray powder diffractometry (VT-XRPD), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). Hydrated β-sitosterol crystals in an oil-suspension, dehydrated, despite the composition of the suspensions, at low temperatures. At high β-sitosterol concentration, the monohydrate crystal form changed partially to a hemihydrated form, and when only a small amount of water was initially incorporated, the hemihydrate crystal form dehydrated to a mostly anhydrate crystal form. The released water, which was immiscible in the surrounding oil, caused the recrystallization of hydrated β-sitosterol during cooling. This procedure indicated a reversible dehydration process. Structural and thermal analysis of β-sitosterol crystals in suspensions, together with mechanical analysis made it possible to understand various physical changes during heating. Published: October 19, 2005