Energetic metabolism during individual development of <Emphasis Type="Italic">Lymnaea stagnalis</Emphasis> (Lymnaeidae,gastropoda): III. Late postlarval ontogeny

Changes in the rate and intensity of oxygen consumption during individual ontogeny of 14 specimens of Lymnaea stagnalis in the period from the 10th week after emergence until death was investigated in aquaculture. It was demonstrated that the rate of oxygen consumption increased and the intensity of this process decreased during the whole period of observations. Alterations of these parameters were accompanied with permanent oscillations of their meanings. The correlation between intensity of oxygen consumption (q) and age (t) can be described with the equation q = q _st/(1-exp(−k _g (t+t ₀))). The values of coefficients of this equation do not differ significantly between individuals and, on average, comprise k _g = 0.0696 ± 0.0072 weeks⁻¹; q _st = 60.4 ± 2.6 mcl O₂/(h · g); t ₀ = −3.0 ± 0.7 weeks. The dependence of the rate of oxygen consumption (Q, μl O₂/h) on body weight (M, g) for all data is significantly described with the allometric equation Q = 0.369M ^0.779.     

Adult survival and reproductive rate are linked to habitat preference in territorial,year‐round resident Song Sparrows Melospiza melodia

Individual animal fitness can be strongly influenced by the ability to recognize habitat features which may be beneficial. Many studies focus on the effects of habitat on annual reproductive rate, even though adult survival is typically a greater influence on fitness and population growth in vertebrate species with intermediate to long lifespans. Understanding the effects of preferred habitat on individuals over the annual cycle is therefore necessary to predict its influences on individual fitness. This is particularly true in species that are resident and territorial year‐round in the temperate zone, which may face potential trade‐offs between habitat that maximizes reproduction and that which maximizes non‐breeding season (‘over‐winter’) survival. We used a 37‐year study of Song Sparrows Melospiza melodia residing territorially year‐round on a small island to examine what habitat features influenced adult over‐winter survival, how site‐specific variation in adult survival vs. annual reproductive rate influenced long‐term habitat preference, and if preferred sites on average conferred higher individual fitness. Habitat features such as area of shrub cover and exposure to intertidal coastline predicted adult over‐winter survival independent of individual age or sex, population size, or winter weather. Long‐term habitat preference (measured as occupation rate) was better predicted by site‐specific annual reproductive rate than by expected over‐winter survival, but preferred sites maximized fitness on average over the entire annual cycle,. Although adult over‐winter survival had a greater influence on population growth (λ) than did reproductive rate, the influence of reproductive rate on λ increased in preferred sites because site‐specific variation in reproductive rate was higher than variation in expected over‐winter survival. Because preferred habitats tended to have higher mean site‐specific reproductive and adult survival rates, territorial birds in this population do not appear to experience seasonal trade‐offs in preferred habitat but are predicted to incur substantial fitness costs of settling in less‐preferred sites.     

The growth and energy metabolism of <Emphasis Type="Italic">Lymnaea stagnalis</Emphasis> (Lymnaeidae,Gastropoda): I. Early postlarval period

The growth and the oxygen consumption rate of Lymnaea stagnalis were studied during the first ten weeks after hatching. It is shown that these processes are atypical during early ontogenesis in comparison with adult mollusks. The obtained data on linear (height of shell) and weight growth can be equally well approximated with the von Bertalanffy equation or exponential and power equations. Both linear and weight growth are characterized by an approximately constant specific rate associated with synchronous oscillations of a week period. The oscillations were observed also for the oxygen consumption rate, but of another period (about 2.6 weeks). On average the metabolic rate after the initial triple increase during the first three days remains stable. The power coefficient of the allometric dependence of the total weight on the shell height is significantly less than that of the adult.     

Mechanism and role of furosemide-sensitive K+ transport in L cells: A genetic approach

Summary As part of a genetic study of the mechanisms for cation transport in cultured mammalian cells, two mouse fibroblastic cell lines have been compared with respect to unidirectional⁴²K⁺ influx. The cell lines areLM(TK ^–) andLTK-5, a mutant selected fromLM(TK ^–) by the ability to grow in medium containing 0.2mm K⁺. In both cell lines, the overall influx can be resolved into three components: (i) a ouabain- and vanadate-sensitive component ( ⁱ M_K ^f), presumably the Na/K pump, which is a saturable function of extracellular K⁺ with aK _1/2 of 1.3mm; (ii) a furosemide-sensitive component ( ⁱ M_k ^fx), also a saturable function of extracellular K⁺, with aK _1/2 of 6mm; and (iii) a diffusional component ( ⁱ M_k ^d); which is a linear function of extracellular K⁺.By several independent criteria, ⁱ M_k ^o and ⁱ M_k ^f appear to be distinct transport processes. First, as indicated above, they can be separated with the use of inhibitors. In addition, they can be separated genetically, since theLTK-5 mutant shows a threefold elevation in ⁱ M_k ^f with no change in ⁱ M_k ^o. And finally, extracellular Na⁺ has no effect on ⁱ M_k ^o, but stimulates ⁱ M_k ^f, a result consistent with the notion that ⁱ M_k ^f influx occurs by Na–K cotransport.Further experiments were directed towards understanding the nature of theLTK-5 mutation and the physiological role of ⁱ M_k ^f. LTK-5 differs from the parental cell line, not only in having an increased ⁱ M_k ^f, but also in having a large cell volume, a slow maximal growth rate, and an ability to grow at 0.2mm K⁺. The most straightforward interpretation — that the increased ⁱ M_k ^f is itself responsible—is unlikely since the addition of furosemide to the growth medium had no effect upon the growth rate or cell volume of the mutant at either normal or low extracellular K⁺ concentrations. It did, however, render the parent capable of growth at 0.2mm K⁺. Possible interpretations are discussed.     

Interconvertible Kinetic States of t-Butylbicycloorthobenzoate Binding Sites of the γ-Aminobutyric AcidA Ionophores

The kinetics of t-[³H]butylbicycloorthobenzoate (TBOB) binding to the convulsant sites of the γ-aminobutyric acid_A (GABA_A) receptor-ionophore complex were examined in synaptosomal membrane preparations of rat brain. On and off rates of TBOB binding were accelerated by 1 μM GABA and decelerated by 1 μM bicuculline methochloride, a GABA_A antagonist. The presence of GABA and bicuculline methochloride created rapid and slow phases of dissociation, respectively. The three groups of rate constants distinguished for the dissociation of 4 nM and 30 nM [³H]TBOB represent multiaffinity states of the convulsant sites depending on the presence of GABA or bicuculline methochloride. Apparent association rate constants do not obey the equation k_app=k_off±k_on [TBOB] without assuming interconvertibility of the kinetic states during binding. Avermectin B_1a (AVM B_1a), a chloride channel opening agent, accelerated the association and dissociation of TBOB and resulted in a biphasic effect on TBOB binding, i.e., enhancement at low concentrations (EC₅₀, 7.8 nM) followed by displacement at high concentrations (IC₅₀ 6.3 μM) of AVM B_1a. AVM B_1a resulted in similar biphasic effects on t- [³⁵S]butylbicyclophosphorothionate binding. DIDS, an isothiocyanatostilbene derivative with irreversible anion channel blocking effect, selectively inhibited basal [³H]TBOB binding (IC₅₀ 125 μM DIDS) leaving the enhancement by AVM B_1a unaffected.     

Bordet‐Gengou agar medium supplemented with albumin‐containing biologics for cultivation of bordetellae

Bordetella pertussis, B. parapertussis, and B. bronchiseptica cause respiratory infections in mammals, including humans, and are generally cultivated on Bordet‐Gengou (BG) agar plates in laboratories. The medium requires animal blood as a supplement for better bacterial growth. However, using blood is problematic, as its constant supply is occasionally difficult because of the limited shelf‐life. This study proposes modified BG agar plates supplemented with bovine serum albumin and fetal bovine serum as a simple and convenient medium that confers sufficient growth of bordetellae.     

Mortality pattern and age structure in two carabid populations with different seasonal life cycles

1. Adult populations of two carabid species, a spring breeder, Carabus yaconinus, and an autumn breeder, Leptocarabus kumagaii, were studied in a lowland habitat (area: 16,500 m²) by pitfall sampling and mark-recapture method. The seasonal change in population number, age structure and mortality pattern were clarified and related to their seasonal life cycles.
2. The survival rate of new adults from emergence to the first reproductive season was on the average 48% in C. yaconinus and 55% in L. kumagaii. In C. yaconinus, beetles which emerged later in the season survived more to the first reproductive season than those emerged earlier. C. yaconinus which had survived the pre-reproductive period mostly died out during the first reproductive season of 5 months, and about 8% survived until the second season. In L. kumagaii which had a short reproductive period in autumn, about 20% survived to the second reproductive season, and a small proportion even to the third reproductive season. Accordingly, the proportion of old beetles in the reproductive population was higher in L. kumagaii than in C. yaconinus.
3. The reproductive population of C. yaconinus contained on the average 1600 beetles and produced 3300 new adults. the L. kumagaii population contained on the average about 530 reproductives in autumn, and about 820 beetles emerged in the following year. The recruitment rate of new adults of C. yaconinus was higher than that of L. kumagaii, and this resulted in its higher population density. In L. kumagaii, however, the high adult survivorship and iteroparous reproduction were important for its population growth.
4. Relationship between seasonal adaptation and demographic strategies in the carabid populations were discussed.

     

A novel bioluminogenic assay for α-chymotrypsin

The use of 6-(N-acetyl-L -phenylalanyl)-aminoluciferin as a novel substrate for α-chymotrypsin has been demonstrated. The kinetic parameters determined are K_M = 0.38mmol/L, k_cat = 6.5 s^?1 and k_cat/k_M = 17,100 (L/mols). The test principle of the coupled assay is the release of aminoluciferin by enzymatic cleavage of 6-(N-acetyl-L -phenylalanyl)-aminoluciferin. Aminoluciferin is oxidized, with light emission, by firefly luciferase (Photinus pyralis) and can be quantified in a luminometric assay. The detection limit for chymotrypsin was found to be 0.3 ng per assay. 6-(N-acetyl-L -phenylalanyl)-aminoluciferin has been synthesized as an example for a new class of highly sensitive substrates. By modification of the peptide residue these new substrates may be suitable for ultrasensitive detection of different proteinases.     

Relationship between the Molecular Weight and the Color Intensity of Color Components of Melanoidin from the Glycine-Xylose System

The molecular weights of color components (designated as P1, P2, P3, P4, P5, P6, P7 and P8 in order of elution from a DEAE-cellulose column) isolated by the conversion of color components of melanoidin produced from the glycine-xylose system in an oxidative browning were studied in relation to the color intensity. The molecular weights of P5, P6, P7 and P8 estimated by gel filtration on Sephadex G–50, G–75 and G–150 using dextran as a standard were approximately 2,140, 3,550, 5,600 and 14,200, respectively. The molecular weights of P1, P2, P3 and P4 could not be estimated by the gel filtration method because of their low values.

On the other hand, a linear relationship between Kd, the distribution coefficient in dextran gel, and E₄₅₀ (E) of the color components was observed. Thus, there is considered to be a linear relationship between log E and log molecular weight (M). The correlation coefficient between log E and log M was calculated to be from 0.96 to 0.98 in the visible wavelength region. Therefore, the equation, E=k × M^α was adopted. The value, E=2.15 × M^0.29 was obtained from melanoidin prepared from the glycine-xylose system. The molecular weights of P1, P2, P3 and P4 were calculated from the equation to be 290, 360, 700 and 1,200, respectively. The equation, E=k × M^α, was demonstrated to be reasonably applicable to the melanoidin from Glu-, Lys-, Gly₂-, Gly-Leu-, and Gly₃-xylose systems. It is concluded that the polymerization of the structural unit in melanoidin occurs in an oxidative browning and that their color tone is darkened and the color in melanoidin is increased by polymerization according to the equation, E=k × M^α.     

Consequences of diapause on post‐diapause development,reproductive physiology and population growth of Chilo partellus (Swinhoe)

We investigate the effects of diapause on post‐diapause development, reproductive physiology and population growth of Chilo partellus (Swinhoe) (Crambidae: Lepidoptera). Aestivating and hibernating larvae of C. partellus are exposed to diapause terminating conditions (consisting of an LD 12 : 12 h photocycle at 27 ± 1 °C and 65 ± 5% relative humidity with a fresh diet) to terminate the diapause and observations are made on percentage pupation, pupal duration and weight, adult reproductive performance and population growth parameters. We find that the diapause in C. partellus significantly reduces the percentage pupation and weights of pupae, ultimately lowering the weight and reproductive performance of adults. Reduced weights of adult females are found to be directly associated with a lower number of egg cells in ovaries. Nevertheless, the reproductive performance of C. partellus males is also found to be greatly affected in the diapause (hibernation and aestivation) experiencing population in terms of the deposition of a lower number of spermatophores and eupyrene sperm in the reproductive tracts of females compared with the nondiapausing population. The results of the present study clearly indicate that a reduction in longevity, fecundity and egg viability, as well as a reduced rate of deposition of spermatophores and eupyrene sperm, in a diapause experiencing population of C. partellus ultimately leads to a reduction in population growth parameters, thus having implications for bio‐ecology and population dynamics under a changing climatic scenario.     

Generation and quenching of singlet molecular oxygen by aggregated bacteriochlorophyll d in model systems and chlorosomes

Both photogeneration and quenching of singlet oxygen by monomeric and aggregated (dimeric and oligomeric) molecules of bacteriochlorophyll (BChl) d have been studied in solution and in chlorosomes isolated from the green photosynthetic bacterium Chlorobium vibrioforme f. thiosulfatophilum. The yield of singlet-oxygen photogeneration by pigment dimers was about 6 times less than for monomers. Singlet oxygen formation was not observed in oligomer-containing solutions or in chlorosomes. To estimate the efficiency of singlet oxygen quenching an effective rate constant for ¹O₂ quenching by BChl molecules (k_q ^M) was determined using the Stern-Volmer equation and the total concentration of BChl d in the samples. In solutions containing only monomeric BChl, the k_q ^M values coincide with the real values for ¹O₂ quenching rate constants by BChl molecules. Aggregation weakly influenced the k_q ^M values in pigment solutions. In chlorosomes (which contain both BChl and carotenoids) the k_q ^M value was less than in solutions of BChl alone and much less than in acetone extracts from chlorosomes. Thus ¹O₂ quenching by BChl and carotenoids is much less efficient in chlorosomes than in solution and is likely caused primarily by BChl molecules which are close to the surface of the large chlorosome particles. The data allow a general conclusion that monomeric and dimeric chlorophyll molecules are the most likely sources of ¹O₂ formation in photosynthetic systems and excitation energy trapping by the long wavelength aggregates as well as ¹O₂ physical quenching by monomeric and aggregated chlorophyll can be considered as parts of the protective system against singlet oxygen formation.Abbreviations BChl bacteriochlorophyll - MBpd methyl bacteriopheophorbide - Chl chlorophyll - TPP meso-tetraphenylporphyrin - TPPS meso-tetra (p-sulfophenyl) porphyrin     

α-Synuclein aggregation variable temperature and variable pH kinetic data: A re-analysis using the Finke–Watzky 2-step model of nucleation and autocatalytic growth

The aggregation of proteins is believed to be intimately connected to many neurodegenerative disorders. We recently reported an “Ockham's razor”/minimalistic approach to analyze the kinetic data of protein aggregation using the Finke–Watzky (F–W) 2-step model of nucleation (A → B, rate constant k₁) and autocatalytic growth (A + B → 2B, rate constant k₂). With that kinetic model we have analyzed 41 representative protein aggregation data sets in two recent publications, including amyloid β, α-synuclein, polyglutamine, and prion proteins (Morris, A. M., et al. (2008) Biochemistry 47, 2413-2427; Watzky, M. A., et al. (2008) Biochemistry 47, 10790–10800). Herein we use the F–W model to reanalyze protein aggregation kinetic data obtained under the experimental conditions of variable temperature or pH 2.0 to 8.5. We provide the average nucleation (k₁) and growth (k₂) rate constants and correlations with variable temperature or varying pH for the protein α-synuclein. From the variable temperature data, activation parameters ΔG^‡, ΔH^‡, and ΔS^‡ are provided for nucleation and growth, and those values are compared to the available parameters reported in the previous literature determined using an empirical method. Our activation parameters suggest that nucleation and growth are energetically similar for α-synuclein aggregation (ΔG^‡_nucleation = 23(3) kcal/mol; ΔG^‡_growth = 22(1) kcal/mol at 37 °C). From the variable pH data, the F–W analyses show a maximal k₁ value at pH ~ 3, as well as minimal k₁ near the isoelectric point (pI) of α-synuclein. Since solubility and net charge are minimized at the pI, either or both of these factors may be important in determining the kinetics of the nucleation step. On the other hand, the k₂ values increase with decreasing pH (i.e., do not appear to have a minimum or maximum near the pI) which, when combined with the k₁ vs. pH (and pI) data, suggest that solubility and charge are less important factors for growth, and that charge is important in the k₁, nucleation step of α-synuclein. The chemically well-defined nucleation (k₁) rate constants obtained from the F–W analysis are, as expected, different than the 1/lag-time empirical constants previously obtained. However, k₂ × [A]₀ (where k₂ is the rate constant for autocatalytic growth and [A]₀ is the initial protein concentration) is related to the empirical constant, k_app obtained previously. Overall, the average nucleation and average growth rate constants for α-synuclein aggregation as a function of pH and variable temperature have been quantitated. Those values support the previously suggested formation of a partially folded intermediate that promotes aggregation under high temperature or acidic conditions.     

Microcalorimetric Study on the Effect of Ce<Superscript>3+</Superscript> on <Emphasis Type="Italic">Halobacterium halobium</Emphasis> R1

A microcalorimeric technique was used to evaluate the influence of rare earths Ce³⁺ on Halobacterium halobium R1 growth. By means of TAM air Thermal Activity Monitor, the thermogenic curves of H. halobium R1 growth were obtained. To analyze the results, the growth rate constant k and IC₅₀ were calculated, indicating that the values of k are linked to the concentration of Ce³⁺. The growth rate constant k of H. halobium R1 decreased gradually in the low concentration; thus, rare earths restrained the growth of H. halobium R1. On the contrary, as the concentration of Ce³⁺ became higher, the value of k for H. halobium R1 increased gradually, which showed Ce³⁺ stimulated the growth of H. halobium R1. When the concentration of rare earths became much higher, the value of k for H. halobium R1 also decreased, and the growth of H. halobium R1 was restrained totally in the end. By using transmission electron microscopy (TEM), it was observed that the transforming of H. halobium R1 in the different concentrations of Ce³⁺ confirmed the results derived from microcalorimetry. According to the thermogenic curves and TEM photos of H. halobium R1 under various conditions, it showed that there was some special effect about the interaction between rare earths and H. halobium R1 growth.     

Specific potassium ion interactions facilitate homocysteine binding to betaine‐homocysteine S‐methyltransferase

Betaine‐homocysteine S‐methyltransferase (BHMT) is a zinc‐dependent methyltransferase that uses betaine as the methyl donor for the remethylation of homocysteine to form methionine. This reaction supports S‐adenosylmethionine biosynthesis, which is required for hundreds of methylation reactions in humans. Herein we report that BHMT is activated by potassium ions with an apparent K_M for K⁺ of about 100 µM. The presence of potassium ions lowers the apparent K_M of the enzyme for homocysteine, but it does not affect the apparent K_M for betaine or the apparent k_cat for either substrate. We employed molecular dynamics (MD) simulations to theoretically predict and protein crystallography to experimentally localize the binding site(s) for potassium ion(s). Simulations predicted that K⁺ ion would interact with residues Asp26 and/or Glu159. Our crystal structure of BHMT bound to homocysteine confirms these sites of interaction and reveals further contacts between K⁺ ion and BHMT residues Gly27, Gln72, Gln247, and Gly298. The potassium binding residues in BHMT partially overlap with the previously identified DGG (Asp26‐Gly27‐Gly28) fingerprint in the Pfam 02574 group of methyltransferases. Subsequent biochemical characterization of several site‐specific BHMT mutants confirmed the results obtained by the MD simulations and crystallographic data. Together, the data herein indicate that the role of potassium ions in BHMT is structural and that potassium ion facilitates the specific binding of homocysteine to the active site of the enzyme. Proteins 2014; 82:2552–2564. © 2014 Wiley Periodicals, Inc.     

Micropropagation of calla lily (<Emphasis Type="Italic">Zantedeschia albomaculata</Emphasis>) via <Emphasis Type="Italic">in vitro</Emphasis> shoot tip proliferation

Summary A method for the micropropagation of Zantedeschia albomaculata is presented using shoot tip proliferation onto Murashige and Skoog (MS) medium supplemented with different plant growth regulator concentrations and combinations. Of the four cytokinins tested, 6-benzyladenine (BA) and thidiazuron (TDZ) were found to be more effective. An optimal concentration of BA (8.87 μM) or TDZ (4.54 μM) developed an average of 3.8 and 3.2 shoots per explant, respectively, but increasing concentrations of cytokinins often led to lower proliferation rate and stunted growth. Addition of auxins to the MS medium supplemented with 8.87 μM BA slightly enhanced multiple shoot formation in the explants. Multiplication of six cultivars of Zantedeschia genus comprising different flower types and colors were tested and achieved using only one regeneration medium (MS+8.87 μMBA+2.46 μM IBA). Different MS medium strength, air temperature (15, 20, 25, and 30°C) and light quality [fluorescent, red + blue, red and blue light provided by a LED (light-emitting diode) system] were used (without phytohormone) with the aim of stimulating in vitro shoot and root development. Half-strength MS or MS and cultures maintained at 25°C were found to be equally suitable for shoot tip culture of Z. albomaculata. Shoot elongation as well as fresh and dry weight were significantly increased when cultures were kept under red or blue light.     

Tolerance of submerged germinating rice to 50–200 mM NaCl in aerated solution

This paper concerns tolerance to 50–200 mM NaCl of submerged rice (Oryza sativa cv. Amaroo) during germination and the first 138–186 h of development in aerated solution. Rice was able to germinate and the seedlings even tolerated exposure to 200 mM NaCl, albeit with severe growth restrictions. After return to 0.3 mM NaCl, growth increased, indicating that even at 200 mM NaCl there was no irreparable injury. Osmotic adjustment was achieved by using Na⁺ and Cl^– as the major osmotica. At 200 mM NaCl commenced at sowing, the shoot Na⁺ and Cl^– concentrations between 50–110 h were about 210 and 260 mM, respectively, i.e. above the external concentration. Thus, there was a high tissue tolerance to NaCl. The internal concentrations declined subsequently, concurrent with a decline in growth. At 50–200 mM NaCl, the contributions from ions to π_sap were 81–92% in roots and 62–74% in shoots. The assessed turgor pressures at 200 mM NaCl were 0.33 MPa in shoots and 0.15 MPa in roots, compared to 0.62 and 0.43 MPa at 0.3 mM NaCl. In the General Discussion section, we compare the different responses of submerged seedlings to the responses of transpiring rice plants, reported in the literature, and suggest that the submerged system is useful to evaluate effects of NaCl on turgor pressure and particularly to establish whether there are specific effects of Na⁺ and Cl^– in tissues.     

EFFECTS OF WOUNDING BY THE HERBIVOROUS SNAILS LITTORINA SITKANA AND L. SCUTULATA (MOLLUSCA) ON GROWTH AND REPRODUCTION OF THE INTERTIDAL ALGA FUCUS DISTICHUS (PHAEOPHYTA)1

Small (3–7 cm long) Fucus distichus ssp. edentatus (de la Pyl.) Pow. Plants were tagged at three sites in which densities of the herbivorous snails Littorina sitkana and L. scutulata ranged from 367–4690 animals · M^-2. From April–August 1986, the growth rate, degree of wounding, and reproductive status of individual thalli were monitored at 2–4 week intervals. Grazer-inflicted damage to the thalli varied within and among sites. Mean growth rates at the site with low densities of littorines were about twice those at the site with intermediate densities and about four times those at the high density site. At the site with high densities of littorines, F. distichus growth rates were negatively correlated with the degree to which the plants were wounded. There appeared to be no correlation of grazer density with F. distichus survivorship. Thalli at the site with few herbivores tended to reproduce earlier and at a larger size than did those at the other two sites. In all three areas, only thalli that had received little damage from herbivores became reproductive. By lowering growth rates and delaying reproduction in F. distichus, grazing by littorine snails can potentially cause variation in reproductive output among individual thalli.     

Induction of peroxisome proliferation and increase of catalase activity in yeast,Candida albicans,by cadmium

The effects of cadmium on the growth rate, catalase activity, and peroxisome proliferation in yeast,Candida albicans, were evaluated. The yeast growth was markedly inhibited by 1 mM cadmium at the initial hours. The toxic effect of cadmium on the cell growth persisted. The catalase activity of the cells treated with 1 mM Cd²⁺ first decreased, and then rose at 24 h to about 2.6 times that of the controls. The average number of peroxisomes per cell in the yeast treated with 1 mM Cd²⁺ was about sixfold higher than the control groups. The proliferation of peroxisomes and the increase of catalase activity following cadmium toxicity gives credence to the hypothesis that cadmium toxicity is related to its potential to induce oxidative stress in cells.     

A novel morphological response of maize (Zea mays) adult roots to heterogeneous nitrate supply revealed by a split‐root experiment

Approximately 35–55% of total nitrogen (N) in maize plants is taken up by the root at the reproductive stage. Little is known about how the root of an adult plant responds to heterogeneous nutrient supply. In this study, root morphological and physiological adaptations to nitrate‐rich and nitrate‐poor patches and corresponding gene expression of ZmNrt2.1 and ZmNrt2.2 of maize seedlings and adult plants were characterized. Local high nitrate (LoHN) supply increased both lateral root length (LRL) and density of the treated nodal roots of adult maize plants, but only increased LRL of the treated primary roots of seedlings. LoHN also increased plant total N acquisition but not N influx rate of the treated roots, when expressed as per unit of root length. Furthermore, LoHN markedly increased specific root length (m g^?1) of the treated roots but significantly inhibited the growth of the lateral roots outside of the nitrate‐rich patches, suggesting a systemic carbon saving strategy within a whole root system. Surprisingly, local low nitrate (LoLN) supply stimulated nodal root growth of adult plants although LoLN inhibited growth of primary roots of seedlings. LoLN inhibited the N influx rate of the treated roots and did not change plant total N content. The gene expression of ZmNrt2.1 and ZmNrt2.2 of the treated roots of seedlings and adult plants was inhibited by LoHN but enhanced by LoLN. In conclusion, maize adult roots responded to nitrate‐rich and nitrate‐poor patches by adaptive morphological alterations and displayed carbon saving strategies in response to heterogeneous nitrate supply.