Exogenous Supply Of Nutrients Research Articles

A Smart "Energy NanoLock" Selectively Blocks Oral Cancer Energy Metabolism through Synergistic Inhibition of Exogenous Nutrient Supply and Endogenous Energy Production.

The major challenge in oral cancer is the lack of state-of-the-art treatment modality that effectively cures cancer while preserving oral functions. Recent insights into tumor metabolic dependency provide a therapeutic opportunity for exploring optimal treatment approaches. Herein, a smart responsive "Energy NanoLock" is developed to improve cancer metabolic intervention by simultaneously inhibiting nutrient supply and energy production. NanoLock is a pomegranate-like nanocomplex of cyclicRGD-modified carboxymethyl chitosan (CyclicRC, pI = 6.7) encapsulating indocyanine green and apoptotic peptides functionalized gold nanoparticles (IK-AuNPs), which together form a dual pH- and photoresponsive therapeutic platform. NanoLock exhibits good stability under physiological conditions, but releases small-size CyclicRC and IK-AuNPs in response to the tumor acidic microenvironment, leading to deep tumor penetration. CyclicRC targets integrins to inhibit tumor angiogenesis, and consequently blocks tumor nutrient supply. Meanwhile, IK-AuNPs specifically induce apoptotic peptides and photothermally mediated mitochondrial collapse, and consequently inhibits endogenous energy production, thereby facilitating cell death. Importantly, in both xenograft and orthotopic oral cancer models, NanoLock selectively eliminates tumors with little cross-reactivity with normal tissues, especially oral functions, resulting in prolonged survival of mice. Therefore, NanoLock provides a novel metabolic therapy to exploit synergistic inhibition of exogenous nutrient supply and endogenous energy production, which potentially advances oral cancer treatment.

Nutrient Supply Is Essential for Shifting Tree Peony Reflowering Ahead in Autumn and Sugar Signaling Is Involved.

The flowering time of tree peony is short and concentrated in spring, which limits the development of its industry. We previously achieved tree peony reflowering in autumn. Here, we further shifted its reflowering time ahead through proper gibberellin (GA) treatment plus nutrient supply. GA treatment alone initiated bud differentiation, but it aborted later, whereas GA plus nutrient (G + N) treatment completed the opening process 38 days before the control group. Through microstructural observation of bud differentiation and starch grains, we concluded that GA plays a triggering role in flowering induction, whereas the nutriment supply ensured the continuous developing for final opening, and both are necessary. We further determined the expression of five floral induction pathway genes and found that PsSOC1 and PsLFY probably played key integral roles in flowering induction and nutrient supply, respectively. Considering the GA signaling, PsGA2ox may be mainly involved in GA regulation, whereas PsGAI may regulate further flower formation after nutrient application. Furthermore, G + N treatment, but not GA alone, inhibited the expression of PsTPS1, a key restricting enzyme in sugar signaling, at the early stage, indicating that sugar signaling is also involved in this process; in addition, GA treatment induced high expression of PsSnRK1, a major nutrient insufficiency indicator, and the induction of PsHXK1, a rate-limiting enzyme for synthesis of sugar signaling substances, further confirmed the nutrient shortage. In short, besides GA application, exogenous nutrient supply is essential to shift tree peony reflowering ahead in autumn under current forcing culture technologies.

Global Patterns and Controls of Nutrient Immobilization on Decomposing Cellulose in Riverine Ecosystems

AbstractMicrobes play a critical role in plant litter decomposition and influence the fate of carbon in rivers and riparian zones. When decomposing low‐nutrient plant litter, microbes acquire nitrogen (N) and phosphorus (P) from the environment (i.e., nutrient immobilization), and this process is potentially sensitive to nutrient loading and changing climate. Nonetheless, environmental controls on immobilization are poorly understood because rates are also influenced by plant litter chemistry, which is coupled to the same environmental factors. Here we used a standardized, low‐nutrient organic matter substrate (cotton strips) to quantify nutrient immobilization at 100 paired stream and riparian sites representing 11 biomes worldwide. Immobilization rates varied by three orders of magnitude, were greater in rivers than riparian zones, and were strongly correlated to decomposition rates. In rivers, P immobilization rates were controlled by surface water phosphate concentrations, but N immobilization rates were not related to inorganic N. The N:P of immobilized nutrients was tightly constrained to a molar ratio of 10:1 despite wide variation in surface water N:P. Immobilization rates were temperature‐dependent in riparian zones but not related to temperature in rivers. However, in rivers nutrient supply ultimately controlled whether microbes could achieve the maximum expected decomposition rate at a given temperature. Collectively, we demonstrated that exogenous nutrient supply and immobilization are critical control points for decomposition of organic matter.

Sustaining Rice Production through Biofertilization with N2-Fixing Cyanobacteria

Current agricultural productivity depends on an exogenous nutrient supply to crops. This is of special relevance in cereal production, a fundamental part of the trophic chain that plays a vital role in the human diet. However, our agricultural practices entail highly detrimental side-effects from an environmental point of view. Long-term nitrogen fertilization in croplands results in degradation of soil, water, and air quality, producing eutrophication and subsequently contributing to global warming. In accordance with this, there is a biotechnological interest in using nitrogen-fixing microorganisms to enhance crop growth without adding chemically synthesized nitrogen fertilizers. This is particularly beneficial in paddy fields, where about 60% of the synthetic fertilizer that has been applied is dissolved in the water and washed away. In these agricultural systems, N2-fixing cyanobacteria show a promising biotechnological potential as biofertilizers, improving soil fertility while reducing the environmental impact of the agricultural practice. In the current study, Andalusian paddy fields have been explored to isolate N2-fixing cyanobacteria. These endogenous microorganisms have been subsequently re-introduced in a field trial in order to enhance rice production. Our results provide valuable insights regarding the use of an alternative natural source of nitrogen for rice production.

Subtractive proteomics and systems biology analysis revealed novel drug targets in Mycoplasma genitalium strain G37

Mycoplasma genitalium is one of the sexually transmitted pathogens that cause significant morbidity in the host. The development of effective therapeutic procedures is urgently needed to counter the multi-drug resistant events imposed by this pathogen. In the current version of M. genitalium G37 genome, 512 open reading frames have been identified. The function of 91 proteins encoded by M. genitalium genes was found to be hypothetical and these proteins were termed hypothetical proteins (HPs). This study aims to carry out functional characterization of HPs by a systems biology approach. Functional assignments of 61 HPs were made with high confidence. They belong to different functional groups, such as DNA-binding proteins, helicases and transporters. Approximately 26% of HPs were identified as transporters, suggesting that M. genitalium is likely to rely on the exogenous nutrient supply for survival. A group of 20 proteins was predicted to be virulence factors, indicating the pathogenic characteristics of M. genitalium. Among the coding proteins, six proteins were pathogen-specific and could serve as potential drug targets by subtractive proteomics analysis. Network analysis of the HPs suggested that several critical proteins were involved in SOS response and stringent response in M. genitalium. These findings provided a better picture of M. genitalium genome and novel clues for studying the potential infection mechanism in this bacterium.

Balanced nutrient stoichiometry of organic amendments enhances carbon priming in a poorly structured sodic subsoil

Application of organic amendments (OAs), nutrients and gypsum to sodic subsoils is of great interest to improve soil functionality and crop yield. However, controversy remains about the impact of the priming effect (PE) on native soil organic carbon (SOC), and the mechanisms governing the dynamics of the PE by OAs (with variations in nutrient stoichiometry). To address these gaps in knowledge, this nine-month study applied C4-plant-derived OAs in a C3-plant-derived soil at 6.2 g C kg−1 soil, with and without the exogenous supply of nutrients (nitrogen and/or phosphorus) or gypsum. Across the treatments, the cumulative PE was between 135 and 475 mg CO2–C kg−1 soil over the nine months, equivalent to 2.3–8.2% of native SOC loss. In the first two months, the positive PE by the OAs could be attributed to co-metabolism and nitrogen (N) mining. These theories were supported by (i) the enhanced growth of microbial biomass associated with increased soil labile C (such as dissolved organic C); and (ii) the decreased soil mineral N availability, likely via microbial N immobilization, particularly with the inputs of sorghum stubble or sugarcane bagasse. Towards the end of the incubation, the relative PE (i.e., PE ÷ SOC mineralization in the control soil) was higher in the OA treatments (sorghum stubble and sugarcane bagasse) where nutrients were added to lower the C: nutrient stoichiometric ratios. These results support the theory of microbial stoichiometric decomposition of SOC, which may have become the dominant mechanism of PE over time. The application of gypsum, together with OAs (sorghum stubble or sugarcane bagasse), did not significantly change the magnitude or direction of the PE. In conclusion, the significant native SOC losses and N immobilization induced by the OAs, particularly where we balanced the nutrient stoichiometric ratios, indicate the vulnerability of subsoil SOC, and hence the potential of C sequestration in a sodic subsoil following the application of OAs may be limited.

Nutrient stoichiometry and labile carbon content of organic amendments control microbial biomass and carbon-use efficiency in a poorly structured sodic-subsoil

Application of organic amendments (OAs) combined with inorganic fertilizers or gypsum in poorly structured soils has recently received much attention as an agricultural management practice aiming to ameliorate physicochemical constraints and improving soil carbon (C) storage. Although microbial C-use efficiency (CUE) is recognized as a critical parameter in ecological models to predict soil C cycling and storage, little is known about the effects of OAs with exogenous nutrient supply (to balance the resource nutrient stoichiometry) or gypsum on microbial biomass and CUE. Here, we examined the role of OAs (C4 vegetation-derived: δ13C – 12 to − 15‰) in altering microbial biomass, C mineralization, and CUE, i.e., microbial growth relative to microbial C uptake (microbial growth + respiration + death) over the long-term, in an alkaline sodic-subsoil (C3 vegetation-derived: δ13C – 24‰). Four different OAs (sorghum stubble, sugarcane bagasse, sugarcane mill mud, and sugarcane mill mud + sugarcane mill ash) were used at 6.2 g C kg−1 soil, with and without the exogenous supply of nutrients and/or gypsum. The nutrients were added with the aim to convert OAs to stable soil organic matter (SOM) with a C/nitrogen (N)/phosphorus (P) stoichiometric ratio of 100:8.3:2. Over 90 days, the cumulative mineralization of OA-C varied across OA types and ranged between 42 and 497 mg CO2-C g−1 OA-C. The OA-derived microbial biomass C (MBC) ranged between 20 and 350 mg C kg−1 soil across the treatments, which was highest with sorghum stubble that contained the highest dissolved (labile) organic C. The mill mud with an inherently balanced C/nutrient stoichiometry had the highest CUE, i.e., 0.3–0.8, compared to the sorghum stubble and sugarcane bagasse (with imbalanced nutrient stoichiometry), i.e., 0.1–0.6. Balancing the nutrient stoichiometry of sorghum stubble and sugarcane bagasse via nutrient inputs increased MBC but not CUE. The input of gypsum to the OA-treated soil had no impact on either MBC or CUE. In conclusion, balanced C/nutrient stoichiometry and labile C content of OAs are critical properties to control their impact on C mineralization, MBC, and CUE, with implications for soil C storage upon amendment into a poorly structured sodic-subsoil.

Balancing nutrient stoichiometry facilitates the fate of wheat residue‑carbon in physically defined soil organic matter fractions

Preserving and enhancing soil organic carbon (SOC) stocks is one of the major objectives for sustainable agriculture. The exogenous nutrient supply along with returning crop residues, i.e., integrated residue-nutrient management, may increase carbon (C) cycling and residue-derived microbial biomass, and therefore to affect SOC stocks. However, there is a lack of knowledge about how the integrated residue-nutrient management, that balances the resource nutrient stoichiometry, facilitates the fate (or partitioning) of residue-C in physically defined SOC fractions. Hence, through a laboratory study, we quantified the fate of wheat residue (δ13C-enriched, 494‰) into sequentially separated physical SOC fractions, under the interaction of different residue rates (6.7 and 20.0 g kg−1 soil) and nutrient inputs (nil, low and high supplies of nitrogen, phosphorus, and sulfur) in two contrasting soils (Luvisol and Vertisol). The results showed that after 245 days, 42.7–54.2% of the newly-added residue-13C remained in organic matter (OM) fractions in the soils, with 22.1–40.8% in the light fraction [LF; defined as free particulate organic matter (f-POM)] and 13.9–19.5% in the heavy fraction [HF; defined as aggregate- & mineral-protected OM, which included silt-clay OM and occluded POM (o-POM)]. Following the sequential separation of HF, 8.3–15.3% of residue-13C was distributed to silt-clay OM and 4.2–6.1% to o-POM after 245 days. The high-residue rate (cf. low-residue) increased the amount of residue-C in SOC fractions. Narrowing the C-nutrient stoichiometric ratio in the residue treated soils via the exogenous nutrient input affected the proportional distribution of residue-C in SOC fractions at the high-residue rate only. With the high-residue rate in both soils, nutrient input (cf. no-nutrient) at both rates increased “new” residue-derived stable C formation in the HF by 17% or silt-clay associated OM by 27%, while decreased the distribution of residue-13C in the f-POM (LF) by 26% or o-POM by 18%. In the current study, soil type also affected the incorporation of residue-C in the organo-mineral fractions, i.e., 20% higher residue-C was incorporated in the silt-clay OM in the Vertisol than Luvisol. This study improved our knowledge on the distribution of residue-C in SOC fractions in response to integrated residue-nutrient management, which could be used to refine conceptual and mechanistic models for predicting changes in SOC storage.

Microbial mechanisms of carbon priming effects revealed during the interaction of crop residue and nutrient inputs in contrasting soils.

Agronomic practices such as crop residue return and additional nutrient supply are recommended to increase soil organic carbon (SOC) in arable farmlands. However, changes in the priming effect (PE) on native SOC mineralization in response to integrated inputs of residue and nutrients are not fully known. This knowledge gap along with a lack of understanding of microbial mechanisms hinders the ability to constrain models and to reduce the uncertainty to predict carbon (C) sequestration potential. Using a 13 C-labeled wheat residue, this 126-day incubation study examined the dominant microbial mechanisms that underpin the PE response to inputs of wheat residue and nutrients (nitrogen, phosphorus and sulfur) in two contrasting soils. The residue input caused positive PE through "co-metabolism," supported by increased microbial biomass, C and nitrogen (N) extracellular enzyme activities (EEAs), and gene abundance of certain microbial taxa (Eubacteria, β-Proteobacteria, Acidobacteria, and Fungi). The residue input could have induced nutrient limitation, causing an increase in the PE via "microbial nutrient mining" of native soil organic matter, as suggested by the low C-to-nutrient stoichiometry of EEAs. At the high residue, exogenous nutrient supply (cf. no-nutrient) initially decreased positive PE by alleviating nutrient mining, which was supported by the low gene abundance of Eubacteria and Fungi. However, after an initial decrease in PE at the high residue with nutrients, the PE increased to the same magnitude as without nutrients over time. This suggests the dominance of "microbial stoichiometry decomposition," supported by higher microbial biomass and EEAs, while Eubacteria and Fungi increased over time, at the high residue with nutrients cf. no-nutrient in both soils. Our study provides novel evidence that different microbial mechanisms operate simultaneously depending on organic C and nutrient availability in a residue-amended soil. Our results have consequences for SOC modeling and integrated nutrient management employed to increase SOC in arable farmlands.

Arginine starvation in colorectal carcinoma cells: Sensing, impact on translation control and cell cycle distribution

Tumor cells rely on a continued exogenous nutrient supply in order to maintain a high proliferative activity. Although a strong dependence of some tumor types on exogenous arginine sources has been reported, the mechanisms of arginine sensing by tumor cells and the impact of changes in arginine availability on translation and cell cycle regulation are not fully understood. The results presented herein state that human colorectal carcinoma cells rapidly exhaust the internal arginine sources in the absence of exogenous arginine and repress global translation by activation of the GCN2-mediated pathway and inhibition of mTOR signaling. Tumor suppressor protein p53 activation and G1/G0 cell cycle arrest support cell survival upon prolonged arginine starvation. Cells with the mutant or deleted TP53 fail to stop cell cycle progression at defined cell cycle checkpoints which appears to be associated with reduced recovery after durable metabolic stress triggered by arginine withdrawal.

Peri-operative nutritional management

The metabolic response to surgical trauma is mainly characterised by an increase in BMR, a negative N balance, increased gluconeogenesis and increased synthesis of acute-phase proteins. These reactions aim at ensuring the availability of endogenous substrates for healing wounds while the synthesis of acute-phase proteins enhances the scavenging process and helps repair. However, if this process is excessive or continues for too long, it leads to a progressive depletion of body compartment with a consequent adverse outcome. Obviously, the severity of such depletion is magnified if the patient is starving or is already malnourished and the consumption of lean body mass is not compensated by an exogenous supply of nutrients. The nutritional control of this metabolic reaction represents the traditional rationale for nutritional support of surgical patients. Subsequent data have shown that the negative effects of starvation are not simply due to the starvation per se but due to the starving gut, and peri-operative enteral nutrition has proven successful in blunting the metabolic response after injury and improving protein kinetics, net balance and amino acid flux across peripheral tissue and consequently in decreasing the complications. Finally, further clinical research has shown that many post-operative infections may result from immune suppression and that such state might be reversed to some degree by modulation of the immune response through specialised nutritional support in surgical patients, regardless of their nutritional status. This paper will focus on the updated evidence-based research on peri-operative nutrition (parenteral, enteral and immune-enhancing) in patients undergoing major surgery.

Litterfall, litter decomposition and nutrient dynamics in a subtropical natural oak forest and managed plantation in northeastern India

In northeastern India, subtropical forests are over-exploited for timber, fuel wood and common agricultural practice like shifting cultivation, which are responsible for the degradation of natural forest. In degraded areas, large-scale plantations of different species of Quercus have been raised since 1980 for the production of economic Tasar silk. Conversion of natural forest into plantation affects the process of nutrient cycling due to management practices. Thus, it would be of importance to study the litterfall, litter decomposition process and the factors regulating the rate of litter decay in these ecosystems to improve recommendations for their management and conservation. We recorded litterfall by using litter traps and decomposition of leaf litter by nylon net bag technique to understand the amount of organic matter and nutrient return and their release in soils of forest and plantation in Manipur, northeast India. Total litterfall was 419.9 g m −2 year −1 in plantation and 547.7 g m −2 year −1 in forest. Litter decomposition rate was faster at plantation site than the forest in the early stage of litter decomposition whereas the reverse was observed at later stages of decomposition. Stepwise regression analysis showed the significant role of relative humidity and mean temperature on mass loss rates in the forest. Relative humidity, maximum temperature, population of fungi and actinomycetes were the best predictor variables for mass loss rates in plantation. Nutrient retranslocation efficiency and the immobilization of N and P in forest litter were higher than plantation. This suggests that Q. serrata growing in natural ecosystem in oligotrophic condition adapted strong nutrient conservation mechanisms to compete with the other plant species for the meager soil nutrients. The same species in plantation loses these adaptive capabilities because of exogenous supply of nutrients and in the absence of intense competition with other plant species. Thus, the optimization of organic and chemical fertilizer input in plantation is recommended for maintaining the soil fertility level to produce quality leaf for silkworm by conserving essential nutrients in the system.

Stimulation of protein synthesis in human tumours by parenteral nutrition: Evidence for modulation of tumour growth

Eighteen patients with localized colorectal carcinoma were randomized to receive intravenous nutrition or to be fasted during the 24 h before surgery. Protein synthesis, an index of tumour growth, was then measured by the incorporation of [13C]leucine into tumour protein immediately before surgery. The mean (s.e.m.) rate of tumour protein synthesis in patients receiving nutrition (42.7(3.5) per cent per day) was 89 per cent higher than the rate in the fasted group (22.6(1.9) per cent per day) (P = 0.002). As tumours consist of a variety of different cell types, in vitro rates of protein synthesis were measured in malignant cells isolated from colorectal tumours and cultured with autologous serum obtained from the patient in either the fasted or the fed state. There was a mean increase of 81 per cent in protein synthesis when fed rather than fasted serum was used (P less than 0.02), indicating that the malignant cells themselves respond to nutrient supply. This increase in tumour protein synthesis provides the first evidence in vivo that the exogenous supply of nutrients can modulate the rate of growth of a human tumour.

Bacterial Interactions in Early Life Stages of Marine Cold Water Fish.

> Abstract The intensive rearing of various fish species in aquaculture has revealed intimate relationships between fish and bacteria that eventually may affect establishment of a "normal" mucosal microflora or result in disease epizootics. Interactions between bacteria and mucosal surfaces play important roles both at the egg and larval stages of marine fish. Bacterial adhesion and colonization of the egg surface occur within hours after fertilization. The diverse flora which eventually develops on the egg appears to reflect the bacterial composition and load of the ambient water, but species-specific adhesion at the egg surface may also play a role in development of the egg epiflora. Proteolytic enzymes produced by members of the adherent epiflora may cause serious damage to the developing egg and may also affect further adhesion of the epiflora. Ingestion of bacteria at the yolk sac stage results in establishment of a primary intestinal microflora which seems to persist beyond first feeding. Establishment of a gut microflora is likely to undergo several stages, resulting in an "adult" microflora weeks to months after first feeding. Ingested bacteria may serve as an exogenous supply of nutrients or essential factors at an early life stage. Early exposure to high bacterial densities is probably important for immune tolerance, and thus for the establishment of a protective intestinal microflora. Successful rearing of early life stages of several marine fish species depends on knowledge of the complex interactions among the cultured organisms and the bacterial communities which develop at the mucosal surfaces and in the ambient water and rearing systems. The routine use of antibiotics during rearing of fish larvae is not advisable, since it may increase the risk of promoting antibiotic resistance and adversely affect the indigenous microflora of the larvae. The use of probiotics has proven advantageous in domestic animal production, and the search for effective probiotics may have a great potential in aquaculture of marine organisms. Bacteria with antagonistic effects against fish pathogens have been successfully administered to several fish species, resulting in decreased mortality or increased growth rate.http://link.springer-ny.com/link/service/journals/00248/bibs/38n1p1.html

Litter breakdown in streams of the Agüera catchment: influence of dissolved nutrients and land use

1. The breakdown of oak (Quercus robur L.), chestnut (Castanea sativa Miller) and eucalypt (Eucalyptus globulus Labill.) litter enclosed in 5‐mm mesh bags was compared between first‐order headwaters (two with native riparian forest and two with eucalypt plantations) and a third‐order reach of Agüera stream. Weight loss and dynamics of phosphorus and nitrogen in litter were studied for a period of 155 days.2. Among the different sites, processing rates ranged from 0.0045 to 0.0080 day–1 for chestnut leaf litter, from 0.0036 to 0.0051 day–1 for oak, and from 0.0027 to 0.0158 day–1 for eucalypt.3. The availability of nutrients in water clearly influenced nitrogen and phosphorus dynamics in litter. In headwater reaches, net immobilization was not observed and losses of phosphorus and nitrogen followed mass loss. However, there was an enrichment of litter at the low reach, where influence of human settlements—located upstream—could lead to a greater availability of phosphorus in water.4. The enhancement of litter decay by the exogenous nutrient supply depended on leaf quality, as only the processing rate of eucalypt increased at the nutrient‐rich site.5. The processing rates differed little among headwaters, suggesting that riparian forest type, i.e. deciduous forest v eucalypt plantations, did not affect litter decay in the stream.

Growth, decomposition, and nutrient retention of Cladium jamaicense Crantz and Typha domingensis Pers. in the Florida Everglades

Estimates of phosphorus (P) and nitrogen (N) gains and losses during annual macrophyte growth, death and 2 years decomposition were made along a gradient of surface water nutrient concentrations in the Florida Everglades. Annual rates of P and N allocation to growing leaves, translocation or leaching from dying leaves, and retention in dead leaves of Cladium jamaicense Crantz and Typha domingensis Pers. were correlated to soluble reactive P and nitrate concentrations in surface water. Rates of each of these processes were higher in T. domingensis than in C. jamaicense, Cladium jamaicense rates increased linearly along the nutrient gradients, but did not fluctuate with yearly variations in soluble reactive P or nitrate concentrations. For T. domingensis, annual rates were strongly correlated with mean annual soluble reactive P and nitrate concentrations during specific sampling years. Responses of C. jamaicense to the nutrient gradient were characteristic of species competitive in an infertile habitat, while responses of T. domingensis were characteristic of species competitive in a fertile habitat. The main effect of P and N enrichment on leaf nutrient flux was to accelerate translocation or leaching from dying tissue, rather than to increase retention in standing dead leaves. Freshly dead leaves retained only slightly greater quantities of P and N under enriched conditions in comparison to background conditions. After 2 years of decomposition, approximately half of the leaf litter mass remained intact. Increasing P and N concentrations in decomposing leaf litter resulted in net uptake or retention of these elements after 2 years despite decreasing litter mass. The total amounts of P and N that were sequestered annually by T. domingensis after processes of leaf production, mortality and 2 years decomposition were lowest under non-enriched conditions and reached a maximum under a moderate level of enrichment. Wetland ecosystems such as the Everglades, which developed under conditions of low nutrient supply, may offer a finite potential for accelerated nutrient retention when the exogenous nutrient supply increases as a result of human activities. However, a plant species such as C. jamaicense, that is adapted to a low-nutrient environment, may have a low nutrient threshold before it loses its competitive capability and its habitat is invaded by a species such as T. domingensis that is better adapted to a high-nutrient environment.

Studies on the selection of a suitable packaging material for pre- and post-irradiation storage of cereal grains in Ghana

Twenty different species of fungi belonging to the genera Aspergillus, Cephalosporium, Dreschlera, Fusarium, Mucor, Neurospora, Rhizoctonia, Rhizopus, Penicillium and Trichoderma were isolated from jute and woven polypropylene sacks using the blotter test, solid medium test and the decimal serial dilution technique. There was a highly significant difference (Students' t-test, P < 0.05) between the larger number of fungal colonies associated with jute sacks than with woven polypropylene sacks. Correspondingly, more fungal species (16) were isolated from jute sacks than from woven polypropylene sacks (9). The blotter test showed that in the absence of an exogenous supply of nutrients, 88% of the sections of jute sacks supported in vivo growth of fungal spores whilst woven polypropylene sacks could not support the growth of contaminating spores. Evidence is presented that mould and yeast counts on sections of new-woven polypropylene sacks incubated at 80 and 90% relative humidity (R.H.) for four months increased by less than 1 log cycle, whilst in similar sections hung on a line under ambient conditions (75 ± 10% R.H. and 28 ± 3°C) viable counts of spores decreased. Sections of fresh jute sacks similarly treated supported 1 log cycle increase in mould and yeast counts at 80% R.H. and 2 log cycles increase at 90% R.H. after four months of storage. Gamma-ray irradiation (4.0 kGy) reduced the mould and yeast counts on new jute and new woven polypropylene sacks by 1 and 2 log cycles, respectively, but post-irradiation storage at 80% R.H. allowed moulds like Aspergillus flavus, A. niger, Fusarium nivale and Penicillium verrucosum var. cyclopium to commence growth on jute sacks. This presumably, may act as a springboard for infecting grain contents of jute sacks. Inert woven polypropylene sacks failed to support fungal growth.

Behaviour of Cochliobolus sativus during its infection of barley and wheat leaves

Similar incidences of germination and appressoria formation, with or without added nutrients to the infection drops, suggested that the nutrients contained in C. sativus conidia were sufficient for germination and formation of appressoria. Appressoria developed poorly on glass slides compared with development on leaf surfaces. Sharp, fine infection pegs developed within 12-15 h and 14-18 h after inoculation onto cleared and uncleared leaves respectively. Percentages of penetration and colonization of cleared leaves were lower than those of uncleared leaves and increased significantly when various nutrients including leaf leachates were added to the infection drops. Carbohydrate and protein levels were much lower in cleared than in uncleared leaves. Leaf leachates contained sugars and amino acids which made up an adequate food supply for the pathogen. Sugar and amino acid contents of the infection drops decreased during the penetration phase on healthy leaves as well as on the glass surface. Within this period, however, the degree of change in sugar content was much greater on leaves than on the glass surface. These observations led to the conclusion that C. sativus conidia required an exogenous supply of nutrients to enable successful penetration. Nutrients leached from cells of healthy leaves were absorbed by the spores and utilized to provide the energy required for penetration. The parasite population on healthy leaves of barley and wheat was generally synchronous, suggesting that this host-pathogen combination is conducive to the early host-parasite interactions.