Histochemistry of the juxtaglomerular apparatus in the toad Bufo bufo

Summary An investigation regarding the question of whether there exists a macula densa as part of the juxtaglomerular apparatus in the kidney of amphibians has been carried out. With the aid of a histochemical reaction for glucose-6-phosphate dehydrogenase activity, the presence of a macula densa zone as a specialized part of the distal tubule in the toad Bufo bufo was demonstrated. The functional significance of the high glucose-6-phosphate dehydrogenase activity in the macula densa cells is discussed.     

Current Status of Cereal Root Diseases in Western Australia Under Intensive Cereal Production and Their Comparison with the Historical Survey Conducted During 1976–1982

Two separate surveys of root diseases of cereals in the Western Australian (WA) cereal belt were conducted: the first conducted annually for wheat and barley during 1976–1982 and the second for wheat during 2005–2007. For the 1976–1982 survey, the cereal belt was divided into 15 zones based on the location and rainfall. Sampling was representative of the actual cropping area, with both wheat and barley sampling sites selected by zone as a percentage of total sites. Over 31 000 plants were assessed from a total of 996 fields. Average take‐all incidence ranged from 3% in the northern low rainfall zone to 57% in the southern high rainfall zone. Other root diseases assessed included rhizoctonia root rot, fusarium crown rot and subcrown internode discolouration. During the 2005–2007 survey, around 20 000 plants from a total of 210 fields being intensively cropped with cereals were surveyed for take‐all, rhizoctonia root rot, fusarium crown rot, common root rot, root lesion nematode and cereal cyst nematode. The 2005–2007 survey results indicated that root and crown diseases prevailed in paddocks frequently cropped with cereals and occurred at damaging levels across all WA cropping districts surveyed. The more recent root disease survey identified that the fungal diseases rhizoctonia root rot and fusarium crown rot and the root lesion nematode were the most serious impediments to intensive cereal production, particularly in the southern region of WA. Comparing the 2005–2007 results with the previous survey of 1976–1982, the relative importance of take‐all appears to have declined over the past 30 years.     

Impact of food processing and detoxification treatments on mycotoxin contamination

Mycotoxins are fungal metabolites commonly occurring in food, which pose a health risk to the consumer. Maximum levels for major mycotoxins allowed in food have been established worldwide. Good agricultural practices, plant disease management, and adequate storage conditions limit mycotoxin levels in the food chain yet do not eliminate mycotoxins completely. Food processing can further reduce mycotoxin levels by physical removal and decontamination by chemical or enzymatic transformation of mycotoxins into less toxic products. Physical removal of mycotoxins is very efficient: manual sorting of grains, nuts, and fruits by farmers as well as automatic sorting by the industry significantly lowers the mean mycotoxin content. Further processing such as milling, steeping, and extrusion can also reduce mycotoxin content. Mycotoxins can be detoxified chemically by reacting with food components and technical aids; these reactions are facilitated by high temperature and alkaline or acidic conditions. Detoxification of mycotoxins can also be achieved enzymatically. Some enzymes able to transform mycotoxins naturally occur in food commodities or are produced during fermentation but more efficient detoxification can be achieved by deliberate introduction of purified enzymes. We recommend integrating evaluation of processing technologies for their impact on mycotoxins into risk management. Processing steps proven to mitigate mycotoxin contamination should be used whenever necessary. Development of detoxification technologies for high-risk commodities should be a priority for research. While physical techniques currently offer the most efficient post-harvest reduction of mycotoxin content in food, biotechnology possesses the largest potential for future developments.     

Competing drivers lead to non-linear native–exotic relationships in endangered temperate grassy woodlands

Relationships between the diversity and abundance of native versus exotic species underpin management of disturbance regimes for conservation. Theory predicts negative, positive or neutral relationships depending on respective drivers, with greatest potential benefit when natives and exotics show opposing responses to management. We examined drivers of exotic plant cover and relationships with native plant richness using 12-year burning, mowing and grazing experiments in two representative temperate grassy eucalypt woodlands with contrasting histories of frequent versus infrequent disturbance. We hypothesized that disturbance and high resources favour exotics, and assessed whether natives and exotics covary positively due to common external drivers or negatively due to contrasting external drivers and/or competition. Positive relationships with rainfall and disturbance explained >80 % of the variation in exotic cover at both sites, supporting our first hypothesis. Native–exotic relationships were non-linear, with native richness first increasing rapidly with increasing exotic cover, then levelling and beginning to decrease. Common external drivers, particularly inter-annual rainfall, explained initial positive relationships, highlighting a prevalence of positive relationships at long temporal (as well as large spatial) scales. At the historically frequently-burnt site, a concomitant increase in native richness and exotic cover after fire contributed to the positive relationship, indicating a management trade-off. At the long-unburnt site, exotics increased but natives decreased with fire, suggesting dual benefits of low fire frequency. We conclude that relationships between exotic cover and native richness emerge from interactions among external drivers and competitive responses, with responses to external drivers dominating at low resources and negative interactions gaining importance as resources increase.     

Effects of genotype and plane of nutrition on growth and carcass characteristics of lambs from hill sheep systems

The objective of this study was to determine the effect of lamb genotype and plane of nutrition on post-weaning lamb growth, and carcass characteristics in hill sheep systems. The lamb genotypes compared were as follows: purebred Scottish Blackface, Swaledale × Scottish Blackface, Cheviot × Scottish Blackface, Lleyn × Scottish Blackface and Texel × Scottish Blackface lambs. During the finishing period, lambs were allocated to a (i) low plane of nutrition (LP), based on a fixed allowance of dried grass pellets representing a grass-based system; (ii) high plane of nutrition (HP-cereal), with a diet consisting proportionately of 0.20 dried grass pellets : 0.80 cereal-based concentrate offered ad libitum; (iii) high plane of nutrition (HP-cereal/oil), with a diet consisting proportionately of 0.20 dried grass pellets : 0.80 cereal-based concentrate containing oilseed rape offered ad libitum. There were significant genotype × diet interactions for dry matter (DM) intake (P < 0.001), live weight gain (P < 0.05) and carcass gain (P < 0.05). On the LP diet, carcass gains were higher for Texel cross compared to Blackface and Swaledale cross lambs (P < 0.05). On both HP diets, carcass gains were lower in Blackface and Swaledale crosses compared with the Cheviot, Lleyn and Texel cross lambs (P < 0.01). Feed conversion efficiency, expressed in terms of carcass gain per unit of DM, was highest for Texel cross and Cheviot cross, lowest in Swaledale cross and Blackface and intermediate for Lleyn cross lambs (P < 0.001). Conformation classification was lowest for Swaledale cross (P < 0.05) and highest for Texel cross lambs (P < 0.001), whilst those of Blackface, Cheviot and Lleyn cross lambs were similar. Carcasses from Blackface and Lleyn cross lambs had higher fat classifications than Texel and Cheviot cross lambs (P < 0.01). Feed conversion efficiency was lowest with the LP diet compared with the HP diets, resulting in a 5-week longer finishing period and lower carcass weights, fat scores, dressing proportions and subcutaneous fat depth measurements. These results indicate that crossbreeding can have a major effect on lamb performance in the hill sheep sector. Feeding a HP increased lamb growth rates, particularly for high growth-potential genotypes, improved feed efficiency, shortened the finishing period but increased carcass fatness. Including oilseed rape in concentrate-based diets did not affect performance.     

Activation of K+ Channels in the Plasma Membrane of Arabidopsis by ATP Produced Photosynthetically

Light activates a K+ channel and transiently depolarizes the plasma membrane of Arabidopsis mesophyll cells. Genetically or chemically impairing photosynthesis abolished this electrical response to light. These results indicate that illuminated chloroplasts produce a factor that activated K+ channels in the plasma membrane. By patch clamping at the single-channel level, we have obtained evidence that ATP is one such factor. Application of 0.2 to 2 mM ATP to the cytoplasmic side of excised patches of membrane reversibly activated the type of channel that was activated by light in cell-attached patches. In addition, an outward-rectifying K+ channel and an outward-rectifying nonselective cation channel were similarly activated by ATP, whereas a nonselective stretch-activated channel was unaffected by this treatment. This novel mechanism for controlling the permeability of the plasma membrane to K+ may be important to photosynthetic metabolism.     

Effects of ensiled forage legumes on performance of store finishing lambs

Male Beulah speckled face lambs (initial live weight (LW) 28.8 ± 0.31 kg) were allocated to three dietary treatments to evaluate the performance of store lambs of a hill breed when offered ensiled lucerne (Medicago sativa), red clover (Trifolium pratense) or ryegrass. Second-cut silage bales (wilted and inoculated) were prepared from 3-year old lucerne and red clover stands and a 1-year old ryegrass sward. All the lambs were group-housed and offered ad libitum ryegrass silage during a 3-week co-variate period. This was followed by a week of dietary changeover period, after which the lambs were housed individually and offered their treatment diet ad libitum. All the lambs received a flat rate supplement of pelleted molassed sugarbeet (250 g fresh weight/day). Individual intakes were determined daily, and weekly measurements of LW and body condition score (CS) were made. Additional measurements were taken by scanning the lambs for depth of Longissimus dorsi (LD) muscle and subcutaneous fat. Over an experimental period of 7 weeks, the lambs offered red clover silage had a higher voluntary silage dry matter (DM) intake, total DM intake and metabolisable energy (ME) intake (P < 0.001) than lambs offered either lucerne or ryegrass silage. This resulted in a faster (P < 0.001) growth rate and increase (P < 0.001) in CS, with no difference between lucerne and ryegrass silages. The feed conversion efficiency (FCE) was 8.0 ± 0.61 kg feed/kg gain for lambs fed red clover silage, compared with 16.6 ± 2.82 and 10.6 ± 1.94 kg feed/kg gain for lucerne and ryegrass silage, respectively. The CP intake was higher (P < 0.001) for lambs fed the lucerne and red clover silages than for the ryegrass silage treatment. The concentration of plasma total protein (TP) was higher (P < 0.05) for lambs offered ryegrass silage versus lucerne and red clover silage. Urea concentrations were highest for lambs fed lucerne silage and lowest for those fed ryegrass silage (P < 0.05). The glucose concentration was higher (P < 0.05) for lambs offered red clover silage, whereas non-esterified fatty acids (NEFA) concentration was higher (P < 0.05) for lambs offered lucerne silage. Substituting ryegrass silage with red clover silage has the potential to improve the performance of finishing store lambs.     

Leaf Respiration in Light and Darkness (A Comparison of Slow- and Fast-Growing Poa Species)

We investigated whether leaf dark respiration (nonphotorespiratory mitochondrial CO2 release) is inhibited by light in several Poa species, and whether differences in light inhibition between the species are related to differences in the rate of leaf net photosynthesis. Four lowland (Poa annua L., Poa compressa L., Poa pratensis L., and Poa trivialis L.), one subalpine (Poa alpina L.), and two alpine (Poa costiniana Vick. and Poa fawcettiae Vick.) Poa species differing in whole plant relative growth rates were grown under identical controlled conditions. Nonphotorespiratory mitochondrial CO2 release in the light (Rd) was estimated according to the Laisk method. Photosynthesis was measured at ambient CO2 partial pressure (35 Pa) and 500 [mu]mol photons m-2 s-1. The rate of photosynthesis per unit leaf mass was positively correlated with the relative growth rate, with the slow-growing alpine Poa species exhibiting the lowest photosynthetic rates. Rates of both Rd and respiration in darkness were also substantially lower in the alpine species. Nonphotorespiratory CO2 release in darkness was higher than Rd in all species. However, despite some variation between the species in the level of light inhibition of respiration, no relationship was observed between the level of inhibition and the rate of photosynthesis. Similarly, the level of inhibition was not correlated with the relative growth rate. Our results support the suggestion that rates of leaf respiration in the light are closely associated with rates in darkness.     

Effects of sire breed on ewe dystocia, lamb survival and weaned lamb output in hill sheep systems

A study was carried out on six hill farms, located in the main hill regions of Northern Ireland, over three breeding seasons to investigate the effect of sire breed on ewe dystocia, lamb survival and weaned lamb output. On each farm, groups of 26 to 40 purebred Scottish Blackface ewes (n = 3174) were crossed with Blackface, Swaledale, North Country Cheviot, Lleyn and Texel sires by natural service (year 1) and artificial insemination (years 2 and 3). Each of the mating groups was initially balanced for ewe age, live weight and condition score, and a total of 15 sires of each breed were used over the 3 years. In total, 2272 ewes were recorded at lambing, producing 3451 lambs, over the 3 years. Sire breed had a significant effect (P < 0.001) on lamb birth weight with Blackface and Swaledale the lowest and Texel the highest. The proportion of ewes with dystocia was higher with Texel sires compared with Lleyn, Swaledale and Blackface sires (P < 0.05). Ewes mated to Cheviot sires had more dystocia than those mated to Blackface and Swaledale sires (P < 0.05), while ewes mated to Lleyn sire breed had more dystocia (P < 0.05) than those mated to Blackface sire breed. Most of the incidence of dystocia was attributable to increased lamb birth weight (P < 0.001), and some to litter size (P < 0.05). Swaledale, Cheviot, Lleyn and Texel sire breeds increased the incidence of malpresentations (P < 0.05). Lamb live weight at weaning was higher with Texel- and Cheviot- and Lleyn-sired lambs compared with Blackface- and Swaledale-sired lambs (P < 0.01). The level of lamb mortality at birth was not affected by sire breed. However, lamb mortality at weaning was lower for Lleyn-sired lambs compared with the other lamb genotypes (P < 0.05). These results indicate that the use of sires from larger breeds, such as Lleyn and Texel, within the Blackface ewe flocks can increase lamb output, with no apparent detrimental effects on lamb mortality or ewe survival, but increased assistance at lambing will be required.