The molecular basis of potassium nutrition in plants

Over the last five years, the cloning and characterization of K⁺ transport genes corresponding to K⁺ channels (KAT1, AKT1, KST1, AKT2), associated subunits (KAB1) and a high-affinity transporter (HKT1) has opened up important new avenues for research on plant K⁺ nutrition. With the abundance of molecular data now available it seems timely to link this information with the wealth of data previously accumulated on the physiology of plant K⁺ acquisition. The ultimate goal of all this research is to gain a better understanding of K⁺ transport and nutrition in the intact plant. Thus it is important to begin to integrate the molecular research with results from biochemical and physiological research conducted at the cellular, root and whole plant levels. This article will focus on describing the features of the cloned K⁺ transporters and their possible roles in mediating high- and low-affinity K⁺ uptake from the soil, as well as how K⁺ acquisition may be regulated.Abbreviations NEM N-ethyl maleimide - PCMBS p-chloromercuribenzene sulphonic acid     

Inhibition of Spores of Clostridium spp. by Sodium Nitrite

S ummary . Sodium nitrite heated in a laboratory medium was more inhibitory to spores of Clostridium spp. than nitrite added as a filter-sterilized solution to the same medium. Most spores remained refractile after inhibition for >3 months and some proved viable when inoculated into fresh nitrite-free medium. The inhibitory activity of heated nitrite medium was not stable indefinitely, growth sometimes occurred on re-inoculation with vegetative cells.     

Nest trampling and ground nesting birds: Quantifying temporal and spatial overlap between cattle activity and breeding redshank

Conservation grazing for breeding birds needs to balance the positive effects on vegetation structure and negative effects of nest trampling. In the UK, populations of Common redshank Tringa totanus breeding on saltmarshes declined by >50% between 1985 and 2011. These declines have been linked to changes in grazing management. The highest breeding densities of redshank on saltmarshes are found in lightly grazed areas. Conservation initiatives have encouraged low‐intensity grazing at <1 cattle/ha, but even these levels of grazing can result in high levels of nest trampling. If livestock distribution is not spatially or temporally homogenous but concentrated where and when redshank breed, rates of nest trampling may be much higher than expected based on livestock density alone. By GPS tracking cattle on saltmarshes and monitoring trampling of dummy nests, this study quantified (i) the spatial and temporal distribution of cattle in relation to the distribution of redshank nesting habitats and (ii) trampling rates of dummy nests. The distribution of livestock was highly variable depending on both time in the season and the saltmarsh under study, with cattle using between 3% and 42% of the saltmarsh extent and spending most their time on higher elevation habitat within 500 m of the sea wall, but moving further onto the saltmarsh as the season progressed. Breeding redshank also nest on these higher elevation zones, and this breeding coincides with the early period of grazing. Probability of nest trampling was correlated to livestock density and was up to six times higher in the areas where redshank breed. This overlap in both space and time of the habitat use of cattle and redshank means that the trampling probability of a nest can be much higher than would be expected based on standard measures of cattle density. Synthesis and applications: Because saltmarsh grazing is required to maintain a favorable vegetation structure for redshank breeding, grazing management should aim to keep livestock away from redshank nesting habitat between mid‐April and mid‐July when nests are active, through delaying the onset of grazing or introducing a rotational grazing system.     

Root hydrocarbons as potential markers for determining species composition

Grasslands can be a complex mixture of plant species. A method is described to allow the identification of both roots and shoots of five different grass species, thus permitting greater knowledge about whole plant allocation and competition in mixed pastures. The five species were Lolium perenne, Festuca ovina, Festuca rubra, Poa trivialis and Agrostis capillaris. N‐alkanes with odd‐numbers of carbon atoms in the chains predominate in plants and in the five grass species studied, concentrations of alkanes of chain length of C₂₉, C₃₁ and C₃₃ were highest. Average concentrations of C₂₇‐C₃₃ alkanes in shoots and roots were 187 and 11 mg kg ^{? 1}, respectively. This wide range of values required considerable modifications to the method of analysis, including expressing concentrations on an organic matter basis and scaling‐down the procedure. The n‐alkane concentrations in roots are different from those in shoots and therefore values from shoots cannot be used to predict the composition in roots. Using a canonical variate analysis, all five grass species could be separated using concentrations of C₂₆, C₃₁ and C₃₃ values in the roots. The greatest difference occurred between A. capillaris and the others, whereas discrimination was least between the two Festuca species. Defoliation had contrasting effects on the concentration of a few n‐alkanes, but not in the n‐alkanes used to discriminate between grass species. Alkane analysis shows great potential as a method to quantify the species composition of the root biomass beneath mixed pasture species.     

Changing land management of lowland wet grasslands of the UK: impacts on snipe abundance and habitat quality

Snipe Gallinago gallinago breeding on lowland wet grasslands in England have undergone widespread and dramatic declines in abundance and distribution since at least the 1970s. There are many potential drivers of the decline but reductions in habitat quality, driven by land management, are often proposed as a contributing factor in the historical declines of breeding waders. Breeding snipe are now restricted to a few key places such as nature reserves and environmentally sensitive areas where management for breeding waders is implemented. On average, populations have continued to decline, even in these key areas, though population trends vary from a decline of 98% to an increase of 61% between the early 1990s and 2006. We examined the relationship between regional variation in snipe population trends and soil conditions, other habitat features and land management. Snipe were more likely to persist in fields where the soil conditions were wet and soft. Fields are wetter and softer now than in the early 1990s and management influenced these conditions. Soil softness increased with decreasing grazing pressure and increasing surface flooding. Soil moisture increased with surface flooding and was higher in organic soils. Changes in field condition were consistent with decreases in grazing pressure and increases in surface flooding. In spite of habitat condition being altered in a way that should have been beneficial to snipe, the numbers have continued to decline. Thus, it is unlikely that the measures of habitat condition examined here have been the driver of the decline and other factors must be involved. Research efforts should now focus on alternative explanations of the decline, for example, changes in other key aspects of habitat quality such as prey abundance, or changes in snipe productivity or mortality.     

Wd(a+) red blood cells in two sisters of a Hei//om Khoisan family in Namibia

Two sisters in a Hei//om family of the southern African Khoisan race in Namibia were found to have Wd(a+) red blood cells. Wda is a low-frequency antigen identified so far only in a European family in Canada and a family in Holland. The Wda gene may have had an independent origin in the Khoisan. Alternatively, the Hei//om population may have acquired it through miscegenation.     

Root Penetration by Meloidogyne incognita Juveniles Infected with Bacillus Penetrans

Bacillus penetrans inhibited penetration by Meloidogyne incognita second-stage juveniles (J2) into tomato roots in the laboratory and greenhouse. Spores from this Florida population of B. penetrans attached to J2 of M. javanica, M. incognita, and M. arenaria. A greater proportion of J2 of M. javanica were infected than were J2 of either M. incognita or M. arenaria, and a greater number of spores attached to M. incognita than to M. arenaria.