Leaf cuticles behave as asymmetric membranes : evidence from the measurement of diffusion potentials

Cuticles were isolated enzymatically from the leaves of two maple species (Acer saccharum Marsh and A. platanoides L.) and from orange (Citrus aurantium L.). The cuticles were placed in a plastic cuvette and different concentrations of KCl were perfused over the physiological inner and outer surfaces while the electrical potential (E¹⁰) that developed across the cuticles and was caused by ion diffusion was measured. E¹⁰ was always positive, indicating that the permeability of K⁺ was always greater than that of Cl^-. Measured E¹⁰ in cuticles did not fit the Goldman equation, whereas, E¹⁰ measured during KCl diffusion across selected artificial membranes fit the equation. The magnitude of E¹⁰ in cuticles and artificial membranes also was dependent on ionic strength, decreasing as ionic strength increased. These observations are explained by combining classical transport equations with equations that describe the equilibrium ion distribution between ionic double layers in the cuticle or membranes and the bathing solution.     

Palatability and efficacy to possums and rats of pest control baits containing bird repellents

Repellents used to reduce by-kill of birds during pest control must not compromise acceptance by target species. Two repellents combined, anthraquinone (AQ; 0.4 g kg^?1) and d-pulegone (DP; 1.0) did not reduce the palatability of blue-coloured carrot baits to laboratory rats (Rattus norvegicus); nor did DP (2.0). Green-coloured carrot baits coated with AQ, DP or AQ + DP were taken from bait stations by wild possums (Trichosurus vulpecula) and rats. Toxic (1080) bait coated with AQ (0.4) and peanut oil (0.1) had reduced palatability but was accepted by laboratory rats. However, laboratory rats did not consume enough baits coated with AQ and bacon, peanut butter, cinnamon or DP to be killed. Anthraquinone (0.4 or 0.8) plus cinnamon and DP (0.5) did not affect palatability or lethality to captive ship rats (R. rattus) or possums. Anthraquinone and DP as surface coatings on baits are therefore acceptable to possums and possibly rats, at concentrations that deter some bird species.     

The ecological integrity of the Lower Olifants River,Limpopo province,South Africa: 2009–2015 – Part A: Olifants River main stem

The major rivers of the South African ‘Lowveld’ (low-latitude savanna) suffer numerous impacts from upstream economic activities. Whereas monitoring these rivers is required to detect biodiversity losses, record pollution events and devise mitigation strategies, current monitoring programmes are inadequate. In 2009, the South African Earth Observation Network initiated an intensive long-term research programme on the Lowveld reaches of the Olifants River. Physico-chemical parameters, aquatic macroinvertebrates and fish abundances were recorded at four Lowveld sites in the Olifants River. We review six years of this programme. The results suggest deterioration in the ecological condition of the Olifants River with no discernible improvement through protected areas. Trends could not be detected. The parameters measured, sampling methods and/or sampling frequency might be responsible for the limited trends observed, or alternatively the results simply reflect stable conditions despite on-going pollution. Real time monitoring and an expansion in the parameters monitored would add value to the monitoring programme.