Photosynthetic Changes in the Inducible CAM Plant Sedum telephium L Following the Imposition of Water Stress. II. Changes in the Activity of Phosphoenolpyruvate Carboxylase

In Sedum telephium, the switch from a weak-CAM to a full-CAMmode of photosynthesis in response to water stress, is accompaniedby a marked increase in the activity of the enzyme phosphoenolpyruatecarboxylase (PEPC) during the dark period of a diurnal cycle.Fractionation of the enzyme by non-denaturing polyacrylamidegel electrophoresis gives two active species; the activity ofthe more mobile species increases with the switch into a full-CAMmode of photosynthesis. Fractionation of the enzyme by denaturing electrophoresis andby gel filtration indicates that the molecular species particularlyactive in CAM is a monomeric protein, whilst the other readilyobservable species is a dimer. Sedum telephium, CAM, water stress, phosphoenolpyruvate carboxylase, night-time activation dimer, monomer     

Nocturnal Accumulation of Acid in Leaves of Wall Pennywort (Umbilicus rupestris) Following Exposure to Water Stress

Physiological responses to water stress (drought) have beeninvestigated in Umbilicus rupestris (wall pennywort) by comparingcontrol (well-watered) and draughted plants with respect to(i) diurnal fluctuations in the acid content of the leaves,(ii) CO₂ exchange patterns and (iii) stomatal conductance. Controlplants show no diurnal fluctuations in acid content, whereasafter 6 d of drought a clear CAM-type pattern (nocturnal acidificationfollowed by deacidification in the light) is observed. In controlplants, the CO₂ exchange pattern over a 24 h period is of atypical C-3 ‘square-wave’ type, with extensive CO₂uptake in the light and CO₂ output in the dark. In droughtedplants the day-time CO₂ uptake is confined to a morning ‘burst’,whilst night-time CO₂ output is markedly reduced. There is howeverno net noctural uptake of CO₂. In control plants, stomatal conductanceis high during the day (especially in the first half of theday) falling to a low level at the onset of darkness, and thenrising slowly through the remainder of the night. In droughtedplants, stomatal conductance is very low, except that thereis morning ‘burst’ of high conductance and a periodduring the night when conductance is higher than in controlplants. These results are discussed in relation to the response of U.rupestris to drought both in laboratory and in field conditions. Umbilicus rupestris, wall pennywort, CO₂ exchange, Crassulacean acid metabolism, drought, stomatal conductance, water stress     

Using isolation‐by‐distance‐based approaches to assess the barrier effect of linear landscape elements on badger (Meles meles) dispersal

As the European badger (Meles meles) can be of conservation or management concern, it is important to have a good understanding of the species’ dispersal ability. In particular, knowledge of landscape elements that affect dispersal can contribute to devising effective management strategies. However, the standard approach of using Bayesian clustering methods to correlate genetic discontinuities with landscape elements cannot easily be applied to this problem, as badger populations are often characterized by a strong confounding isolation‐by‐distance (IBD) pattern. We therefore developed a two‐step method that compares the location of pairs of related badgers relative to a putative barrier and utilizes the expected spatial genetic structure characterized by IBD as a null model to test for the presence of a barrier. If a linear feature disrupts dispersal, the IBD pattern characterising pairs of individuals located on different sides of a putative barrier should differ significantly from the pattern obtained with pairs of individuals located on the same side. We used our new approach to assess the impact of rivers and roads of different sizes on badger dispersal in western England. We show that a large, wide river represented a barrier to badger dispersal and found evidence that a motorway may also restrict badger movement. Conversely, we did not find any evidence for small rivers and roads interfering with badger movement. One of the advantages of our approach is that potentially it can detect features that disrupt gene flow locally, without necessarily creating distinct identifiable genetic units.     

Studies on the Production of Extracellular Proteinases by a Non-pigmented Strain of Chromobacterium lividum Isolated from Abattoir Effluent

A highly proteolytic bacterium isolated from abattoir effluent was identified as a non-pigmented strain of Chromobacterium lividum. Ferrous or ferric ions at concentrations between 1·8 × 10^-5 and 9 × 10^-4 g ions/1, which is 2–3 orders of magnitude greater than that required for growth, were essential for extracellular proteinase production in aerated but not in static culture. Co²⁺, Ni²⁺, Mn²⁺, Cu²⁺ or Zn²⁺ ions could not replace iron. Four proteinases (I-IV) were produced in static culture, but only proteinase I was formed in significant quantities in aerated culture. With both forms of culture amino nitrogen was essential for proteinase production; glucose inhibited formation in aerated, but not static, cultures. Growth occurred over the range 1–33 °C, whereas proteinase production ceased at 27 °C, with maximum activity at 13 °C. Proteinase production appeared to be controlled by an interaction between iron, oxygen tension and glucose.     

Measurement of Photosynthesis and Transpiration in Controlled Environments with particular reference to Microclimate Control in Leaf Cuvettes

A technique has been developed which permits measurements ofphotosynthesis and transpiration of single, attached leaves.The relative turgidity of leaves inside and outside the leafcuvettes was used as a parameter of the microclimate and thegas streams so adjusted that internal and external values werethe same. Some problems of using the technique in the fieldare discussed.