Growth Responses of Dwarf Bean to Infection by Pseudomonas phaseolicola (Burk) Dows

At an early growth stage inoculation of both unifoliates ofdwarf beans with Pseudomonas phaseolicola (Burk) Dows. Race1 inhibited trifoliate production, but inoculation of one unifoliateonly reduced subsequent leaf expansion, and the opposite uninfectedunifoliate became significantly larger than unifoliates on uninfectedplants. Inoculation of the first or second trifoliates or thecotyledonary node at a later developmental stage all reducedprimary-shoot growth by 25 to 30 per cent, but there were markeddifferences in the extent of secondary-shoot development inleaf axils below the inoculation point. The growth effects were related to the distribution and activityof the bacterial toxin within the plant, particularly to differencesin the rate of invasion of apical regions. The primary toxineffects appear to be on apical function and leaf expansion.     

The osmoregulatory role of the filter-chamber in relation to phloem-feeding in Eurymela distincta (Cicadelloidea, Homoptera)

ABSTRACT. The cicadelloid leaf-hoppers, Eurymela distincta (Signoret) and Eurymela fenestrata (Le Pelletier & Serville), feed on the phloem sap of Eucalyptus spp. The osmotic pressure profile of haemolymph and gut fluids is consistent with a filtration mechanism based on passive osmosis. This is responsible for shunting water rapidly from foregut to hindgut in the relatively simple filter chamber. The osmotic gradient which drives the system is probably produced by active secretion of sodium and potassium into the Malpighian tubules and posterior midgut. Although the osmotic pressures in all parts of the system are higher, the mechanism is probably similar to that previously described for xylem-feeding cicadas.
The major haemolymph cations are sodium and magnesium and the concentrations of sodium and magnesium in the urine are higher than potassium. A variety of storage granules in the midgut contain calcium, phosphorus (as phosphate), ferric iron, zinc, magnesium, manganese and copper.     

Reintroducing capercaillie (Tetrao urogallus) into southern Scotland: identification of minimum viable populations at potential release sites

Capercaillie (Tetrao urogallus) populations are declining in western parts of their range, including Scotland. It has been proposed that their numbers, and the extent of their range in Scotland be increased to reduce the risk of a second extinction in the UK. The feasibility of a reintroduction of capercaillie to coniferous plantations in southern Scotland was assessed by undertaking a population viability analysis. Following a review of capercaillie ecology and habitat requirements, VORTEX population simulation software was used to identify a minimum viable population (MVP). From this the minimum dynamic area of suitable habitat required in order to support such a MVP was then calculated. It was estimated that a minimum of 60 individuals would be required in approximately 5000ha of habitat in order for the population to have a >0.95 probability of surviving for 50 years. Supplementation of populations with two unrelated individuals every five years reduced the MVP to ten individuals. Further simulations were run in order to establish the sensitivity of the model to changes in three key parameters. Assessment of areas of suitable habitat identified two potential release sites, Wauchope and Newcastleton forests, in southern Scotland. Some practical considerations relating to management of a release population are outlined. It was concluded that an appropriately planned and resourced reintroduction was feasible.     

Photosynthetic gas exchange and the stable isotope composition of leaf water: comparison of a xylem-tapping mistletoe and its host

Photosynthetic gas exchange and the stable isotopic composition of foliage water were measured for a xylem tapping mistletoe, Phoradendron juniperinum, and its host tree, Juniperus osteosperma, growing in southern Utah. The observed isotopic composition of water extracted from foliage was compared to predictions of the Craig-Gordon model of isotopic enrichment at evaporative sites within leaves. Assimilation rates of juniper were higher and stomatal conductance was lower than the values observed for the mistletoe. This resulted in lower intercellular/ ambient CO₂ values in the juniper tree relative to its mistletoe parasite. For mistletoe, the observed foliage water hydrogen and oxygen isotopic enrichment was less than that predicted by the model. In juniper, foliage water hydrogen isotopic enrichment was also lower than that predicted by the evaporative enrichment model. In contrast, the oxygen isotopic enrichment in juniper foliage water was slightly greater than that predicted for the evaporative sites within leaves. Hydrogen isotopic enrichment in mistletoe foliage shows systematic variation with stem segment, being highest near the tips of the youngest stems and decreasing toward the base of the mistletoe, where isotopic composition is close to that of stem water in the host tree. In a correlated pattern, mid-day stomatal conductance declined abruptly in mistletoe foliage of increasing age.