Applying molecular genetic tools to tiger conservation

The utility of molecular genetic approaches in conservation of endangered taxa is now commonly recognized. Over the past decade, conservation genetic analyses based on mitochondrial DNA sequencing and microsatellite genotyping have provided powerful tools to resolve taxonomy uncertainty of tiger subspecies, to define conservation units, to reconstruct phylogeography and demographic history, to examine the genetic ancestry of extinct subspecies, to assess population genetic status non-invasively, and to verify genetic background of captive tigers worldwide. The genetic status of tiger subspecies and populations and implications for developing strategies for the survival of this charismatic species both in situ and ex situ are discussed.     

Tuber age as a contributory factor in the water relations of potato (solanum tuberosum L.)

Seed tuber age effects on the response of potato plants (cv Alpha) to different drought stress regimes during the pre-tuberization period were evaluated. During a slow drying cycle of approximately 2 weeks’ duration, young expanding leaves on plants grown from young or old seed tubers showed no evidence of osmotic adjustment and pre-stressing the plants did not affect this situation. Pre-stressed plants from young and old tubers possessed a higher relative water content at a zero turgor potential than unstressed plants. However, tuber age did not affect significantly the relative water content at zero turgor potential. Plants derived from young seed tubers exhibited improved drought resistance such as reduced water loss from mature leaves, a larger root/shoot dry weight ratio and possible effects on root distribution in soil.     

Factors affecting diurnal stem contraction in young Douglas-fir

Diurnal fluctuation in a tree's stem diameter is a function of daily growth and of the tree's water balance, as water is temporarily stored in the relatively elastic outer cambial and phloem tissues. On a very productive site in southwestern Washington, U.S.A., we used recording dendrometers to monitor stem diameter fluctuations of Douglas-fir at plantation ages 7 and 8 and related the fluctuations to environmental variables measured on-site. Growing-season diurnal stem contraction (DSC) averaged 0.21% of stem diameter, while dormant-season DSC averaged 0.03% of stem diameter. Maximum daily stem diameter generally occurred between 7:00 and 9:00 Pacific Standard Time (PST) and minimum stem diameter occurred between 17:00 and 20:00 PST. Diurnal stem contraction during the growing season was predicted by a model that included vapor pressure deficit and solar radiation (adjusted R² = 0.84). A similar model predicted DSC during the dormant season with an adjusted R² = 0.26. Soil water availability was high, and soil water content was not correlated with DSC. On four of the coldest winter days (mean daytime air temperature <0 °C), large decreases in stem diameter were observed. Recording dendrometers, used for continuous diameter measurements throughout the growing season, have the potential to provide important information not only on tree growth but also on a tree's water balance.     

Sulfite oxidase enzyme activity in soil

Several methods for measuring sulfite oxidases (EC 1.8.2.1 and EC 1.8.3.1) have been developed for microbial systems, but none have been systematically adopted for soils. We describe an assay method to measure sulfite oxidase in soil that is based on the use of potassium sulfite (K₂SO₃) serving as the substrate and electron donor, and potassium ferricyanide [K₃Fe(CN₆)] serving as the electron acceptor. Sulfite oxidase activity is expressed as micromoles of K₃Fe(CN)₆ reduced g^-1 soil 4 h^-1. Sulfite oxidase activity was linearly related to amount of soil in the assay (up to 3 g) and incubation time (up to 5 h). The average K _m value for K₂SO₃ serving as the substrate for the sulfite oxidase reaction in four diverse soils was 3.48 mM. The activation energy values calculated for soil sulfite oxidase ranged from 40.4 to 61.4 kJ mol^-1. The sulfite oxidase assay does not require any specialized equipment and is expected to be useful in studying biological sulfite oxidation in soils treated with sulfites or in naturally occurring soils where sulfur cycles between reduced (i.e., sulfite) and oxidized (i.e., sulfate) states due to flooding and drying.     

Brucellosis associated with stillbirth in a bottlenose dolphin in Australia

A captive adult female bottlenose dolphin presented with stillbirth. The placenta appeared oedematous. No other gross lesions were evident in the placenta or the stillborn calf. Histopathology revealed mild multifocal placentitis and foetal encephalitis. Brucella sp. was isolated from lung, liver, spleen and kidney. Sequence and phylogenetic analysis demonstrated this organism to be most similar to Brucella ceti sequence type (ST) 27. Brucella sp. DNA was detected in formalin-fixed paraffin-embedded placenta and brain by real-time PCR using primers targeting the IS711 gene. Immunohistochemical staining revealed Brucella sp. antigen in placental inflammation. This is the first report of isolation of Brucella sp. from a marine mammal in the Southern Hemisphere and the first report of marine Brucella-associated disease in Australia.     

Potassium‐transport rate from root to shoot unrelated to potassium‐use efficiency in tomato grown under low‐potassium stress

Four tomato (Lycopersicon esculentum Mill.) strains (203, 474, 546, and 576) that are equally efficient in potassium (K) absorption, but different in efficiency of K use were studied using a continuously flowing solution culture to determine the importance of K‐transport rate from root to shoot in relation to K‐use efficiency. Strains 203 and 546 are inefficient in K use, ratios of K in shoots to roots were found to be three times higher than those of the two K‐use efficient strains 474 and 576 when grown under low‐K stress (0.1 mM). In addition, both the K concentrations and rates of K flow in xylem exudates of decapitated strains 203 and 546 were significantly higher than those of strains 474 and 576. These results suggest that high rates of K transport from roots to shoots are unrelated to K‐use efficiency in the tomato strains grown under low‐K stress. Further studies of K distributions in leaves and stems found that K concentrations in matured leaves and stems of the two efficient strains 474 and 576 were markedly lower than those of the two inefficient strains 203 and 546, while K in young and expanding leaves of the efficient strains were significantly higher than those of the inefficient strains, indicating that the ability to mobilize K from matured leaves to young and expanding leaves is an important factor that contributes to K‐use efficiency in tomato plants grown under low‐K stress.     

Water relations of the potato (Solanum tuberosum L.) cultivars Raritan and Shepody

Physiological responses to drought stress were evaluated in the potato cultivars Raritan and Shepody. Under well-watered conditions, Raritan exhibited a higher transpiration rate than Shepody. This higher rate could be related to a lower calculated stomatal resistance on abaxial leaf surfaces. Under drought stress conditions, Raritan consistently demonstrated superior performance over Shepody in the following areas: leaf water retention, epicuticular wax levels, desiccation tolerance and root growth. The estimated relative water content at a leaf water potential of-1.0 MPa was higher for Raritan than Shepody regardless of leaf age and may indicate a greater drought resistance in the former cultivar.     

A comparison of the water use of tree belts and pasture in recharge and discharge zones in a saline catchment in the Central West of NSW, Australia

Planting trees has been proposed as part of the solution to dryland salinity in Australia. The best location in the landscape and the spatial arrangement of trees however, is difficult to determine. This paper presents a case study of a field experiment that compared the water use of tree belts with that of pastures in recharge and discharge areas of a first order catchment in the Central West of NSW, Australia.The recharge tree belt and both pasture sites used very similar amounts of water but the discharge tree belt used double the water of the other three land uses by accessing groundwater. The discharge tree belt operated in an energy-limited environment, transpiring at a rate equivalent to atmospheric demand whereas the other three land uses were all water-limited. From a land management point of view, the establishment of more trees on the discharge site would have the biggest impact on reducing saline discharge and the least impact on the agricultural operations.