Zinc fluxes into developing barley grains: use of stable Zn isotopes to separate root uptake from remobilization in plants with contrasting Zn status

Background and Aims

Zn imported into developing cereal grains originates from either de novo Zn uptake by the roots or remobilization of Zn from vegetative tissues. The present study was focused on revealing the quantitative importance of the two pathways for grain Zn loading and how their relative contribution varies with the overall plant Zn status.

Methods

The stable isotope ⁶⁷Zn was used to trace Zn uptake and remobilization fluxes in barley (Hordeum vulgare L.) plants growing in hydroponics at 0.1?μM (low Zn), 1.5?μM (medium Zn) or 5?μM Zn (high Zn). When grain development reached 15?days after pollination the Zn source was changed to an enriched ⁶⁷Zn isotope and plants were harvested after 6 to 48?h. Zn concentrations and isotope ratios were determined using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS).

Results

Plants with low Zn status absorbed 3-fold more Zn than plants with medium or high Zn status when roots were exposed to an external concentration of 1.5?μM ⁶⁷Zn. Stems and ears were the primary recipients of the de novo incorporated Zn with preferential allocation to the developing grains over time. The leaves received in all cases a very small proportion (<5?%) of the newly absorbed Zn and the proportion did not increase over time. Zn fluxes derived from uptake and remobilization were almost equal in plants with low Zn status, while at high Zn status remobilization delivered 4 times more Zn to the developing grains than did root Zn uptake.

Conclusions

Stable isotopes in combination with ICP-MS provided a strong tool for quantification of Zn fluxes in intact plants. The importance of Zn remobilization compared to de novo root absorption of Zn increased with increasing plant Zn status. Very little de novo absorbed Zn was translocated to the leaves during generative growth stages.     

Concentration dependent effects of dextran on the physical properties of acid milk gels

The effect of dextran from Leuconostoc mesenteroides (DEX₅₀₀), added to milk prior to acidification with glucono-δ-lactone (GDL) or Streptococcus thermophilus DSM20259, was studied with respect to polysaccharide concentration. The incorporation of 5–30 g/kg DEX₅₀₀ significantly affected gelation behavior. Increasing DEX₅₀₀ concentrations resulted in a linear increase of gel stiffness (GDL gels: R² = 0.96; microbial acidification: R² = 0.94; P < 0.05) and 30 g/kg DEX₅₀₀ resulted in a 2-fold higher stiffness compared to gels without polysaccharide. The respective stirred gels depicted a significant reduction in syneresis, which decreased from 30.4% (0 g/kg DEX₅₀₀) to 22.0% (30 g/kg DEX₅₀₀) for chemically acidified gels after 1 d of storage. Physical characteristics of DEX₅₀₀ in aqueous solution were helpful to explain its behavior in the complex system milk.     

Development and Validation of a New Method to Measure Walking Speed in Free-Living Environments Using the Actibelt? Platform

Walking speed is a fundamental indicator for human well-being. In a clinical setting, walking speed is typically measured by means of walking tests using different protocols. However, walking speed obtained in this way is unlikely to be representative of the conditions in a free-living environment. Recently, mobile accelerometry has opened up the possibility to extract walking speed from long-time observations in free-living individuals, but the validity of these measurements needs to be determined. In this investigation, we have developed algorithms for walking speed prediction based on 3D accelerometry data (actibelt®) and created a framework using a standardized data set with gold standard annotations to facilitate the validation and comparison of these algorithms. For this purpose 17 healthy subjects operated a newly developed mobile gold standard while walking/running on an indoor track. Subsequently, the validity of 12 candidate algorithms for walking speed prediction ranging from well-known simple approaches like combining step length with frequency to more sophisticated algorithms such as linear and non-linear models was assessed using statistical measures. As a result, a novel algorithm employing support vector regression was found to perform best with a concordance correlation coefficient of 0.93 (95%CI 0.92–0.94) and a coverage probability CP1 of 0.46 (95%CI 0.12–0.70) for a deviation of 0.1 m/s (CP2 0.78, CP3 0.94) when compared to the mobile gold standard while walking indoors. A smaller outdoor experiment confirmed those results with even better coverage probability. We conclude that walking speed thus obtained has the potential to help establish walking speed in free-living environments as a patient-oriented outcome measure.     

Microevolutionary change in viscerocranial bones under congeneric sympatry in the Lake Tanganyikan cichlid genus Tropheus

Hydrobiologia - The endemic Lake Tanganyika cichlid genus Tropheus lives at rocky shores all around the lake and comprises six species which are subdivided into about 120 morphologically similar...     

Hybridization and crossability in Caiophora (Loasaceae subfam. Loasoideae): Are interfertile species and inbred populations results of a recent radiation?

Interspecific hybridization is considered a possible mechanism of plant diversification. The Andes are a hotspot of biodiversity, but hybridization in Andean taxa has so far not been investigated intensively. The current study investigates crossability in Caiophora (Loasaceae subfam. Loasoideae) by experimental interspecific hybridization of seven different species. Hand pollination was undertaken, developing fruits counted, thousand (seed) grain weights, and seed viability were examined. Cross pollination led to some fruit set in 36 of the 37 different combinations. Overall fruit set was virtually identical irrespective of the combination of parental plants. Mean germination rates were much higher in hybrid seeds, indicating a marked heterosis effect and the possible presence of an inbreeding depression in the source populations: In experimental hybridization the divergent taxa of Caiophora behave like isolated, inbred populations of a single species. Allopatry and different habitat preferences seem to be the key factors keeping the (interfertile) taxa of Caiophora apart in the apparent absence of both postmating isolating mechanisms and obvious isolating mechanisms in phenology and floral biology. Interspecific hybrids reported from the wild appear to be the result of secondary contact due to human impact.