Do roots mind the gap?

Aims

Roots need to be in good contact with the soil to take up water and nutrients. However, when the soil dries and roots shrink, air-filled gaps form at the root-soil interface. Do gaps actually limit the root water uptake, or do they form after water flow in soil is already limiting?

Methods

Four white lupins were grown in cylinders of 20 cm height and 8 cm diameter. The dynamics of root and soil structure were recorded using X-ray CT at regular intervals during one drying/wetting cycle. Tensiometers were inserted at 5 and 18 cm depth to measure soil matric potential. Transpiration rate was monitored by continuously weighing the columns and gas exchange measurements.

Results

Transpiration started to decrease at soil matric potential ψ between ?5 kPa and ?10 kPa. Air-filled gaps appeared along tap roots between ψ?=??10 kPa and ψ?=??20 kPa. As ψ decreased below ?40 kPa, roots further shrank and gaps expanded to 0.1 to 0.35 mm. Gaps around lateral roots were smaller, but a higher resolution is required to estimate their size.

Conclusions

Gaps formed after the transpiration rate decreased. We conclude that gaps are not the cause but a consequence of reduced water availability for lupins.     

Low temperature constrains growth rates but not short-term ingestion rates of Antarctic ciliates

Low environmental temperature is a major factor affecting the feeding activities, growth rates, and growth efficiencies of metazooplankton, but these features are poorly characterized for most protistan species. Laboratory experiments were conducted to examine the growth and ingestion rates of cultured herbivorous Antarctic ciliates. Three ciliates fed several algal species individually at 0 °C exhibited uniformly low growth rates (<0.26 day^?1), but the algae varied substantially in their ability to support ciliate growth. Specific ingestion rate (prey biomass consumed per unit ciliate biomass per unit time) was strongly affected by ciliate physiological state (starved vs. actively growing). Starved cells ingested many more prey than cells in balanced growth during short-term (minutes-to-hours) experiment but did not grow faster, indicating temperature compensation of ingestion rate but not growth rate. Field experiments were also conducted in the Ross Sea, Antarctica, to characterize the feeding rates of ciliates in natural plankton assemblages. Specific ingestion rates of two dominant ciliates were an order of magnitude lower than rates reported for temperate ciliates, but estimated rates were strongly affected by prey abundance. Our data indicate that short-term ingestion rates of Antarctic ciliates were not constrained by low environmental temperature although overall growth rates were, indicating the need for caution when designing experiments to measure the ingestion rates of these species at low environmental temperature. We present evidence that artifacts arising from estimating ingestion in short-term experiments may lead to errors in estimating feeding impact and growth efficiencies that are particularly large for polar protists.     

CHITIN — A promising biomaterial for tissue engineering and stem cell technologies

Chitin, after cellulose, is the second most abundant natural polymer. With a 200-year history of scientific research, chitin is beginning to see fruitful application in the fields of stem cell and tissue engineering. To date, however, research in chitin as a biomaterial appears to lag far behind that of its close relative, chitosan, due to the perceived difficulty in processing chitin. This review presents methods to improve the processability of chitin, and goes on further to discuss the unique physicochemical and biological characteristics of chitin that favor it as a biomaterial for regenerative medicine applications. Examples of the latter are presented, with special attention on the qualities of chitin that make it inherently suitable as scaffolds and matrices for tissue engineering, stem cell propagation and differentiation.     

Practical considerations in the study of spectral analysis of discrete processes

Abstract

Clock hour independent groups of young female rats received a series of 3 alternate day intra‐articular injections of methylprednisolone acetate. All rats lost body weight, but the change was minimal when the injections were given in the late afternoon (‐30.8 g) vs the night (‐42.4 g, P < .02). The data imply that methylprednisolone acetate, which is designed to be locally active in joint spaces, can be absorbed into the circulation and that the rate of absorption is subject to circadian control.     

Optimization of cultural conditions for the production of antifungal chitinase by Streptomyces sporovirgulis

Actinomycetes were screened from soil in the centre of Poland on chitin medium. Amongst 30 isolated strains one with high activity of chitinase was selected. It was identified as Streptomyces sporovirgulis. Chitinase activity was detected from the second day of cultivation, then increased gradually and reached maximum after 4 days. The maximum chitinase production was observed at pH 8.0 and 25–30°C in the medium with sodium caseinate and asparagine as carbon and nitrogen sources and with shrimp shell waste as inducer of enzyme. Chitinase of S. sporovirgulis was purified from a culture medium by fractionation with ammonium sulphate as well as by chitin affinity chromatography. The molecular weight of the enzyme was 27 kDa. The optimum temperature and pH for the chitinase were 40°C and pH 8.0. The enzyme activity was characterised by high stability at the temperatures between 35 and 40°C after 240 min of preincubation. The activity of the enzyme was strongly inhibited in the presence of Pb²⁺, Hg²⁺ and stabilized by the ions Mg²⁺. Purified chitinase from S. sporovirgulis inhibited growth of fungal phytopathogen Alternaria alternata. Additionally, the crude chitinase inhibited the growth of potential phytopathogens such as Penicillium purpurogenum and Penillium sp.     

An Iterative Framework for EEG-based Image Search: Robust Retrieval with Weak Classifiers

We revisit the framework for brain-coupled image search, where the Electroencephalography (EEG) channel under rapid serial visual presentation protocol is used to detect user preferences. Extending previous works on the synergy between content-based image labeling and EEG-based brain-computer interface (BCI), we propose a different perspective on iterative coupling. Previously, the iterations were used to improve the set of EEG-based image labels before propagating them to the unseen images for the final retrieval. In our approach we accumulate the evidence of the true labels for each image in the database through iterations. This is done by propagating the EEG-based labels of the presented images at each iteration to the rest of images in the database. Our results demonstrate a continuous improvement of the labeling performance across iterations despite the moderate EEG-based labeling (AUC <75%). The overall analysis is done in terms of the single-trial EEG decoding performance and the image database reorganization quality. Furthermore, we discuss the EEG-based labeling performance with respect to a search task given the same image database.     

SOME PROPERTIES OF SUSPENDED SEDIMENT ADSORBED CATIONS IN TURBID FRESHWATERS OF SOUTH AFRICA

SUMMARY

Large quantities of suspended sediments are common in many of South Africa's fresh-waters. Temporal and spatial variations in tile amounts of cations adsorbed were recorded. The adsorption appears to be dependent on valency, because greater quantities of the higher valencies are adsorbed. Ca⁺⁺ dominated the adsorbed cations and Mg the dissolved fraction. Water originating from the Beaufort Series contained high sodium concentrations. Fe⁺⁺ dominated the adsorbed minor cations. Large quantities of sediments transported by rivers enter impoundments. The adsorbed ions transported in this way are influenced by the type of suspended sediment and form a significant part of the total input of ions.