Improved scaling of minirhizotron data using an empirically-derived depth of field and correcting for the underestimation of root diameters

Background and aims

Accurate data on the standing crop, production, and turnover of fine roots is essential to our understanding of major terrestrial ecological processes. Minirhizotrons offer a unique opportunity to study the dynamic processes of root systems, but are susceptible to several measurement biases.

Methods

We use roots extracted from minirhizotron tube surfaces to calculate the depth of field of a minirhizotron image and present a model to correct for the underestimation of root diameters obscured by soil in minirhizotron images.

Results

Non-linear regression analysis resulted in an estimated depth of field of 0.78 mm for minirhizotron images. Unadjusted minirhizotron data underestimated root net primary production and fine root standing crop by 61 % when compared to adjusted data using our depth of field and root diameter corrections. Changes in depth of field accounted for >99 % of standing crop adjustments with root diameter corrections accounting for <1 %.

Conclusions

Our results represent the first effort to empirically derive depth of field for minirhizotron images. This work may explain the commonly reported underestimation of fine roots using minirhizotrons, and stands to improve the ability of researchers to accurately scale minirhizotron data to large soil volumes.     

Behavioral and electrophysiological responses to NaCl in young and old Fischer-344 rats

This study compared both behavioral and electrophysiologicalresponses to NaCl in young and old Fischer-344 rats. These comparisonswere made in the same individuals. Preference for NaCl solutionsversus water was assessed using two-bottle preference tests.The integrated response of the chorda tympani nerve to NaClwas recorded. NaCl neural-response magnitude and correspondingbehavioral sensitivity appear to decrease with age in the Fischer-344rat at concentrations > 0.15 M and neural-response magnitudesincrease at lower concentrations.     

Haploinsufficient Bmp4 ocular phenotypes include anterior segment dysgenesis with elevated intraocular pressure

Background  

Glaucoma is a common disease but its molecular etiology is poorly understood. It involves retinal ganglion cell death and optic nerve damage that is often associated with elevated intraocular pressure. Identifying genes that modify glaucoma associated phenotypes is likely to provide insights to mechanisms of glaucoma. We previously reported glaucoma in DBA/2J mice caused by recessive alleles at two loci, isa and ipd, that cause iris stromal atrophy and iris pigment dispersion, respectively. A approach for identifying modifier genes is to study the effects of specific mutations in different mouse strains. When the phenotypic effect of a mutation is modified upon its introduction into a new strain, crosses between the parental strains can be used to identify modifier genes. The purpose of this study was to determine if the effects of the DBA/2J derived isa and ipd loci are modified in strain AKXD-28/Ty.     

SDS GEL ELECTROPHORESIS OF RAPIDLY TRANSPORTED PROTEINS IN GARFISH OLFACTORY NERVE

Abstract— Proteins undergoing rapid axonal transport in the garfish olfactory nerve were examined by sodium dodecyl sulphate gel electrophoresis. The distribution of polypeptides and the extent of their labeling by transported molecules was determined in several nerve subfractions including: total particulate, total membrane, mitochondrial and two membrane subfractions rich in axolemma. The polypeptide composition of the various fractions was found to be relatively similar, with each showing a major protein with an estimated MW of 58,000. Specific differences in the concentrations of certain proteins were noted between fractions, including differences between the lower and higher density axolemma rich subfractions. Axonally transported radioactivity was predominantly localized among high molecular weight proteins, with all fractions, except mitochondrial pellet, displaying a major peak of radioactivity centered at 126,000-MW. Several major proteins including the 58,000-MW band were labeled by rapid transport to a much smaller extent. Certain labeled peaks were found to be concentrated in individual fractions, particularly a polypeptide (MW 35,000) more predominantly found in the lower density axolemma rich fraction.
Systemic labeling of the nerve is found to give a general distribution of radioactivity on gels, which is clearly different from the pattern obtained after axonal transport labeling.     

Response characteristics of rat taste cells to potassium benzoate

The rat taste cells responded to K-benzoate solutions higher than the threshold concentrations (0.03-0.3 M) with a depolarizing receptor potential, but they responded to K-benzoate lower than the thresholds with a hyperpolarizing receptor potential. In either depolarizing or hyperpolarizing receptor potentials the rise time decreased with increasing amplitude, but the fall time increased with increasing amplitude. During generation of either depolarizing or hyperpolarizing receptor potentials the input resistance of taste cells decreased with increasing amplitude. Application of the mixtures of various concentrations of NaCl and 0.05 M K-benzoate resulted in a reduction of receptor potential amplitude, as compared with that evoked by application of NaCl alone. It is concluded that a depression of gustatory neural impulse frequency by low concentrations of K-benzoate is mainly due to the hyperpolarizing receptor potential of taste cells elicited by the K-benzoate solutions.     

Marine Bacteroidetes enzymatically digest xylans from terrestrial plants

Marine Bacteroidetes that degrade polysaccharides contribute to carbon cycling in the ocean. Organic matter, including glycans from terrestrial plants, might enter the oceans through rivers. Whether marine bacteria degrade structurally related glycans from diverse sources including terrestrial plants and marine algae was previously unknown. We show that the marine bacterium Flavimarina sp. Hel_I_48 encodes two polysaccharide utilization loci (PULs) which degrade xylans from terrestrial plants and marine algae. Biochemical experiments revealed activity and specificity of the encoded xylanases and associated enzymes of these PULs. Proteomics indicated that these genomic regions respond to glucuronoxylans and arabinoxylans. Substrate specificities of key enzymes suggest dedicated metabolic pathways for xylan utilization. Some of the xylanases were active on different xylans with the conserved β-1,4-linked xylose main chain. Enzyme activity was consistent with growth curves showing Flavimarina sp. Hel_I_48 uses structurally different xylans. The observed abundance of related xylan-degrading enzyme repertoires in genomes of other marine Bacteroidetes indicates similar activities are common in the ocean. The here presented data show that certain marine bacteria are genetically and biochemically variable enough to access parts of structurally diverse xylans from terrestrial plants as well as from marine algal sources.     

Sugar best single chorda tympani nerve fiber responses to various sugar stimuli in rat and hamster

1. Sugar best single chorda tympani nerve fiber of rat and hamster were tested with six sugars. 2. Fibers were selected for this experiment, only if they responded to 1.0 M sucrose or 1.0 M maltose and they responded poorly to 0.1 M NaCl. 3. In rat, some single fibers gave larger responses to maltose than to sucrose, while in hamster nearly all nerve fibers responded best to sucrose. 4. The order of effectiveness of sugars was maltose greater than fructose greater than or equal to lactose greater than sucrose greater than glucose greater than galactose in rat and sucrose greater than fructose greater than or equal to glucose greater than or equal to galactose greater than maltose greater than lactose in hamster.