George Menexes

Do arbuscular mycorrhizal fungi affect the allometric partition of host plant biomass to shoots and roots? A meta-analysis of studies from 1990 to 2010

Arbuscular mycorrhizas (AM) are ubiquitous root symbioses with often pervasive effects on the plant host, one of which may be above- and belowground biomass allocation. A meta-analysis was conducted on 516 trials that were described in 90 available articles to examine whether AM colonization could result in a modification of partitioning of plant biomass in shoots and roots. It was hypothesized that alleviating plant nutrient limitations could result in a decrease of root to shoot (R/S) ratio in AM plants or, alternatively, the direction of shifts in the R/S ratio would be determined by the changes in total dry biomass. In our analysis, we considered four types of stresses: drought stress, single heavy metal stress, multiple heavy metal stress, and other potential abiotic plant stress factors. When disregarding any factors that could regulate effects, including stress status and mode of propagation, the overall AM effect was a significant modification of biomass towards shoot growth. However, the responses of stressed and clonally propagated plants differed from those of seed-grown unstressed plants. Our meta-analysis detected a considerable decline in the R/S ratio when plants were grown from seeds in the absence of abiotic stresses. Moreover, we demonstrate that additional regulators of the AM-mediated impact on R/S ratio were presence of competition from other plants, plant growth outcome of the symbiosis, growth substrate volume, experimental duration, and the identities of both plant and AM fungus. Our results indicate that a prediction of AM effects on R/S allocation becomes more accurate when considering regulators, most notably propagation mode and stress. We discuss possible mechanisms through which stress and other regulators may operate.

Impact of inoculation with Azospirillum spp. on growth properties and seed yield of wheat: a meta-analysis of studies in the ISI Web of Science from 1981 to 2008

Azospirillum spp. represents one of the most studied plant growth promoting bacteria. A meta-analysis was conducted on 59 available articles to evaluate the extent to which Azospirillum may contribute to wheat growth properties. A mean increase of 8.9% in seed yield and 17.8% in aboveground dry weight was found to result from inoculation of wheat with Azospirillum. However, key determinants for the plant growth promoting effect were found to be the amount of N fertilization applied–maximum plant growth promoting effect was reported in the absence of N fertilization- and identities of wheat cultivar—Triticum aestivum was superior to Triticum durum-and Azospirillum isolate—Azospirillum lipoferum was more effective than Azospirillum brasilense. Co-inoculation with Azotobacter tended to further increase the growth promoting effect of Azospirillum on seed yield. A weak relationship between plant growth promoting effect on seed yield and aboveground biomass was detected. Inoculation with Azospirillum decreased the shoot:root ratio of wheat in field trials; but for pot trials, a key determinant of the shoot:root effect was the size of the pot used. The authors, thus, raise the scepticism of whether the growth parameters recorded in pot trials are representative of those under field conditions. Results highlight the efficiency of Azospirillum as an inoculant of wheat.

Association between self-reported bruxism activity and occurrence of dental attrition, abfraction, and occlusal pits on natural teeth

STATEMENT OF PROBLEM It is unclear whether subjects who report tooth clenching and/or grinding have more noticeable clinical signs of dental attrition, abfractions, and occlusal pits on their natural teeth than subjects who do not report bruxism activity. PURPOSE The purpose of this study was to determine whether there was an association between self-reported (or not reported) bruxism activity and occurrence of dental attrition (anterior, posterior), abfractions, and occlusal pits on natural teeth. MATERIAL AND METHODS One hundred and two volunteer adult Greek subjects (mean age 44.6 +/-5.7 years) were classified into 2 groups (50 self-reported bruxers and 52 nonbruxers) according to 2 inquires regarding grinding and/or clenching of their teeth. Dental attrition (anterior, posterior) was assessed by 2 calibrated experienced examiners on diagnostic casts on a tooth-by-tooth basis, using a previously well established ordinal scale. Abfraction lesions (V-shaped, in the cervical region) and occlusal pits were recorded if these clinical signs were found on at least 2 natural teeth. Statistical comparisons between the 2 groups relative to the distribution of the occurrence of the 4 clinical signs were performed by means of the exact version of the chi-square test. The Fishers exact test was used for the comparison of percentages. The intra- and interexaminer reliability was assessed by means of the Cohens kappa coefficient (alpha=.05). RESULTS The results demonstrated that there was a significant association between self-reported bruxism and occurrence of the 4 clinical signs. Although the 2 groups were significantly different according to the distribution of the 4 clinical signs, the greatest differences occurred for the anterior and posterior attrition signs. CONCLUSIONS In this study, the occurrence of 4 clinical signs (posterior or anterior dental attrition, abfractions, and occlusal pits) was associated with self-reported bruxers. It is suggested that, primarily, signs of dental attrition may differentiate self-reported bruxers from nonbruxer subjects.

A comparison for acid production, proteolysis, autolysis and inhibitory properties of lactic acid bacteria from fresh and mature Feta PDO Greek cheese, made at three different mountainous areas

Isolates of NSLAB were obtained from fresh (58 isolates) and mature (38) Feta cheese made at household level in three different mountainous areas, in order to study the effect of the area of production on NSLAB composition and their technological characteristics. Results obtained by SDS-PAGE of whole-cell proteins indicated that the microflora of the fresh cheese was composed of either lactococci (areas 1, 2), or lactococci and enterococci (area 3). The NSLAB microflora of mature cheese was composed almost entirely of lactobacilli species, differing according to the area of production. Species allocation by the SDS-PAGE method was confirmed by sequencing representative strains. Lactococci of cheese made in area 1 exhibited a narrow spectrum of antibacterial activity compared to isolates from areas 2 and 3, while for lactobacilli from all three areas a similar spectrum was noticed. Lactococci from area 2 exhibited higher (P<0.05) mean acidifying activity than lactococci from area 1. The isolates from the three areas also differed in respect of their caseinolytic activity, with preferences towards β-CN (areas 1 and 2) or αs-CN (area 3). Mean proteolytic activity of lactococci from area 1 was stronger (P<0.05) than that of lactococci from area 2 and the same was observed for their mean aminopeptidase activity, as well as their extent of autolysis at pH5.1. Mean acidifying activity of lactobacilli after 6h was for strains of area 3>2=1. The strains from areas 1 and 3 degraded preferentially αs-CN, while a clear preference towards β-CN was noticed for strains of area 2; their mean proteolytic activity was for strains of area 1 higher (P<0.05) than strains from area 3. The above results suggest that cheeses from the three areas differ in species composition of NSLAB and their technological properties. Principal component analysis of results on acidifying and proteolytic activities as well as autolysis allowed the distinction of lactococci according to their derivation area enabling the selection of appropriate strains as starters for cheese production in each area.

Salivary concentration of free LL-37 in edentulism, chronic periodontitis and healthy periodontium

OBJECTIVE The antimicrobial peptide LL-37, a component of innate immunity, has an important role in maintaining oral health. This study aimed to investigate the concentration of free LL-37 in whole saliva of periodontally healthy, edentulous and chronic periodontitis subjects. DESIGN Unstimulated whole saliva was sampled from 154 subjects (76 periodontally healthy, 20 edentulous, and 58 subjects with chronic periodontitis). All participants were in good general health. The salivary LL-37 was determined by ELISA. RESULTS The median salivary concentrations of free LL-37 were 30.5, 22.5, and 1.8ng/ml for the healthy, the chronic periodontitis and the edentulous group, respectively. The differences in concentration between the edentulous and the others were statistically significant (Mann-Whitney test, p<0.001). In the healthy subjects, women displayed significantly higher peptide concentrations compared to men (Mann-Whitney test, p<0.05). The intra-subject variation in LL-37 concentration was wider for the healthy (range 0.75-285ng/ml) and chronic periodontitis patients (range 1-207ng/ml) than for the edentulous subjects (range 0.15-4.4ng/ml). CONCLUSIONS The present findings show that edentulism correlates with a substantial decrease in salivary levels of free LL-37, thus indicating the considerable contribution of the gingival tissues in the secretion of the peptide in the oral environment.

The CHIC Analysis Software v1.0

In this paper we describe CHIC (Correspondence & HIerarchical Cluster) Analysis, a specialized software package for Correspondence Analysis-CA (Simple and Multiple) and Hierarchical Cluster Analysis (Benzecri’s chi-square distance, Ward’s linkage criterion). The implementation of CA is in line with both the French approach and the Gifi System of data analysis. CHIC Analysis combines the graphical interface features of CodeGear Delphi with the computational power of MatLab. The software was implemented as an attempt to contribute to the effectiveness and reliability of CA. For this purpose, it offers a variety of aids to the results’ interpretation and tools for the construction of special data tables. A modified version of the CA algorithm is implemented in the multivariate case. Special emphasis has been put on the graphical options for biplots, maps and dendrograms.

Polyamine profile in ovine and caprine colostrum and milk.

The objective of this study was to monitor the post-partum variation of polyamine content, in ovine and caprine milk, from indigenous Greek breeds. Twenty samples of ewe and 20 samples of goat colostrum and milk were collected at the 1st, 2nd, 3rd, 4th, 5th and 15th day post-partum. Putrescine, spermidine and spermine were measured as dansylated derivatives by high-performance liquid chromatography. Putrescine was the least concentrated of these substances in both milk types. Spermidine was the prevailing polyamine in caprine samples, reaching levels up to 4.41 μmol/l on the 3rd day post-partum. In ovine milk, the profile of the mean concentrations showed greater levels of spermine than spermidine, except for the 5th day post-partum. These data suggest that goat colostrum and ewe milk (15th day) could be considered as good natural sources for these bioactive growth factors, and may become useful raw materials for designing tailored dairy products for specific population groups.

Correlation of 2nd trimester amniotic fluid amino acid profile with gestational age and estimated fetal weight

Objectives. Our aim was to identify and quantitate free amino acids in human amniotic fluid (AF) specimens collected during 2nd trimester amniocentesis and determine the correlation between amino acid concentrations, gestational age, and estimated fetal weight. Methods. Seventy-eight AF samples were retrieved between 18 and 22 weeks of gestation. Fetal weight estimation was based on fetal biometric measurements. Results. Twenty-one amino acids were quantified. The concentration of glutamine exhibited the greatest correlation with gestational age (r = 0.477, p < 0.01). Additionally, significant negative correlations were recorded between gestational age and levels of alanine, proline, lysine, valine, taurine, leucine, glutamic acid, tyrosine, phenylalanine, isoleucine, ornithine, methionine, and tryptophane (p < 0.05). After adjusting for maternal age, fetal gender, intervals between consecutive pregnancies, pre-pregnancy body mass index, and smoking during pregnancy the strength of the correlation for proline and lysine decreased. A stepwise multiple linear regression model including gestational age as a first level predictor of fetal weight indicated that lysine and cysteine concentrations were additional predictors. Conclusions. Our results suggest that AF amino acids are crucial for fetal growth. Our purpose was not to establish an immediate diagnostic application. However, further exploration is likely to be fruitful, especially in high-risk pregnancies.

Assessment of vegetation indices derived by UAV imagery for durum wheat phenotyping under a water limited and heat stressed Mediterranean environment

There is growing interest for using Spectral Vegetation Indices (SVI) derived by Unmanned Aerial Vehicle (UAV) imagery as a fast and cost-efficient tool for plant phenotyping. The development of such tools is of paramount importance to continue progress through plant breeding, especially in the Mediterranean basin, where climate change is expected to further increase yield uncertainty. In the present study, Normalized Difference Vegetation Index (NDVI), Simple Ratio (SR) and Green Normalized Difference Vegetation Index (GNDVI) derived from UAV imagery were calculated for two consecutive years in a set of twenty durum wheat varieties grown under a water limited and heat stressed environment. Statistically significant differences between genotypes were observed for SVIs. GNDVI explained more variability than NDVI and SR, when recorded at booting. GNDVI was significantly correlated with grain yield when recorded at booting and anthesis during the 1st and 2nd year, respectively, while NDVI was correlated to grain yield when recorded at booting, but only for the 1st year. These results suggest that GNDVI has a better discriminating efficiency and can be a better predictor of yield when recorded at early reproductive stages. The predictive ability of SVIs was affected by plant phenology. Correlations of grain yield with SVIs were stronger as the correlations of SVIs with heading were weaker or not significant. NDVIs recorded at the experimental site were significantly correlated with grain yield of the same set of genotypes grown in other environments. Both positive and negative correlations were observed indicating that the environmental conditions during grain filling can affect the sign of the correlations. These findings highlight the potential use of SVIs derived by UAV imagery for durum wheat phenotyping under low yielding Mediterranean conditions.

Soil Fertilization Leads to a Decline in Between-Samples Variability of Microbial Community δ13C Profiles in a Grassland Fertilization Experiment

Gas chromatography combustion isotope ratio mass spectrometry (GC-C-IRMS) was used to measure the 13C/12C ratios of PLFAs at natural abundance levels from a temperate grassland nitrogen (N) and phosphorus (P) factorial fertilization experiment in northern Greece. In each plot two rhizosphere samples were derived centred around individual Agrostis capillaris and Prunella vulgaris plants. It was hypothesized that the isotopic signal of microbes that preferentially feed on recalcitrant litter such as fungi would be modified by fertilization more strongly than that of opportunistic microbes using labile C. Microbial community δ13C was affected by both P and N fertilization regime and plant species identity. However, we have been unable to detect significant nutrient effects on individual groups of microbes when analyzed separately in contrast to our original hypothesis. Intra-treatment variability, as evaluated from Hartley’s F max tests in the five first PCA components axes as well as the size of the convex hulls in PCA scoreplots and Mahalanobis distances, was considerably higher in the non-fertilized controls. Moreover, a significant relationship was established between the change in PLFA abundances and their respective changes in δ13C for the aggregate of samples and those simultaneously fertilized with N and P. We conclude that use of compound specific isotope analysis in the absence of labelling represents a valuable and overlooked tool in obtaining an insight of microbial community functioning.