Root exudation of contrasting drought-stressed pearl millet genotypes conveys varying biological nitrification inhibition (BNI) activity

Roots secrete a vast array of low molecular weight compounds into the soil broadly referred to as root exudates. It is a key mechanism by which plants and soil microbes interact in the rhizosphere. The effect of drought stress on the exudation process and composition is rarely studied, especially in cereal crops. This study focuses on comparative metabolic profiling of the exudates from sensitive and tolerant genotypes of pearl millet after a period of drought stress. We employed a combined platform of gas and liquid chromatography coupled to mass spectrometry to cover both primary and secondary metabolites. The results obtained demonstrate that both genotype and drought stress have a significant impact on the concentration and composition of root exudates. The complexity and function of these differential root exudates are discussed. To reveal the potential effect of root exudates on the soil microbial community after a period of drought stress, we also tested for biological nitrification inhibition (BNI) activity. The analysis revealed a genotype-dependent enhancement of BNI activity after a defined period of drought stress. In parallel, we observed a genotype-specific relation of elongated root growth and root exudation under drought stress. These data suggest that the drought stress-dependent change in root exudation can manipulate the microbial soil communities to adapt and survive under harsh conditions

Quantifying the selection of maxillary anterior teeth using intraoral and extraoral anatomical landmarks

Background: One of the major hurdles in clinical prosthodontics has been the selection and replacement of maxillary anterior teeth in the absence of pre-extraction records. The aim of this study was to determine if a relationship exists between intraoral and extraoral facial measurements that could assist dental practitioners in selecting esthetically appropriate maxillary anterior teeth in the absence of pre-extraction records. Materials and methods: A cross-sectional study design was used with a sample size of one hundred and twenty participants. A questionnaire was used to identify the selection criteria and a photograph was taken for facial measurements using digitally calibrated software. Ninety-eight participants met the selection criteria and were included in the study. Measurements of intraoral landmarks were taken from stone casts of maxillary impressions using calibrated digital calipers. Each measurement was completed by two assessors to obtain mean values. Data were statistically analyzed using SPSS version 17 software. Data were assessed by one way analysis of variance (ANOVA) followed by post hoc (p < 0.05) to find any difference between tested groups. Pearson coefficients were used to determine whether correlation exists between measurements. Results: The mean values for intraoral maxillary landmarks were: Central incisor width = 8.39 mm, circumferential canine tip to canine tip distance = 34.89 mm, arch width = 48.24 mm, left arch length = 45.24 mm, right arch length = 45.56 mm. The mean values for extraoral landmarks were: Intercanthal distance = 33.24 mm, interpupillary distance = 60.68 mm, interalar distance = 38.27 mm, intercommissure distance = 50.61 mm. Differences existed within subgroups for all intraoral and extraoral measures. A weak positive correlation existed between intraoral (r < 0.4) and extraoral measurements (r < 0.38) that remained consistent when examined by gender. Conclusion: This study showed that the average length and width of the maxillary arch and interalar width were the anatomical landmarks that provided the strongest predictive relationship with anterior maxillary teeth (r = 0.38 - 0.4). Using these dimensions an average multiplying factor can be used to calculate maxillary incisor width or canine tip to canine tip distance. As the predictive strength is not strong, the authors recommend its use as a preliminary guide for determining the width of the maxillary anterior teeth during the initial selection of artificial teeth in the absence of pre-extraction records. Clinical Significance: The results of this study can be used to help dentists select the size of artificial maxillary anterior teeth in the absence of pre-extraction records