Cortical potential imaging using L-curve and GCV method to choose the regularisation parameter

Background

The electroencephalography (EEG) is an attractive and a simple technique to measure the brain activity. It is attractive due its excellent temporal resolution and simple due to its non-invasiveness and sensor design. However, the spatial resolution of EEG is reduced due to the low conducting skull. In this paper, we compute the potential distribution over the closed surface covering the brain (cortex) from the EEG scalp potential. We compare two methods – L-curve and generalised cross validation (GCV) used to obtain the regularisation parameter and also investigate the feasibility in applying such techniques to N170 component of the visually evoked potential (VEP) data.

Methods

Using the image data set of the visible human man (VHM), a finite difference method (FDM) model of the head was constructed. The EEG dataset (256-channel) used was the N170 component of the VEP. A forward transfer matrix relating the cortical potential to the scalp potential was obtained. Using Tikhonov regularisation, the potential distribution over the cortex was obtained.

Results

The cortical potential distribution for three subjects was solved using both L-curve and GCV method. A total of 18 cortical potential distributions were obtained (3 subjects with three stimuli each – fearful face, neutral face, control objects).

Conclusions

The GCV method is a more robust method compared to L-curve to find the optimal regularisation parameter. Cortical potential imaging is a reliable method to obtain the potential distribution over cortex for VEP data.

     

Nitric oxide and hydrogen sulfide crosstalk during heavy metal stress in plants

Gases such as ethylene, hydrogen peroxide (H₂O₂), nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H₂S) have been recognized as vital signaling molecules in plants and animals. Of these gasotransmitters, NO and H₂S have recently gained momentum mainly because of their involvement in numerous cellular processes. It is therefore important to study their various attributes including their biosynthetic and signaling pathways. The present review provides an insight into various routes for the biosynthesis of NO and H₂S as well as their signaling role in plant cells under different conditions, more particularly under heavy metal stress. Their beneficial roles in the plant's protection against abiotic and biotic stresses as well as their adverse effects have been addressed. This review describes how H₂S and NO, being very small-sized molecules, can quickly pass through the cell membranes and trigger a multitude of responses to various factors, notably to various stress conditions such as drought, heat, osmotic, heavy metal and multiple biotic stresses. The versatile interactions between H₂S and NO involved in the different molecular pathways have been discussed. In addition to the signaling role of H₂S and NO, their direct role in posttranslational modifications is also considered. The information provided here will be helpful to better understand the multifaceted roles of H₂S and NO in plants, particularly under stress conditions.     

Molecular and Pathological Characterization of Colletotrichum falcatum Infecting Subtropical Indian Sugarcane

Red rot, caused by Colletotrichum falcatum, is the most significant problem of sugarcane worldwide. Pathological studies and three different marker systems were used to characterize 25 C. falcatum isolates collected from 18 subtropical sugarcane cultivars from 15 different sugarcane‐growing regions of three north‐eastern states of India to assess pathogen diversity. Of these 25 isolates, three were new (RR2A, RR15, RR83) from cultivars Co 7717, Co J83 and Co S88230, respectively, pathologically characterized on 13 standard differential hosts. Isolates Cf 01, Cf 08 and RR15 were the most, and Cf‐07 the least virulent. Molecular characterization using random amplified polymorphic DNA, universal rice primers (URP) and inter simple sequence repeat markers amplified a total of 161 alleles of which 159 were polymorphic (98.76%). Unweighted paired group method with arithmetic averages analysis of combined data of all the DNA markers obtained by three marker systems classified 25 isolates into six clusters at 34% genetic similarity with high Mantel matrix correlation (r = 0.83). The principal component analysis (PCA) of marker data explained 68% of the variation by first three components. Molecular diversity as revealed in these isolates is very high, but non‐structured. Isolate Co Pant 84212 was found to be genetically most diverse. We demonstrated for the first time that URPs derived from weed rice could successfully assess genetic diversity in C. falcatum. Molecular characterization of the C. falcatum isolates prevalent in north‐eastern India would enable red rot management strate‐gies, selection for resistance genes and development of resistant cultivars.     

Molecular phylogenetics unveils the ancient evolutionary origins of the enigmatic fairy armadillos

Fairy armadillos or pichiciegos (Xenarthra, Dasypodidae) are among the most elusive mammals. Due to their subterranean and nocturnal lifestyle, their basic biology and evolutionary history remain virtually unknown. Two distinct species with allopatric distributions are recognized: Chlamyphorus truncatus is restricted to central Argentina, while Calyptophractus retusus occurs in the Gran Chaco of Argentina, Paraguay, and Bolivia. To test their monophyly and resolve their phylogenetic affinities within armadillos, we obtained sequence data from modern and museum specimens for two mitochondrial genes (12S RNA [MT-RNR1] and NADH dehydrogenase 1 [MT-ND1]) and two nuclear exons (breast cancer 1 early onset exon 11 [BRCA1] and von Willebrand factor exon 28 [VWF]). Phylogenetic analyses provided a reference phylogeny and timescale for living xenarthran genera. Our results reveal monophyletic pichiciegos as members of a major armadillo subfamily (Chlamyphorinae). Their strictly fossorial lifestyle probably evolved as a response to the Oligocene aridification that occurred in South America after their divergence from Tolypeutinae around 32 million years ago (Mya). The ancient divergence date (～17Mya) for separation between the two species supports their taxonomic classification into distinct genera. The synchronicity with Middle Miocene marine incursions along the Paraná river basin suggests a vicariant origin for pichiciegos by the disruption of their ancestral range. Their phylogenetic distinctiveness and rarity in the wild argue in favor of high conservation priority.     

Genetic and phytochemical diversity analysis in <Emphasis Type="Italic">Bunium persicum</Emphasis> populations of north-western Himalaya

The present study explores morphological, genetic and phytochemical composition of Bunium persicum populations belonging to high altitudinal areas of Indian Himalayan region. In total, 23 morphological traits (13 quantitative and 10 qualitative traits) and 32 Random Amplified Polymorphic DNA primers were employed to infer the population structure of the species. Of the fourteen populations, five genetically diverse populations were analyzed for phytochemical diversity. Among morphological traits, inflorescence, seed and branch traits were most significant in detecting variation. At molecular level, primers TIBMBA-06 and OPR-16 were found most polymorphic with respect to Polymorphism Information Content and Marker Index values. Dendrogram grouped all populations into two major clusters while population from Shong region out grouped separately showing its distantness from all other populations. STRUCTURE analysis was done by using Bayesian model, which characterised all populations into four clusters and some degree of admixture was also observed within individuals. Shong population showed distinct genetic makeup as also suggested by dendrogram. Phytochemical analysis showed the presence of 55 components, of which, 2-methyl-3-phenyl propanal, benzeneacetic acid, 1-phellandrene, γ-terpene, α-terpinolene, Δ0.3-carene and sabinene were major components in its essential oils. The present study revealed high genetic and phytochemical diversity in B. persicum accessions from north-western Himalayan regions. Specifically, accessions from Saptal regions were having higher quantity of essential oils and can be selected for cultivation to meet the commercial demand to some extent. Further, the diversity information provided herein can be useful in management and improvement of this species through future breeding programmes.     

Leaf respiration is differentially affected by leaf vs. stand-level night-time warming

Plant respiration is an important physiological process in the global carbon cycle serving as a major carbon flux from the biosphere to the atmosphere. Respiration is sensitive to temperature providing a link between environmental variability, climate change and the global carbon cycle. We measured leaf respiration in Populus deltoides after manipulating the air temperature surrounding part of a single leaf, and compared this to the temperature response of the same leaves after manipulating the temperature of the stand. The short‐term temperature response of respiration (Q₁₀– change in the respiration rate with a 10 °C increase in leaf temperature) was 1.7 when the leaf temperature was manipulated, but 2.1 when the stand‐level temperature was changed. As a result, total night‐time carbon release during the five‐day experiment was 21% lower when using the Q₁₀ estimates from the tradition leaf manipulation compared to the stand‐level manipulation. We conclude that the temperature response of leaf respiration is related to whole plant carbon and energy demands, and that appropriate experimental procedures are required in examining respiratory CO₂ release under variable temperature conditions.