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Water deficit is the most limiting factor for wheat production, so wheat-breeding programmes are currently focused on developing high-performance genotypes under such conditions. Carbon isotope dis...

Wheat plants growing under Mediterranean rain-fed conditions are exposed to water deficit, particularly during the grain filling period, and this can lead to a strong reduction in grain yield (GY). This study examines the effects of water deficit after during the grain filling period on photosynthetic and water-use efficiencies at the leaf and whole-plant level for 14 bread wheat genotypes grown in pots under glasshouse conditions. Two glasshouse experiments were conducted, one in a conventional glasshouse at the Universidad de Talca, Chile (Experiment 1), and another at the National Plant Phenomics Centre (NPPC), Aberystwyth, UK (Experiment 2), in 2015. Plants were grown under well-watered (WW) and water-limited (WL) conditions during grain filling. The reductions in leaf water potential (Ψ), net CO2 assimilation (An) and stomatal conductance (gs) due to water deficit were 79, 35 and 55%, respectively, during grain filling but no significant differences were found among genotypes. However, chlorophyll fluorescence parameters (as determined on dark-adapted and illuminated leaves) and chlorophyll content (Chl) were significantly different among genotypes, but not between water conditions. Under both water conditions, An presented a positive and linear relationship with the effective photochemical quantum yield of Photosystem II (Y(II)) and the maximum rate of electron transport (ETRmax), and negative with the quantum yield of non-photochemical energy conversion in Photosystem II (Y(NPQ)). The relationship between An and Chl was positive and linear for both water conditions, but under WL conditions An tended to be lower at any Chl value. Both, instantaneous (An/E) and intrinsic (An/gs) water-use efficiencies at the leaf level exhibited a positive and linear relationship with plant water-use efficiency (WUEp = plant dry weight/water use). Carbon discrimination (Δ13C) in kernels presented a negative relationship with WUEp, at both WW and WL conditions, and a positive relationship with GY. Our results indicate that during grain filling wheat plants face limitations to the assimilation process due to natural senesce and water stress. The reduction in An and gs after anthesis in both water conditions was mainly due a decline in the chlorophyll content (non-stomatal limitation), whereas the observed differences between water conditions were mainly due to a stomatal limitation.

Grain development in cereals depends on synthesis and remobilisation compounds such as water-soluble carbohydrates (WSCs), amino acids (AAs), minerals and environmental conditions during pre-and post-anthesis. This study analyses the impact of water stress on metabolite (WSCs, AAs and nitrogen) dynamics between the source (leaves and stems) and sink (grain) organs in triticale, bread wheat, durum wheat and barley. Plants were grown in glasshouse conditions under well-watered (WW) and water-limited (WL) regimes (from flag leaf fully expanded until maturity). The results showed that the stem WSC content and the apparent mobilisation of WSC to the grain were much higher in triticale and were associated with its larger grain size and grain number. In the four cereals, grain weight and the number of kernels per spike were positively associated with stem WSC mobilisation. After anthesis, the AA concentration in leaves was much lower than in the grain. In grain, the main AAs in terms of concentration were Asn, Pro and Gln in triticale, bread, and durum wheat, and Asn, Pro and Val in barley. The water-limited regime reduced grain weight per plant in the four cereal species, but it had no clear effects on WSC content and AAs in leaves and grain. In general, triticale was less affected by WL than the other cereals., The first author (A.M.M.-E.) was supported by FONDECYT Postdoc 3160687. The research was funded by the grants, FONDECYT N 1150353 and 1180252

23 Pags.- 4 Figs. © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license., Increased periods of water shortage and higher temperatures, together with a reduction in nutrient availability, have been proposed as major factors that negatively impact plant development. Photosynthetic CO2 assimilation is the basis of crop production for animal and human food, and for this reason, it has been selected as a primary target for crop phenotyping/breeding studies. Within this context, knowledge of the mechanisms involved in the response and acclimation of photosynthetic CO2 assimilation to multiple changing environmental conditions (including nutrients, water availability, and rising temperature) is a matter of great concern for the understanding of plant behavior under stress conditions, and for the development of new strategies and tools for enhancing plant growth in the future. The current review aims to analyze, from a multi-perspective approach (ranging across breeding, gas exchange, genomics, etc.) the impact of changing environmental conditions on the performance of the photosynthetic apparatus and, consequently, plant growth., This work was supported by the Spanish Innovation and Universities Ministry (AGL2016-79868-R; PCIN-2017-007).

The commercial strawberry (Fragaria×ananassa Duch.) is a salt sensitive species, in which salinity adversely affects its growth and fruit production. Because of its varied geographic distribution, including coastal areas, the Chilean strawberry (Fragaria chiloensis) genotypes may be less sensitive to salt stress. The aim of this study was to determine the effect of salinity on vegetative growth, physiological parameters, as well as production and fruit quality of three genotypes of Fragaria spp. (one of commercial strawberry cv. Camarosa, and two Chilean strawberry genotypes of the botanical forms chiloensis and patagonica, respectively). Plants were subjected to 0, 30, or 60 mM NaCl. In ‘Camarosa’ plants, vegetative growth, leaf relative water content (LRWC), pigment concentrations, yield, and fruit size were reduced under salt stress, while proline and malondialdehyde (MDA) concentrations were increased. Although it has been suggested that F. chiloensis is more tolerant to salinity than F.×ananassa, similar effects were observed in the vegetative development of the plants of F. chiloensis f. chiloensis. No differences in fruit weight, size and firmness of this genotype were detected as a result of salt stress. However, salinity affected fruit quality attributes such as total soluble solids (TSS) and titratable acidity (TA). By contrast, morphological and physiological variables measured in the genotype of F. chiloensis f. patagonica were not affected by the stress imposed. In addition, salinity had no effect on weight, size, firmness and TSS of fruits, with only TA being increased. These results suggest a higher tolerance of patagonica genotype to salt stress.

Phenotyping, via remote and proximal sensing techniques, of the agronomic and physiological traits associated with yield potential and drought adaptation could contribute to improvements in breeding programs. In the present study, 384 genotypes of wheat (Triticum aestivum L.) were tested under fully irrigated (FI) and water stress (WS) conditions. The following traits were evaluated and assessed via spectral reflectance: Grain yield (GY), spikes per square meter (SM2), kernels per spike (KPS), thousand-kernel weight (TKW), chlorophyll content (SPAD), stem water soluble carbohydrate concentration and content (WSC and WSCC, respectively), carbon isotope discrimination (Δ13C), and leaf area index (LAI). The performances of spectral reflectance indices (SRIs), four regression algorithms (PCR, PLSR, ridge regression RR, and SVR), and three classification methods (PCA-LDA, PLS-DA, and kNN) were evaluated for the prediction of each trait. For the classification approaches, two classes were established for each trait: The lower 80% of the trait variability range (Class 1) and the remaining 20% (Class 2 or elite genotypes). Both the SRIs and regression methods performed better when data from FI and WS were combined. The traits that were best estimated by SRIs and regression methods were GY and Δ13C. For most traits and conditions, the estimations provided by RR and SVR were the same, or better than, those provided by the SRIs. PLS-DA showed the best performance among the categorical methods and, unlike the SRI and regression models, most traits were relatively well-classified within a specific hydric condition (FI or WS), proving that classification approach is an effective tool to be explored in future studies related to genotype selection.

Lucerne (alfalfa, Medicago sativa L.) is grown extensively worldwide owing to its high forage biomass production and nutritional value. Although this crop is characterised as being tolerant to drought, its production and persistence are affected by water stress. Selection of genotypes of high yield potential and persistence after a long period of drought is a major objective for lucerne-breeding programmes in Mediterranean environments. This selection could be enhanced and accelerated by the use of physiological and productivity traits and their estimation through remote-sensing methods. A set of nine cultivars of lucerne from Australia and the USA were assessed in four locations in Mediterranean central-south Chile. Several physiological and productivity traits were evaluated: forage yield (FY), stomatal conductance (gs), water potential (WP), leaf area index (LAI), nitrogen (N) content, and isotope composition (δ13C and δ18O) of the dry matter. Spectral-reflectance data were used to estimate the traits through spectral-reflectance indices (SRIs) and multivariate regression methods. For the SRI-based estimations, the R2 values for each assessment were

Chlorophyll and anthocyanin contents provide a valuable indicator of the status of a plant's physiology, but to be more widely utilized it needs to be assessed easily and non-destructively. This is particularly evident in terms of assessing and exploiting germplasm for plant-breeding programs. We report, for the first time, experiments with Fragaria chiloensis (L.) Duch. and the estimation of the effects of response to salinity stress (0, 30, and 60 mmol NaCl/L) in terms of these pigments content and gas exchange. It is shown that both pigments (which interestingly, themselves show a high correlation) give a good indication of stress response. Both pigments can be accurately predicted using spectral reflectance indices (SRI); however, the accuracy of the predictions was slightly improved using multilinear regression analysis models and genetic algorithm analysis. Specifically for chlorophyll content, unlike other species, the use of published SRI gave better indications of stress response than Normalized Difference Vegetation Index. The effect of salt on gas exchange is only evident at the highest concentration and some SRI gave better prediction performance than the known Photochemical Reflectance Index. This information will therefore be useful for identifying tolerant genotypes to salt stress for incorporation in breeding programs.

Garriga, M., Parra, P. A., Caligari, P. D. S., Retamales, J. B., Carrasco, B. A., Lobos, G. A. and García-Gonzáles, R. 2013. Application of inter-simple sequence repeats relative to simple sequence repeats as a molecular marker system for indexing blueberry cultivars. Can. J. Plant Sci. 93: 913–921. Chile, the major exporter of blueberries in South America, grows two species commercially, the highbush blueberry (Vaccinium corymbosum L.) and the rabbiteye blueberry (Vaccinium ashei Reade). Considering the increasing demands for this fruit, it is necessary to have reliable methods for genotyping and genetic traceability of the commercially grown cultivars. In this study, an inter-simple sequence repeat (ISSR) marker-based system was established to perform the genetic identification of these cultivars. Ten cultivars of V. corymbosum: ‘Bluecrop’, ‘Bluegold’, ‘Duke’, ‘Elliott’, ‘Legacy’, ‘Misty’, ‘Nelson’, ‘O'Neal’, ‘Sierra’ and ‘Toro’ and three of V. ashei: ‘Climax’, ‘Premier’ and ‘Tifblue’ were analyzed. The sensitivity and reliability of this molecular marker system was compared with identification by simple sequence repeats (SSR). Six ISSR primers were used and high levels of polymorphism among the cultivars (80% of polymorphic loci) were detected, with high repeatability. Using individual primers, distinguishing among cultivars was possible in three cases. However, using pairs of ISSR primers provided greater reliability in cultivar identification. This ISSR-based technology is a simpler, faster, and less expensive alternative to SSRs for genotyping blueberry cultivars and can be used in genetic traceability studies as well as genetic improvement programs.

Cedrela odorata L. is one of the most important timber species currently traded in the Caribbean and Central America; however, it has been intensively exploited. In vitro techniques and clonal propagation can help to develop new plantations and assist in establishing improvement programs for this species. The aim of this study was to develop a protocol to establish in vitro conditions and to micropropagate this species from nodal explants from juvenile cuttings taken from field trees. Disinfection of node explants with 5% propiconazole CE 25 during 3 min resulted in 100% explant disinfection and 60% morphogenic response on those established explants. Shoot development was optimized by cultivating in vitro node explants in Murashige and Skoog basal medium supplemented with 2 mg L-1 6-bencilaminopurine and 3 mg L-1 naphthaleneacetic acid. This medium resulted in 100% shoot development from the in vitro node explants with a 3.93 cm mean height. Rooting was also stimulated 6 wk after individualization of the regenerated plants on the same micropropagation medium with a mean of 3.9 roots per plant. In vitro plants did not show morphologic differences when compared to ex vitro seeds.El cedro (Cedrela odorata L.) es una de las especies más importantes para el sector agroforestal caribeño y centroamericano pero se encuentra bajo una presión intensa de explotación debido a su alta demanda. Las técnicas de cultivo in vitro y propagación clonal pueden contribuir a atenuar este inconveniente y dotar a los productores con plantas de alta calidad genética y de ciclos biológicos y productivos más reducidos. El objetivo de este trabajo fue desarrollar un protocolo de establecimiento in vitro y micropropagar la especie a partir de segmentos nodales de estacas juveniles obtenidas de plantas de campo. El estudio de ocho métodos de desinfección dejó establecido que lavados de los segmentos nodales con propiconazol CE 25 al 5% durante 3 min posibilita un 100% de desinfección de los segmentos nodales y un 60% de brotación de las yemas. La adición de 2 mg L-1 de 6-bencilaminopurina y 3 mg L-1 de ácido naftalenacético al medio basal Murashige y Skoog propició una brotación del 100% de los segmentos nodales in vitro y una altura promedio de 3,93 cm a las 8 semanas. La misma concentración de reguladores del crecimiento propició la formación de 3,9 raíces por planta a las 6 semanas de individualizada. Las plantas adaptadas ex vitro no presentaron diferencias morfológicas con las plantas germinadas a partir de semillas.

Substituted urea compounds are well-known as potent inhibitors of juvenile hormone epoxide hydrolase (JHEH) of the tobacco hornworm Manduca sexta. Docking simulations of 47 derivatives inside JHEH were performed to gain insight into the structural characteristics of these complexes. The obtained orientations show a strong similitude with the observed in the known X-ray crystal structures of human soluble epoxide hydrolase (sEH) complexed with dialkylurea inhibitors. In addition, the predicted inhibitor concentration (IC₅₀) of the above-mentioned compounds as JHEH inhibitors were obtained by a quantitative structure-activity relationship (QSAR) method by using comparative molecular field analysis (CoMFA) applied to aligned dataset. The best models included steric and electrostatic fields and had adequate predictive abilities. In addition, these models were used to predict the activity of an external test set of compounds that was not used for building the model. Furthermore, plots of the CoMFA fields allowed conclusions to be drawn for the choice of suitable inhibitors.

Henequen (Agave fourcroydes Lem.) is a high value plant species both for agricultural and ecological uses. The species is very well known worldwide by the quality of its fiber that is widely used for industrial purposes. This species is propagated at a large scale by asexual methods but current propagation technologies are not satisfying the grower’s demands. A. fourcroydes has been cultivated n vitro but it has shown some recalcitrant behaviour during the multiplication and rooting stages. The combination of 6-benzylamynopurine (BAP) (0.75 mg L-1) and indolebutyric acid (IBA) (1.0 mg L-1) instead of 2,4-dichlorophenoxyacetic acid (2,4-D) significantly improved explant survival and shooting during the establishment of n vitro young shoots. Combining thidiazuron (TDZ) (0.5 or 0.75 mg L-1) with BAP (1.0 mg L-1) and IBA (1.0 mg L-1) in the basal medium increased the multiplication rate of henequen and significantly speeded out bud dormancy breaking. To improve rooting of the micropropagated shoots, the addition of IBA and naphthylacetic acid (NAA) was tested. The best rooting efficiency was obtained when the basal medium was supplemented with 0.5 or 0.75 mg L-1 of NAA, giving 100% of rooted explants and an average of 9.40 and 11.55 roots per explants, respectively. Over 94% of micropropagated plants survived the ex vitro weaning step and no morphological disorders were observed in any of the plants. Modification of plant growth regulators composition in the medium was a key factor to improve the efficiency of the micropropagation technology of henequen.El henequén (Agave fourcroydes Lem.) es una especie vegetal de gran valor agrícola y ecológico conocida mundialmente por la calidad de su fibra usada con fines industriales. Esta especie se propaga a gran escala por métodos asexuales, pero las tecnologías de propagación actuales no son capaces de satisfacer la demanda de los productores. A. fourcroydes ha sido propagado n vitro pero muestra comportamiento recalcitrante durante las fases de multiplicación y enraizamiento. En este estudio se demostró que la combinación de 6-benzilaminopurina (BAP) (0.75 mg L-1) y ácido indolbutírico (IBA) (1.0 mg L-1), en lugar de ácido 2,4-diclorofenoxiacético (2,4-D), mejoró significativamente la supervivencia de los explantes y la brotación durante la fase de establecimiento n vitro a partir de brotes jóvenes. La combinación de thidiazuron (TDZ) (0.5 ó 0.75 mg L-1) con BAP (1.0 mg L-1) e IBA (1.0 mg L-1) en el medio basal incrementó la tasa de multiplicación del henequén y aceleró la ruptura de la dormancia de las yemas. La mayor eficiencia de enraizamiento se obtuvo cuando el medio basal fue suplementado con 0.5 o 0.75 mg L-1 de ácido naftalenacético (NAA), obteniéndose un 100% de plantas enraizadas y un promedio de 9.40 y 11.55 raíces por planta. El 94% de las plantas sobrevivió el proceso de aclimatización ex vitro y no se observaron desórdenes fisiológicos en ninguna de las plantas. La modificación de la composición de reguladores del crecimiento vegetal en el medio de cultivo fue un factor clave para mejorar la eficiencia de la tecnología de micropropagación de henequén.

Commercial strawberry, Fragaria x ananassa Duch., is a species sensitive to salinity. Under saline conditions, Na(+) uptake by the plant is increased, while K(+) uptake is significantly reduced. Maintaining an adequate K(+)/Na(+) cytosolic ratio determines the ability of the plant to survive in saline environments. The goal of the present work was to clone and functionally characterize the genes AKT1 and HKT1 involved in K(+) and Na(+) transport in strawberry and to determine the relationship of these genes with the responses of three Fragaria spp. genotypes having different ecological adaptations to salt stress. FaHKT1 and FcHKT1 proteins from F. x ananassa and F. chiloensis have 98.1% of identity, while FaAKT1 and FcAKT1 identity is 99.7%. FaHKT1 and FaAKT1 from F. x ananassa, were functionally characterized in Xenopus oocytes. FaHKT1, belongs to the group I of HKT transporters and is selective for Na(+). Expression of FaAKT1 in oocytes showed that the protein is a typical inward-rectifying and highly K(+)-selective channel. The relative expression of Fragaria HKT1 and AKT1 genes was studied in roots of F. x ananassa cv. Camarosa and of F. chiloensis (accessions Bau and Cucao) grown under salt stress. The expression of AKT1 was transiently increased in 'Camarosa', decreased in 'Cucao' and was not affected in 'Bau' upon salt stress. HKT1 expression was significantly increased in roots of 'Cucao' and was not affected in the other two genotypes. The increased relative expression of HKT1 and decreased expression of AKT1 in 'Cucao' roots correlates with the higher tolerance to salinity of this genotype in comparison with 'Camarosa' and 'Bau'.

Predicting protein stability changes upon point mutation is important for understanding protein structure and designing new proteins. Autocorrelation vector formalism was extended to amino acid sequences and 3D conformations for encoding protein structural information with modeling purpose. Protein autocorrelation vectors were weighted by 48 amino acid/residue properties selected from the AAindex database. Ensembles of Bayesian-regularized genetic neural networks (BRGNNs) trained with amino acid sequence autocorrelation (AASA) vectors and amino acid 3D autocorrelation (AA3DA) vectors yielded predictive models of the change of unfolding Gibbs free energy change (ΔΔG) of chymotrypsin Inhibitor 2 protein mutants. The ensemble predictor described about 58 and 72% of the data variances in test sets for AASA and AA3DA models, respectively. Optimum sequence and 3D-based ensembles exhibit high effects on relevant structural (volume, solvent-accessible surface area), physico-chemical (hydrophilicity/hydrophobicity...

Development of novel computational approaches for modeling protein properties is a main goal in applied Proteomics. In this work, we reported the extension of the radial distribution function (RDF) scores formalism to proteins for encoding 3D structural information with modeling purposes. Protein-RDF (P-RDF) scores measure spherical distributions on protein 3D structure of 48 amino acids/residues properties selected from the AAindex data base. P-RDF scores were tested for building predictive models of the change of thermal unfolding Gibbs free energy change (DeltaDeltaG) of chymotrypsin inhibitor 2 upon mutations. In this sense, an ensemble of Bayesian-Regularized Genetic Neural Networks (BRGNNs) yielded an optimum nonlinear model for the conformational stability. The ensemble predictor described about 84% and 70% variance of the data in training and test sets, respectively.

Functional variations on the human ghrelin receptor upon mutations have been associated with a syndrome of short stature and obesity, of which the obesity appears to develop around puberty. In this work, we reported a proteometrics analysis of the constitutive and ghrelin-induced activities of wild-type and mutant ghrelin receptors using amino acid sequence autocorrelation (AASA) approach for protein structural information encoding. AASA vectors were calculated by measuring the autocorrelations at sequence lags ranging from 1 to 15 on the protein primary structure of 48 amino acid/residue properties selected from the AAindex database. Genetic algorithm-based multilinear regression analysis (GA-MRA) and genetic algorithm-based least square support vector machines (GA-LSSVM) were used for building linear and non-linear models of the receptor activity. A genetic optimized radial basis function (RBF) kernel yielded the optimum GA-LSSVM models describing 88% and 95% of the cross-validation variance for the constitutive and ghrelin-induced activities, respectively. AASA vectors in the optimum models mainly appeared weighted by hydrophobicity-related properties. However, differently to the constitutive activity, the ghrelin-induced activity was also highly dependent of the steric features of the receptor.

Chlorophyll and anthocyanin contents provide a valuable indicator of the status of a plant's physiology, but to be more widely utilized it needs to be assessed easily and non-destructively. This is particularly evident in terms of assessing and exploiting germplasm for plant-breeding programs. We report, for the first time, experiments with Fragaria chiloensis (L.) Duch. and the estimation of the effects of response to salinity stress (0, 30, and 60 mmol NaCl/L) in terms of these pigments content and gas exchange. It is shown that both pigments (which interestingly, themselves show a high correlation) give a good indication of stress response. Both pigments can be accurately predicted using spectral reflectance indices (SRI); however, the accuracy of the predictions was slightly improved using multilinear regression analysis models and genetic algorithm analysis. Specifically for chlorophyll content, unlike other species, the use of published SRI gave better indications of stress response than Normalized Difference Vegetation Index. The effect of salt on gas exchange is only evident at the highest concentration and some SRI gave better prediction performance than the known Photochemical Reflectance Index. This information will therefore be useful for identifying tolerant genotypes to salt stress for incorporation in breeding programs.

Cedrela odorata L. is one of the most important timber species currently traded in the Caribbean and Central America; however, it has been intensively exploited. In vitro techniques and clonal propagation can help to develop new plantations and assist in establishing improvement programs for this species. The aim of this study was to develop a protocol to establish in vitro conditions and to micropropagate this species from nodal explants from juvenile cuttings taken from field trees. Disinfection of node explants with 5% propiconazole CE 25 during 3 min resulted in 100% explant disinfection and 60% morphogenic response on those established explants. Shoot development was optimized by cultivating in vitro node explants in Murashige and Skoog basal medium supplemented with 2 mg L-1 6-bencilaminopurine and 3 mg L-1 naphthaleneacetic acid. This medium resulted in 100% shoot development from the in vitro node explants with a 3.93 cm mean height. Rooting was also stimulated 6 wk after individualization of the regenerated plants on the same micropropagation medium with a mean of 3.9 roots per plant. In vitro plants did not show morphologic differences when compared to ex vitro seeds.

Henequen (Agave fourcroydes Lem.) is a high value plant species both for agricultural and ecological uses. The species is very well known worldwide by the quality of its fiber that is widely used for industrial purposes. This species is propagated at a large scale by asexual methods but current propagation technologies are not satisfying the grower’s demands. A. fourcroydes has been cultivated in vitro but it has shown some recalcitrant behaviour during the multiplication and rooting stages. The combination of 6-benzylamynopurine (BAP) (0.75 mg L -1 ) and indolebutyric acid (IBA) (1.0 mg L -1 ) instead of 2,4-dichlorophenoxyacetic acid (2,4-D) significantly improved explant survival and shooting during the establishment of in vitro young shoots. Combining thidiazuron (TDZ) (0.5 or 0.75 mg L -1 ) with BAP (1.0 mg L -1 ) and IBA (1.0 mg L -1 ) in the basal medium increased the multiplication rate of henequen and significantly speeded out bud dormancy breaking. To improve rooting of the micropropagated shoots, the addition of IBA and naphthylacetic acid (NAA) was tested. The best rooting efficiency was obtained when the basal medium was supplemented with 0.5 or 0.75 mg L -1 of NAA, giving 100% of rooted explants and an average of 9.40 and 11.55 roots per explants, respectively. Over 94% of micropropagated plants survived the ex vitro weaning step and no morphological disorders were observed in any of the plants. Modification of plant growth regulators composition in the medium was a key factor to improve the efficiency of the micropropagation technology of henequen.

Voltage-gated K(+) ion channels (VKCs) are membrane proteins that regulate the passage of potassium ions through membranes. This work reports a classification scheme of VKCs according to the signs of three electrophysiological variables: activation threshold voltage (V(t)), half-activation voltage (V(a50)) and half-inactivation voltage (V(h50)). A novel 3D pseudo-folding graph representation of protein sequences encoded the VKC sequences. Amino acid pseudo-folding 3D distances count (AAp3DC) descriptors, calculated from the Euclidean distances matrices (EDMs) were tested for building the classifiers. Genetic algorithm (GA)-optimized support vector machines (SVMs) with a radial basis function (RBF) kernel well discriminated between VKCs having negative and positive/zero V(t), V(a50) and V(h50) values with overall accuracies about 80, 90 and 86%, respectively, in crossvalidation test. We found contributions of the "pseudo-core" and "pseudo-surface" of the 3D pseudo-folded proteins to the discrimination between VKCs according to the three electrophysiological variables.

Negative inotropic potency of 60 benzothiazepine-like calcium entry blockers (CEBs), Diltiazem analogs, was successfully modeled using Bayesian-regularized genetic neural networks (BRGNNs) and 2D autocorrelation vectors. This approach yielded reliable and robust models whilst by means of a linear genetic algorithm (GA) search routine no multilinear regression model was found describing more than 50% of the training set. On the contrary, the optimum neural network predictor with five inputs described about 84% and 65% variances of 50 randomly selected training and test sets. Autocorrelation vectors in the nonlinear model contained information regarding 2D spatial distributions on the CEB structure of van der Waals volumes, electronegativities, and polarizabilities. However, a sensitivity analysis of the network inputs pointed out to the electronegativity and polarizability 2D topological distributions at substructural fragments of sizes 3 and 4 as the most relevant features governing the nonlinear modeling of the negative inotropic potency.

The inhibitory activity towards p34 cdc 2/cyclin b kinase (CBK) enzyme of 30 cytokinin-derived compounds has been successfully modelled using 2D spatial autocorrelation vectors. Predictive linear and non-linear models were obtained by forward stepwise multi-linear regression analysis (MRA) and artificial neural network (ANN) approaches respectively. A variable selection routine that selected relevant non-linear information from the data set was employed prior to networks training. The best ANN with three input variables was able to explain about 87% data variance in comparison with 80% by the linear equation using the same number of descriptors. Similarly, the neural network had higher predictive power. The MRA model showed a linear dependence between the inhibitory activities and the spatial distributions of masses, electronegativities and van der Waals volumes on the inhibitors molecules. Meanwhile, ANN model evidenced the occurrence of non-linear relationships between the inhibitory activity and the mass distribution at different topological distance on the cytokinin-derived compounds. Furthermore, inhibitors were well distributed regarding its activity levels in a Kohonen self-organizing map (SOM) built using the input variables of the best neural network.