Estimation of the solubility parameters of model plant surfaces and agrochemicals: a valuable tool for understanding plant surface interactions

Background Most aerial plant parts are covered with a hydrophobic lipid-rich cuticle, which is the interface between the plant organs and the surrounding environment. Plant surfaces may have a high degree of hydrophobicity because of the combined effects of surface chemistry and roughness. The physical and chemical complexity of the plant cuticle limits the development of models that explain its internal structure and interactions with surface-applied agrochemicals. In this article we introduce a thermodynamic method for estimating the solubilities of model plant surface constituents and relating them to the effects of agrochemicals. Results Following the van Krevelen and Hoftyzer method, we calculated the solubility parameters of three model plant species and eight compounds that differ in hydrophobicity and polarity. In addition, intact tissues were examined by scanning electron microscopy and the surface free energy, polarity, solubility parameter and work of adhesion of each were calculated from contact angle measurements of three liquids with different polarities. By comparing the affinities between plant surface constituents and agrochemicals derived from (a) theoretical calculations and (b) contact angle measurements we were able to distinguish the physical effect of surface roughness from the effect of the chemical nature of the epicuticular waxes. A solubility parameter model for plant surfaces is proposed on the basis of an increasing gradient from the cuticular surface towards the underlying cell wall. Conclusions The procedure enabled us to predict the interactions among agrochemicals, plant surfaces, and cuticular and cell wall components, and promises to be a useful tool for improving our understanding of biological surface interactions

Differential association of the Na+/H+ exchanger regulatory factor (NHERF) family of adaptor proteins with the raft- and the non-raft brush border membrane fractions of NHE3

Background/Aims: Trafficking, brush border membrane (BBM) retention, and signal-specific regulation of the Na+/H+ exchanger NHE3 is regulated by the Na+/H+ Exchanger Regulatory Factor (NHERF) family of PDZ-adaptor proteins, which enable the formation of multiprotein complexes. It is unclear, however, what determines signal specificity of these NHERFs. Thus, we studied the association of NHE3, NHERF1 (EBP50), NHERF2 (E3KARP), and NHERF3 (PDZK1) with lipid rafts in murine small intestinal BBM. Methods: Detergent resistant membranes ('lipid rafts') were isolated by floatation of Triton X-incubated small intestinal BBM from a variety of knockout mouse strains in an Optiprep step gradient. Acid-activated NHE3 activity was measured fluorometrically in BCECF-loaded microdissected villi, or by assessment of CO2/HCO3 - mediated increase in fluid absorption in perfused jejunal loops of anethetized mice. Results: NHE3 was found to partially associate with lipid rafts in the native BBM, and NHE3 raft association had an impact on NHE3 transport activity and regulation in vivo. NHERF1, 2 and 3 were differentially distributed to rafts and non-rafts, with NHERF2 being most raft-associated and NHERF3 entirely non-raft associated. NHERF2 expression enhanced the localization of NHE3 to membrane rafts. The use of acid sphingomyelinase-deficient mice, which have altered membrane lipid as well as lipid raft composition, allowed us to test the validity of the lipid raft concept in vivo. Conclusions: The differential association of the NHERFs with the raft-associated and the non-raft fraction of NHE3 in the brush border membrane is one component of the differential and signal-specific NHE3 regulation by the different NHERFs

Family-wide characterization of the DENN domain Rab GDP-GTP exchange factors

Target or substrate Rab GTPases are identified for 17 proteins with DENN domains

Remarkable Reduction of MAP2 in the Brains of Scrapie-Infected Rodents and Human Prion Disease Possibly Correlated with the Increase of Calpain

Microtubule-associated protein 2 (MAP2) belongs to the family of heat stable MAPs, which takes part in neuronal morphogenesis, maintenance of cellular architecture and internal organization, cell division and cellular processes. To obtain insight into the possible alteration and the role of MAP2 in transmissible spongiform encephalopathies (TSEs), the MAP2 levels in the brain tissues of agent 263K-infected hamsters and human prion diseases were evaluated. Western blots and IHC revealed that at the terminal stages of the diseases, MAP2 levels in the brain tissues of scrapie infected hamsters, a patient with genetic Creutzfeldt-Jakob disease (G114V gCJD) and a patient with fatal familial insomnia (FFI) were almost undetectable. The decline of MAP2 was closely related with prolonged incubation time. Exposure of SK-N-SH neuroblastoma cell line to cytotoxic PrP106-126 peptide significantly down-regulated the cellular MAP2 level and remarkably disrupted the microtubule structure, but did not alter the level of tubulin. Moreover, the levels of calpain, which mediated the degradation of a broad of cytoskeletal proteins, were significantly increased in both PrP106-126 treated SK-N-SH cells and brain tissues of 263K prion-infected hamsters. Our data indicate that the decline of MAP2 is a common phenomenon in TSEs, which seems to occur at an early stage of incubation period. Markedly increased calpain level might contribute to the reduction of MAP2

A Permeable Cuticle Is Associated with the Release of Reactive Oxygen Species and Induction of Innate Immunity

Wounded leaves of Arabidopsis thaliana show transient immunity to Botrytis cinerea, the causal agent of grey mould. Using a fluorescent probe, histological staining and a luminol assay, we now show that reactive oxygen species (ROS), including H2O2 and O2−, are produced within minutes after wounding. ROS are formed in the absence of the enzymes Atrboh D and F and can be prevented by diphenylene iodonium (DPI) or catalase. H2O2 was shown to protect plants upon exogenous application. ROS accumulation and resistance to B. cinerea were abolished when wounded leaves were incubated under dry conditions, an effect that was found to depend on abscisic acid (ABA). Accordingly, ABA biosynthesis mutants (aba2 and aba3) were still fully resistant under dry conditions even without wounding. Under dry conditions, wounded plants contained higher ABA levels and displayed enhanced expression of ABA-dependent and ABA-reporter genes. Mutants impaired in cutin synthesis such as bdg and lacs2.3 are already known to display a high level of resistance to B. cinerea and were found to produce ROS even when leaves were not wounded. An increased permeability of the cuticle and enhanced ROS production were detected in aba2 and aba3 mutants as described for bdg and lacs2.3. Moreover, leaf surfaces treated with cutinase produced ROS and became more protected to B. cinerea. Thus, increased permeability of the cuticle is strongly linked with ROS formation and resistance to B. cinerea. The amount of oxalic acid, an inhibitor of ROS secreted by B. cinerea could be reduced using plants over expressing a fungal oxalate decarboxylase of Trametes versicolor. Infection of such plants resulted in a faster ROS accumulation and resistance to B. cinerea than that observed in untransformed controls, demonstrating the importance of fungal suppression of ROS formation by oxalic acid. Thus, changes in the diffusive properties of the cuticle are linked with the induction ROS and attending innate defenses

The application of cortical layer markers in the evaluation of cortical dysplasias in epilepsy

The diagnostic criteria for focal cortical dysplasia type I (FCD I) remain to be well and consistently defined. Cortical layer-specific markers (CLM) provide a potential tool for the objective assessment of any dyslamination. We studied expression patterns of recognised CLM using immunohistochemistry for N200, ER81, Otx1, Map1b (subsets of V/VI projection neurones), Pax6, Tbr1, Tbr2 (differentially expressed in cortical neurones from intermediate progenitor cells), Cux 1 (outer cortical layers) and MASH1 (ventricular zone progenitors). Dysplasia subtypes included FCD I and II, dysplasias adjacent to hippocampal sclerosis (HS) or dysembryoplastic neuroepithelial tumours (DNTs); all were compared to neonatal and adult controls. Laminar expression patterns in normal cortex were observed with Tbr1, Map1b, N200 and Otx1. FCDI cases in younger patients were characterised by abnormal expression in layer II for Tbr1 and Otx1. FCDII showed distinct labelling of balloon cells (Pax6, ER81 and Otx1) and dysmorphic neurones (Tbr 1, N200 and Map1b) supporting origins from radial glia and intermediate progenitor cells, respectively. In temporal lobe sclerosis cases with dysplasia adjacent to HS, Tbr1 and Map1b highlighted abnormal orientation of neurones in layer II. Dyslamination was not confirmed in the perilesional cortex of DNT with CLM. Finally, immature cell types (Otx1, Pax6 and Tbr2) were noted in varied pathologies. One possibility is activation of progenitor cell populations which could contribute to the pathophysiology of these lesions