Phytochrome-mediated delay of plastid senescence in mustard cotyledons: changes in pigment contents and ultrastructure

Changes in pigment contents and ultrastructure have followed in cotyledons of mustard (Sinapis alba L.) seedlings during dark-mediated senescence. The seedlings were kept in white light for 7 d, treated with 5 min long wavelength far-red light and then kept in darkness up to 14 d after sowing. Under these conditions the chloroplasts remain stable for 2 d before a sequential plastidal disintegration commences. The data indicate a selective breakdown of the light-harvesting chlorophyll a/b protein. Phytochrome retards the differential loss of chlorophyll a, b and carotenoids and preserves the fine structure of chloroplasts.     

Ageing of chloroplasts in vitro — III. Comparison of the effects of ageing in vitro and senescence on the red absorption band and primary photochemical reactions of sunflower chloroplasts

A comparison of changes in absorption properties and electron transport activities of chloroplasts ageing in vivo and in vitro is made. Chloroplasts from sunflower leaves senescing in vivo during 7 days in dark do not show a blue shift of the red absorption band; in contrast, the shift becomes apparent within 24 h of in vitro ageing of isolated organelles. Photosynthetic activity by chloroplasts is lost much faster during in vitro than in vivo ageing. During in vitro ageing, the rate of degradation of thylakoid membranes as characterised by the shift in the red absorption band and loss in Hill reaction is further accelerated in chloroplasts isolated from dark-induced senescing leaves, suggesting the influence of the in vivo status of the chloroplasts on their in vitro stability.Abbreviations DCPIP 2,6-dichlorophenol indophenol - PSI Photosystem I - Chl+ Chlorophyll     

Response of senescing wheat leaves to ultraviolet a light: Changes in energy transfer efficiency and PS II photochemistry

Response of senescing leaves of wheat seedlings to ultraviolet A (UVA) radiation (365 nm) has been examined. The results indicate that senescence-induced disorganization of thylakoid membrane, decline in carotenoid-to-chlorophyll energy transfer, and enhancement of lipid peroxidation are furthered by radiation. The senescence-induced decline in photochemical activity of photosystem II further declines on irradiation. UVA does not specifically alter any site other than those damaged by senescence.     

Photodynamic treatment of herpes simplex virus during its replicative cycle.

Photodynamic treatment of herpes simplex virus type 1-infected hamster embryo fibroblasts (LSH strain) with a low concentration of proflavine (0.08 mug/10(5) cells per ml), a 3-9-diamine acridine dye, inhibited production not only of infectious progeny but also of virion particles. However, there was no appreciable inhibition of viral or cellular DNA synthesis, even when the infected cells were repeatedly exposed to this low concentration of dye and light during the replication cycle of the virus. It thus appears that photodynamic treatment of infected cells interferes with the processes involved in virus maturation.     

Effect of phytohormones on chlorophyll degradation during aging of chloroplastsin vivo andin vitro

Summary Phytohormones like IAA and kinetin inhibit chlorophyll loss during aging of wheat chloroplasts duringin vivo andin vitro. GA, on the other hand, stimulates the pigment degradation during aging of attached leaves in contrast to its senescence inhibiting action in detached leaves and isolated chloroplasts. A shift in optimum concentration of hormone in inhibiting chlorophyll degradation suggests a differential pool size of endogenous hormone regulating aging of chloroplastsin vivo andin vitro. The retardation of chlorophyll loss by kinetin, IAA and GA during aging of chloroplastsin vitro would indicate that the effect of hormones in preventing yellowing of senescing leaves may be mediated through their direct action on chloroplasts.     

Aging induced changes in photosynthetic electron transport of detached barley leaves

Primary leaf segments of 11-day-old seedlings of barley (Hordtumvulgare L. cv IB 65) were floated on distilled water in darknessat 25°C to induce senescence. This stress induced agingbrings significant loss in the total content of pigments, proteinsand nucleic acids (DNA, RNA) of the leaves and of chloroplastsisolated from the senescing leaves. Of the three macromolecularcomponents, RNA content of theisolated chloroplasts was foundmost susceptible to stress-induced aging. Loss of DCPIP Hill activity of the isolated chloroplasts couldbe correlated, in a general way, with the loss of pigments,proteins and nucleic acids of the leaves and chloroplasts isolatedfrom them. However, during the stress period, the ability ofdifferent exogenous electron donors like MnCl₂ and diphenylcarbazide(DPC) to feed electrons to Photo System II (PS II) was foundto be different. MnCl₂ supported photoreduction of DCPIP onlyup to the fourth day, whereas DPC sustained its ability to donateelectrons up to the seventh day of incubation of the leavesin darkness. These results suggest a sequential alteration ofthe sites in the electron-transport chain between H₂O and PSII reaction centers of chloroplasts during dark-induced senescence.Kinetin not only prevented the loss of pigments and proteinsduring senescence, but also preserved the integrity of the electron-transportchain. (Received November 15, 1975; )     

Identification of Pak1 inhibitors using water thermodynamic analysis

Abstract

p21-activated kinases (Paks) play an integral component in various cellular diverse processes. The full activation of Pak is dependent upon several serine residues present in the N-terminal region, a threonine present at the activation loop, and finally the phosphorylation of these residues ensure the complete activation of Pak1. The present study deals with the identification of novel potent candidates of Pak1 using computational methods as anti-cancer compounds. A diverse energy based pharmacophore (e-pharmacophore) was developed using four co-crystal inhibitors of Pak1 having pharmacophore features of 5 (DRDRR), 6 (DRHADR), and 7 (RRARDRP and DRRDADH) hypotheses. These models were used for rigorous screening against e-molecule database. The obtained hits were filtered using ADME/T and molecular docking to identify the high affinity binders. These hits were subjected to hierarchical clustering using dendritic fingerprint inorder to identify structurally diverse molecules. The diverse hits were scored against generated water maps to obtain WM/MM ΔG binding energy. Furthermore, molecular dynamics simulation and density functional theory calculations were performed on the final hits to understand the stability of the complexes. Five structurally diverse novel Pak1 inhibitors (4835785, 32198676, 32407813, 76038049, and 32945545) were obtained from virtual screening, water thermodynamics and WM/MM ΔG binding energy. All hits revealed similar mode of binding pattern with the hinge region residues replacing the unstable water molecules in the binding site. The obtained novel hits could be used as a platform to design potent drugs that could be experimentally tested against cancer patients having increased Pak1 expression.     

Biological and Physicochemical Wastewater Treatment Processes Reduce the Prevalence of Virulent Escherichia coli

Effluents discharged from wastewater treatment plants are possible sources of pathogenic bacteria, including Escherichia coli, in the freshwater environment, and determining the possible selection of pathogens is important. This study evaluated the impact of activated sludge and physicochemical wastewater treatment processes on the prevalence of potentially virulent E. coli. A total of 719 E. coli isolates collected from four municipal plants in Québec before and after treatment were characterized by using a customized DNA microarray to determine the impact of treatment processes on the frequency of specific pathotypes and virulence genes. The percentages of potentially pathogenic E. coli isolates in the plant influents varied between 26 and 51%, and in the effluents, the percentages were 14 to 31%, for a reduction observed at all plants ranging between 14 and 45%. Pathotypes associated with extraintestinal pathogenic E. coli (ExPEC) were the most abundant at three of the four plants and represented 24% of all isolates, while intestinal pathogenic E. coli pathotypes (IPEC) represented 10% of the isolates. At the plant where ExPEC isolates were not the most abundant, a large number of isolates were classified as both ExPEC and IPEC; overall, 6% of the isolates were classified in both groups, with the majority being from the same plant. The reduction of the proportion of pathogenic E. coli could not be explained by the preferential loss of one virulence gene or one type of virulence factor; however, the quinolone resistance gene (qnrS) appears to enhance the loss of virulence genes, suggesting a mechanism involving the loss of pathogenicity islands.     

In-silico analysis of caspase-3 and -7 proteases from blood-parasitic Schistosoma species (Trematoda) and their human host

Proteolytic enzymes of the caspase family, which reside as latent precursors in most nucleated metazoan cells, are core effectors of apoptosis. Of them, the executioner caspases- 3 and -7 exist within the cytosol as inactive dimers and are activated by a process called dimerization. Caspase inhibition is looked upon as a promising approach for treating multiple diseases. Though caspases have been extensively studied in the human system, their role in eukaryotic pathogens and parasites of human hosts has not drawn enough attention. In protein sequence analysis, caspases of blood flukes (Schistosoma spp) were revealed to have a low sequence identity with their counterparts in human and other mammalian hosts, which encouraged us to analyse interacting domains that participate in dimerization of caspases in the parasite and to reveal differences, if any, between the host-parasite systems. Significant differences in the molecular surface arrangement of the dimer interfaces reveal that in schistosomal caspases only eight out of forty dimer conformations are similar to human caspase structures. Thus, the parasite-specific dimer conformations (that are different from caspases of the host) may emerge as potential drug targets of therapeutic value against schistosomal infections. Three important factors namely, the size of amino acids, secondary structures and geometrical arrangement of interacting domains influence the pattern of caspase dimer formation, which, in turn, is manifested in varied structural conformations of caspases in the parasite and its human hosts.     

On the Reversibility and Fragility of Sodium Metal Electrodes

Metallic sodium is receiving renewed interest as a battery anode material because the metal is earth‐abundant, inexpensive, and offers a high specific storage capacity (1166 mAh g^?1 at ?2.71 V vs the standard hydrogen potential). Unlike metallic lithium, the case for Na as the anode in rechargeable batteries has already been demonstrated on a commercial scale in high‐temperature Na||S and Na||NiCl₂ secondary batteries, which increases interest. The reversibility of room temperature sodium anodes is investigated in galvanostatic plating/stripping reactions using in situ optical visualization and galvanostatic polarization measurements. It is discovered that electronic disconnection of mossy metallic Na deposits (“orphaning”) is a dominant source of anode irreversibility in liquid electrolytes. The disconnection is shown by means of direct visualization studies to be triggered by a root‐breakage process during the stripping cycle. As a further step toward electrode designs that are able to accommodate the fragile Na deposits, electrodeposition of Na is demonstrated in nonplanar electrode architectures, which provide continuous and morphology agnostic access to the metal at all stages of electrochemical cycling. On this basis, nonplanar Na electrodes are reported, which exhibit exceptionally high levels of reversibility (Coulombic efficiency >99.6% for 1 mAh cm^?2 Na throughput) in room‐temperature, liquid electrolytes.