Growth and physiological response of lemongrass (Cymbopogon citratus (D.C.) Stapf.) under different levels of fly ash-amended soil

Revegetation with metal tolerant plants for management of fly ash deposits is an important environmental perspective nowadays. Growth performance, photosynthesis, and antioxidant defense of lemongrass (Cymbopogon citratus (D.C.) Stapf.) were evaluated under various combination of fly ash amended with garden soil in order to assess its fly ash tolerance potential. Under low level of fly ash (25%) amended soil, the plant growth parameters such as shoot, root, and total plant biomass as well as metal tolerance index were increased compared to the control plants grown on garden soil, followed by decline under higher concentration of fly ash (50%, 75% and 100%). In addition, leaf photosynthetic rate, stomatal conductance, and photosystem (PS) II activity were not significantly changed under low level of fly ash (25%) amended soil compared to the garden soil but these parameters were significantly decreased further with increase of fly ash concentrations. Furthermore, increase of activities of some antioxidant enzymes such as superoxide dismutase, ascorbate peroxidase, and guaiacol peroxidase over control were noticed in lemongrass under all fly ash treatments. Taken together, the study suggests that lemongrass can be used for phytoremediation of fly ash at 25% amended soil.     

Modulation of microtubule dynamics by drugs: a paradigm for the actions of cellular regulators

Microtubules are intrinsically dynamic polymers. Two kinds of dynamic behaviors, dynamic instability and treadmilling, are important for microtubule function in cells. Both dynamic behaviors appear to be tightly regulated, but the cellular molecules and the mechanisms responsible for the regulation remain largely unexplored. While microtubule dynamics can be modulated transiently by the interaction of regulatory molecules with soluble tubulin, the microtubule itself is likely to be the primary target of cellular molecules that regulate microtubule dynamics. The antimitotic drugs that modulate microtubule dynamics serve as excellent models for such cellular molecules. Our laboratory has been investigating the interactions of small drug molecules and stabilizing microtubule-associated proteins (MAPs) with microtubule surfaces and ends. We find that drugs such as colchicine, vinblastine, and taxol, and stabilizing MAPs such as tau, strongly modulate microtubule dynamics at extremely low concentrations under conditions in which the microtubule polymer mass is minimally affected. The powerful modulation of the dynamics is brought about by the binding of only a few drug or MAP molecules to distinct binding sites at the microtubule surface or end. Based upon our understanding of the well-studied drugs and stabilizing MAPs, it is clear that molecules that regulate dynamics such as Kin 1 and stathmin could bind to a large number of distinct tubulin sites on microtubules and employ an array of mechanisms to selectively and powerfully regulate microtubule dynamics and dynamics-dependent cellular functions.     

Distinct dimer interaction and regulation in nitric-oxide synthase types I,II, and III

Homodimer formation activates all nitric-oxide synthases (NOSs). It involves the interaction between two oxygenase domains (NOSoxy) that each bind heme and (6R)-tetrahydrobiopterin (H4B) and catalyze NO synthesis from L-Arg. Here we compared three NOSoxy isozymes regarding dimer strength, interface composition, and the ability of L-Arg and H4B to stabilize the dimer, promote its formation, and protect it from proteolysis. Urea dissociation studies indicated that the relative dimer strengths were NOSIIIoxy > NOSIoxy > NOSIIoxy (endothelial NOSoxy (eNOSoxy) > neuronal NOSOXY (nNOSoxy) > inducible NOSoxy (iNOSoxy)). Dimer strengths of the full-length NOSs had the same rank order as judged by their urea-induced loss of NO synthesis activity. NOSoxy dimers containing L-Arg plus H4B exhibited the greatest resistance to urea-induced dissociation followed by those containing either molecule and then by those containing neither. Analysis of crystallographic structures of eNOSoxy and iNOSoxy dimers showed more intersubunit contacts and buried surface area in the dimer interface of eNOSoxy than iNOSoxy, thus revealing a potential basis for their different stabilities. L-Arg plus H4B promoted dimerization of urea-generated iNOSoxy and nNOSoxy monomers, which otherwise was minimal in their absence, and also protected both dimers against trypsin proteolysis. In these respects, L-Arg alone was more effective than H4B alone for nNOSoxy, whereas for iNOSoxy the converse was true. The eNOSoxy dimer was insensitive to proteolysis under all conditions. Our results indicate that the three NOS isozymes, despite their general structural similarity, differ markedly in their strengths, interfaces, and in how L-Arg and H4B influence their formation and stability. These distinguishing features may provide a basis for selective control and likely help to regulate each NOS in its particular biologic milieu.     

Genome relationship among nine species of Millettieae (Leguminosae: Papilionoideae) based on random amplified polymorphic DNA (RAPD)

Random amplified polymorphic DNA (RAPD) marker was used to establish intergeneric classification and phylogeny of the tribe Millettieae sensu Geesink (1984) (Leguminosae: Papilionoideae) and to assess genetic relationship between 9 constituent species belonging to 5 traditionally recognized genera under the tribe. DNA from pooled leaf samples was isolated and RAPD analysis performed using 25 decamer primers. The genetic similarities were derived from the dendrogram constructed by the pooled RAPD data using a similarity index, which supported clear grouping of species under their respective genera, inter- and intra-generic classification and phylogeny and also merger of Pongamia with Millettia. Elevation of Tephrosia purpurea var. pumila to the rank of a species (T. pumila) based on morphological characteristics is also supported through this study of molecular markers.     

The hemagglutinin-neuraminidase protein of Newcastle disease virus determines tropism and virulence

The hemagglutinin-neuraminidase (HN) protein of Newcastle disease virus (NDV) plays a crucial role in the process of infection. However, the exact contribution of the HN gene to NDV pathogenesis is not known. In this study, the role of the HN gene in NDV virulence was examined. By use of reverse genetics procedures, the HN genes of a virulent recombinant NDV strain, rBeaudette C (rBC), and an avirulent recombinant NDV strain, rLaSota, were exchanged. The hemadsorption and neuraminidase activities of the chimeric viruses showed significant differences from those of their parental strains, but heterotypic F and HN pairs were equally effective in fusion promotion. The tissue tropism of the viruses was shown to be dependent on the origin of the HN protein. The chimeric virus with the HN protein derived from the virulent virus exhibited a tissue predilection similar to that of the virulent virus, and vice versa. The chimeric viruses with reciprocal HN proteins either gained or lost virulence, as determined by a standard intracerebral pathogenicity index test of chickens and by the mean death time in chicken embryos (a measure devised to classify these viruses), indicating that virulence is a function of the amino acid differences in the HN protein. These results are consistent with the hypothesis that the virulence of NDV is multigenic and that the cleavability of F protein alone does not determine the virulence of a strain.     

Mitochondrial alterations related to programmed cell death in tobacco cells under aluminium stress

The present investigation was undertaken to verify whether mitochondria play a significant role in aluminium (Al) toxicity, using the mitochondria isolated from tobacco cells (Nicotiana tabacum, non-chlorophyllic cell line SL) under Al stress. An inhibition of respiration was observed in terms of state-III, state-IV, succinate-dependent, alternative oxidase (AOX)-pathway capacity and cytochrome (CYT)-pathway capacity, respectively, in the mitochondria isolated from tobacco cells subjected to Al stress for 18 h. In accordance with the respiratory inhibition, the mitochondrial ATP content showed a significant decrease under Al treatment. An enhancement of reactive oxygen species (ROS) production under state-III respiration was observed in the mitochondria isolated from Al-treated cells, which would create an oxidative stress situation. The opening of mitochondrial permeability transition pore (MPTP) was seen more extensively in mitochondria isolated from Al-treated cells than in those isolated from control cells. This was Ca(2+) dependent and well modulated by dithioerythritol (DTE) and Pi, but insensitive to cyclosporine A (CsA). The collapse of inner mitochondrial membrane potential (DeltaPsi(m)) was also observed with a release of cytochrome c from mitochondria. A great decrease in the ATP content was also seen under Al stress. Transmission electron microscopy analysis of Al-treated cells also corroborated our biochemical data with distortion in membrane architecture in mitochondria. TUNEL-positive nuclei in Al-treated cells strongly indicated the occurrence of nuclear fragmentation. From the above study, it was concluded that Al toxicity affects severely the mitochondrial respiratory functions and alters the redox status studied in vitro and also the internal structure, which seems to cause finally cell death in tobacco cells.     

A membrane protein, EzrA, regulates assembly dynamics of FtsZ by interacting with the C-terminal tail of FtsZ

FtsZ polymerizes to form a dynamic ring structure called the Z-ring at the midcell of bacteria. EzrA, a membrane protein, has been shown to prevent the formation of aberrant Z-rings in the low GC Gram-positive bacteria by inhibiting FtsZ assembly. In this study, we show that Bacillus subtilis (B. subtilis) EzrA inhibited the assembly and bundling of B. subtilis FtsZ. It increased the critical concentration of FtsZ assembly and depolymerized the preformed FtsZ polymers in vitro. We obtained evidence suggesting that B. subtilis EzrA forms complex with B. subtilis FtsZ in vitro. EzrA was found to bind to FtsZ at a single site with a dissociation constant of 4.3 +/- 0.6 microM. EzrA-FtsZ interaction has a significant electrostatic contribution as apparent from the effect of salt on their binding interactions. To elucidate the site of interaction between EzrA and FtsZ, we deleted 16 amino acid residues from the extreme C-terminal tail of B. subtilis FtsZ, which are conserved in FtsZ orthologues. EzrA did not inhibit the assembly of C-terminal truncated B. subtilis FtsZ. It also did not bind to the C-terminal truncated FtsZ detectably, suggesting that EzrA interacts with FtsZ through its conserved C-terminal tail residues. Further, a 17-residue synthetic peptide (365-382) of the C-terminal tail of FtsZ (CTP17) was used to probe the interaction of EzrA with the C-terminal tail of FtsZ. CTP17 bound to EzrA, inhibited the binding of EzrA to FtsZ, and surmounted the inhibitory effects of EzrA on the assembly of FtsZ in vitro. The data together showed that EzrA binds to the C-terminal tail of FtsZ. FtsA, a positive regulator of FtsZ assembly, is also known to interact with the C-terminal tail of FtsZ. The results indicated an interesting possibility that the assembly dynamics of FtsZ in the Z-ring is regulated by the competition between positive and negative regulators sharing the same binding site on FtsZ.