Plant-disperser mutualisms in a semi-arid habitat invaded by <Emphasis Type="Italic">Lantana camara</Emphasis> L.

Dispersal is an important ecological process that affects plant population structure and community composition. Invasive plants with fleshy fruits rapidly form associations with native and invasive dispersers, and may affect existing native plant-disperser associations. We asked whether frugivore visitation rate and fruit removal was associated with plant characteristics in a community of fleshy-fruited plants and whether an invasive plant receives more visitation and greater fruit removal than native plants in a semi-arid habitat of Andhra Pradesh, India. Tree-watches were undertaken at individuals of nine native and one invasive shrub species to assess the identity, number and fruit removal by avian frugivores. Network analyses and generalised linear mixed-effects models were used to understand species and community-level patterns. All plants received most number of visits from abundant, generalist avian frugivores. Number of frugivore visits and time spent by frugivores at individual plants was positively associated with fruit crop size, while fruit removal was positively associated with number of frugivore visits and their mean foraging time at individual plants. The invasive shrub, Lantana camara L. (Lantana), had lower average frugivore visit rate than the community of fleshy-fruited plants and received similar average frugivore visits but greater average per-hour fruit removal than two other concurrently fruiting native species. Based on the results of our study, we infer that there is little evidence of competition between native plants and Lantana for the dispersal services of native frugivores and that more data are required to assess the nature of these interactions over the long term. We speculate that plant associations with generalist frugivores may increase the functional redundancy of this frugivory network, buffering it against loss of participating species.     

Identification of a consensus site for TRAF6/p62 polyubiquitination

Tumor necrosis factor receptor-associated factor 6 (TRAF6) is an ubiquitin ligase that regulates a diverse array of physiological processes via forming Lys-63 linked polyubiquitin chains. In this study, the lysine selection process for TRAF6/p62 ubiquitination was examined. The protein sequence of two characterized TRAF6/p62 substrates, NRIF and TrkA, revealed a conserved consensus pattern for the ubiquitination site of these two TRAF6 substrates. The consensus pattern established in the verified substrates was common to the other Trk receptor family members, TrkB and TrkC. Interestingly, Lysine 811 in TrkB was selected for ubiquination, and mutation of Lysine 811 diminished the formation of TRAF6/p62 complex that is necessary for effective ubiquination. Moreover, downstream signaling was affected upon binding of BDNF to the mutant TrkB receptor. These findings reveal a possible selection process for targeting a specific lysine residue by a single E3 ligase and underscore the role of the scaffold, p62, in this process.     

Nerve Growth Factor Stimulates Multisite Tyrosine Phosphorylation and Activation of the Atypical Protein Kinase C's via a src Kinase Pathway

Atypical protein kinase C (PKC) isoforms are required for nerve growth factor (NGF)-initiated differentiation of PC12 cells. In the present study, we report that PKC-iota becomes tyrosine phosphorylated in the membrane coincident with activation posttreatment with nerve growth factor. Tyrosine phosphorylation and activation of PKC-iota were inhibited in a dose-dependent manner by both PP2 and K252a, src and TrkA kinase inhibitors. Purified src was observed to phosphorylate and activate PKC-iota in vitro. In PC12 cells deficient in src kinase activity, both NGF-induced tyrosine phosphorylation and activation of PKC-iota were also diminished. Furthermore, we demonstrate activation of src by NGF along with formation of a signal complex including the TrkA receptor, src, and PKC-iota. Recruitment of PKC-iota into the complex was dependent on the tyrosine phosphorylation state of PKC-iota. The association of src and PKC-iota was constitutive but was enhanced by NGF treatment, with the src homology 3 domain interacting with a PXXP sequence within the regulatory domain of PKC-iota (amino acids 98 to 114). Altogether, these findings support a role for src in regulation of PKC-iota. Tyrosine 256, 271, and 325 were identified as major sites phosphorylated by src in the catalytic domain. Y256F and Y271F mutations did not alter src-induced activation of PKC-iota, whereas the Y325F mutation significantly reduced src-induced activation of PKC-iota. The functional relevance of these mutations was tested by determining the ability of each mutant to support TRAF6 activation of NF-kappaB, with significant impairment by the Y325F PKC-iota mutant. Moreover, when the Y352F mutant was expressed in PC12 cells, NGF's ability to promote survival in serum-free media was reduced. In summary, we have identified a novel mechanism for NGF-induced activation of atypical PKC involving tyrosine phosphorylation by c-Src.     

Effect of doxorubicin on heart mitochondrial enzymes in rats: a protective role for alpha-tocopherol.

Effect of doxorubicin on heart mitochondrial enzymes was studied in rats with or without the administration of alpha-tocopherol. Rats were treated with doxorubicin 2.5 mg/kg, ip body wt once a week for 8 weeks. Alpha-tocopherol was co-administered orally for 2 months (400 mg/kg body wt daily). TCA cycle enzyme, NADH-dehydrogenase, cytochrome-C-oxidase and Na+,K(+)-ATPase activities were found to be decreased in doxorubicin treatment. A significant decrease in protease activity was observed with a concomitant increase in mitochondrial protein level. Mitochondrial lipid peroxide level was found to be increased with a decrease in thiol content. Alpha-tocopherol co-administration was found to maintain the mitochondrial enzyme activities as well as the thiol content. The results are discussed with reference to the antioxidant nature of alpha-tocopherol.     

A biochemical study on the level of lipids and glycoproteins in the serum and platelets of liver cirrhotic bleeders

Bleeding complication and abnormal platelet functions are associated with liver cirrhosis. The aim of the present investigation was to assess the functional integrity of platelets in terms of lipids like cholesterol and phospholipids, glycoproteins and membrane-bound enzymes. Liver cirrhotic patients with bleeding complications were studied. Age and sex matched normal healthy volunteers were also involved in this study as a control group. Levels of cholesterol, phospholipids, glycoproteins and adenosine triphosphatases were assessed in isolated platelet membrane fraction. The level of glycoproteins and the activity of adenosine triphosphatases were found to be decreased significantly in cirrhotic patients. The cholesterol/phospholipid ratio was found to be altered significantly, indicating an alteration in the fluidity of platelet membrane. The results of this study reveal that the functional impairment of platelets in liver cirrhotic patients which is responsible for their bleeding tendency might also be due to altered lipid and enzyme levels in platelet membrane.     

Characterization of Pneumocystis Major Surface Glycoprotein Gene (msg) Promoter Activity in Saccharomyces cerevisiae

Major surface glycoprotein (Msg), the most abundant cell surface protein of Pneumocystis, plays an important role in the interaction of this opportunistic pathogen with host cells, and its potential for antigenic variation may facilitate evasion of host immune responses. In the present study, we have identified and characterized the promoter region of msg in 3 species of Pneumocystis: P. carinii, P. jirovecii, and P. murina. Because Pneumocystis cannot be cultured, promoter activity was measured in Saccharomyces cerevisiae, a related fungus, using a yeast vector modified to utilize the gene coding for Renilla luciferase as a reporter gene. The 5′-flanking sequences of msg from all three Pneumocystis species showed considerable promoter activity, with increases in luciferase activity up to 15- to 44-fold above baseline. Progressive deletions helped define an ∼13-bp sequence in each Pneumocystis species that appears to be critical for promoter activity. Electrophoretic mobility shift analysis using P. carinii-specific msg promoter sequences demonstrated binding of nuclear proteins of S. cerevisiae. The 144-bp 5′-flanking region of P. murinamsg showed 72% identity to that of P. carinii. The 5′-flanking region of P. jiroveciimsg showed 58 and 61% identity to those of P. murina and P. carinii, respectively. The msg promoter is a good candidate for inclusion in a construct designed for genetic manipulation of Pneumocystis species.     

Agrobacterium-mediated genetic transformation of groundnut (arachis hypogaea L.): An assessment of factors affecting regeneration of transgenic plants

Transgenic groundnut (Arachis hypogaea L.) plants were produced efficiently by inoculating different explants withAgrobacterium tumefaciens strain LBA4404 harbouring a binary vector pBM21 containinguidA (GUS) andnptll (neomycin phosphotransferase) genes. Genetic transformation frequency was found to be high with cotyledonary node explants followed by 4 d cocultivation. This method required 3 days of precultivation period before cocultivation withAgrobacterium. A concentration of 75 mg/l kanamycin sulfate was added to regeneration medium in order to select transformed shoots. Shoot regeneration occurred within 4 weeks; excised shoots were rooted on MS medium containing 50 mg/I kanamycin sulfate before transferring to soil. The expression of GUS gene (uidA gene) in the regenerated plants was verified by histochemical and fluorimetric assays. The presence ofuidA andnptll genes in the putative transgenic lines was confirmed by PCR analysis. Insertion of thenptll gene in the nuclear genome of transgenic plants was verified by genomic Southern hybridization analysis. Factors affecting transformation efficiency are discussed.     

Functional expression of Escherichia coli fhuA gene in Rhizobium spp. of Cajanus cajan provides growth advantage in presence of Fe3+: ferrichrome as iron source

Cajanus cajan rhizobial isolates were found to be unable to utilize iron bound to ferrichrome, desferrioxamine B or rhodotorulic acid, all being hydroxamate type siderophores. A broad host range expression vector containing the Escherichia coli fhuA gene, encoding the outer membrane receptor for Fe-ferrichrome, was constructed. The plasmid construct (pGR1), designed to express fhuA under the lac promoter of E. coli, complemented E. coli MB97 ΔfhuA mutant for ferri-ferrichrome utilization and also allowed Rhizobium spp. ST1 and Rhizobium spp. IC3123 to grow using iron bound to ferrichrome. Sensitivity to the antibiotic albomycin, transported via the FhuA receptor, was found in case of MB97 as well as rhizobial transformants harboring pGR1. The rhizobial transformants expressing fhuA showed growth stimulation when co-inoculated with Ustilago maydis, a fungal species known to produce ferrichrome under iron starved conditions. Growth stimulation was also observed in the presence of externally supplied ferrichrome. The significance of these findings in terms of the potential for improving the survivability of rhizobial bioinoculant strains in natural soils is discussed.