Tomato polyphenol oxidase B is spatially and temporally regulated during development and in response to ethylene

Plant polyphenol oxidases (PPOs) are ubiquitous plastid-localized enzymes. A precise analysis of PPO function in plants has been complicated by the presence of several family members with immunological cross reactivity. Previously we reported the isolation of genomic clones coding for the seven members of the tomato (Solanum lycopersicum) PPO family (A, A', B, C, D, E, and F). Here we report the complex spatial and temporal expression of one of the members, PPO B. The PPO B promoter was sequenced and subjected to homology analysis. Sequence similarities were found to nucleotide sequences of genes encoding enzymes/proteins active in the following systems: phenylpropanoid biosynthesis, signal transduction and responsiveness to hormones and stresses, fruit and seed proteins/enzymes, and photosynthesis. Chimeric gene fusions were constructed linking PPO B 5' flanking regions to the reporter gene, b-glucuronidase (GUS). The resultant transgenic plants were histochemically analyzed for GUS activity in various vegetative and reproductive tissues, and evaluated for PPO B responsiveness to ethylene induction. It was shown that PPO B expression was tissue specific, developmentally regulated, ethylene induced, and localized predominantly to mitotic or apoptotic tissues.     

Enhanced photocatalytic properties of Bi2MoO6 nanoplates deposited with intermetallic AgPd nanoparticles by photoreduction method

Bi₂MoO₆ nanoplates modified with intermetallic AgPd nanoparticles synthesized by photoreduction deposition method were used for visible-light-driven photodegradation of rhodamine B. The as-synthesized AgPd/Bi₂MoO₆ nanocomposites were identified by XRD. The 2θ diffraction angle of the (111) plane of pure metallic cubic Ag at 38.11° of heterostructure 10% Ag/Bi₂MoO₆ nanocomposites shifted to a higher diffraction angle at 38.17° of heterostructure 10% Ag_0.7Pd_0.3/Bi₂MoO₆ nanocomposites. TEM images of the as-synthesized nanocomposites showed good metallic Ag and intermetallic AgPd nanoparticles with particle size of 10–12 nm which were fully supported on top of Bi₂MoO₆ nanoplates. Bi₂MoO₆ nanoplates deposited with intermetallic AgPd nanoparticles show significant photocatalytic activity better than Ag/Bi₂MoO₆ and Bi₂MoO₆ due to the formation of AgPd/Bi₂MoO₆ Schottky barrier.

     

Synthesis and characterisation of branched polyarylethers

Polyarylethers (Polysulfone: PSU, Polyethersulfone: PES) belong to the group of high performance polymers, having high glass transition temperature as well as high continuous use temperature. As a consequence of their high glass transition temperature, these polymers display high melt viscosity, which limits the number of accessible applications. Since the conventional methods to improve the flow characteristics are limited, the influence of branching by incorporation of the tri-functional monomer 1,1,1-Tris-(4-hydroxyphenyl)ethane (THPE) on the flow and the mechanical performance of PES was studied. Branching enhances the flow of Polyethersulfone significantly, but has a deleterious effect on the toughness, especially Charpy impact and tensile elongation.     

Functional analysis of polyphenol oxidases by antisense/sense technology

Polyphenol oxidases (PPOs) catalyze the oxidation of phenolics to quinones, the secondary reactions of which lead to oxidative browning and postharvest losses of many fruits and vegetables. PPOs are ubiquitous in angiosperms, are inducible by both biotic and abiotic stresses, and have been implicated in several physiological processes including plant defense against pathogens and insects, the Mehler reaction, photoreduction of molecular oxygen by PSI, regulation of plastidic oxygen levels, aurone biosynthesis and the phenylpropanoid pathway. Here we review experiments in which the roles of PPO in disease and insect resistance as well as in the Mehler reaction were investigated using transgenic tomato (Lycopersicon esculentum) plants with modified PPO expression levels (suppressed PPO and overexpressing PPO). These transgenic plants showed normal growth, development and reproduction under laboratory, growth chamber and greenhouse conditions. Antisense PPO expression dramatically increased susceptibility while PPO overexpression increased resistance of tomato plants to Pseudomonas syringae. Similarly, PPO-overexpressing transgenic plants showed an increase in resistance to various insects, including common cutworm (Spodoptera litura (F.)), cotton bollworm (Helicoverpa armigera (Hübner)) and beet army worm (Spodoptera exigua (Hübner)), whereas larvae feeding on plants with suppressed PPO activity had higher larval growth rates and consumed more foliage. Similar increases in weight gain, foliage consumption, and survival were also observed with Colorado potato beetles (Leptinotarsa decemlineata (Say)) feeding on antisense PPO transgenic tomatoes. The putative defensive mechanisms conferred by PPO and its interaction with other defense proteins are discussed. In addition, transgenic plants with suppressed PPO exhibited more favorable water relations and decreased photoinhibition compared to nontransformed controls and transgenic plants overexpressing PPO, suggesting that PPO may have a role in the development of plant water stress and potential for photoinhibition and photooxidative damage that may be unrelated to any effects on the Mehler reaction. These results substantiate the defensive role of PPO and suggest that manipulation of PPO activity in specific tissues has the potential to provide broad-spectrum resistance simultaneously to both disease and insect pests, however, effects of PPO on postharvest quality as well as water stress physiology should also be considered. In addition to the functional analysis of tomato PPO, the application of antisense/sense technology to decipher the functions of PPO in other plant species as well as for commercial uses are discussed.     

Reactivity of chlorinating agents/PPh3 for the chlorination of alcohols and carboxylic acids: a comparative study

The reactivity of chlorinating agents was examined with the aid of ¹H NMR using competitive reactions between selected chlorinating agents and CBr₄ towards alcohols and carboxylic acids. The reactivity was greatly dependent on the type of substituent on the chlorinating agents. COCCl₃ and CN substituted trichloromethyl groups enhanced the reactivity of the chlorinating agent with PPh₃ for the chlorination of alcohols and carboxylic acids.