Peroxidases during adventitious rooting in cuttings of <Emphasis Type="Italic">Arbutus unedo</Emphasis> and <Emphasis Type="Italic">Taxus baccata</Emphasis> as affected by plant genotype and growth regulator treatment

Cuttings of Arbutus unedo (strawberry tree) and Taxus baccata (yew) were treated with 8.0 and 10.0 g l^–1, respectively, of KIBA, IBA, IAA, NAA and Paclobutrazol. No rooting occurred without growth regulator treatment. The effect of growth regulators on percentage of rooting followed the order KIBA > IBA > IAA = NAA = Paclobutrazol = 0% (for A. unedo) and KIBA > IBA > IAA > NAA > Paclobutrazol = 0% (for T. baccata). Genotypes of the above plant species had significant effects on the number and length of roots, percentage of rooting and peroxidase specific activity (PA) on KIBA-treated cuttings. High PA seems to be related with low percentage of rooting in the case of A. unedo cuttings while no similar results were noticed in the case of T. baccata. Electrophoretic analysis revealed the appearance of two to three anionic and one cationic peroxidase isoforms in A. unedo cuttings, while six to nine anionic and no cationic peroxidases isoforms appeared in the case of T. baccata genotypes. During adventitious rooting, the PA showed the three interdependent phases (induction, initiation, expression) in both K-IBA treated cuttings of A. unedo and T. baccata, but in a different time course.     

Morphological and physiological traits of three major Arabidopsis thaliana accessions

Arabidopsis is currently the most studied organism in plant biology. Its short life cycle and small genome size have rendered it one of the principal model systems. Additionally, numerous large T-DNA insertion mutant collections are available. The advent of molecular biology and the completion of the Arabidopsis genome sequence have contributed to helping researchers discover a large variety of mutants identified for their phenotypes. Yet, it is important to consider that natural phenotypic variations exist and appear in natural ecotypes, differing greatly in several traits. Although there are a vast number of ecotypes available, only a few have been extensively studied, and some have been created in laboratories. In order to identify new phenotypic differences, we chose to study the differences observed between three ecotypes: Columbia (Col-0), Landsberg erecta (Laer-0) and Wassilewskija (Ws-0). Our research focuses on observable morphological traits throughout plant growth and development along the entire plant life cycle. We then attempted to shed some light on phenotypic discrepancies through the study of the class III peroxidase protein family, which is involved in many aspects of plant growth and tissue differentiation. Both morphological and molecular aspects reveal that there are major variations between ecotypes, hence indicating a possibly interesting heterotic effect in the F1 from crosses between different Arabidopsis ecotypes.     

The Activity of the Peroxidase System in the Course of Stress-Induced CAM Development

The activity of the peroxidase system in Mesembryanthemum crystallinum L. plants in relation to the shift from C₃ to CAM photosynthesis was studied. In detached leaves of the fourth and fifth stories treated with NaCl (0.3 M), a rapid (after 30 min) transient induction of the ionically bound peroxidase (the first maximum) was observed followed by a second weak increase in the enzyme activity (90 min after salt treatment). In the leaves of intact plants, which received a longer treatment with NaCl, a two-phase change in the enzyme activity was also observed. It was most pronounced at the early stages of the NaCl-induced plant shift from C₃ to CAM photosynthesis. In this case, in both detached and intact leaves of juvenile plants, the activity of soluble peroxidase was at a low steady-state level. The situation changed dramatically when M. crystallinum plants transitioned to the reproductive developmental phase and photosynthesis switched from C₃ to CAM. The time dependence of the activities of both peroxidase types, the soluble ones in particular, was characterized by marked diurnal oscillations (light–dark), which coincided with the fluctuations of the total titratable acidity. In this case, the activity of the soluble enzyme was several orders of magnitude higher than the activity of the ionically bound peroxidase, even though the optimum pH for both isoforms was similar (pH 5.0). Three acid isoforms of soluble peroxidases, which operated more actively when the cytoplasm had a higher acidity, were distinguished by isoelectrofocusing. Their activity increased under salinity. Alkaline and neutral components were predominant in more than 30 molecular forms of the soluble peroxidase detected. We concluded that the operation of the peroxidase system changed substantially when plants shifted from the juvenile to the reproductive state and switched from C₃ to CAM photosynthesis: the activity of stress-induced ionically bound peroxidase was drastically inhibited with a concurrent increase in the activity of soluble peroxidase and a change in the spectrum of its molecular forms.     

Ferulic acid impairs rhizogenesis and root growth,and alters associated biochemical changes in mung bean (Vigna radiata) hypocotyls

The present study investigated the effect of ferulic acid (FA; 0–1000 µM) on early growth, and rhizogenesis in mung bean (Vigna radiata) hypocotyls and associated biochemical changes. FA severely affected the radicle elongation and number of secondary roots after 72 h. The root and shoot length, number and length of secondary roots, and seedling dry weight of one-week-old seedlings of mung bean were decreased by 64%. The rooting potential (percent rooting, number and length of adventitious roots) of mung bean hypocotyls under in vitro conditions was significantly inhibited in response to 1–100 µM FA. At 1000 µM there was complete cessation of rooting. FA caused a reduction in the contents of water-soluble proteins and endogenous total phenolics, whereas the activities of proteases, peroxidases, and polyphenol peroxidases increased. The study concludes that FA inhibits root growth and development, and in vitro rooting process in mung bean by interfering with biochemical processes that are crucial for root formation.     

Glycans of higher plant peroxidases: recent observations and future speculations

Plant peroxidases are composed of a peptide and associated heme, calcium and glycans. The 3D structure of the major cationic peanut peroxidase has revealed the sites of the heme and calcium. But the diffraction of the glycans was not sufficient to show their structure. This review presents research that has been executed to obtain putative glycans and their binding sites, and to gain an indirect insight into these glycans. It also offers approaches that will be used to determine the function of the glycans on the peanut peroxidase. Some comparisons are made with other plant glycoproteins including peroxidases from plants other than peanut.     

Function and Compensatory Mechanisms Among the Components of the Chloroplastic Redox Network

Life on earth depends on the presence of photoautotrophic organisms that are able to input carbon into the ecosystems through the process of photosynthesis which, with a few specialized exceptions, takes place within the chloroplast. This organelle contains the most complex redox system in plants being composed of numerous players including thiol reductases, peroxidases, and glutathione-related enzymes. It seems likely that these proteins act together to adjust redox metabolism enabling plants to grow efficiently under both normal and stressed conditions. However, our knowledge concerning how these proteins interact and if they can compensate one another is relatively limited. This is in part due to the failure of considering these components from a systemic perspective. Here, we provide a systemic view of the chloroplastic-redox network highlighting how it operates and how its components co-operate to maintain efficient chloroplastic function. We further explore the cross-talk between chloroplastic-redox metabolism and that of other subcellular compartments. Given the complexity of plant redox metabolism and the compensatory role played by different redox systems, we argue that a unique possibility to understand this system is afforded by systems biology approaches and by characterizing mutants for multiple genes. Taking this into account, we highlight how gene co-expression and protein–protein network analyses coupled with different reverse genetic strategies could be used to reveal the function, potential redundancies, and complementarities among the components of the chloroplastic redox network.     

Anatomy and Phenylpropanoid Metabolism in the Incompatible Interaction of Lycopersicon esculentum and Cuscuta reflexa

A time-dependent correlation of anatomical and chemical defence reactions was shown during the incompatible reaction of tomato against the phanerogamic parasite Cuscuta reflexa. Microscopical analysis of the infection sites at the tomato stem revealed the elongation of epidermal, hypodermal and collenchymatic cells beneath the parasitic prehaustorium. After 9–11 days of infection the elongated cells had collapsed forming a visible brownish plaque at the tomato stem followed by a scalariform tissue with lignified and suberized cell walls. Concomitantly, an enhanced accumulation of soluble phenolic compounds (chlorogenic acid and an unidentified hydroxycinnamic acid derivative), as well as a stimulation of peroxidases, was observed. In contrast, PAL activity was not increased. Whereas the stimulation of phenylpropanoid metabolism could also be induced by artificial wounding, the described anatomical changes were only observed during attack of Cuscuta.     

Crystalline Thymidylate Synthetase From Dichloromethotrexate Resistant Lactobacillus Case I

A procedure is described for the isolation and crystallization of thymidylate synthetase from a dichloromethotrexate resistant strain of Lactobacillus casei. The recrystallized enzyme shows one band on polyacrylamide gel electrophoresis. The specific activity of the recrystallized enzyme is 216 μmoles of thymidylate formed per hour per mg. at30°C.     

Radical formation on a conserved tyrosine residue is crucial for DyP activity

Dye-decolorizing peroxidases (DyPs) are able to cleave bulky anthraquinone dyes. The recently published crystal structure of AauDyPI reveals that a direct oxidation in the distal heme cavity can be excluded for most DyP substrates. It is shown that a surface-exposed tyrosine residue acts as a substrate interaction site for bulky substrates. This amino acid is conserved in eucaryotic DyPs but is missing in the structurally related chlorite dismutases (Clds). Dye-decolorizing peroxidases of procaryotic origin equally possess a conserved tyrosine in the same region of the polypeptide albeit not at the homologous position.