A Method for the Quantitative Assessment of Wound-induced Chitinase Activity in Potato Tubers

A method for the quantitative assessment of chitinase activity was developed. Dilution series of crude potato tuber chitinase extracts were assayed with a colorimetric microtitre plate assay. using CM-chitin-RBV as enzyme substrate. Linearity between absorbance values mea-sured (540 nm) and enzyme concentration was found to be limited to the low concentration range. where depletion of the substrate was no longer limiting. As as absorbance of 0.1 always fell within the concentration range for which absorbance-concentration linearity was valid. one unit of enzyme activity was defined as the amount of enzyme needed to yield and A of 0.1. A more reliable method for the assessment of chitinase activity was established by basing the difinition of enzyme, activity on a concentration rather than on as absorbance value. as was done previously. Using this method, differences in the rate of chitinase induction upon wounding were demonstrated for six commercial potato cultivars.     

Effects of jasmonic acid, branching and girdling on carbon and nitrogen transport in poplar

? Here, we examined the impact of jasmonate (JA) treatment, branching and phloem girdling on 13C and 1?N import, invertase activity and polyphenol accumulation in juvenile tissues of unbranched and branched hybrid poplar saplings (Populus nigra?×?P. deltoides). ? The import of 13C to juvenile tissues was positively correlated with invertase activity at the treatment site and enhanced by JA. Both invertase activity and 13C import were greater in shorter, younger branches and smaller, younger leaves. By contrast, JA treatments, branching and girdling had little or no impact on 1?N import. ? In poplar saplings with multiple lateral branches, we observed almost no 13C movement from subtending source leaves into lateral branches above them, with or without JA treatment. The presence of potentially competing branches, treated with JA or not, girdled or not, had no impact on carbohydrate (CHO) import or polyphenol accumulation in target branches. ? We conclude that poplar branches comprise modules that are relatively independent from each other and from the stem below in terms of CHO movement, carbon-based defence production and response to elicitors. By contrast, branches are closely linked modules in terms of nitrogen movement. This should produce trees that are highly heterogeneous in quality for herbivores.     

Inhibition of respiration and nitrate assimilation enhances photohydrogen evolution under low oxygen concentrations in Synechocystis sp. PCC 6803

In cyanobacterial membranes photosynthetic light reaction and respiration are intertwined. It was shown that the single hydrogenase of Synechocystis sp. PCC 6803 is connected to the light reaction. We conducted measurements of hydrogenase activity, fermentative hydrogen evolution and photohydrogen production of deletion mutants of respiratory electron transport complexes. All single, double and triple mutants of the three terminal respiratory oxidases and the ndhB-mutant without a functional complex I were studied. After activating the hydrogenase by applying anaerobic conditions in the dark hydrogen production was measured at the onset of light. Under these conditions respiratory capacity and amount of photohydrogen produced were found to be inversely correlated. Especially the absence of the quinol oxidase induced an increased hydrogenase activity and an increased production of hydrogen in the light compared to wild type cells. Our results support that the hydrogenase as well as the quinol oxidase function as electron valves under low oxygen concentrations. When the activities of photosystem II and I (PSII and PSI) are not in equilibrium or in case that the light reaction is working at a higher pace than the dark reaction, the hydrogenase is necessary to prevent an acceptor side limitation of PSI, and the quinol oxidase to prevent an overreduction of the plastoquinone pool (acceptor side of PSII). Besides oxygen, nitrate assimilation was found to be an important electron sink. Inhibition of nitrate reductase resulted in an increased fermentative hydrogen production as well as higher amounts of photohydrogen.     

Delta-Notch signaling induces hypochord development in zebrafish

Different cell types that occupy the midline of vertebrate embryos originate within the Spemann-Mangold or gastrula organizer. One such cell type is hypochord, which lies ventral to notochord in anamniote embryos. We show that hypochord precursors arise from the lateral edges of the organizer in zebrafish. During gastrulation, hypochord precursors are closely associated with no tail-expressing midline precursors and paraxial mesoderm, which expresses deltaC and deltaD. Loss-of-function experiments revealed that deltaC and deltaD were required for her4 expression in presumptive hypochord precursors and for hypochord development. Conversely, ectopic, unregulated Notch activity blocked no tail expression and promoted her4 expression. We propose that Delta signaling from paraxial mesoderm diversifies midline cell fate by inducing a subset of neighboring midline precursors to develop as hypochord, rather than as notochord.     

Sublethal effects of insecticides on adult longevity and fecundity of German cockroaches (Dictyoptera: Blattellidae).

The effects of sublethal concentrations of chlorpyrifos, cyfluthrin, and hydramethylnon on adult longevity and fecundity of German cockroaches, Blattella germanica (L.), were investigated. Longevity of males declined linearly with increasing doses of insecticide. An LD50 of cyfluthrin decreased male longevity by 52%, whereas an LD50 of hydramethylnon reduced male longevity by 81%. Longevity of females increased linearly with increasing sublethal doses of chlorpyrifos, whereas all doses of both cyfluthrin and hydramethylnon decreased longevity of females. Fecundity increased linearly with increasing sublethal doses of chlorpyrifos. Number of oothecae formed, oothecae hatched, and number of offspring produced in each ootheca increased with increasing sublethal concentrations of chlorpyrifos. In contrast, fecundity declined with increasing sublethal concentrations of cyfluthrin and hydramethylnon. Formation of the first ootheca occurred approximately 8 d after mating for untreated females but generally longer with sublethal concentrations of all insecticides. The period between oothecae hatch and the formation of subsequent oothecae increased with successive oothecae in all treatments.