Effect of ascorbate oxidase over-expression on ascorbate recycling gene expression in response to agents imposing oxidative stress

Ascorbate oxidase (AO) is a cell wall-localized enzyme that uses oxygen to catalyse the oxidation of ascorbate (AA) to the unstable radical monodehydroascorbate (MDHA) which rapidly disproportionates to yield dehydroascorbate (DHA) and AA, and thus contributes to the regulation of the AA redox state. Here, it is reported that in vivo lowering of the apoplast AA redox state, through increased AO expression in transgenic tobacco (Nicotiana tabacum L. cv. Xanthi), exerts no effects on the expression levels of genes involved in AA recycling under normal growth conditions, but plants display enhanced sensitivity to various oxidative stress-promoting agents. RNA blot analyses suggest that this response correlates with a general suppression of the plant's antioxidative metabolism as demonstrated by lower expression levels of AA recycling genes. Furthermore, studies using Botrytis cinerea reveal that transgenic plants exhibit increased sensitivity to fungal infection, although the response is not accompanied by a similar suppression of AA recycling gene expression. Our current findings, combined with previous studies which showed the contribution of AO in the regulation of AA redox state, suggest that the reduction in the AA redox state in the leaf apoplast of these transgenic plants results in shifts in their capacity to withstand oxidative stress imposed by agents imposing oxidative stress.     

Vergleichende Untersuchungen Der Wildtypen Verschiedener Drosophila-Arten An Hand Von Transplantationen Der Augenanlagen

Zusammenfassung 1. Zwischen den Arten Drosophila miranda und Drosophila melanogaster wurden intra- und interspezifische Transplantationen von Augenimaginalscheiben durchgeführt. Homöo- sowie heteroplastische Transplantationen lieferten gleich gut entwickelte Implantate.2. Das autonom ausgefärbte +(mir)-Implantatauge ist dunkler als das, ebenfalls autonom ausgefärbte, +(m)-Implantatauge.3. Die (mir)-Lymphe enthält etwas mehr ca ⁺- und etwas weniger v ⁺- und cn ⁺-Stoff als die (m)-Lymphe.Mit 2 Textabbildungen.     

Zur Frage der Steigerung der Mutationsrate Nach Generationenlanger Vorbehandlung mit Follikelhormon und Anschliessender R?ntgenbestrahlung bei Drosophila

Ohne Zusammenfassung     

Elg1 forms an alternative PCNA-interacting RFC complex required to maintain genome stability

BACKGROUND: Genome instability is a hallmark of cancer and plays a critical role in generating the myriad of phenotypes selected for during tumor progression. However, the mechanisms that prevent genome rearrangements remain poorly understood. RESULTS: To elucidate the mechanisms that ensure genome stability, we screened a collection of candidate genes for suppressors of gross chromosomal rearrangements (GCRs) in budding yeast. One potent suppressor gene encodes Elg1, a conserved but uncharacterized homolog of the large RFC subunit Rfc1 and the alternative RFC subunits Ctf18/Chl12 and Rad24. Our results are consistent with the hypothesis that Elg1 forms a novel and distinct RFC-like complex in both yeast and human cells. We find that Elg1 is required for efficient S phase progression and telomere homeostasis in yeast. Elg1 interacts physically with the PCNA homolog Pol30 and the FEN-1 homolog Rad27. The physical and genetic interactions suggest a role for Elg1 in Okazaki fragment maturation. Furthermore, Elg1 acts in concert with the alternative Rfc1-like proteins Rad24 and Ctf18 to enable Rad53 checkpoint kinase activation in response to replication stress. CONCLUSIONS: Collectively, these results reveal that Elg1 forms a novel and conserved alternative RFC complex. Furthermore, we propose that genome instability arises at high frequency in elg1 mutants due to a defect in Okazaki fragment maturation.     

Altered stomatal dynamics in ascorbate oxidase over-expressing tobacco plants suggest a role for dehydroascorbate signalling

Control of stomatal aperture is of paramount importance forplant adaptation to the surrounding environment. Here, we reporton several parameters related to stomatal dynamics and performancein transgenic tobacco plants (Nicotiana tabacum L., cv. Xanthi)over-expressing cucumber ascorbate oxidase (AO), a cell wall-localizedenzyme of uncertain biological function that oxidizes ascorbicacid (AA) to monodehydroascorbic acid which dismutates yieldingAA and dehydroascorbic acid (DHA). In comparison to WT plants,leaves of AO over-expressing plants exhibited reduced stomatalconductance (due to partial stomatal closure), higher watercontent, and reduced rates of water loss on detachment. Transgenicplants also exhibited elevated levels of hydrogen peroxide anda decline in hydrogen peroxide-scavenging enzyme activity. LeafABA content was also higher in AO over-expressing plants. Treatmentof epidermal strips with either 1 mM DHA or 100 µM hydrogenperoxide resulted in rapid stomatal closure in WT plants, butnot in AO-over-expressing plants. This suggests that signalperception and/or transduction associated with stomatal closureis altered by AO over-expression. These data support a specificrole for cell wall-localized AA in the perception of environmentalcues, and suggest that DHA acts as a regulator of stomatal dynamics. Key words: ABA, apoplast, ascorbic acid, ascorbate oxidase, dehydroascorbic acid (DHA), hydrogen peroxide, Nicotiana tabacum L., cv. Xanthi, stomata, transgenic plants, water stress Received 26 September 2007; Revised 11 December 2007 Accepted 12 December 2007     

Differences in Protein Synthesis and Peroxidase isoenzymes between recalcitrant and regenerating ProtoPlasts

The reasons for the inability of recalcitrant mesophyll protoplasts to divide and re-enter the cell cycle are unknown. Changes in protein profile, indole-3-acetic acid (IAA)-oxidase and peroxidase activities, and isoenzymes were compared in protoplasts of recalcitrant grapcvine ( Vitis vinifera ) L. cv. Sultanina) and regenerating tobacco ( Nicotiana tabacum ) L. cv. Xanthi). Using [³⁵S]-methionine. SDS-PAGE and two-dimensional separation of proteins, differences in protein profile during protoplast culture were assessed. The changes in the de novo synthesized proteins were both qualitative and quantitative between the two species. The number of proteins which changed was double in tobacco compared to grapevine protoplasts. Peroxidase and IAA-oxidase activities increased significantly in tobacco protoplasts during culture whereas in grapevine they remained low. In tobacco protoplasts. 3 and 7 basic and acidic peroxidases, respectively, were induced during protoplast culture. which were not detected in the intact leaf, whereas in grapevine no new peroxidases were induced during protoplast culture.