Survival of Helicoverpa armigera larvae on and Bt toxin expression in various parts of transgenic Bt cotton (Bollgard II) plants

There is no conclusive evidence that Helicoverpa spp. (Lepidoptera: Noctuidae) in Australia have evolved significant levels of resistance to Bollgard II^® cotton (which expresses two Bt toxin genes, cry1Ac and cry2Ab). However, there is evidence of surviving larvae on Bollgard II cotton in the field. The distribution and survival of early‐instar Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) larvae were examined on whole Bollgard II and non‐Bt cotton plants in greenhouse bioassays. The expression of Cry toxins in various parts of Bollgard II plants was compared to the survival of larvae in those locations. Only 1% of larvae survived after 6 days on greenhouse‐grown Bollgard II plants compared to 31% on non‐Bt cotton plants. Overall, and across all time intervals, more larvae survived on reproductive parts (squares, flowers, and bolls) than on vegetative parts (leaves, stems, and petioles) on Bollgard II plants. The concentration of Cry1Ac toxin did not differ between plant structures, whereas Cry2Ab toxin differed significantly, but there was no relationship between the level of expression and the location of larvae. This study provides no evidence that lower expression of Cry toxins in the reproductive parts of plants explains the survival of H. armigera larvae on Bollgard II cotton.     

Arabidopsis GDSL1 overexpression enhances rapeseed Sclerotinia sclerotiorum resistance and the functional identification of its homolog in Brassica napus

Sclerotinia stem rot (SSR) caused by Sclerotinia sclerotiorum is a devastating disease of rapeseed (Brassica napus L.). To date, the genetic mechanisms of rapeseed’ interactions with S. sclerotiorum are not fully understood, and molecular‐based breeding is still the most effective control strategy for this disease. Here, Arabidopsis thaliana GDSL1 was characterized as an extracellular GDSL lipase gene functioning in Sclerotinia resistance. Loss of AtGDSL1 function resulted in enhanced susceptibility to S. sclerotiorum. Conversely, overexpression of AtGDSL1 in B. napus enhanced resistance, which was associated with increased reactive oxygen species (ROS) and salicylic acid (SA) levels, and reduced jasmonic acid levels. In addition, AtGDSL1 can cause an increase in lipid precursor phosphatidic acid levels, which may lead to the activation of downstream ROS/SA defence‐related pathways. However, the rapeseed BnGDSL1 with highest sequence similarity to AtGDSL1 had no effect on SSR resistance. A candidate gene association study revealed that only one AtGDSL1 homolog from rapeseed, BnaC07g35650D (BnGLIP1), significantly contributed to resistance traits in a natural B. napus population, and the resistance function was also confirmed by a transient expression assay in tobacco leaves. Moreover, genomic analyses revealed that BnGLIP1 locus was embedded in a selected region associated with SSR resistance during the breeding process, and its elite allele type belonged to a minor allele in the population. Thus, BnGLIP1 is the functional equivalent of AtGDSL1 and has a broad application in rapeseed S. sclerotiorum‐resistance breeding.     

Effect of ozone exposure on polyamines in Scots pine trees

Effects of ozone exposure on polyamines in Pinus sylvestris L. were studied in a long-term experiment. Ten- to 15-year-old Scots pines were exposed to target ozone levels which began at ambient + 40 ppb in May, decreasing to ambient air only by September for 3 growing seasons. The amount of ozone applied followed the natural pattern of variation in ozone concentrations in Northern Finland. The free, soluble conjugated and insoluble conjugated polyamines were analyzed during the experiment and shortly after termination of exposure as well as at the beginning of the following growing season. A carry-over effect was observed as ozone-induced reduction of free spermidine in the oldest needle year class, which developed during the first exposure season of the experiment. This reduction was observed both after the second and the third ozone exposure season. Conversely, after termination of the experiment, levels of free polyamines increased in the following growing season, and soluble conjugated polyamines decreased in the developing needles. The post-treatment changes in polyamine concentrations are hypothesized to be caused by stress-induced injuries or delayed recovery of metabolic processes rather than protective responses. It is noteworthy that some responses in polyamines were found in the developing needles nine months after terminating the ozone exposure. This suggests that stress-induced injuries to older needles affected metabolism of new developing needles.     

Inhibitors of the 5-lipoxygenase arachidonic acid pathway induce ATP release and ATP-dependent organic cation transport in macrophages

We have previously described that arachidonic acid (AA)-5-lipoxygenase (5-LO) metabolism inhibitors such as NDGA and MK886, inhibit cell death by apoptosis, but not by necrosis, induced by extracellular ATP (ATPe) binding to P2X7 receptors in macrophages. ATPe binding to P2X7 also induces large cationic and anionic organic molecules uptake in these cells, a process that involves at least two distinct transport mechanisms: one for cations and another for anions. Here we show that inhibitors of the AA-5-LO pathway do not inhibit P2X7 receptors, as judged by the maintenance of the ATPe-induced uptake of fluorescent anionic dyes. In addition, we describe two new transport phenomena induced by these inhibitors in macrophages: a cation-selective uptake of fluorescent dyes and the release of ATP. The cation uptake requires secreted ATPe, but, differently from the P2X7/ATPe-induced phenomena, it is also present in macrophages derived from mice deficient in the P2X7 gene. Inhibitors of phospholipase A2 and of the AA-cyclooxygenase pathway did not induce the cation uptake. The uptake of non-organic cations was investigated by measuring the free intracellular Ca^2 + concentration ([Ca^2 +]_i) by Fura-2 fluorescence. NDGA, but not MK886, induced an increase in [Ca^2 +]_i. Chelating Ca^2 + ions in the extracellular medium suppressed the intracellular Ca^2 + signal without interfering in the uptake of cationic dyes. We conclude that inhibitors of the AA-5-LO pathway do not block P2X7 receptors, trigger the release of ATP, and induce an ATP-dependent uptake of organic cations by a Ca^2 +- and P2X7-independent transport mechanism in macrophages.     

Superoxide oxidase and reductase activity of cytochrome b559 in photosystem II

This study provides evidence for the superoxide oxidase and the superoxide reductase activity of cytochrome b₅₅₉ (cyt b₅₅₉) in PSII. It is reported that in Tris-treated PSII membranes upon illumination, both the intermediate potential (IP) and the reduced high potential (HP^red) forms of cyt b₅₅₉ exhibit superoxide scavenging activity and interconversion between IP and HP^red form. When Tris-treated PSII membranes were illuminated in the presence of spin trap EMPO, the formation of superoxide anion radical (O₂⁻) was observed, as confirmed by EPR spin-trapping spectroscopy. The observations that the addition of enzymatic (superoxide dismutase) and non-enzymatic (cytochrome c, α-tocopherol and Trolox) O₂⁻ scavengers prevented the light-induced conversion of IP ↔ HP^red cyt b₅₅₉ confirmed that IP and HP^red cyt b₅₅₉ are reduced and oxidized by O₂⁻, respectively. Redox changes in cyt b₅₅₉ by an exogenous source of O₂⁻ reconfirmed the superoxide oxidase and reductase activity of cyt b₅₅₉. Furthermore, the light-induced conversion of IP to HP^red form of cyt b₅₅₉ was completely inhibited at pH > 8 and by chemical modification of the imidazole ring of histidine residues using diethyl pyrocarbonate. We proposed that a change in the environment around the heme iron, induced by the protonation and deprotonation of His²² residue generates a favorable condition for the oxidation and reduction of O₂⁻, respectively.     

The dual face of connexin-based astroglial Ca communication: A key player in brain physiology and a prime target in pathology

For decades, studies have been focusing on the neuronal abnormalities that accompany neurodegenerative disorders. Yet, glial cells are emerging as important players in numerous neurological diseases. Astrocytes, the main type of glia in the central nervous system , form extensive networks that physically and functionally connect neuronal synapses with cerebral blood vessels. Normal brain functioning strictly depends on highly specialized cellular cross-talk between these different partners to which Ca^2 +, as a signaling ion, largely contributes. Altered intracellular Ca^2 + levels are associated with neurodegenerative disorders and play a crucial role in the glial responses to injury. Intracellular Ca^2 + increases in single astrocytes can be propagated toward neighboring cells as intercellular Ca^2 + waves, thereby recruiting a larger group of cells. Intercellular Ca²⁺ wave propagation depends on two, parallel, connexin (Cx) channel-based mechanisms: i) the diffusion of inositol 1,4,5-trisphosphate through gap junction channels that directly connect the cytoplasm of neighboring cells, and ii) the release of paracrine messengers such as glutamate and ATP through hemichannels (‘half of a gap junction channel’). This review gives an overview of the current knowledge on Cx-mediated Ca^2 + communication among astrocytes as well as between astrocytes and other brain cell types in physiology and pathology, with a focus on the processes of neurodegeneration and reactive gliosis. Research on Cx-mediated astroglial Ca^2 + communication may ultimately shed light on the development of targeted therapies for neurodegenerative disorders in which astrocytes participate. This article is part of a Special Issue entitled: Calcium signaling in health and disease. Guest Editors: Geert Bultynck, Jacques Haiech, Claus W. Heizmann, Joachim Krebs, and Marc Moreau.     

Excess iron-induced changes in the photosynthetic characteristics of sweet potato

Iron (Fe) is an essential nutrient for plant growth and development. In plant tissues, approximately 80% of Fe is found in photosynthetic cells. This study was carried out to determine the effect of different iron concentrations on the photosynthetic characteristics of sweet potato plants. The fluorescence transient of chlorophyll a (OJIP), chlorophyll index and gas exchange were measured in plants grown for seven days in Hoagland solution containing an iron concentration of 0.45, 0.90, 4.50 or 9.00 mM Fe (as Fe-EDTA). The initial and maximum fluorescence increased in the plants receiving 9.00 mM Fe. In the analysis of the fluorescence kinetic difference, L- and K-bands appeared in all of the treatments, but the amplitude was higher in plants receiving 4.50 or 9.00 mM Fe. In plants grown in 9.00 mM Fe, the parameters of the JIP-Test indicated a better efficiency in the capture, absorption and use of light energy, and although the chlorophyll index was higher, the net photosynthesis was lower. The overall data showed that sweet potato plants subjected to high iron concentrations may not exhibit the toxicity symptoms, but the light reactions of photosynthesis can be affect, which may result in a declining net assimilation rate.