Sucrose-phosphate synthase activity and yield analysis of tomato plants transformed with maize sucrose-phosphate synthase

Sucrose synthesis is a major element of the interactions between photosynthesis and plant growth and development. Tomato (Lycopersicon esculentum Mill. cv. UC82B) plants transformed with maize sucrose-phosphate synthase (SPS; EC 2.3.1.14) expressed from either a ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) small subunit promoter (SSU) or the cauliflower mosaic virus 35S promoter (35S) were used to study effects of increased sucrose synthesis rates on plant growth. The plants were grown in growth chambers, field plots, and open-top chambers. The 35S plants had a 2 to 3-fold increase in young-leaf SPS activity, a 10 to 20-fold increase in young-root SPS activity and no increase in young-fruit SPS activity. The leaf SPS activity in one of the 35S lines fell to control levels by two months of age. The SSU plants had a 4 to 5-fold increase in leaf SPS activity and no significant increase in root or young-fruit SPS activity. One 35S line, which maintained high leaf SPS activity throughout development, yielded 70–80% more than controls at both normal and elevated CO₂ in open-top chambers in the field and 20–30% more than controls in two additional field trials. The other 35S line and the two SSU lines either yielded less or did not differ from controls under several growth conditions. Since only one of four transformed lines showed an increase in yield, we can not yet conclude that increased leaf SPS activity leads to increased yield. However, increased leaf SPS activity appears to result in increased fruit sugar content since all three lines with increased leaf SPS usually also had increased fruit sugars. Received: 18 November 1996 / Accepted: 22 January 1997     

Real-time detection of interactions between the human oxytocin receptor and G protein-coupled receptor kinase-2

Although the oxytocin receptor (OTR) mediates many important functions including uterine contractions, milk ejection, and maternal behavior, the mechanisms controlling agonist-induced OTR desensitization have remained unclear, and attempts to demonstrate involvement of a G protein-coupled receptor kinase (GRK) have so far failed. Using the OTR as a model, we demonstrate here directly for the first time the dynamics of agonist-induced interactions of a GRK with a G protein-coupled receptor in real time, using time-resolved bioluminescence resonance energy transfer. GRK2/receptor interactions started within 4 sec, peaked at 10 sec, and decreased to less than 40% within 8 min. By contrast, beta-arrestin/OTR interactions initiated only at 10 sec, reached plateau levels at 120 sec, but remained stable with little decrease thereafter. Physical GRK2/OTR association was further demonstrated by coimmunoprecipitation of endogenous GRK2 with activated OTR. In COS-7 cells, which express low levels of GRK2 and beta-arrestin, overexpression of GRK2 and beta-arrestin increased receptor phosphorylation, desensitization, and internalization to the high levels observed in human embryonic kidney 293 cells. By contrast, specific inhibition of endogenous GRK2 by dominant-negative mutants robustly inhibited OTR phosphorylation and internalization as well as arrestin/OTR interactions. These data characterize the temporal and causal relationship of GRK-2/OTR and beta-arrestin/OTR interactions and establish GRK/OTR interaction as a prerequisite for beta-arrestin-mediated OTR desensitization.     

A necrotic cell death model in a protist

While necrotic cell death is attracting considerable interest, its molecular bases are still poorly understood. Investigations in simple biological models, taken for instance outside the animal kingdom, may benefit from less interference from other cell death mechanisms and from better experimental accessibility, while providing phylogenetic information. Can necrotic cell death occur outside the animal kingdom? In the protist Dictyostelium, developmental stimuli induced in an autophagy mutant a stereotyped sequence of events characteristic of necrotic cell death. This sequence included swift mitochondrial uncoupling with mitochondrial 2',7'-dichlorofluorescein diacetate fluorescence, ATP depletion and increased oxygen consumption. This was followed by perinuclear clustering of dilated mitochondria. Rapid plasma membrane rupture then occurred, which was evidenced by time-lapse videos and quantified by FACS. Of additional interest, developmental stimuli and classical mitochondrial uncouplers triggered a similar sequence of events, and exogenous glucose delayed plasma membrane rupture in a nonglycolytic manner. The occurrence of necrotic cell death in the protist Dictyostelium (1) provides a very favorable model for further study of this type of cell death, and (2) strongly suggests that the mechanism underlying necrotic cell death was present in an ancestor common to the Amoebozoa protists and to animals and has been conserved in evolution.     

TGFβ-induced GRK2 expression attenuates AngII-regulated vascular smooth muscle cell proliferation and migration

Through diametric actions, the transforming growth factor β (TGFβ) and Angiotensin II (AngII) play important roles in regulating various biological responses such as cell proliferation and migration. Signaling initiated by TGFβ and AngII occurs through two structurally and functionally distinct receptor super families, the serine/threonine kinase and G protein-coupled receptors (GPCRs). Previously, we identified the G protein-coupled receptor kinase-2 (GRK2), a key regulatory factor in the desensitization of GPCRs, as a direct downstream target of the TGFβ signaling cascade. GRK2 acts through a negative feed-back loop mechanism to terminate TGFβ-induced smad signaling. To investigate the impact of TGFβ-induced GRK2 expression on GPCR signaling, we examined its effect on AngII signaling in vascular smooth muscle cells (VSMCs). In this study, we show that activation of the TGFβ signaling cascade in VSMCs results in increased GRK2 expression levels, which consequently inhibits AngII-induced ERK phosphorylation and antagonizes AngII-induced VSMC proliferation and migration. Moreover, the inhibitory effect of TGFβ on AngII signaling occurs at the Mek-Erk interface and is abrogated when an anti-sense oligonucleotide directed against GRK2 is used. Thus, we conclude that TGFβ signaling antagonizes AngII-induced VSMC proliferation and migration through the inhibition of ERK phosphorylation and that GRK2 is a key factor mediating the cross-talk between these two receptor super families.     

Zinc supplementation does not alter plasma homocysteine,vitamin B12 and red blood cell folate concentrations in French elderly subjects

Background/aimsIn ageing, low folates and vitamin B12 status are frequent and can explain the increase of plasma homocysteine level. Zinc is involved in the folates and vitamin B12 metabolism with opposite actions. The aim of this study was to investigate the effects of zinc supplementation on homocysteine and vitamin B12 plasma levels as well as red blood cell folate level in French ageing subjects participating in the ZENITH study.MethodsApparently healthy middle-aged (55–70 years) and free-living older (70–85 years) subjects were enrolled. They were randomly allocated to three groups: 0, 15 or 30 mg Zn per day for 6 months as zinc gluconate in addition to their usual dietary intake.ResultsAt baseline, plasma homocysteine levels (15.2±3.5 μmol/L) in older people were higher than in the middle-aged subjects (12.7±2.7 μmol/L) and was negatively correlated with vitamin B12 values (p=0.0036, r=?0.215) and with RBC folate levels (p<0.0001, r=?0.30). These results are in agreement with previous data. However, we found no correlation between the biomarkers of zinc status and homocysteine, vitamin B12 or folate levels at baseline. Moreover, 6-month zinc supplementation did not modify homocysteine, vitamin B12 and RBC folate values in either of the groups.ConclusionsZinc supplementation at moderate doses do not lead to deleterious effect on folate or vitamin B12 status in ageing healthy free-living people, but does not have any beneficial effects on homocysteine metabolism either.