Hormonal Profiling Reveals a Hormonal Cross-Talk During Fruit Decay in Sweet Cherries

Journal of Plant Growth Regulation - Although fruit decay in sweet cherries has been studied in some detail, information is still scarce about the possible role of phytohormones during postharvest....     

Spontaneous dimerization of titin protein Z1Z2 domains induces strong nanomechanical anchoring

Muscle elasticity strongly relies on the mechanical anchoring of the giant protein titin to both the sarcomere M-band and the Z-disk. Such strong attachment ensures the reversible dynamics of the stretching-relaxing cycles determining the muscle passive elasticity. Similarly, the design of biomaterials with enhanced elastic function requires experimental strategies able to secure the constituent molecules to avoid mechanical failure. Here we show that an engineered titin-mimicking protein is able to spontaneously dimerize in solution. Our observations reveal that the titin Z1Z2 domains are key to induce dimerization over a long-range distance in proteins that would otherwise remain in their monomeric form. Using single molecule force spectroscopy, we measure the threshold force that triggers the noncovalent transition from protein dimer to monomer, occurring at ～700 piconewtons. Such extremely high mechanical stability is likely to be a natural protective mechanism that guarantees muscle integrity. We propose a simple molecular model to understand the force-induced dimer-to-monomer transition based on the geometric distribution of forces occurring within a dimeric protein under mechanical tension.     

The Ascorbate-deficient vtc-1 Arabidopsis Mutant Shows Altered ABA Accumulation in Leaves and Chloroplasts

Abscisic acid (ABA) accumulation has been analyzed in irrigated and water-stressed wild-type and the vtc-1 mutant of Arabidopsis thaliana, which shows an ascorbate deficiency in leaves of approximately 60%. The amounts of ABA increased progressively up to 2.3-fold in water-stressed wild-type plants, whereas levels were kept at low levels in the irrigated plants. In contrast, initial increases followed by a sharp decrease of abscisic acid levels were observed in water-stressed vtc-1 mutants. Furthermore, the levels of this phytohormone increased up to fivefold in irrigated mutants. This differential accumulation of ABA in the mutant strongly correlated with the ascorbate redox state, but not with ascorbate levels. Changes in ABA levels in leaves paralleled those of chloroplasts. Immunolocalization studies showed a differential ABA accumulation in chloroplasts of vtc-1 mutants, which displayed the highest ABA labeling in irrigated plants. Our results indicate an altered pattern of ABA accumulation in the vtc-1 mutant compared to the wild type, under both irrigated conditions and water-stress conditions, which is strongly dependent on the ascorbate redox state.     

Glutathione and transpiration as key factors conditioning oxidative stress in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> exposed to uranium

Although oxidative stress has been previously described in plants exposed to uranium (U), some uncertainty remains about the role of glutathione and tocopherol availability in the different responsiveness of plants to photo-oxidative damage. Moreover, in most cases, little consideration is given to the role of water transport in shoot heavy metal accumulation. Here, we investigated the effect of uranyl nitrate exposure (50 μM) on PSII and parameters involved in water transport (leaf transpiration and aquaporin gene expression) of Arabidopsis wild type (WT) and mutant plants that are deficient in tocopherol (vte1: null α/γ-tocopherol and vte4: null α-tocopherol) and glutathione biosynthesis (high content: cad1.3 and low content: cad2.1). We show how U exposure induced photosynthetic inhibition that entailed an electron sink/source imbalance that caused PSII photoinhibition in the mutants. The WT was the only line where U did not damage PSII. The increase in energy thermal dissipation observed in all the plants exposed to U did not avoid photo-oxidative damage of mutants. The maintenance of control of glutathione and malondialdehyde contents probed to be target points for the overcoming of photoinhibition in the WT. The relationship between leaf U content and leaf transpiration confirmed the relevance of water transport in heavy metals partitioning and accumulation in leaves, with the consequent implication of susceptibility to oxidative stress.     

Circadian-related heteromerization of adrenergic and dopamine D₄ receptors modulates melatonin synthesis and release in the pineal gland

The role of the pineal gland is to translate the rhythmic cycles of night and day encoded by the retina into hormonal signals that are transmitted to the rest of the neuronal system in the form of serotonin and melatonin synthesis and release. Here we describe that the production of both melatonin and serotonin by the pineal gland is regulated by a circadian-related heteromerization of adrenergic and dopamine D₄ receptors. Through α_{1 B}-D₄ and β₁-D₄ receptor heteromers dopamine inhibits adrenergic receptor signaling and blocks the synthesis of melatonin induced by adrenergic receptor ligands. This inhibition was not observed at hours of the day when D₄ was not expressed. These data provide a new perspective on dopamine function and constitute the first example of a circadian-controlled receptor heteromer. The unanticipated heteromerization between adrenergic and dopamine D₄ receptors provides a feedback mechanism for the neuronal hormone system in the form of dopamine to control circadian inputs.     

Striatal pre- and postsynaptic profile of adenosine A(2A) receptor antagonists

Striatal adenosine A(2A) receptors (A(2A)Rs) are highly expressed in medium spiny neurons (MSNs) of the indirect efferent pathway, where they heteromerize with dopamine D(2) receptors (D(2)Rs). A(2A)Rs are also localized presynaptically in cortico-striatal glutamatergic terminals contacting MSNs of the direct efferent pathway, where they heteromerize with adenosine A(1) receptors (A(1)Rs). It has been hypothesized that postsynaptic A(2A)R antagonists should be useful in Parkinson's disease, while presynaptic A(2A)R antagonists could be beneficial in dyskinetic disorders, such as Huntington's disease, obsessive-compulsive disorders and drug addiction. The aim or this work was to determine whether selective A(2A)R antagonists may be subdivided according to a preferential pre- versus postsynaptic mechanism of action. The potency at blocking the motor output and striatal glutamate release induced by cortical electrical stimulation and the potency at inducing locomotor activation were used as in vivo measures of pre- and postsynaptic activities, respectively. SCH-442416 and KW-6002 showed a significant preferential pre- and postsynaptic profile, respectively, while the other tested compounds (MSX-2, SCH-420814, ZM-241385 and SCH-58261) showed no clear preference. Radioligand-binding experiments were performed in cells expressing A(2A)R-D(2)R and A(1)R-A(2A)R heteromers to determine possible differences in the affinity of these compounds for different A(2A)R heteromers. Heteromerization played a key role in the presynaptic profile of SCH-442416, since it bound with much less affinity to A(2A)R when co-expressed with D(2)R than with A(1)R. KW-6002 showed the best relative affinity for A(2A)R co-expressed with D(2)R than co-expressed with A(1)R, which can at least partially explain the postsynaptic profile of this compound. Also, the in vitro pharmacological profile of MSX-2, SCH-420814, ZM-241385 and SCH-58261 was is in accordance with their mixed pre- and postsynaptic profile. On the basis of their preferential pre- versus postsynaptic actions, SCH-442416 and KW-6002 may be used as lead compounds to obtain more effective antidyskinetic and antiparkinsonian compounds, respectively.     

α<Subscript>2A</Subscript>- and α<Subscript>2C</Subscript>-Adrenoceptors as Potential Targets for Dopamine and Dopamine Receptor Ligands

The poor norepinephrine innervation and high density of Gi/o-coupled α_2A- and α_2C-adrenoceptors in the striatum and the dense striatal dopamine innervation have prompted the possibility that dopamine could be an effective adrenoceptor ligand. Nevertheless, the reported adrenoceptor agonistic properties of dopamine are still inconclusive. In this study, we analyzed the binding of norepinephrine, dopamine, and several compounds reported as selective dopamine D₂-like receptor ligands, such as the D₃ receptor agonist 7-OH-PIPAT and the D₄ receptor agonist RO-105824, to α₂-adrenoceptors in cortical and striatal tissue, which express α_2A-adrenoceptors and both α_2A- and α_2C-adrenoceptors, respectively. The affinity of dopamine for α₂-adrenoceptors was found to be similar to that for D₁-like and D₂-like receptors. Moreover, the exogenous dopamine receptor ligands also showed high affinity for α_2A- and α_2C-adrenoceptors. Their ability to activate Gi/o proteins through α_2A- and α_2C-adrenoceptors was also analyzed in transfected cells with bioluminescent resonance energy transfer techniques. The relative ligand potencies and efficacies were dependent on the Gi/o protein subtype. Furthermore, dopamine binding to α₂-adrenoceptors was functional, inducing changes in dynamic mass redistribution, adenylyl cyclase activity, and ERK1/2 phosphorylation. Binding events were further studied with computer modeling of ligand docking. Docking of dopamine at α_2A- and α_2C-adrenoceptors was nearly identical to its binding to the crystallized D₃ receptor. Therefore, we provide conclusive evidence that α_2A- and α_2C-adrenoceptors are functional receptors for norepinephrine, dopamine, and other previously assumed selective D₂-like receptor ligands, which calls for revisiting previous studies with those ligands.     

Interplay between vitamin E and phosphorus availability in the control of longevity in Arabidopsis thaliana

Background and Aims Vitamin E helps to control the cellular redox state by reacting with singlet oxygen and preventing the propagation of lipid peroxidation in thylakoid membranes. Both plant ageing and phosphorus deficiency can trigger accumulation of reactive oxygen species, leading to damage to the photosynthetic apparatus. This study investigates how phosphorus availability and vitamin E interact in the control of plant longevity in the short-lived annual Arabidopsis thaliana.Methods The responses of tocopherol cyclase (VTE1)- and γ-tocopherol methyltransferase (VTE4)-null mutants to various levels of phosphorus availability was compared with that of wild-type plants. Longevity (time from germination to rosette death) and the time taken to pass through different developmental stages were determined, and measurements were taken of photosynthetic efficiency, pigment concentration, lipid peroxidation, vitamin E content and jasmonate content.Key Results The vte1 mutant showed accelerated senescence under control conditions, excess phosphorus and mild phosphorus deficiency, suggesting a delaying, protective effect of α-tocopherol during plant senescence. However, under severe phosphorus deficiency the lack of α-tocopherol paradoxically increased longevity in the vte1 mutant, while senescence was accelerated in wild-type plants. Reduced photoprotection in vitamin E-deficient mutants led to increased levels of defence chemicals (as indicated by jasmonate levels) under severe phosphorus starvation in the vte4 mutant and under excess phosphorus and mild phosphorus starvation in the vte1 mutant, indicating a trade-off between the capacity for photoprotection and the activation of chemical defences (jasmonate accumulation).Conclusions Vitamin E increases plant longevity under control conditions and mild phosphorus starvation, but accelerates senescence under severe phosphorus limitation. Complex interactions are revealed between phosphorus availability, vitamin E and the potential to synthesize jasmonates, suggesting a trade-off between photoprotection and the activation of chemical defences in the plants.