117,430 research outputs found
Specific leaf area variations drive acclimation of Cistus salvifolius in different light environments
No full textCistus salvifolius L. is the most widely spread Cistus species around the Mediterranean basin. It colonizes a wide range of habitats growing from sea level to 1,800 m a.s.l., on silicolous and calcicolous soils, in sun areas as well as in the understory of wooded areas. Nevertheless, this species has been mainly investigated in term of its responsiveness to drought. Our aim was to understand which leaf traits allow C. salvifolius to cope with low-light environments. We questioned if biochemical and physiological leaf trait variations in response to a reduced photosynthetic photon flux density were related to leaf morphological plasticity, expressed by variations of specific leaf area (SLA) and its anatomical components (leaf tissue density and thickness). C. salvifolius shrubs growing along the Latium coast (41°43ʹN,12°18ʹE, 14 m a.s.l., Italy) in the open and in the understory of a Pinus pinea forest, were selected and the relationships between anatomical, gas exchange, chlorophyll (Chl) fluorescence, and biochemical parameters with SLA and PFD variations were tested. The obtained results suggested long-term acclimation of the selected shrubs to contrasting light environments. In high-light conditions, leaf nitrogen and Chl contents per leaf area unit, leaf thickness, and Chl a/b ratio increased, thus maximizing net photosynthesis, while in shade photosynthesis was downregulated by a significant reduction in the electron transport rate. Nevertheless, the increased pigment-protein complexes and the decreased Chl a/b in shade drove to an increased lightharvesting capacity (i.e. higher actual quantum efficiency of PSII). Moreover, the measured vitality index highlighted the photosynthetic acclimation of C. salvifolius to contrasting light environments. Overall, our results demonstrated the morphological, anatomical, and physiological acclimation of C. salvifolius to a reduced light environment
Leaf rolling as indicator of water stress in Cistus incanus from different provenances
No full textLeaf movements such as leaf rolling affect plant physiological performance by reducing light capture. The relationship between leaf rolling and physiological traits under imposed water stress conditions was analyzed in two population of Cistus incanus. We tested the hypothesis that leaf rolling reflected physiological changes occurring during water stress irrespective of the different acclimation in order to cope with water stress. On the whole, our results confirmed our hypothesis since leaf rolling significantly reflected physiological activity changes. Moreover, leaf rolling might be involved in protecting the PSII complex under water stress during the progressive inhibition of photosynthetic metabolism. Thus, leaf rolling could be part of C. incanus adaptive strategy to cope with water stress by sustaining leaf turgor. As such, leaf rolling may be used as a morphological index to evaluate the progressive inhibition of photosynthesis irrespective of the different acclimation to cope with water stress
Diachronic adjustments of functional traits scaling relationships to track environmental changes. Revisiting Cistus species leaf cohort classification
No full textLeaf functional traits and their relationships can differ between leaf flushes, particularly for species characterized by an extended growing season such as Mediterranean ones. Among them, Cistus spp. are generally reported to display two different leaf cohorts (i.e. summer and winter leaves) during the same growing season. We tested the generality of such leaf cohort classification by analyzing the diachronic adjustments of relationships between different leaf functional traits in 3 Cistus spp. Traits included were: leaf mass per area (LMA), leaf thickness (LT), leaf dry matter content (LDMC) and net photosynthesis on a mass basis (Am). The slopes of the relationships between morphological traits were then regressed against climate variables. The slopes were also regressed against leaf production rate (LPR) and the scores of the positioning as Competitors (%C), Stress tolerators (%S) and Ruderals (%R) in the tertiary CSR scheme. The different leaf flushes reshaped the well-known trait covariation patterns thus reflecting shifts in leaf-level resource-acquisition and -use strategies. This was achieved through an opposite response of the relationships LMA–LT and LMA–LDMC to temperature changes. In fact, the relationship LMA–LT was better modulated in leaves produced at different temperatures, while the LMA–LDMC one was possibly constrained due to the tighter negative relationship LDMC–Am (i.e. higher costs in terms of carbon assimilation). Accordingly, changes in LMA–LDMC coordination were significantly related to %C. Our results provide an evidence that while Cistus spp. leaf cohort classification generally holds, it does not necessarily capture the entire seasonal spectrum of traits covariation. We propose to move forward from the generally accepted winter–summer leaf classification shown in literature providing a new framework that can better describe Cistus species potential response to environmental changes
Atteggiamenti educativi e insegnamento linguistico: fattori di inserimento o di dispersione scolastica
No full textIl contributo affronta i problemi dell’inserimento scolastico, della dispersione scolastica e della riuscita dei percorsi educativi in relazione all’insegnamento/apprendimento dell’italiano L
Atteggiamenti educativi e insegnamento linguistico: fattori di inserimento o di dispersione scolastica
No full textIl contributo affronta i problemi dell’inserimento scolastico, della dispersione scolastica e della riuscita dei percorsi educativi in relazione all’insegnamento/apprendimento dell’italiano L
Caloric restriction prevents the age-associated activation of amyloidβ-peptide generation induced by the p75NTR-ceramide signaling pathway
No full textLate-onset Alzheimer’s disease (AD) represents 95 to 97% of all cases of AD. The age-associated increase in the prevalence of late-onset AD does not reach a plateau. Our group has recently shown that the second messenger ceramide regulates the rate of amyloid β-peptide (Aβ) generation by affecting the molecular stability of BACE1 (J. Biol. Chem. 2003). Here we explored the role of ceramide during aging by analyzing sphingomyelin/ceramide metabolism, amyloid precursor protein (APP) processing, and Aβ generation in the brain of normally aged mice. We found that aging of the brain is accompanied by a progressive activation of neutral sphingomyelinase (nSMase) that leads to increased production of ceramide. The activation of nSMase is induced by “re-expression” of the neurotrophin receptor p75NTR. We also found that aging is accompanied by increased levels of the β-secretase BACE1 and by increased β-cleavage of APP. To further confirm the role of aging on the above events, normally aged mice were restricted in their food intake, a condition that has been proved to extend the maximum-life-span and to delay many biological changes that are associated with aging. We found that caloric restriction down-regulates both the expression of p75NTR and the production of ceramide, blocking the increase of BACE1 steady-state levels and Aβ generation associated with aging. We conclude that p75NTR-ceramide is a molecular link between normal aging and late-onset AD, and that caloric restriction may represent a novel dietetic approach for the prevention of AD
IGF-R, the common regulator of life span, acts upstream of p75NTR in the regulation of Aβ generation during aging.
No full textOne of the main characteristics of Alzheimer’s disease is the abnormal accumulation of amyloid β-peptide (Aβ) in the form of senile (or amyloid) plaques. Even though aging is the single most important risk factor for Alzheimer’s disease (AD), the molecular events that connect normal aging to AD are unknown. We have recently shown that aging is characterized by a TrkA to p75NTR switch that activates the rate of Aβ generation through the second messenger ceramide. Here we have used neuroblastoma cell lines, primary neurons, and p44+/+ mice to identify the up-stream event that controls the TrkA to p75NTR transition. Our results indicate that the insulin-like growth factor receptor (IGF-R) controls the rate of Aβ generation by acting up-stream p75NTR/TrkA. Indeed, IGF-R signaling activates p75NTR expression while down-regulating TrkA; such effect is accompanied by activation of ceramide, increased expression of BACE1, and increased β cleavage of APP. Both antisense oligonucleotides and siRNA against IGF-R successfully blocked the activation of the p75NTR-ceramide signaling pathway with consequent reduction in β cleavage of APP. Similar results were obtained by over-expressing the phosphate and tensin homologue deleted on chromosome ten (PTEN), which blocks IGF-R signaling. In contrast, over-expression of p44, which releases the block of IGF-R signaling mediated by PTEN, was followed by up-regulation of p75NTR, down-regulation of TrkA, and consequent activation of BACE1-mediated cleavage of APP. Finally, pharmacologic inhibiton of IGF-R signaling, down-stream phosphatidyilinositol triphosphate (PIP3) successfully blocked the effects induced by IGF1. In conclusion, our results show that IGF-R, the common regulator of lifespan, controls the rate of Aβ generation during aging by switching neurotrophin signaling from TrkA to p75NTR, and consequent activation of the second messenger ceramide
An aging pathway controls the TrkA to p75NTR receptor switch and amyloid beta-peptide generation
No full textAging of the brain is characterized by marked changes in the expression levels of the neurotrophin receptors, TrkA and p75(NTR). An expression pattern in which TrkA predominates in younger animals switches to one in which p75(NTR) predominates in older animals. This TrkA-to-p75(NTR) switch is accompanied by activation of the second messenger ceramide, stabilization of beta-site amyloid precursor protein-cleaving enzyme-1 (BACE1), and increased production of amyloid beta-peptide (Abeta). Here, we show that the insulin-like growth factor-1 receptor (IGF1-R), the common regulator of lifespan and age-related events in many different organisms, is responsible for the TrkA-to-p75(NTR) switch in both human neuroblastoma cell lines and primary neurons from mouse brain. The signaling pathway that controls the level of TrkA and p75(NTR) downstream of the IGF1-R requires IRS2, PIP3/Akt, and is under the control of PTEN and p44, the short isoform of p53. We also show that hyperactivation of IGF1-R signaling in p44 transgenic animals, which show an accelerated form of aging, is characterized by early TrkA-to-p75(NTR) switch and increased production of Abeta in the brai
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