1,721,079 research outputs found
Effetto del cadmio e della solfocarenza sull’espressione di un trasportatore del solfato ad alta affinità di Brassica juncea
No full textL’assorbimento e la distribuzione sistemica del solfato nelle piante sono processi mediati da
specifici trasportatori la cui attività è altamente regolata per controllare il flusso di zolfo in
funzione della loro richiesta metabolica, nonché del loro stato nutrizionale. L’esposizione a
cadmio (Cd) influenza profondamente il metabolismo dello zolfo ed induce aumenti della
capacità delle radici di assumere solfato dal mezzo, come risposta ad un incremento dei
fabbisogni di zolfo della pianta guidato dall’attività di biosintesi delle fitochelatine. Tali
comportamenti sono simili a quelli riscontrati in piante solfocarenti, dove tuttavia l’aumento
della capacità di assumere solfato non è relazionabile a un incremento dei fabbisogni di zolfo
bensì alla sola esigenza di mantenere l’omeostasi dei flussi di questo elemento lungo le vie
assimilative. Entrambe le risposte sono controllate prevalentemente a livello trascrizionale e
sono state a lungo indicate come risultanti di uno stesso segnale nutrizionale, peraltro
controverso.
Nel presente lavoro viene evidenziata e discussa la possibilità che Cd e solfocarenza
modulino l’espressione dei trasportatori del solfato ad alta affinità di Brassica juncea
attraverso segnali indipendenti e parzialmente sovrapponibili. La scelta di B. juncea come
modello sperimentale risiede nella complessità del suo genoma; tale specie possiede infatti
entrambi i corredi cromosomici (AANN; 2n=36) dei due progenitori ancestrali che l’hanno
generata per incrocio interspecifico: B. campestris (AA; 2n=20) e B. nigra (NN; 2n=16).
Precedenti lavori condotti da questo gruppo hanno evidenziato un accumulo di trascritto di
BjST1;2 – un gene codificante per un trasportatore del solfato ad alta affinità espresso nelle
radici di B. juncea – in risposta sia a Cd sia a solfocarenza. Per questo trasportatore sono state
identificate tre diverse varianti geniche (a, b, c) derivanti dai due set cromosomici della
specie, presenti ed espresse contemporaneamente in un unico individuo. La presenza di
polimorfismi nelle loro sequenze permette di accoppiare l’uso di enzimi di restrizione alle
tecniche di RT-PCR semiquantitativa, allo scopo di evidenziare eventuali comportamenti
differenziali nell’attività di trascrizione delle tre varianti. In particolare, l’incremento nei
livelli di trascritto di BjST1;2 in seguito a limitata disponibilità di solfato risulta imputabile a
tutte e tre le varianti individuate; diversamente, l’esposizione a Cd determina l’accumulo di
trascritto di due sole varianti (b e c).
I risultati ottenuti evidenziano chiaramente che geni codificanti per lo stesso trasportatore
rispondono in modo differenziale a Cd e solfocarenza, suggerendo l’esist enza di vie multisegnale
a controllo dei processi di assunzione e assimilazione del solfato in condizioni di
diverso stato nutrizionale.
L’impiego di specie anfidiploidi negli studi di controllo trascrizionale del trasporto
consente quindi di evidenziare eventuali vie multi-segnale di regolazione. La complessità del
genoma di tali specie, soprattutto in relazione alla presenza di geni duplicati, consente infatti
l’accumulo di mutazioni altrimenti eliminate dalla selezione naturale, che possono invece
fornire preziose informazioni sui meccanismi di regolazione trascrizionale. Nel caso in esame
la perdita della capacità della variante a di rispondere al Cd non compromette la risposta
complessiva di BjST1;2 al metallo, che viene infatti garantita dalle varianti b e c
Cadmium increases the optimal external concentration for sulfate in Arabidopsis thaliana
No full textThe main sulfur (S) source for plants is the sulfate ion (SO42-), which is taken up by roots through specific plasma membrane high-affinity SO42- transporters. Once inside the plant, SO42- is allocated to different sinks where it is first assimilated into cysteine (Cys), a key intermediate from which most of S-containing compounds are synthetized. Considering the central role of Cys, it appears evident that both SO42- uptake and assimilation have to be finely modulated to meet the metabolic demand for S arising from Cys consuming activities, which largely contribute to define the total S requirement of plants. Such a demand may consistently vary under the different environmental conditions that plants may experience during their growth. Abiotic stresses may increase the metabolic demand for some Cys derived compounds, causing an increase in the activity of the SO4 2- assimilatory pathway. An example of this has been largely described in plants exposed to cadmium (Cd) in which the activation of glutathione- (GSH) consuming adaptive responses may increase the demand for both SO42- and S metabolites. Indeed, GSH is the key intermediate for the synthesis of phytochelatins (PCs), a class of Cys-rich metal-binding peptides involved in Cd detoxification. The large amount of PCs produced by plants represents an additional sink for S, which generates a typical demand-driven transcriptional regulation of genes involved in SO42- uptake, SO42- assimilation and GSH biosynthesis. To better understand the relationship existing between Cd accumulation and S metabolism, we analyzed the growth of Arabidopsis thaliana under a wide range of SO42- external concentrations (from 1 to 150 μM), in the presence or absence of 0.1 μM Cd2+. Plant growth was dependent on SO42- external concentration in both the experimental conditions. The growth isotherms were saturating curves properly described by the following single exponential rise to maximum function:
= !"# ∙ (1 − !! !"! !! )
Such a function allowed us to estimate the theoretical critical concentration for SO42-, defined as the external concentration of the anion, which produces 95% of the maximum fresh weight. Data analysis indicated that the presence of Cd significantly changed the demand for S to maximize shoot growth, since the critical value for SO42- external concentration was higher in Cd treated (40 μM) than in control plants (29 μM). Moreover, the negative effect exerted by Cd on shoot growth decreased as SO42- concentration in the external medium increased. No effects of Cd on shoot growth were observed for SO42- external concentrations higher than the critical one. Differently, the detrimental effect exerted by Cd on root growth was independent of SO42- external concentration. Finally, Cd exposure negatively affected thiol metabolism, since shoot GSH concentration was lower in Cd-treated than in control plants, in all the experimental conditions. However, the effect of Cd on GSH levels decreased as SO42- external concentration increased, up to reach the critical value. Thus, at least our experimental conditions, the minimum shoot GSH concentration that have to be maintained to contrast Cd toxicity is around 375 nmol g-1 FW
Nuovi approcci per il miglioramento dell’efficienza d’uso dei nutrienti nelle piante : il caso dello zolfo
No full textL’efficienza con cui le piante usano un nutriente minerale (Nutrient Use Efficiency, NUE), definita come l’incremento di produzione determinato da un aumento del livello dell’elemento in seguito ad una sua somministrazione al suolo, è un tratto agronomico controllato da diversi geni e dalla loro interazione con l’ambiente. Approcci genetici in specie modello quali Arabidopsis thaliana e Oryza sativa hanno permesso di identificare geni o gruppi di geni strettamente associati al carattere NUE relativamente a macronutrienti quali N, P e K, ed utilizzabili come marcatori molecolari in programmi di selezione assistita. Nel caso dello zolfo, invece, esistono solo informazioni frammentarie. Attraverso approcci diversi sono stati identificati e caratterizzati in Arabidopsis geni e promotori coinvolti nelle risposte precoci della pianta a variazioni dello stato nutrizionale solfatico. Viene discussa la possibilità di utilizzare tali elementi per la costituzione di un bioindicatore transgenico in grado di segnalare rapidamente e in modo sito-specifico le necessità di zolfo della coltura, così da poter programmare interventi adeguati di fertilizzazione. La definizione della dose corretta e delle variabili spazio-temporali delle fertilizzazioni sono infatti elementi determinanti nel miglioramento dell’efficienza d’uso dei nutrienti minerali
Using an amphidiploid species to study sulfate transporter regulation
No full textPlant sulfate uptake and systemic distribution are processes mediated by specific transporters whose activity is finely tuned to control sulfur fluxes in the plants depending on their metabolic needs, and their sulfur nutritional status. Cd exposure deeply affects sulfur metabolism and increases the root capability to take up sulfate, as a consequence of the increased plant sulfur needs depending on phytochelatin biosynthesis. Such a behavior is similar to that of sulfur starved plants, although in this case the increased capability to take up sulfate does not derive from increased plant sulfur needs but from the need to maintain the homeostasis of sulfur fluxes along the assimilatory pathway. Both the responses are mainly controlled at transcriptional level and have often been indicated as resulting from the same, although controversial, nutritional signal.
We think that the use of amphidiploid species in the transcriptional control studies of sulfate transporters could be useful in order to underline possible multi-signalling regulatory pathways. In fact, the complexity of the amphidiploid genome, mainly concerning the existence of duplicated genes, may have led to the accumulation of mutations, which otherwise would have been eliminated by natural selection, that could give precious information on the transcriptional regulation mechanisms. Here we discuss the possibility that Cd and sulfur starvation modulate the expression of a high affinity sulfate transporter of Brassica juncea, an amphidiploid species carrying both the chromosomal sets of the ancestral parents Brassica nigra and Brassica campestris, through independent and partially overlapping signal
Effect of NO3- transport and reduction on intracellular pH : An in vivo NMR study in maize roots
No full textThe effect of NO3- uptake on cellular pH was studied in maize roots by an in vivo 31P-NMR technique. In order to
separate the effects on cytoplasmic pH due to NO3- uptake from those due to NO3- reduction, tungstate was used to inhibit nitrate reductase (NR). The results confirm that in maize roots tungstate inhibited NR activity. 15N-NMR in vivo experiments demonstrated the cessation of nitrogen flux from nitrate to organic compounds. Tungstate affected neither NO3- uptake nor the levels of the main phosphorylated compounds.
Slight changes in cytoplasmic pH were observed during NO3- uptake and reduction (i.e. control). By contrast, in the presence of tungstate, a consistent decrease in cytoplasmic pH occurred. The vacuolar pH did not change in any of the conditions tested. These data show that NO3- uptake is an acidifying process and suggest a possible involvement of NO3- reduction in pH homeostasis. In the presence of NO3-, a transient depolarization of transmembrane electric potential difference Em) was observed in all the conditions analysed.
However, in tungstate-treated roots, a lesser depolarization
accompanied by a greater ability to recover Em was found. This was related to a higher activity of the plasma membrane (PM) H+-ATPase. When NO3- was administered as potassium salt, its uptake increased and a greater depolarization of Em took place, whilst the changes in cytoplasmic pH were remarkably reduced, according to the central role played by K+ in the control of plasma membrane activities and cell pH homeostasis.
A possible involvement of cytoplasmic pH in the control of PM H+-ATPase expression during nitrate exposure is suggested
Possibile ruolo del pH cellulare nel controllo dei processi di trasporto ed assimilazione del NO3- in radici di mais (Zea Mays L.)
No full textMonitoring plant nutritional status
No full textMethods and techniques effective in achieving yield objectives, optimizing the use of resources and preventing environmental contamination are defined as agronomic Best Management Practices (BMPs). Considering fertilisations BMPs pursue the aims to match mineral nutrient supply with crop requirements, minimizing their losses from the field. If spatial and temporal information about crop needs were available, precision fertilisation approaches could be planned in order to increase fertiliser use efficiency and to improve some economic and environmental aspects related to the crop systems. The state of the art and the research perspectives on the fine tuning of optical devices allowing proximal or remote sensing at sub-field scale of crops traits related to plant nutritional status, as well as on the exploitation of the gene fusion concept in developing transgenic bioindicators monitoring the nutritional status of the plants are here reviewed and discussed. Concerning the latter aspect particular attention is paid to the development of synthetic promoters conferring to the biondicator nutrient specificity and also able to target the expression of the associated reporter genes in organs in which their signals should be early and easily detectable
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