1,232 research outputs found
Un tipo di crescita cellulare particolare: la crescita apicale del tubetto pollinico.
No full textLa comprensione degli eventi correlati con l’impollinazione e la gamia nelle piante a fiore è attualmente al centro di molte ricerche volte a chiarire i meccanismi di riconoscimento polline/stilo durante la riproduzione sessuale. Perché la riproduzione possa andare a buon fine è necessario che il polline, una volta arrivato sullo stigma del pistillo, abbia la capacità di germinare emettendo il tubetto pollinico che è il vettore del gamete maschile. Il tubetto cresce a velocità considerevole ed attraversa i tessuti femminili, stigma e stilo, fino a raggiungere l’ovulo contenuto nell’ovario, dove rilascia il gamete consentendo la gamia con la cellula uovo. La crescita del tubetto è peculiare poiché è dovuta alla crescita calcio-dipendente dell’estremità apicale. Essa coinvolge la riorganizzazione dinamica del citoscheletro ed il trasporto apicale degli organelli e di vescicole diverse (Tirlapur et al., 1995). I microtubuli, colocalizzati con i microfilamenti insieme alle proteine motrici (dineina, chinesina e miosina) (Romagnoli et al., 2003) sono responsabili del trasporto apicale dell’ ”unità generativa maschile”.
Si sta indagando il ruolo della transglutaminasi, una famiglia di enzimi che catalizzano la modificazione post-traduzionale di proteine causando la formazione di reti sopramolecolari. Tali enzimi sono in grado di coniugare un residuo glutaminico ad uno lisinico o alle poliammine, formando ponti di diversa lunghezza fra proteine diverse o nell’ambito della stessa proteina inoltre “cationizzando” la proteina stessa (Del Duca and Serafini Fracassini, 2005). Nel polline di melo fra le proteine substrato di tali enzimi sono state riportate anche l’actina e la tubulina (Del Duca et al.,1997). L’enzima è stato purificato dal polline di Rosaceae ed è stato studiato al microscopio il suo effetto su proteine purificate citoscheletriche e di movimento in presenza o meno di poliammine; inoltre la sua presenza è stata studiata in vivo negli stili impollinati con osservazioni al microscopio confocale.
Di particolare interesse sono i meccanismi di incompatibilità gametofitica, che causano il blocco della crescita del tubetto pollinico e la sua morte cellulare programmata, nei quali il ruolo del citoscheletro è scarsamente studiato. In taluni tessuti animali la transglutaminasi è considerata un importante fattore dell’apoptosi (Piredda et al., 1999). Nelle piante, solo nelle Papaveraceae è riportata la formazione di foci di actina mediata da meccanismi di cross-linking non individuati. Tali foci sono ritenuti responsabili del blocco della crescita del tubetto. Vengono riportati i primi dati sul possibile ruolo della transglutaminasi nell’incompatibilità gametofitica delle Rosaceae.
Questa ricerca è stata finanziata da un progetto PRIN (MIUR) 2005-2007 “Interaction mechanism for protein mediators of flower incompatibility in fertilization of fruit trees”.
Del Duca, S. and Serafini-Fracassini, D. 2005. Transglutaminases of higher, lower plants and fungi. In K Mehta, R Eckert, eds, Transglutaminases. Prog Exp Tum Res Basel, Kager, 38:223-247.
Del Duca, S., Bregoli, A.M., Bergamini, C. and Serafini-Fracassini, D. 1997. Sex Plant Reprod 10:89-95.
Piredda, L., Farrace, M.G., Lo Bello, M., Malorni, W., Melino, G., Petruzzelli, R. and Piacentini, M. 1999. FASEB J. 13:355-64.
Romagnoli, S., Cai, G. & Cresti, M. 2003. Plant Cell 15: 251-269.
Tirlapur, U.K., Cai, G., Faleri, C., Moscatelli, A., Scali, M., Del Casino, C., Tiezzi, A. and Cresti, M. 1995. Eur J Cell Biol. 67:209-17
Pollen tube and plant reproduction
No full textThe pollen tube was a fundamental step forward in the evolution of terrestrial plants; in fact,
it allowed plants to liberate themselves from water demand during reproduction. The importance
of this simple organism (the plant gametophyte) is also due to its peculiar cytological structure,
characterized by tip growth and a cell wall that is not canonically structured but perfectly adapted to
the growth mechanism. Being both a critical factor in sexual reproduction and an excellent cell model
has made the pollen tube attractive to many researchers around the world. The growth of pollen tubes
is a complex mechanism that summarizes the basic machineries of cellular expansion: polysaccharides
and enzymes are transported by secretory vesicles to a specific location, a set of molecules and proteins
translate external signals that influence the cytoskeleton of pollen tubes and thus its growth direction
Fattori che influenzano la crescita apicale del polline nell’autoincompatibilità
No full textFattori che influenzano la crescita apicale del polline nell’autoincompatibilità
Iorio RA1, Aloisi I 1, De Franceschi P2, Dondini L 2, Cai G3, SansaviniS2, Serafini Fracassini D1, Del Duca S*1
1 Dipartimento di Biologia, Università di Bologna, Via Irnerio 42, Bologna (Italy), [email protected]
2 Dipartimento di Colture Arboree, Università di Bologna, 3 Dipartimento di Scienze Ambientali, Università di Siena
La risposta di autoincompatibilità (SI) nella riproduzione sessuale delle piante è il sistema più importante per prevenire l’autofecondazione; dal punto di vista evolutivo si ritiene che il grande successo delle angiosperme sia dovuto, almeno in parte, all’affermarsi della SI. Questa risposta prevede l’interazione polline-pistillo ed un sistema di riconoscimento fra le cellule che regola l’accettazione o il rigetto del polline, così che quello incompatibile venga inibito selettivamente in stadi specifici durante l’impollinazione. Un aspetto intrigante della biologia riproduttiva delle piante è capire come questa risposta si manifesti e quali siano i protagonisti dell’ interazione polline-pistillo. Un ruolo chiave nella SI, almeno nelle Rosaceae, è attribuito al locus genico S dello stilo che codifica per una glicoproteina con attività ribonucleasica (S-RNasi) che entra nei tubetti in crescita bloccando quelli incompatibili (1, 2). Fra i fattori che potrebbero giocare un ruolo vi sono le poliammine (PAs) che sono essenziali per la crescita cellulare negli animali e nelle piante e che durante l’impollinazione dello stilo vengono rilasciate negli spazi intercellulari (3,4), probabilmente svolgendo un ruolo nell’interazione polline-pistillo (5). Per verificare questa ipotesi il polline germinante è stato trattato con diverse ammine; quelle che si sono dimostrate più efficaci sono la spermina (spm) ed il BD23 (un’ammina artificiale) che bloccano completamente la crescita del tubetto già alla concentrazione di 0.1 mM. Analizzando il contenuto delle PAs naturali nei pistilli impollinati con polline “self” o con polline compatibile si è visto che nei due sistemi il pattern di queste molecole varia sia in funzione del tipo di poliammina, sia che siano libere o legate. Il ruolo delle PAs nel tubetto pollinico non è stato ancora chiarito, ma sembra essere in relazione all’interazione con altre molecole ad es. proteine (7) e/o al metabolismo dei diversi RNAs ed al controllo dell’attività RNasica durante l’emergenza e la crescita del tubetto (4, 6). In Pyrus c., le PAs alifatiche libere sono più concentrate negli stili impollinati con polline compatibile rispetto a quelli con polline incompatibile. I risultati sono in accordo con una possibile inibizione dell’attività RNasica da parte delle PAs poiché un’inibizione dell’attività RNasica ha luogo nella SI (1). Il trattamento del polline germinante con una S-RNasi ricombinante (allele S105) blocca completamente l’allungamento del tubetto in circa il 50% dei pollini dimostrando che anche in Pyrus c. l’attività S-RNasica gioca un ruolo chiave. Inoltre, poichè in letteratura è riportato che le PAs possano avere un ruolo “scavengers” delle Specie Reattive dell’Ossigeno (ROS) (8), si è analizzato anche quest’aspetto. Si sa che i ROS sono prodotti fisiologicamente durante la germinazione e la crescita del tubetto (9,10) e quando la loro formazione viene inibita la crescita del tubetto si arresta. Utilizzando tests con l’NBT per mettere in evidenza i ROS nel polline germinante, abbiamo visto che la spm ed il BD23 alle concentrazione 0.1 mM inibiscono drasticamente la formazione di ROS lasciando ipotizzare un meccanismo in cui le PAs potrebbero agire controllandone la concentrazione nei tubetti in crescita.
Bibliografia
1. McClure BA, Franklin-Tong V (2006) Planta 224:233–245
2. Di Sandro A, Serafini-Fracassini D, Del Duca S, ., et al. (2007) Acta Hort. 800, 423-426.
3. Bagni N, Adamo P, Serafini-Fracassini D, Villanueva VR (1981) Plant Physiol 68:727–730
4. Speranza A, Cal..
Transglutaminases from plant sources
No full textThis chapter presents the specific characteristics of transglutaminases (TGases) in different plant species by comparing them with those of the best-known TGases of animal origin. It, therefore, explains the involvement of TGases in specific aspects of the physiology of plant organisms, highlighting, above all at the cellular level, similar roles, and differences concerning those performed by animal TGases. The features of the putative gene sequences encoding for plant TGases are illustrated with special emphasis on the characteristics of the best-known mammalian TGase 2, among which the presence of the catalytic triad, the binding site for calcium and guanosine triphosphate (GTP), which are present in various plant organisms. The bioinformatics approach has enabled the comparison of the three-dimensional structures of plant TGases with their animal counterparts, suggesting that plant and animal TGases might exhibit a similar three-dimensional conformation from an energetic standpoint. Such similarity holds great significance for catalytic reactions
Alimenti biologici e consuatori umbri
No full textComportamenti di acquisto e di consumo alimentare bio; Il questionario proposto; Canali di distribuzione del prodotto bio; Percezione del consumatore sugli aspetti del prodotto bio; Considerazioni conclusive
Post-Translational Modification by Transglutaminase of Proteins Involved in Pear Self-Incompatibility
No full textGametophytic self-incompatibility (SI) is one of the mechanisms adopted by plants to prevent self-fertilisation, by blocking the growth of pollen tubes recognised as “self”. Among the known models of interaction between pistil-S and pollen S determinants, the S-RNase-based system has been described in the Rosaceae, Solanaceae
and Plantaginaceae. Another model is that of Papaver rhoeas, in which the pistil S locus product is a small protein that interacts with incompatible pollen, triggering a Ca2+-dependent signalling pathway which results in cytoskelton modifications and finally leads
to programmed cell death (PCD). In fact there is a specific relationship between the polymerization/depolymerization of actin and the onset of PCD of the pollen tube (Thomas et al., 2006; Wheeler et al., 2009). Aggregates of tubulin and punctuate aggregates of actin were also observed in Pyrus communis SI, suggesting a role for the
cytoskeleton in Rosaceae SI (Di Sandro et al., 2007), and later this role was verified in vivo and in vitro (Del Duca et al., 2009, 2010). Liu et al. (2007) in Pyrus pyrifolia observed that stylar S-RNases modified the actin cytoskeleton. Recently the role of the cytoskeleton in Pyrinae SI has been reported: the S-RNase acts on depolymerization of actin and formation of high mass aggregates, DNA degradation, collapse of mitochondrial potential, leakage of cyt C, ROS disruption (Wang et al., 2010; Poulter et al., 2011). Thus the Papaver and Pyrinae models share common features of PCD
Interpreting the mechanism of action of polyamines: twenty years of plant transglutaminases
No full textThe post-translational modification of proteins by polyamines forming inter- or intra-molecular cross-links has been the main transglutaminase (TGase) reaction studied in plants. Plant transglutaminases have been studied in our laboratory since 1987 in investigations aimed at interpreting some of the molecular mechanisms by which polyamines affect plant growth, differentiation, reaction to stresses, PCD. Transglutaminase activity is ubiquitous: it has been detected in algae and in angiosperms in different organs and sub-cellular compartments: chloroplasts, cytosol, microsomal fraction, cell walls (1).
Possible roles concern the structural modification of specific proteins. In the cytosol, they modify actin and tubulin, also influencing motor proteins, thus exerting a role on cell growth and cell structure (2). In chloroplasts, transglutaminases appear to stabilise the photosynthetic complexes and Rubisco, being regulated by light and other factors, and possibly exerting a positive effect on photosynthesis and photoprotection (1). Recent reports suggest an involvement in construction/organisation of the cell wall and extracellular matrix in relationship with fertilisation and a possible role of pollen extracellular TGase in cross-allergenicity. Other roles appear to be related to stresses, senescence and programmed cell death, including the hypersensitive reaction caused by TMV virus. The cross recognition of substrates between plant and animal enzymes suggest both similarities and differences. Proofs of their catalytic activity are: 1. their ability to produce glutamyl-polyamine derivatives, 2. their recognition by animal transglutaminase antibodies, 3. biochemical features such as calcium- and GTP-dependency, etc. 4. Inhibition by specific inhibitors of animal transglutaminases. However, many of their fundamental physiological properties still remain elusive. The few plant transglutaminases sequenced so far have little sequence homology with the best-known animal enzymes, except for the catalytic triad; however, they share a possible structural homology (3). Specificity and similarity with animal transglutaminases are discussed in the light of their biochemical characteristics and functional roles.
1. Serafini-Fracassini D and Del Duca S (2008) Tranglutaminases: widespread cross-linking enzymes in plants. Ann. Bot. 102, 145-152. DOI 10.1093/aob/mcn075. 2. Del Duca S. et al. (2008) Effects of post-translational modifications catalyzed by pollen transglutaminase on the functional properties of microtubules and actin filaments. Biochem. J., 418 3,651-664. 3. Serafini-Fracassini D, et al. (2008) Plant and animal transglutaminases: do similar functions imply similar structures? Amino Acids 36 (4) 643-657, DOI: 10.1007/s00726-008-0131-9
FUNDING: MUR-PRIN, Interaction mechanisms for protein mediators of flower incompatibility in fertilisation of fruit trees,to D.S-F;“Crossallergenicity”, Progetto Strategico d’Ateneo 2006 to D.S-F
An unconventional road for the secretion of transglutaminase in pollen tubes?
No full textThe transglutaminase (TGase) is present in the pollen tube where it most likely participates in the regulation of different activities including the organization of cytoskeletal elements (microtubules and actin filaments). In addition to a cytosolic form of TGase, new data suggest the existence of TGase forms associated with the internal membranes and with the cell wall of pollen tubes. This different localization extends the functional range of pollen TGase but also raises the question how TGase can be precisely (and in harmony with the pollen tube growth) redistributed in different cellular compartments. The discovery that TGase exists as different isoforms may suggest a pathway to achieve this result
TRANSGLUTAMINASES IN SENESCENCE AND PROGRAMMED CELL DEATH OF LEAVES AND PETALS: THEIR SIMILARITIES TO ANIMAL TRANSGLUTAMINASES
No full textFree polyamines (PAs) have a contrasting role in the delay of senescence in animals, whereas in plants its protective effect is better established, eventhough the molecular mechanism is not clarified. We hypothesised that PAs can be conjugated to specific proteins by catalysis of Ca++-dependent transglutaminases (TGases). TGases are involved in PCD in animals, whereas few data are available in plants. Plants utilized were: Nicotiana tabacum corolla, models of short-lived flowers and Lactuca sativa leaves, commercially utilised for food purposes. Many morphological and physiological parameters were examined.
The supply of spermine (SM) to excised flowers or entire plant efficiently delayed senescence and PCD in petals or leaves respectively. SM caused an increase also of putrescine (PU) and spermidine (SD) levels. Only in senescent plants a new TGase band was immunodetected and, in concomitance, high molecular mass and other protein bands were PA-modified. During senescence mainly mono-, bis-PU and bis-SD catalysis increased. This data suggests that the protective effect of PAs could be mediated by TGase. SM effect on the retention of leaf proteins and chlorophylls was analysed in Valeriana young and senescent plants. Most of chlorophyll is bound to the antennae of light-harvesting complexes (LHC), known preferential thylakoid TGase substrates under light2. In Valeriana LHC enriched fractions, different TGase isoforms, immunologically related to TGases of animal origin, were co-purified. PA conjugation to both photosystems was light-stimulated.
The capacity of plants to express animal TGases and the similarities in the TGase sequences and activity in animals and plants have also been explored. Rat TGase (DP1 ORF) introduced into mature rice embryos by bombardment was expressed by the plant. It is Ca2+-dependent and active in in vitro assay, showing that plants could produce functional mammalian TGases3. Thylakoid TGase recognises animal substrates as well as animal TGases plant substrates, but only the plant TGase/plant substrate catalysis is light regulated2.
As in both the investigated senescence models any TGase has been fully-purified until now, another approach was undertaken. On the basis of the identification of a TGase-like domain in an A. thaliana gene, AtPng1p, we have cloned its codifying sequence on E. coli and purified the over-expressed recombinant protein. All biochemical assays showed a clear Ca++, pH, and DTT dependent TGase activity. This TGase was immunodetected by three antibodies raised against animal TGases. Data and bio-informatic analysis also suggest a possible protease activity for this first plant sequenced TGase4.
1 D Serafini-Fracassini, S Del Duca, F Monti, F Poli, G Sacchetti, AM Bregoli, S Biondi and M Della Mea (2002) -Transglutaminase activity during senescence and programmed cell death in the corolla of tobacco (Nicotian a tabacum) flowers. Cell Death and Diff. 9 (3) 309-321.
2 M. Della Mea, A. Di Sandro, L. Dondini, S. Del Duca, F.Vantini, C.Bergamini, R. Bassi and D. Serafini-Fracassini - A Zea mays 39 kDa thylakoidal transglutaminase catalyses the modification by polyamines of light harvesting complex II in a light-dependent way. Planta, in press. DOI 10.1007/s00425-004-1278-6
Programmed Cell Death Reversal: Polyamines, Effectors of the U-Turn from the Program of Death in Helianthus tuberosus L
No full textThis review describes a 50-year-long research study on the characteristics of Helianthus tuberosus L. tuber dormancy, its natural release and programmed cell death (PCD), as well as on the ability to change the PCD so as to return the tuber to a life program. The experimentation on the tuber over the years is due to its particular properties of being naturally deficient in polyamines (PAs) during dormancy and of immediately reacting to transplants by growing and synthesizing PAs. This review summarizes the research conducted in a unicum body. As in nature, the tuber tissue has to furnish its storage substances to grow vegetative buds, whereby its destiny is PCD. The review's main objective concerns data on PCD, the link with free and conjugated PAs and their capacity to switch the destiny of the tuber from a program of death to one of new life. PCD reversibility is an important biological challenge that is verified here but not reported in other experimental models. Important aspects of PA features are their capacity to change the cell functions from storage to meristematic ones and their involvement in amitosis and differentiation. Other roles reported here have also been confirmed in other plants. PAs exert multiple diverse roles, suggesting that they are not simply growth substances, as also further described in other plants
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