Mario Bellando

Stimulation of oxygen uptake by fusicoccin in conditions of inhibited H+ extrusion

InElodea densa leaves, the fusicoccin-induced increase of H+ extrusion and K+ uptake is associated with an increase of respiration by some 20%, interpreted as depending on a decrease of the ATP/AP ratio. In the absence of K+ as a permeant cation, no effect of fusicoccin on either H+ extrusion or on the ATP/ADP ratio is observed, while the hyperpolarization of the transmembrane electrical potential difference (Em) is maximal, and the increase of QO2 is increased from 20 to about 80%. This effect of fusicoccin on oxygen uptake in condition of inhibited operation of the ATP-dependent H+ pump suggests that the interaction between fusicoccin and its receptor at the plasma membrane can involve other systems besides the proton transporting ATPase.RiassuntoLo stimolo dell’estrusione di H+ (elettrogenica ed ATPasi-dipendente) da parte della fusicoccina (FC) richiede la presenza nel mezzo di K+ o altri cationi permeanti. In assenza di questi, l’effetto della fusicoccina sull’perpolarizzazione del potenziale transmembrana (Em) è amplificato, e il consumo di O2 sale a circa l’80%. Tale effetto della tossina in condizione di blocco della pompa protonica suggerisce che l’interazione tra la fusicoccina e il suo recettore possa coinvolgere a livello della membrana plasmatica anche altri sistemi oltre alla H+ -ATPasi.

The induction of the oxidative burst inElodea densa by sulfhydryl reagents is independent of the inhibiting action of these reagents on photosynthesis

The sulfhydryl group-reagents NEM (N-ethylmaleimide), p-CMBS (parachloromercurybenzenesulfonate), Ag+ and Cu2+ inhibit very rapidly and drastically photosynthetic O2 evolution inElodea densa leaves. This effect has been compared with that of the same reagents in inducing in non illuminated leaves a strong increase of O2 consumption (oxygen burst), presumably due to activation of some plasma membrane redox systems. The results suggest that the structures and mechanisms involved in induction of the oxidative burst on one hand and in the inhibition of photosynthesis on the other are substantially independent.RiassuntoReagenti che modificano i sulfidrili (NEM, p-CMBS, Ag+ e Cu+2) risultano inibire precoeemente e drasticamente la fotosintesi in foglie diElodea densa. Questo effetto è stato confrontato con quello indotto da questi reagenti in foglie non illuminate nell’indurre un forte aumento della respirazione, presumibilmente imputabile all’attivazione di sistemi ossidativi del plasmalemma. I risultati indicano una completa indipendenza nei meccanismi dei due ordini di fenomeni considerati.

Lipophilic properties of some quaternary ammonium ions and dissociation of −Δ H+ from K+ uptake: A tentative correlation

Abstract The capability of some lipophilic quaternary ammonium ions to substitute to a certain extent for the K + in the active (metabolic-dependent) acid extrusion process in fusicoccin-treated pea root segments was correlated, at least in a semi-quantitative way, with their increasing lipophilicity and size. This finding supports the view of an electric coupling between active H + extrusion and monovalent cation (especially K-ion) uptake.

L'azione fitotossica dell'Irpexil (acetidrossamoilacetato di metile) sulle piante superiori. Nota seconda: Variazioni del contenuto di aminoacidi liberi, di carboidrati solubili e di alcuni componenti minerali in plantule di Triticum vulgare

Abstract The phytotoxic action of Irpexil (methyl acethydroxamoil-acetate) on higher plants. Note II. Modification of free aminoacids, soluble carbohydrates and some essential ash components levels in Triticum vulgare seedlings.—The fungal metabolite Irpexil (methyl acethydroxamoilacetate) at moderate concentrations (2–3.10−4M) increase both free aminoacids and soluble carbohydrates levels in wheat seedlings grown in Whites solution. Particularly, asparagine, cystine, glycine and oligosaccharides are increased in the whole plant, sucrose increases more significantly in the roots. The quantities of some essential ash components as P, K, Mg, Mn, Ca and Fe are also significantly affected.

L'azione fitotossica dell'Irpexil (acetidrossamoilacetato di metile) sulle piante superiori. Nota prima: Azione brachizzante ed inibizione mitotica

Abstract The phytotoxic action of Irpexil (Methylacethydroxamoilacetate) on higher plants. 1: action on growth and mitotic inhibition.—The fungal secondary metabolite Irpexil (Methylacethydroxamoilacetate) shows a rather marked inhibiting effect on the growth of mono-and dycotiledons seedlings. Both length and fresh weight of the axial parts are affected, particularly in wheat and pea seedlings. The inhibiting effect is at least partially due to the antimitotic activity of this compound; Irpexil does not seem to interfere at any stage of the mitotic cycle, at least at moderate concentrations (up to 70 ppm).

The alkaline tetraphenylborates: a tool for maintaining a low and controlled K+ activity in the high- affinity K+ uptake process

The use of a suspension of a sparingly soluble K-salt may be useful as a K+-buffering system whenever low K+ concentrations are needed but the volume of medium limits the amount of K+ available for the tissue. In this investigation we propose K tetraphenylborate (K-PhB) as a candidate. The anion tetraphenylborate up to a concentration of 0.35 mol m-3 onElodea densa leaves and maize roots segments does not influence the transmembrane electric potential nor enter the cell in detectable amount, and no aspecific electrolite leakage can be detected. Moreover, it does not affect the rate and percentage of germination of lettuce seeds.RiassuntoL’uso di sospensioni di sali potassici poco solubili può essere utilizzato per creare sistemi tamponanti per il K+ stesso, quando le condizioni operative (volume ridotto del mezzo, basso rapporto tra questo e la quantità di tessuto) limitino il K+ disponibile. In questaNota proponiamo l’uso del tetrafenilborato di K+ o di RB+ , il cui anione, qui usato fino alla concentratione di 0,35 moli m-3 non influenza il potenziale cellulare inElodea densa e segmenti subapicali di radici di mais, non entra in quantità apprezzabile nel tessuto, non provoca da questo erflusso aspecifico di elettroliti e non sembra influenzare la germinabilità dei semi (lattuga).

Irpexil (Methyl-acethydroxamoilacetate)-induced changes in some membrane functions and transmembrane potential in wheat seedling root segments

Abstract A strong K+-dependent, fusicoccin-sensitive increase in acidic extrusion paralleled by a corresponding increase in net K+ uptake and hyperpolarization of transmembrane electrical potential was observed in the root segments of wheat seedlings cultured in diluite CaSO4+0.27 mM Methyl-acethydroxamoilacetate. Moreover, K+-induced depolarization was also increased up to three times.

Su alcuni aspetti biochimici della micorrizia

Abstract Notes on some biochemical aspects of mycorrhizia. – Biochemically speaking, ectomycorrhizia represents a complementary exploitation of metabolic potentialityes. In addition, reciprocal advantages, not necessarily dependent on simbiosis, mai be found in the form of «good neighbour» benefits. The first phase of the relationship (chemotaxis of the micelium and its rapid growth) is the result of a number of factors (slight N and P deficiency) root exudate sugar content, etc.) whose interpretation however, is still debated. It is generally thought that fungus auxins are responsible for the morphologic alterations associated with root infection. In the mycorrhiza the roots are largely or at all dependent on the fungus for inorganic ions; Mycorrhizia assists the plants mineral nutrition and N and K uptake may often be double that observed in axenic control, or three times in the case of phosphate, which is stored in two virtually independent hyphal pools, one (10%) being used for metabolism and the oth...