Oreste Arrigoni

Sulphoglutathione reductase of pea tissues

Abstract An enzyme system catalysing the reaction TPNH + GSSO3H ⇋ GSH + SO3H− + TPN+. has been partially purified from pea tissues. The characteristics of the enzyme have been studied.

In vivoelicitation of ascorbate oxidase activity by dioxygen and its possible role in photosynthesizing leaves

Ascorbate oxidase (AAO, EC 1.10.3.3) is a complex blue copper-protein capable to reduce molecular oxygen to water without generating reactive oxygen intermediates, by using ascorbic acid (AA) as an electron donor. We detected higher AAO activity when O2 concentration was experimentally increasedin vivo, whereas AA concentration did not affect AAO activity. A rise in AAO activity also occurred in illuminated leaf disks. DCMU largely prevented light-dependent stimulation of enzyme activity. AAO activity was absent in the parasitic non-green plantCuscuta reflexa. Taken together, our data strongly suggest that AAO up-regulation induced by O2 and light could have a fundamental role in regulating dioxygen diffusion in leaves performing dioxygenic photosynthesis.RiassuntoL’enzima ascorbico ossidasi (AAO, EC 1.10.3.3) è una complessa proteina contenente rame che catalizza la riduzione dell’ossigeno molecolare ad acqua senza la formazione di intermedi reattivi dell’ossigeno (ROI) utilizzando acido ascorbico (AA) come donatore di equivalenti riducenti. L’attività di AAO viene elicitata dall’aumento sperimentale della concentrazione di ossigenoin vivo. Anche la luce incrementa l’attività di AAO in dischetti di foglia, e l’inibitore del trasporto elettronico fotosintetico DCMU previene largamente la stimolazione dell’attività causata dalla luce. L’attività di AAO era assente nell’angiosperma oloparassita non fotosinteticaCuscuta reflexa. I dati riportati indicano come l’aumento dell’attività di AAO indotto da O2 e dalla luce potrebbe avere un ruolo fondamentale nel regolare la diffusione dell’ossigeno in foglie che svolgono attività fotosintetica.

I Lomasomi: Loro Probabili Rapporti con la Crescita per Distensione della Parete Cellulare

Abstract « Lomasomes »: their probable role in the expansion growth of the cell wall. — It was previously reported that lomasomes are present in higher plant cells. In a preliminary comunication Authors described the morfological characteristics of the lomasomes and their position in the cell. It was shown that lomasomes vary in organization which appears to be granular or vescicular and in distribution along the cell wall. Both these characters seemed directly related with the level of cellular differentiation. In this paper it has been reported that the number of lomasomes per cell was sharply decreased when Avena Coleoptiles were illuminated per 3 hours. During this period of time also the growth of the Coleoptiles was inhibited about 8%. These data seem favorable to the hypothesis that lomasomes are tigtly involved in the mechanisms controlling the expansion growth of the cell wall.

Ascorbic acid and photosynthesis. II. Anaerobic photo-oxidation of ascorbic acid by chloroplast fragments and by whole chloroplasts

Abstract The relatively low ability of whole chloroplasts of photo-oxidize AA in the absence of intermediate electron carriers (such as DPIP or quinones) is greatly increased when the chloroplasts are disrupted either by hypotonic treatment or with digitonin. High values of AA photo-oxidation are observed even in the absence of oxygen, provide that an [H] trapping system ( e.g. TPN, glutathione reductase and oxidized glutathione) is present. However, even whole chloroplasts supplemented with the glutathione trapping system photo-oxidize AA (under aerobic or anaerobic conditions) at rates similar to or higher than those observed for chloroplast fragments. These results are interpreted as indicating that the ultimate electron acceptor in AA photo-oxidation is the oxidizing agent produced in photolysis of water, and that in the illuminated whole chloroplasts, an AA/MDHA system is continuously subjected to two opposite processes, one of oxidation and the other of reduction, both strictly depending on the photolysis of water.

Osservazioni Sulla Morfologia Dei Lomasomi

Abstract Morphological organization of the lomasomes. — From a study on morphological organization of the lomasomes, in Avena coleoptile cells, it has been reported: 1) lomasomes form is quite variable, nevertheless, usually they resemble to a cone having a flattened tip and the base line against the cellular wall. 2) the external border of the lomasoma towards the cytoplasm is represented by the plasma membrane; such external profile results very sinuous and deep invaginations are present. 3) the internal structure is characterized by the presence of an unstructurated matrix containing spherical vescicles, flattened vescicles and tubules all showing an higher density to the electron radiations than the cytoplasmic matrix. Both vescicles and tubules are delimited by a single membrane.

Determinazione “Invivo“ Dell'attività Deidrogenasica Mediante la Tecnica al Tetrazolio

Summary The adaptability of the tetrazolium reaction for the determination of the activity of dehydrogenasic systems «in vivo», in free cells, tissue slices and isolated plant parts has been investigated. In experiments on Helianthus tuber disks it has been found that only for high concentrations (1,5%) of triphenyl tetrazolium chloride (TTC) in the medium, a concentration of the reagent high enough to saturate the reducing systems in the cell penetrates the tissue. At concentrations of TTC higher than 2% the rate of the reaction decreased. The most convenable value of pH for the reaction «in vivo» appeared to be slightly above neutrality. Oxygen was found to compete efficiently with TTC for the hydrogen freed from respiratory substrates by dehydrogenase action. TTC reduction in tuber disks kept in vacuum for the period of the reaction, or put into solutions previously deaereated, was by far more intense than in the controls, kept in not deaereated solutions. These results appeared fully confirmed by othe...

Azione del 2–4 Dinitrofenolo, del Cianuro, Dell'azide e di Alcuni Inibitori Dell'attività Deidrogenasica Sulla Riduzione “In Vivo“ del Cloruro di Trifeniltetrazolio

Summary The effects of some dehydrogenase inhibitors (iodoacetate, fluoride, malonate), of some inhibitors of metal containing-enzymes (diethyldithiocarbamate, azide, cyanide) and of a compound uncoupling oxidations from phosphorylations, (2–4 dinitrophenol), on triphenyltetrazolium chloride (TTC), reduction in disks from Helianthus tubers was investigated. Fluoride and iodacetate, at concentrations resp. 2.5 × 10−2 and 3 × 10−3 M, inhibited of more than 75% the TTC reduction. Malonate at cone. 5 × 10−2 inhibited the TTC reduction of about 33%. Diethyldithiocarbamate, at a conc, clearly active on catecol oxidase (2 × 10−3 M), was practically ineffective on TTC reduction. On the countrary, azide and cyanide at concentrazions 10−2 M and even lower, distinctly inhibited the reaction. The effect of these inhibitors appeared by far more evident in tissues incubated in air then in vacuum. As both compounds are known to inhibit catalase, and thus the breakdown of oxigen peroxide, a strong poison of sulphydryl gr...

Ricerche Sull'ultrastruttura della Parete Cellulare

Abstract A study about the cell wall of AVENA coleoptile epidermis cells. — A new type of lamellae structures embedded in the outer periclinal wall of oat coleoptile epidermis cells has been observed. These structures are present more frequently in the inner non-cutinized portion of the cell wall; their orientation, most often parallel to the cell surface, follows a regular pattern. They are formed by alternate layers of electrontransparent and electron-dense bands. The thickness of these lamellar bodies is about 200–300 A; their length is rather difficult to determinate. They are bounded by a 30–40 A thick membrane; the inner compartment is formed by a central highly manganophilic zone 50–70 A thick where several thin lamellae can be seen and by two lateral zones about 40–50 A in thickness. Embedded in the cutinized portion of the wall some elliptical bodies have also been observed, surroundedd by a single membrane, 20 A in thickness. The interior of these bodies shows thin lamellae enclosed in an electr...

Ricerche Sull'infrastruttura del Coleottile di Avena

Abstract Researches on ultrastructure of Avena coleoptile. 3. The sieve elements. — A study on the ultrastructural organization of the mature sieve elements of Avena coleoptile has been carried out. Data suggest that functional phloem tubes are alive and remain alive until they are working. Judging on morphological basis, the metabolic activity of sieve elements should be of peculiar type and low in comparison to that of the companion cells. In fact the cytoplasm is located in a narrow parietal strand, mitochondria, Golgi apparatus and endoplasmic reticulum are present, but they appear very modified; plastids and nucleus are absent. The cytoplasm is bounded externally by a normal plasmalemma, whilst the vacuole has no visible limits: a tonoplast is, therefore not identifiable. The strands connecting the superimposed sieve elements with one another through the sieve plate result to be made by a double membrane system very similar to the endoplasmic reticulum, which we believe to realize cytoplasmic continu...

Effetto dei Ritardanti di Crescita Sulla Fosforilazione Ossidativa e Sulla Fotofosforilazione Ciclica. II

Abstract Effects of growth retardants on oxidative phosphorylation and on cyclic photophosphorylation. The effects of some growth retardants on energy interconversion mechanisms has been studied. It has been reported that Amo 1618 and CCC greatly inhibit oxidative phosphorylation in isolated pea mitochondria. The inhibition of Pi esterification is higher than the oxygen uptake using succinate; this suggests a weak uncoupling effect. However substituting succinate with malate the inhibition of oxygen consuption approaches that of Pi esterification so that the uncoupling effect is quite dubious. On the other hand Amo 1618 does not stimulate oxygen uptake of mitochondria in « state 4 ». For this reason it is not possible to consider growth retardants definitely uncoupling agents, as Heatherbell et al. suggest, and it will be necessary to clarify this point using more appropriate techniques. It has been reported that Amo 1618 and CCC do not inhibit cyclic photophosphorylation with phenazine or FMN in isolated...