Marisa Antonielli

Multiple forms of barley root acid phosphatase: purification and some characteristics of the major cytoplasmic isoenzyme.

The major acid phosphatase form (orthophosphoric-monoester phosphohydrolase (acid optimum), EC 3.1.3.2) was purified from the soluble extract of barley roots. The enzyme is homogeneous on polyacrylamide gel electrophoresis and moves as a single band of Mr approximately 38,000 in the presence of sodium dodecyl sulphate. The molecular weight of the native enzyme was Mr 77,600 and 79,000 as determined, respectively, by gel filtration on a Sephadex G-100 column and by density gradient ultracentrifugation. The isoelectric point was about 6.28. The enzyme is competitively inhibited by molybdate (Ki = 9 x 10(-7) M). NaF, Ag(+), Hg(2+), Pb(2+) and Zn(2+) are also inhibitors, while other cations showed no effect. The enzyme hydrolyzes a wide variety of natural and synthetic phosphate esters. In particular, the enzyme seems to be active on ATP, o-phosphotyrosine, o-phosphoserine and glucose 1-phosphate. The pH dependence studies between pH 4-8 using p-nitrophenylphosphate as substrate and diethylpyrocarbonate inactivation indicate the presence of essential histidine residue at the active site.

Photoinhibition and oxidative stress : effects on xanthophyll cycle, scavenger enzymes and abscisic acid content in tobacco plants

Summary The effects of short-term ozone pollution at high doses (300 ppb for 30 min) on the xanthophyll cycle under photoinhibitory conditions (1800 μmol m − 2 s − 1) were studied. The experiments were conducted on two different tobacco ( Nicotiana tabacum L.) cultivars, one O 3 -tolerant (Havana) and the other O 3 -sensi-tive (Bel-W3). Given that the phytotoxicity of O 3 is due to the formation of active oxygen species, the plants were also subjected to direct treatment with H 2 O 2 , · O 2 − , · OH and paraquat, a herbicide that, under certain conditions, produces the above-mentioned toxic forms. Our results show that in both cultivars oxidative stress inhibits the function of the xanthophyll cycle with a consequent decrease of anthera-xanthin and zeaxanthin synthesis, particularly during exposure to the superoxide ion and the · OH radical. In addition, we determined the activities of the scavenger enzymes, i.e. ascorbate peroxidase, dehydroas-corbate reductase, glutathione reductase, and glutathione-S-transferase involved in the ascorbate metabolism, the basic substrate for the de-epoxidation reaction of violaxanthin. The quantity of abscisic acid was also determined after ozone exposure. The results showed a greater presence of this hormone in the leaves of the O 3 -treated plants, a simultaneous degradation of violaxanthin was observed, which was not compensated by the transformation into antheraxanthin + zeaxanthin. It is hypothesized that, under photoinhibitory conditions combined with strong oxidative stress, violaxanthin is used in large part not for the xanthophyll cycle reaction but for the synthesis of growth inhibitory substances such as abscisic acid.

Structural properties of the rachis and hypsophyll of the maize ear

Abstract Green tissues of the maize ear (i.e., the rachis and the hypsophyll) have been studied with regard to: (i) the structure of the chlorophyllous parenchyma and (ii) the ultrastructure of the chloroplasts. Both the rachis and the hypsophyll lack Kranz anatomy and contain only one kind of chloroplast. Rachidial chloroplasts appear small with large grana and show abundant starch and periferal reticulum. Hypsophyll chloroplast structure is similar to that to the leaf mesophyll, except for the presence of starch.

Some characteristics of the chlorophyllous parenchyma of maize outside the leaf lamina

Abstract The characteristics of the different chlorophyllous parenchymas of maize examined are: the anatomy, the ultrastructure of the chloroplasts, the pigment contents and their ratios, the CO 2 compensation points of the separate organs, the malate content and some enzymatic activities. The Kranz-anatomy and the chloroplast dimorphism are missing even in the stem, leaf sheath and ligula, as previously observed in the rachis and the hypsophylls. The only type of chloroplast observed contains grana, starch and the peripheral reticulum. The CO 2 compensation point is between 30 and 70 vpm for the stem and the leaf sheaths; for the hypsophylls a CO 2 yield is observed in the early hours of experiment in a closed system, but after this stage the CO 2 concentration falls to a CO 2 compensation point of 110 vpm. Both phosphoenolpyruvate carboxylase (EC 4.1.1.31) and ribulosebisphosphate carboxylase (EC 4.1.1.39) activities are widely present; their ratios vary but are quite high in all the organs examined. NAD-malate dehydrogenase (EC 1.1.1.37) is more active in all the other organs than it is in the leaf lamina, while NADP + -malic enzyme activity is higher in the lamina. The malate content is at its highest both in the leaf sheath and in the hypsophylls. On the basis of these results, the maize chloroplasts situated outside the leaf lamina cannot be identified with the known types.

Physiological characteristics of tobacco cultivars with contrasting sensitivity to ozone

Abstract Two cultivars of tobacco with contrasting sensitivity to ozone have similar photosynthesis at low light intensity, but at high light, photosynthesis of the sensitive cultivar Bel-W3 was lower than that of the resistant cultivar Havana. In contrast, the electron transport rate at photosynthesis saturated light intensity was higher in Bel-W3 than in Havana. This excess may require efficient mechanisms to dissipate energy and oxygen radicals. We found that the non-radiative dissipation was lower in Bel-W3 than in Havana and that the conversion between violaxanthin and anther-axanthin + zeaxanthin was not complete in the ozone sensitive cultivar. Violaxanthin may have been partly converted in ABA. The high content of ABA may have caused stomatal closure and explain why photosynthesis at high light was reduced in Bel-W3 in comparison to Havana. β-Carotene content was also lower in Bel-W3 than in Havana. A low β-carotene content coupled with an inefficient use of the xanthophyll mechanism may contribute to determine the ozone sensitivity of Bel-W3 leaves

High molecular weight acid phosphatase from barley coleoptiles

Abstract The high M , acid phosphatase (EC 3.1.3.2) from barley ( Hordeum vulgare ) coleoptiles was purified 57-fold by ammonium sulphate fractionation, DEAE-cellulose, Con A-Sepharose 4B and gel filtration chromatography. The molecular weight of the native enzyme was 104 000 and 106 000 measured by gel filtration on a Sephadex G-100 column and by density gradient ultracentrifugation, respectively. The enzyme is a heterodymer and consists of two subunits of 79 400 and 26 000 as determined by SDS-PAGE. The apparent K m value with p -nitrophenyl phosphate ( p NPP) as substrate was 0.10 mM. The enzyme activity was unaffected by phosphate acceptors such as glycerol, methanol, ethanol and glucose, but was strongly inhibited by Hg 2+ , Cu 2+ , molybdate ion and NaF. The acid phosphatase from barley coleoptiles hydrolysed a wide variety of phosphate esters and the highest activity was observed with ATP, inorganic pyrophosphate, p NPP and ADP.

Attività Fosfatasica Acida in Rapporto a CCC, Idrazide Maleica e Colchicina

Abstract Acide phosphatase activity in relation to ccc, maleic hydrazide and colchicine — The acid phosphatase at pH 5 were determined on homogenates of roots and seedlings obtained from barley seeds germinated in a solution of CCC, maleic hydrazide, colchicine and water. The acid phosphatase is strongly stimulated from colchicine, CCC and maleic hydrazide, but the minimum time of treatment to obtain the above activation is different. It is discussed if the obtained results can be put in relation to the ATP level required for mitosis and to the auxins properties to intervene on the phosphors transfer.

Carbon Isotope Discrimination, PEP-Carboxylase Activity and Stomatal Resistance in Various Organs of Zea mays L.

In previous researches we had already taken into consideration some structural and metabolic properties of various organs of maize, cv. Asgrow 66, in an attempt to find out how these take part in the productivity of the plant. We found four types of chloroplasts: two already described in the leaf lamina; one with grana and starch in the stem, sheaths and hypsophylls and a very small one in the rachis with all the tylakoids packed in grana. We also found kranz-anatomy to be absent in extralaminar photosynthetic tissues such as leaf sheath hypsophyll and stem (Antonielli, Venanzi 1979). These organs although l3eking kranz-anatomy showed a CO2-fixation pattern typical of a C4 plant (Soldatini et al. 1982).To clarify definitely this point we determined the δ 3C values and the PEP-Carboxylase activity in all aerial organs of a maize plant.