Trace metals, peroxidase activity, PAHs contents and ecophysiological changes in Quercus ilex leaves in the urban area of Caserta (Italy).

Trace metals and polycyclic aromatic hydrocarbons, severely affecting human, animal and plants health, highly contribute to the air pollution in urban areas mainly due to car traffic. In this study the air biomonitoring of the city of Caserta (South Italy) has been performed by using Quercus ilex L., a widespread ornamental plant in parks, gardens and avenues. The plant leaves from different sites within the urban area were collected and used to determine the concentrations of V, Cd, Cr, Pb, Ni, Cu, and PAHs as well as the free amino acid content and peroxidase enzyme activity as indices of the leaf physiological conditions. All the tested trace metals showed concentrations higher than the control site. Lead was positively correlated to Cd and Cr and showed, also, a positive trend with Ni and Cu that, in their turn, were highly correlated between them. Positive and significant correlations were evidenced between total PAHs and carcinogenic PAHs and negative correlations between those and all trace metals assayed except V. Cu and Cd contents evidence negative correlations with peroxidase activity, and the free amino acid contents. The PAHs, in particular Carc-PAHs, were negatively correlated to the tested heavy metals. POD was positively correlated only with V and negatively correlated with Cu and Cd.

Sea urchin DNA methyltransferases.

DNA methyltransferase activities have been partially purified from unfertilized eggs and blastula nuclei of sea urchin embryos. Comparative studies, using different DNAs as substrates, show that the two preparations are most active on hemimethylated and single-strand DNA, but they methylate, though at a lower rate, also on double-strand DNA. The two activities show distinctive efficiencies in methylating plasmid DNAs and marked differences in the rate of methyl transfer to DNAs in different structural states: linear, relaxed, or supercoiled. The ratio of the apparent specific activity of the two preparations depends on the particular DNA used as substrate and its structure. Methylation analysis of the restriction fragments of methylated plasmid DNAs shows a linear correlation between introduced methyl groups and the percent of CpG of each particular fragment, indicating that methylation is substantially random and sequence is less relevant than conformation in determining enzyme efficiency. The data do not permit us to decide if the two activities are different enzymes or the same enzyme with different modulating factors.

Depression of nitrate reductase in the presence of excess ammonium in a unicellular alga growing under conditions of phosphate limitation.

Chemostat cultures of the unicellular alga Cyanidium caldarium have shown that under conditions of phosphate limitation nitrate reductase is completely derepressed even in cells growing in a large excess of ammonium, but that it occurs mainly in a catalytically inactive form. It is hypothesized that phosphate limitation contributes to maintaining intracellular level of glutamine suitable to stimulate inactivation but not repression of nitrate reductase. It is not excluded that in addition to variations in the intracellular level of glutamine, there are other metabolic events of the cell by which repression and inactivation of nitrate reductase could be differently influenced.

Active and inactive nitrate reductase. Effects of mild treatment with denaturing agents of protein.

Nitrate reductase (NAD(P)H:nitrate oxidoreductase, EC 1.6.6.2) of the unicellular alga Cyanidium caldarium can exist in two interconvertible forms; one catalytically active and one inactive. The inactive nitrate reductase can be activated by mild treatment with denaturing agents of protein. By treatment with urea or mersalyl, activation of both the NADPH and benzyl viologen activities can be realized under mild conditions, whereas by treatment with heat, the activation of benzyl viologen activity is concomitant with loss of the NADPH activity. On the other hand, both activities are activated and destroyed concomitantly by ethylene glycol. In the present of FAD, either activation of benzyl viologen activity or loss of NADPH activity upon heating occur only at higher temperatures. The existence of a controlling region in the nitrate reductase molecule is postulated.

Studies on utilization of 2-ketoglutarate, glutamate and other amino acids by the unicellular alga Cyanidium caldarium.

Two strains of Cyandium caladarium which possess different biochemical and nutritional characteristics were examined with respect to their ability to utilize amino acids or 2-ketoglutarate as substrates. One strain utilizes alanine, glutamate or aspartate as nitrogen sources, and glutamate, alanine, or 2-ketoglutarate as carbon and energy sources for growth in the dark. The growth rate in the dark on 2-ketoglutarate is almost twice as high or higher than that on glutamate or alanine. During growth or incubation of this alga on amino acids, large amounts of ammonia are formed; however, ammonia formation is strongly inhibited by 2-ketoglutarate. The capacity of the alga and develops fully only when the cells are grown or incubated in the presence of glutamate.