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Yeast cell

The DL of temperature sensitive Saccharomyces Cerevisiae CDC 28-1 was measured in two different conditions: yeast that has been maintained at the restrictive temperature of 38.5 °C for some hours (and for this should be at the same step of the division cycle) and samples that remained always at 23 °C. In both cases DL shows a typical hyperbolic trend but the DL parameters appears to be different according the previous history of the culture. The connection between the DL parameters and some parameters of the culture (thermal treatment, glucose contents of extracellular liquid, density and age of the culture) has been evinced. 

Ionizing radiation 

In the framework of the interaction between the ionizing radiation and the biological systems, the analysis of the ultraweak luminescence could give information about the answer of the living systems to the radiation. The measurement of photoinduced luminescence has been carried on biological samples that has been irradiated by gamma rays, X rays and UV, at doses where it has been possible to measure a change of the biological behaviour of the samples. In collaboration with other researchers from Modena University (I) it has been made the measurement of delayed luminescence from yeast cell irradiated by soft X-rays. The total remitted radiation shows for this experiment a monotonic decrease vs the X-rays dose. The above results have been obtained for relatively high doses and have shown that also in the case of damage induced by ionizing radiation it is possible to discriminate the effects by means of the ultraweak luminescence analysis.

Acetabularia Acetabulum

In order to study the connection between stress condition and DL behaviour, several experiments are performed on the green giant unicellular alga Acetabularia Acetabulum (AA). In particular we studied: 

a) The dependence of the DL emission spectrum on the temperature. These spectra show a very weak dependence on the temperature; it appears that, on decreasing the temperature the spectrum moves towards higher frequencies while a measurable change of the form is not noticed

b) The dependence of the DL dynamics on the wavelength and on the intensity of the source. There is a small but clear change in the slope of the curves dependent on the excitation wavelength. On the other hand there is a strong dependence of the slope on the intensity of illumination: in fact on increasing the intensity of the illumination source the slope of the curves increases up to a saturation value and then the slope begins to decrease while characteristic oscillations appears. Another aspect of the problems connected to the interpretation of the dependence of the dynamics on the intensity of the source is the fact that the same AA sample illuminated with light of the same frequency and with the same times of illumination but with different intensities present decay curves that often cross each other. This fact is incompatible with a simple description of the phenomenon that involves the population and the following depletion of electronic levels

c) The dependence of the DL dynamics on the temperature. As it concerns the dependence of the dynamics on the temperature the existence of two regimes is evident: in the first regime, which is the range of temperature within which the AA could survive, it is possible to bring the AA to the initial conditions again, even if not immediately but following a kind of cycle; instead in the second regime, characterised by excessively high temperatures, the DL emission from the AA decreases in a irreversible way and after some time the sample dies. This decreasing of the DL emission probably is connected to the damages that the extreme temperatures causes on the functional structure of the AA. In fact even if, after a rapid freezing in liquid air, an AA sample is incubated at its normal temperature, the DL emission practically disappears as in the samples submitted to high temperatures

d) The dependence of the DL dynamics on some specific ions. It seems that the presence of Ca++ seems to produce a strong decrement both of the total number of excited levels and of the decay probability. In fact if it is present only Na+ and Ca++ the total number of excited levels go down very speedily (reaching 10% of the initial value in about 1 hour) and the AA appear strongly damaged. The presence of others cations K+ and Mg++ seems to reduce the effect of Ca++. In fact if they are presents together the AA lives a long time and its DL is quite constant. Moreover if only they are present there is no big effect on the behaviour of DL at least in the first hours. This fact is confirmed also if only K+ is present for the first 4 hours. On the contrary the presence of Mg++ produce strong changes of DL. Moreover it is shown clearly that the decreasing of the absolute value of the membrane potential causes a quenching of the DL with a diminution of the total number of excited centres and an increase of the decay probability.

e) Correlation between DL and cellular organization. A microscopic procedure was used to register massive intracellular movements in of Acetabularia cells. Results of "simultaneous" measurements of chloroplast streaming and delayed luminescence of Acetabularia cells showed that when the chloroplasts movement was inhibited by rapid freezing in liquid nitrogen or incubation in chloroform drastic changes in DL occur too. It is known that chloroplast movement is connected to the underling cytoskeleton. In addition the link between DL and cellular organization appeared also evident in an other study where the effect of cations in the extracellular medium on the parameters of DL was compared to morphological changes in Acetabularia cells. Calcium ion influx has indeed been shown to cause rearrangement of the underlying cytoskeleton in Acetabularia. Results suggest the idea that delayed luminescence is related to the integrity of the dynamic chloroplast organization, even if both the relation between chloroplast streaming and DL has not been yet unambiguously determined and the source of such a relation is still not clear.


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