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F.Musumeci, A.Scordino, A.Triglia
Instituto di Fisica della Facolta' di Ingegneria - Universita' di Catania
Vle A Doria 6 - 95129 - Catania - Italia
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IIB Home |
 Introduction
Material
and Methods
Experimental
Results and Discussion
Experimental
Results and Discussion (cont.)
Experimental
Results and Discussion (cont.)
Conclusion
References |
Page 4 of 7 |
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In a first phase, the emission spectra of DL and Fluorescence, relative to A.A. samples, have been compared (fig. 5a). It appears evident that the maximum of emission spectrum of the DL is moved to longer wavelength than that of the Fluorescence spectrum; this last coincides with the principal emission peak of the PSII system. A subsequent comparison performed on the corresponding excitation spectra (fig. 5b) show that also these two spectra result to be rather different.
This fact, in addition to the presence of DL in biological system lacking of photosystems, leads to think that the DL is a phenomenon not directly dependent from the behaviour of the photosystems connected to the photosynthesis.
fig. 5 - Spectra of fluorescence (solid
line) and of D.L. (histogram) of a living Acetabularia :
a)emission spectrum for excitation
light wavelength equal to 470 nm
b)excitation spectrum for emission
light wavelength equal to 750 nm
b) The dependence of the dynamics on the wavelength and the intensity of the source
Experiments show that there is a little but clear dependence of the slope of the curves on the excitation wavelength. On the other side there is (fig. 6) 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 becomes to decrease while characteristics oscillations appears.
Fig. 6 - D.L. trend of acetabularia
for different intensity of exciting light at the same light wavelength
(450 nm ) :
(n)
5 1014 phot/s/cm2, (o)
2.5 1014 phot/s/cm2, (+) 1.2 1014 phot/s/cm2,
(*) 6 1013 phot/s/cm2
The behaviour of the parameters I0 and m which characterise the DL (see Fig 7a and 7b referred respectively to an Acetabularia and to a yeast cell sample illuminated with blue light of the same intensity ) on varying the intensity of illumination is fairly general from a qualitative point of view in fact both the parameters values increase on increasing the intensity of illumination, at least for intensity values far from the saturation ones.
fig. 7 - Behaviour of two parameters
of D.L., slope m of eq. 1 (triangle) , and total number of counts
(square) for two biological samples on varying the intensity of impinging
light .
a)Acetabularia sample
b)dried yeast cells.
It is particularly important to understand if a functional relation exists between the parameters of the decay and the characteristics of the source.
Up to now it has not been possible to find such a relation that is valid in all the experimental cases examined. At first approximation it looks as if, far from the saturation, one might depict Io like:
where k1 and k2 depend on the biologic system and have little changes from individual to individual.
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