INQUIMAE   12526
INSTITUTO DE QUIMICA, FISICA DE LOS MATERIALES, MEDIOAMBIENTE Y ENERGIA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Photosystems ratio in Schefflera arboricola variegata leaves. Fluorescence spectra and
Autor/es:
GABRIELA B. CORDON Y M. GABRIELA LAGORIO
Lugar:
Cubatao. Brasil
Reunión:
Congreso; IX Encontro Latinoamericano de Fotoquímica e Fotobiologia; 2008
Institución organizadora:
CEPEMA
Resumen:
Abstract
Variegation is the appearance of differently colored areas in the leaves. White or yellow colored zones
are usually connected with a strong decrease of chlorophyll in plastids. In the present work we used
biospectroscopical methodologies to study comparatively the optical properties and fluorescence emission of
green and white leaves of Schefflera arboricola variegata, covering an important shortage in literature on this
field.
Non-destructive optical methods are relevant nowadays due to field applications and remote sensing to
assess plant health. In particular, reflectance, transmittance and emission spectroscopies are useful tools to
develop such methodologies. From reflectance and transmittance spectra, important optical parameters as the
absorption (k) and the scattering coefficient (s) may be obtained. Determination of these parameters is significant
in heterogeneous media like plant tissues, being connected with photons transport and photosynthesis inside the
leaves (1). On the other hand, fluorescence emission is a sensitive tool giving information on plant physiology and
stress situations.
In the present research, reflectance and transmittance spectra were obtained as a function of wavelength
with a spectrophotometer equipped with an integrating sphere. On the other hand, fluorescence emission was
obtained for both intact leaves at 298K and for diluted suspensions of the same powdered leaves at 77K. As
complementary work, photosynthetic pigments were extracted and quantitatively evaluated (3).
The remission function (F(R)), according the Kubelka-Munk theory, relates the absorption coefficient
and the scattering coefficient (F(R) = k/s). Obtained values for F(R) and for k were higher for green leaves than
for white ones. On the contrary, s values were higher for white leaves, but differences were not as high as for k.
Chlorophyll fluorescence spectra is characterized by two emission maxima, one at 685 nm (Fred), due to
photosystem II (PSII) emission and other at 737 nm (Ffar-red) due to both photosystems I (PSI) and II emission.
The fluorescence ratio F685/F737 is related in literature to the plant response to stress situations, to the
photosynthetic activity and to the photosystems ratio (4). However, spectra from intact leaves are normally
distorted by light re-absorption processes and only corrected spectra should be related with the plant physiological
state. For white leaves, the fluorescence ratio (F685/F737) corrected by a physical model (4) was 4.1 while for green
leaves it decreased to 1.79. This result would indicate a lower PSII content in green leaves. To prove this
hypothesis, fluorescence measurements on dilute suspensions of leaves, at 77K, were performed. Under these
conditions, contributions from both photosystems are well separated, belonging Fred to PSII and Ffar-red to PSI.
Values for the fluorescence ratio under these conditions were 0.99 and 0.59 for white and green leavessuspensions
respectively, proving that effectively, white leaves shows higher PSII/PSI ratio.
Chlorophyll a and chlorophyll b contents were higher for green leaves (0.065 and 0.033 mg/cm2Schefflera arboricola variegata, covering an important shortage in literature on this
field.
Non-destructive optical methods are relevant nowadays due to field applications and remote sensing to
assess plant health. In particular, reflectance, transmittance and emission spectroscopies are useful tools to
develop such methodologies. From reflectance and transmittance spectra, important optical parameters as the
absorption (k) and the scattering coefficient (s) may be obtained. Determination of these parameters is significant
in heterogeneous media like plant tissues, being connected with photons transport and photosynthesis inside the
leaves (1). On the other hand, fluorescence emission is a sensitive tool giving information on plant physiology and
stress situations.
In the present research, reflectance and transmittance spectra were obtained as a function of wavelength
with a spectrophotometer equipped with an integrating sphere. On the other hand, fluorescence emission was
obtained for both intact leaves at 298K and for diluted suspensions of the same powdered leaves at 77K. As
complementary work, photosynthetic pigments were extracted and quantitatively evaluated (3).
The remission function (F(R)), according the Kubelka-Munk theory, relates the absorption coefficient
and the scattering coefficient (F(R) = k/s). Obtained values for F(R) and for k were higher for green leaves than
for white ones. On the contrary, s values were higher for white leaves, but differences were not as high as for k.
Chlorophyll fluorescence spectra is characterized by two emission maxima, one at 685 nm (Fred), due to
photosystem II (PSII) emission and other at 737 nm (Ffar-red) due to both photosystems I (PSI) and II emission.
The fluorescence ratio F685/F737 is related in literature to the plant response to stress situations, to the
photosynthetic activity and to the photosystems ratio (4). However, spectra from intact leaves are normally
distorted by light re-absorption processes and only corrected spectra should be related with the plant physiological
state. For white leaves, the fluorescence ratio (F685/F737) corrected by a physical model (4) was 4.1 while for green
leaves it decreased to 1.79. This result would indicate a lower PSII content in green leaves. To prove this
hypothesis, fluorescence measurements on dilute suspensions of leaves, at 77K, were performed. Under these
conditions, contributions from both photosystems are well separated, belonging Fred to PSII and Ffar-red to PSI.
Values for the fluorescence ratio under these conditions were 0.99 and 0.59 for white and green leavessuspensions
respectively, proving that effectively, white leaves shows higher PSII/PSI ratio.
Chlorophyll a and chlorophyll b contents were higher for green leaves (0.065 and 0.033 mg/cm2red), due to
photosystem II (PSII) emission and other at 737 nm (Ffar-red) due to both photosystems I (PSI) and II emission.
The fluorescence ratio F685/F737 is related in literature to the plant response to stress situations, to the
photosynthetic activity and to the photosystems ratio (4). However, spectra from intact leaves are normally
distorted by light re-absorption processes and only corrected spectra should be related with the plant physiological
state. For white leaves, the fluorescence ratio (F685/F737) corrected by a physical model (4) was 4.1 while for green
leaves it decreased to 1.79. This result would indicate a lower PSII content in green leaves. To prove this
hypothesis, fluorescence measurements on dilute suspensions of leaves, at 77K, were performed. Under these
conditions, contributions from both photosystems are well separated, belonging Fred to PSII and Ffar-red to PSI.
Values for the fluorescence ratio under these conditions were 0.99 and 0.59 for white and green leavessuspensions
respectively, proving that effectively, white leaves shows higher PSII/PSI ratio.
Chlorophyll a and chlorophyll b contents were higher for green leaves (0.065 and 0.033 mg/cm2far-red) due to both photosystems I (PSI) and II emission.
The fluorescence ratio F685/F737 is related in literature to the plant response to stress situations, to the
photosynthetic activity and to the photosystems ratio (4). However, spectra from intact leaves are normally
distorted by light re-absorption processes and only corrected spectra should be related with the plant physiological
state. For white leaves, the fluorescence ratio (F685/F737) corrected by a physical model (4) was 4.1 while for green
leaves it decreased to 1.79. This result would indicate a lower PSII content in green leaves. To prove this
hypothesis, fluorescence measurements on dilute suspensions of leaves, at 77K, were performed. Under these
conditions, contributions from both photosystems are well separated, belonging Fred to PSII and Ffar-red to PSI.
Values for the fluorescence ratio under these conditions were 0.99 and 0.59 for white and green leavessuspensions
respectively, proving that effectively, white leaves shows higher PSII/PSI ratio.
Chlorophyll a and chlorophyll b contents were higher for green leaves (0.065 and 0.033 mg/cm2685/F737 is related in literature to the plant response to stress situations, to the
photosynthetic activity and to the photosystems ratio (4). However, spectra from intact leaves are normally
distorted by light re-absorption processes and only corrected spectra should be related with the plant physiological
state. For white leaves, the fluorescence ratio (F685/F737) corrected by a physical model (4) was 4.1 while for green
leaves it decreased to 1.79. This result would indicate a lower PSII content in green leaves. To prove this
hypothesis, fluorescence measurements on dilute suspensions of leaves, at 77K, were performed. Under these
conditions, contributions from both photosystems are well separated, belonging Fred to PSII and Ffar-red to PSI.
Values for the fluorescence ratio under these conditions were 0.99 and 0.59 for white and green leavessuspensions
respectively, proving that effectively, white leaves shows higher PSII/PSI ratio.
Chlorophyll a and chlorophyll b contents were higher for green leaves (0.065 and 0.033 mg/cm2685/F737) corrected by a physical model (4) was 4.1 while for green
leaves it decreased to 1.79. This result would indicate a lower PSII content in green leaves. To prove this
hypothesis, fluorescence measurements on dilute suspensions of leaves, at 77K, were performed. Under these
conditions, contributions from both photosystems are well separated, belonging Fred to PSII and Ffar-red to PSI.
Values for the fluorescence ratio under these conditions were 0.99 and 0.59 for white and green leavessuspensions
respectively, proving that effectively, white leaves shows higher PSII/PSI ratio.
Chlorophyll a and chlorophyll b contents were higher for green leaves (0.065 and 0.033 mg/cm2red to PSII and Ffar-red to PSI.
Values for the fluorescence ratio under these conditions were 0.99 and 0.59 for white and green leavessuspensions
respectively, proving that effectively, white leaves shows higher PSII/PSI ratio.
Chlorophyll a and chlorophyll b contents were higher for green leaves (0.065 and 0.033 mg/cm22
respectively) than for white leaves (0.006 and 0.098 mg/cm2 respectively), as expected. Additionally, the ratio
Chlorophyll-a/b was also higher for green leaves than for white leaves (1.95 and 0.63).
In conclusion, the results show not only that PSII/PSI is higher for white leaves in Schefflera arboricola2 respectively), as expected. Additionally, the ratio
Chlorophyll-a/b was also higher for green leaves than for white leaves (1.95 and 0.63).
In conclusion, the results show not only that PSII/PSI is higher for white leaves in Schefflera arboricolaSchefflera arboricola
plants but also that this fact may be deduced from room temperature fluorescence emission spectra of intact
leaves, when physical models correcting light re-absorption processes are applied.
Bibliography
1) Cordon G. and Lagorio M. G., J. Chem. Educ., 2007, 85, 1167-1170
2) Subhash, N.; Wenzel, O; Lichtenthaler, H. K., Remote Sens. Environ., 1999, 69, 215-223
3) Sims, D. A.; Gamon, J. A., Remote Sens. Environ., 2002, 81, 337-354
4) Cordon G. and Lagorio M. G., Photochem. Photobiol. Sci., 2007, 6, 873-882
5) Pfundel, E., Photosynth. Res., 1998, 56, 185-195J. Chem. Educ., 2007, 85, 1167-1170
2) Subhash, N.; Wenzel, O; Lichtenthaler, H. K., Remote Sens. Environ., 1999, 69, 215-223
3) Sims, D. A.; Gamon, J. A., Remote Sens. Environ., 2002, 81, 337-354
4) Cordon G. and Lagorio M. G., Photochem. Photobiol. Sci., 2007, 6, 873-882
5) Pfundel, E., Photosynth. Res., 1998, 56, 185-195Remote Sens. Environ., 1999, 69, 215-223
3) Sims, D. A.; Gamon, J. A., Remote Sens. Environ., 2002, 81, 337-354
4) Cordon G. and Lagorio M. G., Photochem. Photobiol. Sci., 2007, 6, 873-882
5) Pfundel, E., Photosynth. Res., 1998, 56, 185-195Remote Sens. Environ., 2002, 81, 337-354
4) Cordon G. and Lagorio M. G., Photochem. Photobiol. Sci., 2007, 6, 873-882
5) Pfundel, E., Photosynth. Res., 1998, 56, 185-195Photochem. Photobiol. Sci., 2007, 6, 873-882
5) Pfundel, E., Photosynth. Res., 1998, 56, 185-195Photosynth. Res., 1998, 56, 185-195