Effects of Gold Nanoparticles on the photophysical parameters and photosynthetic capacity of Leaves and Chloroplasts

ROCÍO TORRES; VIRGINIA DIZ; MARÍA GABRIELA LAGORIO

Congreso; XIII ELAFOT 2017; 2017

When light impinges on a leaf, part of it is reflected, another part is transmitted and a third fraction is absorbed by the pigments and transferred to chlorophyll-a. Excess energy of excited chlorophyll-a can initiate the process of photosynthesis, be dissipated as heat or be emitted as fluorescence. As these three processes are competitive, chlorophyll fluorescence analysis gives information on changes in photosynthetic efficiency and heat dissipation [1].Due to the spectroscopic characteristics of the gold nanoparticles (AuNP), which absorb light in the visible, it was hypothesized that they could have a possible action on photosynthesis when interacting with plant material. Thus, in this work the variations of optical and spectroscopic properties of both leaves and isolated chloroplasts were studied in the presence of AuNP synthesized according to Diz (phD thesis) [2].Leaves of Robinia pseudoacacia were immersed in parallel in a AuNP suspension (17 nm in average diameter) and in a control solution. A significant decrease in the ratio of fluorescence maxima (Fred/Ffar-red) [3-4] was observed for the sample with AuNP relative to the control (reduction of 67% and 42% for excitation wavelengths 460nm and 520 nm respectively). Additionally, from pulse amplitude modulated (PAM) experiments, an augmentation in the photosynthetic parameters of leaves adapted to the light was detected: a 20% increase in the maximum photosynthesis yield (Fv/Fm´ ratio) and a 30% increase in the quantum yield of photosystem II (PSII).Regarding studies on isolated chloroplasts of the same plant species, an analogous decrease in the Fred /Ffar-red relationship was observed in the sample with AuNP relative to the control. Measurements of the Hill Reaction showed an increase in the rate of reduction of the 2,6-dichlorophenolindophenol (DCPIP) probe, which is related with the maximum photosynthetic capacity, up to 280% for the sample with AuNP relative to the control (Figure 1). Preliminary studies of the maximum rate of oxygen production also showed that it doubled in samples containing AuNP.Changes in the Fred/Ffar-red ratio are usually associated with stress either in the leaf or in chloroplasts. Nevertheless, in the presence of gold nanoparticles, the increase in the rate of reduction of DCPIP as well as in the rate of evolution of oxygen for chloroplasts and the increase of photosynthetic parameters from PAM measurements for leaves could indicate a striking increase in the photosynthetic capacity of the plant material.[1] Lagorio, M.G., Chlorophyll Fluorescence Emission Spectra in Photosynthetic Organisms, in Chlorophyll: Structure, Production and Medicinal Uses, ed. Nova Science Publishers, Inc., New York, 2011, pp. 115-150. [2] Diz, V. E., Nanopartículas de Oro, in Fotosensibilizadores Nanoconfinados: Caracterización Fotofísica y Fisicoquímica, Tesis Doctoral en Ciencias Químicas de la Facultad de Ciencias Exactas y Naturales de la Universidad de Buenos Aires, 2012, pp.222-281.[3] Gitelson A., Buschmann C., Lichtenthaler H., J. Plant Physiol., 1998, 152, 283.[4] Ramos M. E., Lagorio M. G., Photochem. Photobiol, Sci., 2004, 3, 1063.