**1. Introduction**

Nanotechnology is an emerging field of natural science dealing with materials of nano (1–100-nm) scale. NASA defined nanotechnology as 'the creation of functional materials,

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

devices and systems through a control of matter on the nanometre scale and exploitation of novel phenomena and properties (physical, chemical, biological) at that length scale' [1]. The different applications of nanotechnology include the designing, characterization, production and application of structures, devices and systems. Nanomaterials (NMs) have unique properties like high surface area and improved optical property. For a chemical or a biological reaction, the rate of reaction depends on the surface area of the reactants, and due to the large surface area, nanomaterial-mediated reactions operate at a high rate. Plant biology is one of the oldest branches of science, aiming the study of different aspects of plants. The combination of plant biology and nanotechnology resulted in nanobionics which employs the nanotechnology for the improvement of plant productivity by improving plant growth, development and photosynthetic efficiency [2]. During the synthesis of materials at nanoscale, different properties of these materials get altered, and these altered properties get translated in various applications. Nanobionics is one of the important applications of nanotechnology which involves the improvement of plant or plant productivity using nanomaterials. The nanomaterial can be prepared by direct and synthetic route followed by milling, grinding, homogenization at high pressure and sonication to reduce its size at nanoscale [3, 4]. With unique physicochemical properties, that is, high surface area, high reactivity, tunable pore size, and particle morphology of nanoparticles, the nanomaterials have a large scope of novel application in the field of biotechnology and agricultural industries [5]. The nanomaterials are of different types:

Nanobiotechnology is an emerging field of bioengineering and has enormous potential to modify or augment the plant function by employing the nanomaterial. With nanobiotechnological advancement, plants (1) are capable of imaging objects in their environment, (2) self-powering themselves as light sources, (3) with infrared communication devices and (4) having self-powered groundwater sensors developed [10]. The solar energy harnessing and biochemical sensing can be improved in plants by introducing nanomaterial in them [11], and nanobionic plants were developed for enhanced photosynthesis and biochemical sensing. Nanobionic plants can detect various chemicals present in the environment and have potential use as a plant-enabled sensor for monitoring environmental changes. The nano-encapsulated nutrients commonly referred to as nanofertilizers release the nutrients on demand basis, and thus these are beneficial for crops to regulate plant growth and enhance the target activity [12, 13]. The engineered carbon nanotubes are shown to boost seed germination, growth and development in plants [14, 15]. Comparatively, very few studies have been conducted on nanoparticles which are beneficial to plants. Nanotechnology has a great potential to develop new tools for the incorporation of nanoparticles into plants to augment

Plant Nanobionics and Its Applications for Developing Plants with Improved Photosynthetic…

http://dx.doi.org/10.5772/intechopen.76815

97

**Figure 1.** Single-walled carbon nanotube (a) and a cross section of single-walled carbon nanotube (b).

The characteristic feature of plant cell is its cellulosic surrounding, that is, cell wall. The plant cell wall behaves as a barrier for superficial ingression of different external agents including nanoparticles into plant cells. Cell wall possesses pores which provide sieving properties to cell walls, and this range from 5 to 20 nm [17]. Nanoparticles or aggregates of nanoparticles with a diameter less than the pore diameter of the cell wall could pass through pores and can reach the plasma membrane [18]. There is additionally a chance for the enlargement of pores or the induction of new cell wall pores upon interaction with engineered nanoparticles which in turn enhance nanoparticle uptake. Further internalization of nanoparticles or aggregates of nanoparticles occurs through endocytosis by forming a cavity-like structure surrounding the nanoparticles by a plasma membrane. Alternatively, they may cross the membrane via carrier proteins or through ion channels. In the cytoplasm, the nanoparticles may bind with different cytoplasmic organelles and interfere with the metabolic processes [19]. In leaf surface applied nanoparticles, the nanoparticles enter through the stomatal apertures or through the bases of trichomes and thereafter get translocated to tissues [20, 21, 22]. The nanoparticles penetrate

the existing functions [16].

**1.1. Entry of nanoparticles in plant cells**

*Natural nanomaterial*—Materials created independently without the involvement of human being. The natural nanomaterials are sea salt, sea spray, soil dust, volcanic dust, sulphates from biogenic gases, and so on.

*Anthropogenic (adventitious) nanomaterial*—Material created as a result of human action. The welding fume and particulates (sulphates and nitrates) resulting from the oxidation of gases [6], and soot resulting from the combustion of fossil fuels are the best example of anthropogenic nanomaterial.

*Engineered nanomaterial*—Nanomaterial designed and manufactured with human interest. The engineered nanomaterials are of organic and inorganic nature.

As the name indicates, the organic nanomaterials consist of carbon atom itself [7] and are polymeric structures with specific nano-characteristics, while inorganic nanomaterials are inorganic by nature. The engineered nanomaterials are of scientific interest because of their huge potential for different applications. The engineered nanomaterials are classified as carbon-based nanomaterials (NMs), metal-based NMs, metal oxides, dendrimers and composites [8]. The nanotubes are linear materials with nanometre size. Carbon nanotubes are long, thin cylinders of carbon molecules having good conductivity of heat, high strength and different electrical properties. The carbon nanotubes (**Figure 1**) are single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs). The double-walled carbon nanotubes are known for higher thermal and chemical stability as compared to single-walled carbon nanotubes [9]. Inorganic nanomaterials are inorganic by nature and consist of metals and metalloid oxides, quantum dots (QD), dendrimers having different kinds of features such as nanofibres, nanowires and nanosheets.

Plant Nanobionics and Its Applications for Developing Plants with Improved Photosynthetic… http://dx.doi.org/10.5772/intechopen.76815 97

**Figure 1.** Single-walled carbon nanotube (a) and a cross section of single-walled carbon nanotube (b).

Nanobiotechnology is an emerging field of bioengineering and has enormous potential to modify or augment the plant function by employing the nanomaterial. With nanobiotechnological advancement, plants (1) are capable of imaging objects in their environment, (2) self-powering themselves as light sources, (3) with infrared communication devices and (4) having self-powered groundwater sensors developed [10]. The solar energy harnessing and biochemical sensing can be improved in plants by introducing nanomaterial in them [11], and nanobionic plants were developed for enhanced photosynthesis and biochemical sensing. Nanobionic plants can detect various chemicals present in the environment and have potential use as a plant-enabled sensor for monitoring environmental changes. The nano-encapsulated nutrients commonly referred to as nanofertilizers release the nutrients on demand basis, and thus these are beneficial for crops to regulate plant growth and enhance the target activity [12, 13]. The engineered carbon nanotubes are shown to boost seed germination, growth and development in plants [14, 15]. Comparatively, very few studies have been conducted on nanoparticles which are beneficial to plants. Nanotechnology has a great potential to develop new tools for the incorporation of nanoparticles into plants to augment the existing functions [16].

#### **1.1. Entry of nanoparticles in plant cells**

devices and systems through a control of matter on the nanometre scale and exploitation of novel phenomena and properties (physical, chemical, biological) at that length scale' [1]. The different applications of nanotechnology include the designing, characterization, production and application of structures, devices and systems. Nanomaterials (NMs) have unique properties like high surface area and improved optical property. For a chemical or a biological reaction, the rate of reaction depends on the surface area of the reactants, and due to the large surface area, nanomaterial-mediated reactions operate at a high rate. Plant biology is one of the oldest branches of science, aiming the study of different aspects of plants. The combination of plant biology and nanotechnology resulted in nanobionics which employs the nanotechnology for the improvement of plant productivity by improving plant growth, development and photosynthetic efficiency [2]. During the synthesis of materials at nanoscale, different properties of these materials get altered, and these altered properties get translated in various applications. Nanobionics is one of the important applications of nanotechnology which involves the improvement of plant or plant productivity using nanomaterials. The nanomaterial can be prepared by direct and synthetic route followed by milling, grinding, homogenization at high pressure and sonication to reduce its size at nanoscale [3, 4]. With unique physicochemical properties, that is, high surface area, high reactivity, tunable pore size, and particle morphology of nanoparticles, the nanomaterials have a large scope of novel application in the field of biotechnology and agricultural industries [5]. The

96 Photosynthesis - From Its Evolution to Future Improvements in Photosynthetic Efficiency Using Nanomaterials

*Natural nanomaterial*—Materials created independently without the involvement of human being. The natural nanomaterials are sea salt, sea spray, soil dust, volcanic dust, sulphates

*Anthropogenic (adventitious) nanomaterial*—Material created as a result of human action. The welding fume and particulates (sulphates and nitrates) resulting from the oxidation of gases [6], and soot resulting from the combustion of fossil fuels are the best example of

*Engineered nanomaterial*—Nanomaterial designed and manufactured with human interest.

As the name indicates, the organic nanomaterials consist of carbon atom itself [7] and are polymeric structures with specific nano-characteristics, while inorganic nanomaterials are inorganic by nature. The engineered nanomaterials are of scientific interest because of their huge potential for different applications. The engineered nanomaterials are classified as carbon-based nanomaterials (NMs), metal-based NMs, metal oxides, dendrimers and composites [8]. The nanotubes are linear materials with nanometre size. Carbon nanotubes are long, thin cylinders of carbon molecules having good conductivity of heat, high strength and different electrical properties. The carbon nanotubes (**Figure 1**) are single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs). The double-walled carbon nanotubes are known for higher thermal and chemical stability as compared to single-walled carbon nanotubes [9]. Inorganic nanomaterials are inorganic by nature and consist of metals and metalloid oxides, quantum dots (QD), dendrimers having different kinds of features such as

The engineered nanomaterials are of organic and inorganic nature.

nanomaterials are of different types:

from biogenic gases, and so on.

anthropogenic nanomaterial.

nanofibres, nanowires and nanosheets.

The characteristic feature of plant cell is its cellulosic surrounding, that is, cell wall. The plant cell wall behaves as a barrier for superficial ingression of different external agents including nanoparticles into plant cells. Cell wall possesses pores which provide sieving properties to cell walls, and this range from 5 to 20 nm [17]. Nanoparticles or aggregates of nanoparticles with a diameter less than the pore diameter of the cell wall could pass through pores and can reach the plasma membrane [18]. There is additionally a chance for the enlargement of pores or the induction of new cell wall pores upon interaction with engineered nanoparticles which in turn enhance nanoparticle uptake. Further internalization of nanoparticles or aggregates of nanoparticles occurs through endocytosis by forming a cavity-like structure surrounding the nanoparticles by a plasma membrane. Alternatively, they may cross the membrane via carrier proteins or through ion channels. In the cytoplasm, the nanoparticles may bind with different cytoplasmic organelles and interfere with the metabolic processes [19]. In leaf surface applied nanoparticles, the nanoparticles enter through the stomatal apertures or through the bases of trichomes and thereafter get translocated to tissues [20, 21, 22]. The nanoparticles penetrate the plant cell wall and enter into the space between plant cell wall and plasma membrane due to small size, capillary action and Van der Waals forces.

are transported into cultured plant cells by endocytosis or internalized in plant root cells via non-endocytic pathways [31, 46]. Silver nanoparticle enters in *Arabidopsis* protoplasts

Plant Nanobionics and Its Applications for Developing Plants with Improved Photosynthetic…

http://dx.doi.org/10.5772/intechopen.76815

99

Different cellular organelles have been reported to uptake the nanomaterials. Serag et al. [48] reported the vacuolar uptake of SWNTs by labelling the SWNTs with fluorescein isothiocyanate (FITC). Following incubation of plant tissues with FITC-labeled SWNTs, fluorescence signals were detected in the cell vacuoles. Further measurement of diffusion coefficient (Deff) supported vacuolar accumulation. To confirm vacuolar uptake, the Deff was measured using fluorescence recovery in a photobleached area (FRAP). The Deff varied according to the size of a macromolecular complex containing fluorescent label. FRAP helped to study the fractions of molecules capable of recovering in the photobleached area and confirmed the accumulation of SW-F inside the vacuoles [48]. Further, the use of probenecid, an inhibitor of carrier-mediated transport, indicated the accumulation of SW-F in

SWNTs transport passively through chloroplast lipid bilayer through kinetic entrapping or by disrupting lipid bilayers [11, 49]. As SWNTs come in contact with the chloroplast's outer envelope, it wraps around the glycerolipid (forming most of the chloroplast's outer envelope). As nanotubes perforated through the envelopes, they are covered with a layer of lipids that irreversibly binds them to the interior side of the chloroplast. The formation of temporary pores has been noticed in the plasma membrane to internalize the nanoparticles like quantum dots and silica nanosphere [49, 50]. Also, the negatively or positively charged nanoparticles spontaneously penetrate lipid envelopes of the extracted

The generational transmission of nanomaterials was studied in rice [52] using a bright field microscopy. Tissue of rice plants at various developmental stages were sampled, washed, sectioned and imaged to track the transmission after 1 week of incubating in 20 mg l−1 C70 solution. Black aggregates were frequently observed in seeds and roots and less frequently in stems and leaves which indicated that the sequence of nanoparticle uptake was from the plant seeds and roots to stems and leaves. The appearance of black aggregates was mostly found in and near vascular system. It was suggested that the transport of C<sup>70</sup> occurred simultaneously with the uptake of water and nutrients in the xylem [52]. Further, to investigate generational transmission of nanomaterials, mature seeds from the control plants and C70-treated plants were germinated and second generation was raised. In second generation, black aggregates were also spotted in the leaf tissues, however, with much less frequency [52]. The results were supported by Fourier transform (FT)-Raman and IR

through mechanosensitive channels [47].

*1.1.2. Uptake of nanomaterial by organelles*

vacuoles.

chloroplasts [51].

**1.2. Generational transmission nanomaterials**

spectra from both first- and second-generation rice plants.

#### *1.1.1. Uptake and distribution of nanomaterials in plant cell*

Improvement in an agronomic attribute of plant system, that is, photosynthetic efficiency with the help of nanomaterial, needs a successful uptake and transfer of nanomaterials in plant cell. The plant cell wall has pores of an average diameter of 5–20 nm. These pores allow the passage of solutes while constraining the diffusion of massive particles and macromolecules including some enzymes [23]. Plants cell employ several strategies to avail nanomaterial (carbon nanotubes) through cell wall and cell membrane depending on the size of the nanomaterial. The entry of nanoparticle in plant cells depends on size and charge [24, 25]. The single-walled carbon nanotubes are of 1–2 nm and are smaller than cell wall pores (5 nm). These nanotubes could be perceived directly through a spontaneous leakage into the apoplast [26]. Thus, for spontaneous leakage, the single-walled carbon nanotubes must be truncated to a commensurable size [27]. The introduction of wide-diameter carbon nanotubes into walled plant cells could also occur through local hydrolysis of the cellulosic cell wall. The cellulose molecules immobilized on the surface of carbon nanotube generate local lesions in the cell wall which facilitate the uptake of carbon nanotubes [28].

The leakage of carbon nanotubes through the cell wall pores has been reported in cells of *Nicotiana tobacum* and *Catharanthus roseus* [29, 30]. The first experimental evidence for the internalization of single-walled carbon nanotubes (SWNTs) has been shown in *N. tobacum* [31]. Temperature-dependent uptake of single-walled carbon nanotubes in *N. tobacum* suggests the internalization of nanotubes through endocytosis [30]. On the other hand, it has been reported that there is no effect of temperature and light on SWNT transfer to lipid bilayer [11]. Multi-walled carbon nanotubes (MWCNTs) could also penetrate the cell membrane of plant protoplasts [30]. When MWCNTs are in close vicinity of protoplast of *C. roseus*, the nanotube aggregations increase the tonicity of cell medium and facilitate the penetration of MWCNTs. Active transport of nanoparticles has also been reported through the lipid bilayer [32].

The metal oxide nanoparticles may be transported through root to leaf or leaf to root in plants [33], and it was studied in hydroponic [34] and soil [35] culture. The negatively charged nanoceria translocates at a higher rate from root to leaf as compared to positively charged nanoceria [36]. The metal oxide nanoparticles are absorbed by root endodermis through apoplastic and symplastic routes, and these are then transported to stem, leaf, fruit and grains [37–39] through a vascular cylinder [40]. Similarly, the mono-dispersed mesoporous silica nanoparticles penetrate into the roots through symplastic/apoplastic pathways and then to the aerial parts of the plants through vascular system [41]. The uptake of metal oxide nanoparticle has been shown by seeds [42], seedlings [38] and mature tubers [43]. The metal oxide nanoparticles may enter through leaf stomata or cuticle and then to stem and root through phloem sap [44, 45]. The single-walled carbon nanotubes and nanosheets are transported into cultured plant cells by endocytosis or internalized in plant root cells via non-endocytic pathways [31, 46]. Silver nanoparticle enters in *Arabidopsis* protoplasts through mechanosensitive channels [47].

## *1.1.2. Uptake of nanomaterial by organelles*

the plant cell wall and enter into the space between plant cell wall and plasma membrane due

98 Photosynthesis - From Its Evolution to Future Improvements in Photosynthetic Efficiency Using Nanomaterials

Improvement in an agronomic attribute of plant system, that is, photosynthetic efficiency with the help of nanomaterial, needs a successful uptake and transfer of nanomaterials in plant cell. The plant cell wall has pores of an average diameter of 5–20 nm. These pores allow the passage of solutes while constraining the diffusion of massive particles and macromolecules including some enzymes [23]. Plants cell employ several strategies to avail nanomaterial (carbon nanotubes) through cell wall and cell membrane depending on the size of the nanomaterial. The entry of nanoparticle in plant cells depends on size and charge [24, 25]. The single-walled carbon nanotubes are of 1–2 nm and are smaller than cell wall pores (5 nm). These nanotubes could be perceived directly through a spontaneous leakage into the apoplast [26]. Thus, for spontaneous leakage, the single-walled carbon nanotubes must be truncated to a commensurable size [27]. The introduction of wide-diameter carbon nanotubes into walled plant cells could also occur through local hydrolysis of the cellulosic cell wall. The cellulose molecules immobilized on the surface of carbon nanotube generate local lesions in the cell wall which facilitate the uptake of

The leakage of carbon nanotubes through the cell wall pores has been reported in cells of *Nicotiana tobacum* and *Catharanthus roseus* [29, 30]. The first experimental evidence for the internalization of single-walled carbon nanotubes (SWNTs) has been shown in *N. tobacum* [31]. Temperature-dependent uptake of single-walled carbon nanotubes in *N. tobacum* suggests the internalization of nanotubes through endocytosis [30]. On the other hand, it has been reported that there is no effect of temperature and light on SWNT transfer to lipid bilayer [11]. Multi-walled carbon nanotubes (MWCNTs) could also penetrate the cell membrane of plant protoplasts [30]. When MWCNTs are in close vicinity of protoplast of *C. roseus*, the nanotube aggregations increase the tonicity of cell medium and facilitate the penetration of MWCNTs. Active transport of nanoparticles has also been reported through the lipid

The metal oxide nanoparticles may be transported through root to leaf or leaf to root in plants [33], and it was studied in hydroponic [34] and soil [35] culture. The negatively charged nanoceria translocates at a higher rate from root to leaf as compared to positively charged nanoceria [36]. The metal oxide nanoparticles are absorbed by root endodermis through apoplastic and symplastic routes, and these are then transported to stem, leaf, fruit and grains [37–39] through a vascular cylinder [40]. Similarly, the mono-dispersed mesoporous silica nanoparticles penetrate into the roots through symplastic/apoplastic pathways and then to the aerial parts of the plants through vascular system [41]. The uptake of metal oxide nanoparticle has been shown by seeds [42], seedlings [38] and mature tubers [43]. The metal oxide nanoparticles may enter through leaf stomata or cuticle and then to stem and root through phloem sap [44, 45]. The single-walled carbon nanotubes and nanosheets

to small size, capillary action and Van der Waals forces.

*1.1.1. Uptake and distribution of nanomaterials in plant cell*

carbon nanotubes [28].

bilayer [32].

Different cellular organelles have been reported to uptake the nanomaterials. Serag et al. [48] reported the vacuolar uptake of SWNTs by labelling the SWNTs with fluorescein isothiocyanate (FITC). Following incubation of plant tissues with FITC-labeled SWNTs, fluorescence signals were detected in the cell vacuoles. Further measurement of diffusion coefficient (Deff) supported vacuolar accumulation. To confirm vacuolar uptake, the Deff was measured using fluorescence recovery in a photobleached area (FRAP). The Deff varied according to the size of a macromolecular complex containing fluorescent label. FRAP helped to study the fractions of molecules capable of recovering in the photobleached area and confirmed the accumulation of SW-F inside the vacuoles [48]. Further, the use of probenecid, an inhibitor of carrier-mediated transport, indicated the accumulation of SW-F in vacuoles.

SWNTs transport passively through chloroplast lipid bilayer through kinetic entrapping or by disrupting lipid bilayers [11, 49]. As SWNTs come in contact with the chloroplast's outer envelope, it wraps around the glycerolipid (forming most of the chloroplast's outer envelope). As nanotubes perforated through the envelopes, they are covered with a layer of lipids that irreversibly binds them to the interior side of the chloroplast. The formation of temporary pores has been noticed in the plasma membrane to internalize the nanoparticles like quantum dots and silica nanosphere [49, 50]. Also, the negatively or positively charged nanoparticles spontaneously penetrate lipid envelopes of the extracted chloroplasts [51].

#### **1.2. Generational transmission nanomaterials**

The generational transmission of nanomaterials was studied in rice [52] using a bright field microscopy. Tissue of rice plants at various developmental stages were sampled, washed, sectioned and imaged to track the transmission after 1 week of incubating in 20 mg l−1 C70 solution. Black aggregates were frequently observed in seeds and roots and less frequently in stems and leaves which indicated that the sequence of nanoparticle uptake was from the plant seeds and roots to stems and leaves. The appearance of black aggregates was mostly found in and near vascular system. It was suggested that the transport of C<sup>70</sup> occurred simultaneously with the uptake of water and nutrients in the xylem [52]. Further, to investigate generational transmission of nanomaterials, mature seeds from the control plants and C70-treated plants were germinated and second generation was raised. In second generation, black aggregates were also spotted in the leaf tissues, however, with much less frequency [52]. The results were supported by Fourier transform (FT)-Raman and IR spectra from both first- and second-generation rice plants.

photosynthetic system strongly increase the rate of production of excited electrons due to the plasmon (metal nanoparticle having an oscillating free electron) enhancement effect. This excited electron can be used for photocurrents or chemical reactions. The association of metal nanoparticle with photosynthetic system has been reported to enhance the efficiency of photosystem. The incorporation of metal nanoparticles with light-absorbing chlorophyll molecules enhances the photon field which is referred as plasmon enhancement effect. Thus, the production of exited electrons has been reported to increase due to plasmon resonance and electronhole separation [60]. In support of this, experimental proofs were generated for the increased rate of the formation of ATP molecules. With hybrid structure, the rate of formation of the excited electron was reported to enhance as compared to photosystem alone [61]. Artificial structures composed of a photosynthetic system and various metal nanoparticles also display strong enhancements of photosynthetic efficiency, and this cause the parallel increases in light absorption by chlorophylls and energy transfer from chlorophylls to nanoparticles [60, 62, 63]. Artificially, the quantum dots (artificial antennae absorbing light efficiently in a wide range of photon energies from solar spectrum) conjugated with a reaction centre complex of *Rhodobactor sphaeroides* purified from natural light-harvesting complexes showed an efficient transfer of excitation energy to reaction centre. The efficient energy transfer from QDs to the bacterial RC clearly offers an opportunity of the utilization of nanocrystals to enhance the photosynthetic biological functioning [59]. A silver nanowire conjugated with light-harvesting complex from the dinoflagellate *Amphidinium carterae* showed strong enhancement in fluorescence intensity of protein-bound chlorophyll molecules [64]. The increase with silver nanowire conjugate was recorded up to an average of 10-fold increase in chlorophyll fluorescence [65], and this

Plant Nanobionics and Its Applications for Developing Plants with Improved Photosynthetic…

http://dx.doi.org/10.5772/intechopen.76815

101

indicates a higher rate of generation of excitations in the chlorophylls [66].

efficiency was reported in Ag nanoparticle-treated Indian mustard [71].

the thylakoid membrane of *A. thaliana* after the application of TiO<sup>2</sup>

TiO<sup>2</sup>

that TiO<sup>2</sup>

Metal nanoparticles have the ability to influence the energy conversion efficiency in photosynthetic systems. The binding to Au and Ag nanoparticles with chlorophyll molecule results in a novel hybrid system, which could produce 10 times more excited electrons due to plasmon resonance and fast electron–hole separation [60]. Electron transfer from excited fluorophore to Au or Ag nanoparticles has been reported [65, 67–69]. The concentration-dependent effects of Au nanoparticles (5–20 nm) on PSII chlorophyll, a fluorescence quenching in soybean leaves, have been observed [70]. Falco et al. [70] observed a shift in fluorescence towards a higher wavelength in Au nanoparticle-treated soybean leaves. An enhanced PSII quantum

Giraldo et al. [11] reported 49% increase in electron transfer rate under *ex vivo* conditions (in extracted chloroplast from baby spinach leaves) after treatment with SWNTs. SWNTs also enhanced the light reaction *in vivo* in leaves of *A. thaliana*. Similarly, carbon nanotubes in spinach thylakoid improved photo-electrochemical activity under illumination [72]. Noji et al. [73] reported that nanomesoporous silica compound (SBA) conjugated with photosystem II (PSII) maintained the high and stable oxygen-evolving ability of PSII in *T. vulcanus*. The applied TiO<sup>2</sup> nanoparticles caused the transfer of charges between light-harvesting complex II (LHCII) and

 NPs because of their photocatalytic properties [74] which induced reduction–oxidation reaction. Ze et al. [75] reported an increased expression of LHCII b and contents of LHCII in

NPs promote the light absorption by chloroplast and regulate the distribution of

nanoparticles. It was found
