rus
Issue #7/2024
Yu. N. Kulchin, S. O. Kozhanov, E. P. Subbotin, A. S. Kholin, N. I. Subbotina, A. S. Gomolsky, O. O. Slugina
Polarization Ellipticity Change of the Red, Green and Blue Ranges of Laser Radiation Transmitted through the Maize Leaves
Polarization Ellipticity Change of the Red, Green and Blue Ranges of Laser Radiation Transmitted through the Maize Leaves
DOI: 10.22184/1993-7296.FRos.2024.18.7.570.579
Polarization Ellipticity Change of the Red, Green and Blue Ranges of Laser Radiation Transmitted Through the Maize Leaves
Yu. N. Kulchin1, S. O. Kozhanov1, E. P. Subbotin1, A. S. Kholin1, N. I. Subbotina1, A. S. Gomolsky2, O. O. Slugina3
Institute of Automation and Control Processes, Far Eastern Branch of Russian Academy of Sciences (IACP FEB RAS), Vladivostok, Russia
Far Eastern Federal University, Ajax Bay, Russky Island, Vladivostok, Russia
Advanced Engineering School “Institute of Biotechnology, Bioengineering and Food Systems” of the Far Eastern Federal University, Ajax Bay, Russky Island, Vladivostok, Russia
The paper shows that when linearly polarized laser radiation of red (633 nm), green (526 nm), and blue (405 nm) ranges passes through the leaves of maize plants, the ellipticity of polarization changes depending on the angle of rotation of the sample. The largest changes in ellipticity occur when passing blue light, for which the ellipticity index k varies from –16° to 16°. When red and green light passes through the sample, the ellipticity varies from –9° to 10° and –9° to 8°, respectively. It is suggested that these variations are due to the interaction of light with the epidermis layer. The layer cells are ordered and have shape of rectangles with wavy edges, which leads to the refractive index anisotropy and the phase shift between the two orthogonal components of the E vector. The interaction of light with greater ellipticity with chiral photosensitive structures should occur more efficiently, thus, allegedly, this is the plants mechanism to use linearly polarized light.
Keywords: polarization, polarized radiation, polarization ellipticity, plant leaves, maize, monocotyledonous plants
Article received: 19.07.2024
Article accepted: 14.10.2024
Introduction
At present, the effect of such light parameters as the wavelength, intensity, and photoperiod on the plants has been widely studied, while only a small number of researches have been devoted to the influence of polarized light on the plants, although the polarized light is not uncommon in the wild and can be used by the plants, while presumably performing a signaling function. As a rule, the studies that consider this issue are devoted to the effect of circularly polarized light on the plants [1–3] that has a greater ellipticity than the linearly polarized light. Although the effect of linearly polarized light on the plant development was investigated at the beginning of the last century [4], it has almost not been studied since then. It is possible to note the paper [3], where the effect of linearly polarized light on the rapeseed plants was mentioned along with the effect of circularly polarized light. The results of the above-mentioned studies demonstrated the greater influence of radiation with the left or right circular polarization on the individual parameters of plant development or on their entire growth process. Moreover, different parameters can be positively affected by randomly twisted circularly polarized light [2]. The authors of such papers relied on the homochirality concept in nature. Having the property of circular dichroism, the left and right twisted chiral structures of photosensitive leaf cells should absorb light with the left and right circular polarization in various ways that should affect the entire plant development.
In our previous studies of the polarized laser radiation interaction with the plant leaves, we showed that the ellipticity of polarized He-Ne laser radiation passing through the onion epidermis is changed depending on the leaf rotation angle [5]. We have found that such changes also occur when the light is passed through the leaves, the epidermal cells of which (similar to those of onions) have a shape close to the rectangular one and generate a two-dimensional lattice [6, 7]. Such an arrangement of the epidermal layer is usually typical for the monocotyledonous plants.
The transformation of linearly polarized light into the elliptically polarized light can lead to its more efficient absorption by the plant pigments and photoreceptors that should affect the entire plant growth. This may be one of the mechanisms by using which the plants respond to the polarized radiation. In [8], we demonstrated that the maize plants grown under the linearly polarized light are developed similarly to the control group of plants, and in some cases even surpass them in terms of the growth rates.
In the paper [7] we have already described some changes in the light ellipticity that occur when the linearly polarized red light passes through the maize leaves. In this paper we consider the comparative changes in the ellipticity of laser radiation of the red, blue and green spectral ranges that occur when it passes through the maize leaves.
Materials and methods
Optical setup
To study anisotropy of the optical properties of maize leaves, an experimental setup was assembled according to the optical circuit given in Figure 1. The laser radiation (1) passes through a λ/4 wave plate (2) and is expanded by the lens (3) to a beam diameter of 5 mm. Further, the light beam is passed through an attenuator (4) that allows regulating the sample irradiation degree (5). The sample is fixed on a turntable and can rotate in a plane perpendicular to the radiation propagation direction. After that, the light beam is gathered on a polarimeter (PAX5710 Thorlabs, USA) (6) to analyze the radiation polarization condition. To obtain radiation in the red, blue, and green ranges, a helium-neon laser (632.8 nm) and diode-pumped solid-state lasers with the radiation peaks of 526.5 and 445 nm were applied, respectively.
The samples studied were the rectangular fragments of maize leaves with the dimensions of 15 × 15 mm. The size was selected so that the defocused laser beam would not go beyond the sample boundaries during the sample rotation. The leaf sample was placed between two glass plates with the thickness of 0.15 mm. For correct calibration and interpretation of the measurement results, the radiation polarization condition was assessed with and without the plant leaf sample between the glass plates. The measurement results of the light transmission through the glass were taken as the control results. The polarization measurement results were processed using the TXP Series Instrumentation software (Starter, Server Control, TPX Polarimeter), USA.
The main parameter during the polarization state analysis was the ellipticity index k (the ellipticity measurement accuracy was ±0.25°) [9]. When the light is polarized linearly, it is equal to 0°; in the case of right circular polarization, it is equal to 45°, and in the case of left circular polarization – 45°.
Plant material
In the experiment to study the changes in the light polarization state as it passes through the plant leaves, the maize (Zea mays L.), variety “Kuban sweet corn”, was used as the plant material.
The plant samples for research were prepared as follows. The seeds were soaked in the distilled water (for 72 hours) and planted into the plastic pots (W × H, cm: 9 × 10, Sady Primoriya LLC, Ussuriysk, Russian Federation) filled with the multipurpose soil for horticultural crops (N1 : P1 : K1, mg / l: 160–240 : 145–215 : 180–290, organic matter, mg / l: 35, pH 5.5–7, Terra Master LLC, Novosibirsk, Russian Federation). The plants were grown for 21 days in a phytobox under the white LED radiation with the intensity of 200 μmol / s m2 (temperature: 22 ± 2°, humidity: 70 ± 5%). Watering was performed once every three days.
Results and discussion
The dependences of the light ellipticity on the sample rotation angle in the plane perpendicular to the radiation propagation direction during the passage of light with three wavelength ranges (blue (405 nm), green (524 nm) and red (633 nm)) are shown in Fig. 2. The negative values of ellipticity k correspond to the light with left elliptical polarization, in the case of which the intensity vector E is rotated counterclockwise. When the index k is positive, the light has right elliptical polarization and the intensity vector of the electric component of the light wave field E is rotated clockwise.
It is evident on the basis of the graphs that the passage of linearly polarized laser radiation through the maize leaves results in a change in the polarization ellipticity. In this case, the light ellipticity is changed harmonically depending on the sample rotation angle relative to the predominant oscillation direction of the incident light intensity vector that has been already noted in the papers [6, 7] when studying the laser radiation passage within the red range (633 nm) through the phalaris and maize leaves. In this case, when the red light passes, any change in the ellipticity occurs within almost the same limits as when the green light passes. It varies for the red light from –9° to 10°, and for the green light – from –9° to 8°. The blue light polarization ellipticity is changed more significant within the range from –16° to 15°. The changes in the light ellipticity when radiation passes through the glass in the absence of the sample are not indicated on the graphs, since they are small and equal to 0.3–0.5°. We believe that the changes in the radiation ellipticity observed during the laser radiation interaction with the maize leaf are due to its interaction with the epidermal layer of the leaves.
The photo of the epidermis layer cells of the maize leaf under study is shown in Fig. 3. It can be seen that the cells in the epidermis layer are arranged in an orderly manner and have the shape of rectangles with the wavy walls. As it was shown in [5], when the linearly polarized laser radiation passes through the onion epidermis, the light becomes elliptically polarized, and its ellipticity is changed depending on the sample rotation in a plane perpendicular to the radiation propagation direction, as in the paper provided, that is explained by the anisotropy of the refractive index being different for the cytosol and the cell membrane.
Analysis of the results has showed (Fig. 2) that the greatest changes in ellipticity are observed when the angle between the incident light intensity vector and the major axis direction of the epidermal cells is 45°. At this angle, the refractive index anisotropy is maximum. This leads to a significant phase shift between two orthogonal components of the light intensity vector. As a result of the obtained phase shift, the incident linearly polarized light is converted into the elliptically polarized light. In this case, the epidermal layer behaves as a retardation plate that, according to the data in Fig. 2, changes the polarization state of blue light most strongly. Moreover, the layer thickness and the refractive index anisotropy in this layer are insufficient to convert this light into the circularly polarized light. However, according to the experimental results, the ellipticity can reach 16°. This may affect the light absorption by the chiral molecules in maize leaves.
It is also worth noting that a significant portion of the incident radiation is scattered when passing through the leaf that leads to its depolarization. The Degree of Polarization (DOP) parameter is used to assess the light polarization degree. It is assumed that it is equal to 100% for the completely polarized light and 0% for unpolarized light. The parameter is calculated using the following formula:
DOP = ,
where Ipol is the intensity of polarized light, and Iunp is the intensity of unpolarized light.
The table shows the values of the degree of polarization (DOP) of the radiation transmitted through the sample, when the ellipticity index k is maximum (kmax) and equal to zero (k0). The radiation initially incident on the leaf has a DOP value of more than 99%.
It is evident according to the table that the linearly polarized light of the red and green ranges is depolarized to the same extent and the DOP value for the ellipticity equal to k0 is 50%, while indicating that the light remains partially polarized even after interaction with the internal leaf tissues. The blue linearly polarized light is depolarized more significantly, and the DOP parameter has a value of 37% that is apparently due to the lower radiation wavelength and optical properties of the medium. At the rotation angle of the leaf sample, when the ellipticity is maximum (kmax), the linear polarization degree for the red and green light is decreased to almost 40%, and for the blue light – to 26%. When the polarized light passes through the onion epidermis layer, the degree of its polarization remains almost unchanged and is equal to 98–99%. Thus, as a result of light transmission through the maize leaf epidermis, the linearly polarized light is transformed into the elliptical light and remains strongly polarized, after which it interacts with the internal leaf cells and is partially depolarized, especially within the blue spectral range.
In the case of plants, the photosensitive structures such as pigments that use the light energy during the photosynthesis process, and photoreceptors that control the plant development and photomorphogenesis, are responsible for light absorption [10, 11]. The main groups of leaf pigments include the chlorophylls, carotenoids, and flavonoids that generally allow the plants to use light of the entire visible range and mainly light of the red and blue spectral bands. Moreover, the photoreceptors use the light of a wide part of the visible range. The red light photoreceptors are phytochromes, the blue light ones – cryptochromes and phototropins, and the leaves absorb ultraviolet radiation using the UVR 8 protein.
The phototropins in the plants regulate phototropism, chloroplast movement, stomatal opening, and leaf expansion [12]. The cryptochromes affect photoperiodic control of flower formation, inhibition of hypocotyl elongation by the blue light, as well as the light reactions, such as the circadian rhythms, root development, stomatal opening, etc. [13, 14]. The phytochromes are responsible for the functions such as seed germination, shade avoidance, flowering, photoperiodic perception, etc. [14–16].
In [13–15] it has been shown that in the case of ground state of phototropins, the mononucleotide of the LOV2 domain flavin demonstrates negative circular dichroism within the blue region of the absorption spectrum. In this case, LOV2 plays an important role in the regulation of physiological reactions. The chromophore of cryptochromes is an adenine flavin dinucleotide. In the oxidized state it also has negative circular dichroism within the blue spectral range, similar to the LOV2 domain chromophore [15, 16]. The availability of negative circular dichroism of the phytochrome chromophore phyB was noted in the paper [2].
The above-mentioned photosensitive chiral structures of plant photoreceptors directly influence the operation of these photoreceptors that in turn control the key processes in plant development. As it has been shown, the linearly polarized light becomes the elliptically polarized one when passing through the maize leaf. Such radiation should be more efficiently absorbed by the chiral photosensitive structures of leaf cells and ultimately lead to the higher growth rates. Moreover, the blue light that has the greatest ellipticity as a result of transmission through the epidermis layer, should be more effectively absorbed than the red and green light when interacting with the receptors.
It is known that the natural sunlight reaching the Earth is not polarized, but it can become polarized when scattered in a direction perpendicular to the sunbeams. Thus, the polarized light falls from the zenith point of the sky in the morning and evening [17]. While using the mechanism described above, the plants could receive information about any changes in the external light conditions and regulate the development processes in accordance with them.
Understanding of the mechanisms used by the plants to obtain the light polarization information can help in determining the ideal light parameters for plants that will contribute to the development of plant growing technologies in the conditions of artificial lighting.
Conclusion
It has been shown that when the linearly polarized monochromatic radiation with the wavelengths of 633, 526 and 405 nm passes through the maize leaves, the light polarization ellipticity is changed that can be explained by the light interaction with the epidermis layer, the cells of which in the maize leaf are well-ordered and have a shape close to rectangular. Depending on the sample rotation angle in the plane perpendicular to the radiation propagation direction, the ellipticity varies harmonically within the range from –9° to 10° for the red light, from –9° to 8° for the green light, and from –16° to 16° for the blue light, thus acting as a retardation plate.
Funding. The paper has been prepared with the financial support of the Ministry of Education and Science of the Russian Federation (Agreement No. 075-15-2022-1143 dated July 07, 2022).
Authors
Kulchin Yuriy Nikolayevich, Doctor of sciences in physical and mathematical sciences, Academic Supervisor, Institute of Automation and Control Processes, Far Eastern Branch of the Russian Academy of Sciences (IACP FEB RAS), Vladivostok, Russian Federation.
ORCID: 0000-0002-8750-4775
Kozhanov Sergey Olegovich, Junior Researcher, Institute of Automation and Control Processes, Far Eastern Branch of the Russian Academy of Sciences (IACP FEB RAS), Vladivostok, Russian Federation.
ORCID: 0009-0001-2629-3521
Subbotin Evgeny Petrovich, Candidate of physical and mathematical sciences, Leading Researcher, Institute of Automation and Control Processes, Far Eastern Branch of the Russian Academy of Sciences (IACP FEB RAS), Vladivostok, Russian Federation.
ORCID: 0000-0002-8658-3504
Kholin Alexander Sergeevich, Research Fellow,, Institute of Automation and Control Processes, Far Eastern Branch of the Russian Academy of Sciences (IACP FEB RAS), Vladivostok, Russian Federation.
ORCID: https://orcid.org/0000-0002-9751-5136
Subbotina Natalia Ivanovna, Junior Researcher, Institute of Automation and Control Processes, Far Eastern Branch of the Russian Academy of Sciences (IACP FEB RAS), Vladivostok, Russian Federation.
ORCID: 0000-0003-0945-3877
Gomolsky Andrey Sergeevich, Graduate student, Far Eastern Federal University (FEFU), Ajax Bay, Russky Island, Vladivostok, Russian Federation.
ORCID: 0009-0003-5606-9648
Slugina Olga Olegovna, Student, Advanced Engineering School “Institute of Biotechnology, Bioengineering and Food Systems” of the Far Eastern Federal University (AES IBBaFS FEFU), Ajax Bay, Russky Island, Vladivostok, Russian Federation.
ORCID: 0009-0008-0805-4544
Author contributions
The authors contributed equally to this article.
Competing interests
The authors declare that they have no conflicts of interest.
Yu. N. Kulchin1, S. O. Kozhanov1, E. P. Subbotin1, A. S. Kholin1, N. I. Subbotina1, A. S. Gomolsky2, O. O. Slugina3
Institute of Automation and Control Processes, Far Eastern Branch of Russian Academy of Sciences (IACP FEB RAS), Vladivostok, Russia
Far Eastern Federal University, Ajax Bay, Russky Island, Vladivostok, Russia
Advanced Engineering School “Institute of Biotechnology, Bioengineering and Food Systems” of the Far Eastern Federal University, Ajax Bay, Russky Island, Vladivostok, Russia
The paper shows that when linearly polarized laser radiation of red (633 nm), green (526 nm), and blue (405 nm) ranges passes through the leaves of maize plants, the ellipticity of polarization changes depending on the angle of rotation of the sample. The largest changes in ellipticity occur when passing blue light, for which the ellipticity index k varies from –16° to 16°. When red and green light passes through the sample, the ellipticity varies from –9° to 10° and –9° to 8°, respectively. It is suggested that these variations are due to the interaction of light with the epidermis layer. The layer cells are ordered and have shape of rectangles with wavy edges, which leads to the refractive index anisotropy and the phase shift between the two orthogonal components of the E vector. The interaction of light with greater ellipticity with chiral photosensitive structures should occur more efficiently, thus, allegedly, this is the plants mechanism to use linearly polarized light.
Keywords: polarization, polarized radiation, polarization ellipticity, plant leaves, maize, monocotyledonous plants
Article received: 19.07.2024
Article accepted: 14.10.2024
Introduction
At present, the effect of such light parameters as the wavelength, intensity, and photoperiod on the plants has been widely studied, while only a small number of researches have been devoted to the influence of polarized light on the plants, although the polarized light is not uncommon in the wild and can be used by the plants, while presumably performing a signaling function. As a rule, the studies that consider this issue are devoted to the effect of circularly polarized light on the plants [1–3] that has a greater ellipticity than the linearly polarized light. Although the effect of linearly polarized light on the plant development was investigated at the beginning of the last century [4], it has almost not been studied since then. It is possible to note the paper [3], where the effect of linearly polarized light on the rapeseed plants was mentioned along with the effect of circularly polarized light. The results of the above-mentioned studies demonstrated the greater influence of radiation with the left or right circular polarization on the individual parameters of plant development or on their entire growth process. Moreover, different parameters can be positively affected by randomly twisted circularly polarized light [2]. The authors of such papers relied on the homochirality concept in nature. Having the property of circular dichroism, the left and right twisted chiral structures of photosensitive leaf cells should absorb light with the left and right circular polarization in various ways that should affect the entire plant development.
In our previous studies of the polarized laser radiation interaction with the plant leaves, we showed that the ellipticity of polarized He-Ne laser radiation passing through the onion epidermis is changed depending on the leaf rotation angle [5]. We have found that such changes also occur when the light is passed through the leaves, the epidermal cells of which (similar to those of onions) have a shape close to the rectangular one and generate a two-dimensional lattice [6, 7]. Such an arrangement of the epidermal layer is usually typical for the monocotyledonous plants.
The transformation of linearly polarized light into the elliptically polarized light can lead to its more efficient absorption by the plant pigments and photoreceptors that should affect the entire plant growth. This may be one of the mechanisms by using which the plants respond to the polarized radiation. In [8], we demonstrated that the maize plants grown under the linearly polarized light are developed similarly to the control group of plants, and in some cases even surpass them in terms of the growth rates.
In the paper [7] we have already described some changes in the light ellipticity that occur when the linearly polarized red light passes through the maize leaves. In this paper we consider the comparative changes in the ellipticity of laser radiation of the red, blue and green spectral ranges that occur when it passes through the maize leaves.
Materials and methods
Optical setup
To study anisotropy of the optical properties of maize leaves, an experimental setup was assembled according to the optical circuit given in Figure 1. The laser radiation (1) passes through a λ/4 wave plate (2) and is expanded by the lens (3) to a beam diameter of 5 mm. Further, the light beam is passed through an attenuator (4) that allows regulating the sample irradiation degree (5). The sample is fixed on a turntable and can rotate in a plane perpendicular to the radiation propagation direction. After that, the light beam is gathered on a polarimeter (PAX5710 Thorlabs, USA) (6) to analyze the radiation polarization condition. To obtain radiation in the red, blue, and green ranges, a helium-neon laser (632.8 nm) and diode-pumped solid-state lasers with the radiation peaks of 526.5 and 445 nm were applied, respectively.
The samples studied were the rectangular fragments of maize leaves with the dimensions of 15 × 15 mm. The size was selected so that the defocused laser beam would not go beyond the sample boundaries during the sample rotation. The leaf sample was placed between two glass plates with the thickness of 0.15 mm. For correct calibration and interpretation of the measurement results, the radiation polarization condition was assessed with and without the plant leaf sample between the glass plates. The measurement results of the light transmission through the glass were taken as the control results. The polarization measurement results were processed using the TXP Series Instrumentation software (Starter, Server Control, TPX Polarimeter), USA.
The main parameter during the polarization state analysis was the ellipticity index k (the ellipticity measurement accuracy was ±0.25°) [9]. When the light is polarized linearly, it is equal to 0°; in the case of right circular polarization, it is equal to 45°, and in the case of left circular polarization – 45°.
Plant material
In the experiment to study the changes in the light polarization state as it passes through the plant leaves, the maize (Zea mays L.), variety “Kuban sweet corn”, was used as the plant material.
The plant samples for research were prepared as follows. The seeds were soaked in the distilled water (for 72 hours) and planted into the plastic pots (W × H, cm: 9 × 10, Sady Primoriya LLC, Ussuriysk, Russian Federation) filled with the multipurpose soil for horticultural crops (N1 : P1 : K1, mg / l: 160–240 : 145–215 : 180–290, organic matter, mg / l: 35, pH 5.5–7, Terra Master LLC, Novosibirsk, Russian Federation). The plants were grown for 21 days in a phytobox under the white LED radiation with the intensity of 200 μmol / s m2 (temperature: 22 ± 2°, humidity: 70 ± 5%). Watering was performed once every three days.
Results and discussion
The dependences of the light ellipticity on the sample rotation angle in the plane perpendicular to the radiation propagation direction during the passage of light with three wavelength ranges (blue (405 nm), green (524 nm) and red (633 nm)) are shown in Fig. 2. The negative values of ellipticity k correspond to the light with left elliptical polarization, in the case of which the intensity vector E is rotated counterclockwise. When the index k is positive, the light has right elliptical polarization and the intensity vector of the electric component of the light wave field E is rotated clockwise.
It is evident on the basis of the graphs that the passage of linearly polarized laser radiation through the maize leaves results in a change in the polarization ellipticity. In this case, the light ellipticity is changed harmonically depending on the sample rotation angle relative to the predominant oscillation direction of the incident light intensity vector that has been already noted in the papers [6, 7] when studying the laser radiation passage within the red range (633 nm) through the phalaris and maize leaves. In this case, when the red light passes, any change in the ellipticity occurs within almost the same limits as when the green light passes. It varies for the red light from –9° to 10°, and for the green light – from –9° to 8°. The blue light polarization ellipticity is changed more significant within the range from –16° to 15°. The changes in the light ellipticity when radiation passes through the glass in the absence of the sample are not indicated on the graphs, since they are small and equal to 0.3–0.5°. We believe that the changes in the radiation ellipticity observed during the laser radiation interaction with the maize leaf are due to its interaction with the epidermal layer of the leaves.
The photo of the epidermis layer cells of the maize leaf under study is shown in Fig. 3. It can be seen that the cells in the epidermis layer are arranged in an orderly manner and have the shape of rectangles with the wavy walls. As it was shown in [5], when the linearly polarized laser radiation passes through the onion epidermis, the light becomes elliptically polarized, and its ellipticity is changed depending on the sample rotation in a plane perpendicular to the radiation propagation direction, as in the paper provided, that is explained by the anisotropy of the refractive index being different for the cytosol and the cell membrane.
Analysis of the results has showed (Fig. 2) that the greatest changes in ellipticity are observed when the angle between the incident light intensity vector and the major axis direction of the epidermal cells is 45°. At this angle, the refractive index anisotropy is maximum. This leads to a significant phase shift between two orthogonal components of the light intensity vector. As a result of the obtained phase shift, the incident linearly polarized light is converted into the elliptically polarized light. In this case, the epidermal layer behaves as a retardation plate that, according to the data in Fig. 2, changes the polarization state of blue light most strongly. Moreover, the layer thickness and the refractive index anisotropy in this layer are insufficient to convert this light into the circularly polarized light. However, according to the experimental results, the ellipticity can reach 16°. This may affect the light absorption by the chiral molecules in maize leaves.
It is also worth noting that a significant portion of the incident radiation is scattered when passing through the leaf that leads to its depolarization. The Degree of Polarization (DOP) parameter is used to assess the light polarization degree. It is assumed that it is equal to 100% for the completely polarized light and 0% for unpolarized light. The parameter is calculated using the following formula:
DOP = ,
where Ipol is the intensity of polarized light, and Iunp is the intensity of unpolarized light.
The table shows the values of the degree of polarization (DOP) of the radiation transmitted through the sample, when the ellipticity index k is maximum (kmax) and equal to zero (k0). The radiation initially incident on the leaf has a DOP value of more than 99%.
It is evident according to the table that the linearly polarized light of the red and green ranges is depolarized to the same extent and the DOP value for the ellipticity equal to k0 is 50%, while indicating that the light remains partially polarized even after interaction with the internal leaf tissues. The blue linearly polarized light is depolarized more significantly, and the DOP parameter has a value of 37% that is apparently due to the lower radiation wavelength and optical properties of the medium. At the rotation angle of the leaf sample, when the ellipticity is maximum (kmax), the linear polarization degree for the red and green light is decreased to almost 40%, and for the blue light – to 26%. When the polarized light passes through the onion epidermis layer, the degree of its polarization remains almost unchanged and is equal to 98–99%. Thus, as a result of light transmission through the maize leaf epidermis, the linearly polarized light is transformed into the elliptical light and remains strongly polarized, after which it interacts with the internal leaf cells and is partially depolarized, especially within the blue spectral range.
In the case of plants, the photosensitive structures such as pigments that use the light energy during the photosynthesis process, and photoreceptors that control the plant development and photomorphogenesis, are responsible for light absorption [10, 11]. The main groups of leaf pigments include the chlorophylls, carotenoids, and flavonoids that generally allow the plants to use light of the entire visible range and mainly light of the red and blue spectral bands. Moreover, the photoreceptors use the light of a wide part of the visible range. The red light photoreceptors are phytochromes, the blue light ones – cryptochromes and phototropins, and the leaves absorb ultraviolet radiation using the UVR 8 protein.
The phototropins in the plants regulate phototropism, chloroplast movement, stomatal opening, and leaf expansion [12]. The cryptochromes affect photoperiodic control of flower formation, inhibition of hypocotyl elongation by the blue light, as well as the light reactions, such as the circadian rhythms, root development, stomatal opening, etc. [13, 14]. The phytochromes are responsible for the functions such as seed germination, shade avoidance, flowering, photoperiodic perception, etc. [14–16].
In [13–15] it has been shown that in the case of ground state of phototropins, the mononucleotide of the LOV2 domain flavin demonstrates negative circular dichroism within the blue region of the absorption spectrum. In this case, LOV2 plays an important role in the regulation of physiological reactions. The chromophore of cryptochromes is an adenine flavin dinucleotide. In the oxidized state it also has negative circular dichroism within the blue spectral range, similar to the LOV2 domain chromophore [15, 16]. The availability of negative circular dichroism of the phytochrome chromophore phyB was noted in the paper [2].
The above-mentioned photosensitive chiral structures of plant photoreceptors directly influence the operation of these photoreceptors that in turn control the key processes in plant development. As it has been shown, the linearly polarized light becomes the elliptically polarized one when passing through the maize leaf. Such radiation should be more efficiently absorbed by the chiral photosensitive structures of leaf cells and ultimately lead to the higher growth rates. Moreover, the blue light that has the greatest ellipticity as a result of transmission through the epidermis layer, should be more effectively absorbed than the red and green light when interacting with the receptors.
It is known that the natural sunlight reaching the Earth is not polarized, but it can become polarized when scattered in a direction perpendicular to the sunbeams. Thus, the polarized light falls from the zenith point of the sky in the morning and evening [17]. While using the mechanism described above, the plants could receive information about any changes in the external light conditions and regulate the development processes in accordance with them.
Understanding of the mechanisms used by the plants to obtain the light polarization information can help in determining the ideal light parameters for plants that will contribute to the development of plant growing technologies in the conditions of artificial lighting.
Conclusion
It has been shown that when the linearly polarized monochromatic radiation with the wavelengths of 633, 526 and 405 nm passes through the maize leaves, the light polarization ellipticity is changed that can be explained by the light interaction with the epidermis layer, the cells of which in the maize leaf are well-ordered and have a shape close to rectangular. Depending on the sample rotation angle in the plane perpendicular to the radiation propagation direction, the ellipticity varies harmonically within the range from –9° to 10° for the red light, from –9° to 8° for the green light, and from –16° to 16° for the blue light, thus acting as a retardation plate.
Funding. The paper has been prepared with the financial support of the Ministry of Education and Science of the Russian Federation (Agreement No. 075-15-2022-1143 dated July 07, 2022).
Authors
Kulchin Yuriy Nikolayevich, Doctor of sciences in physical and mathematical sciences, Academic Supervisor, Institute of Automation and Control Processes, Far Eastern Branch of the Russian Academy of Sciences (IACP FEB RAS), Vladivostok, Russian Federation.
ORCID: 0000-0002-8750-4775
Kozhanov Sergey Olegovich, Junior Researcher, Institute of Automation and Control Processes, Far Eastern Branch of the Russian Academy of Sciences (IACP FEB RAS), Vladivostok, Russian Federation.
ORCID: 0009-0001-2629-3521
Subbotin Evgeny Petrovich, Candidate of physical and mathematical sciences, Leading Researcher, Institute of Automation and Control Processes, Far Eastern Branch of the Russian Academy of Sciences (IACP FEB RAS), Vladivostok, Russian Federation.
ORCID: 0000-0002-8658-3504
Kholin Alexander Sergeevich, Research Fellow,, Institute of Automation and Control Processes, Far Eastern Branch of the Russian Academy of Sciences (IACP FEB RAS), Vladivostok, Russian Federation.
ORCID: https://orcid.org/0000-0002-9751-5136
Subbotina Natalia Ivanovna, Junior Researcher, Institute of Automation and Control Processes, Far Eastern Branch of the Russian Academy of Sciences (IACP FEB RAS), Vladivostok, Russian Federation.
ORCID: 0000-0003-0945-3877
Gomolsky Andrey Sergeevich, Graduate student, Far Eastern Federal University (FEFU), Ajax Bay, Russky Island, Vladivostok, Russian Federation.
ORCID: 0009-0003-5606-9648
Slugina Olga Olegovna, Student, Advanced Engineering School “Institute of Biotechnology, Bioengineering and Food Systems” of the Far Eastern Federal University (AES IBBaFS FEFU), Ajax Bay, Russky Island, Vladivostok, Russian Federation.
ORCID: 0009-0008-0805-4544
Author contributions
The authors contributed equally to this article.
Competing interests
The authors declare that they have no conflicts of interest.
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