rus
Issue #6/2024
O. V. Shelepova, E. N. Baranova, K. A. Sudarikov, L. S. Olekhnovich, L. N. Konovalova, V. V. Latushkin, P. A. Vernik, A. A. Gulevich
Evaluation of the Use of LED Lighting in Combination with the Use of γ-PGA SAP Peptide on the Growth and Development of Peppermint Plants in a Closed Biosystem
Evaluation of the Use of LED Lighting in Combination with the Use of γ-PGA SAP Peptide on the Growth and Development of Peppermint Plants in a Closed Biosystem
DOI: 10.22184/1993-7296.FRos.2024.18.6.486.498
The article shows the possibility of regulating the biomass and productivity of Mentha piperita L. when grown in a closed Synergotron system. The results of the influence of modulation of light cultivation parameters and the use of treatments with low concentrations of the peptide due to changes in the intensity of growth and the formation of vegetative mass are presented. It has been established that the closed system makes it possible to identify subtle mechanisms of changes in plants and their morphology and metabolism when using the vegetation indices GLI, EXG, VARI and traditional criteria for assessing productivity, opening up new opportunities in the development of modern approaches in the biotechnology of essential oil plants.
The article shows the possibility of regulating the biomass and productivity of Mentha piperita L. when grown in a closed Synergotron system. The results of the influence of modulation of light cultivation parameters and the use of treatments with low concentrations of the peptide due to changes in the intensity of growth and the formation of vegetative mass are presented. It has been established that the closed system makes it possible to identify subtle mechanisms of changes in plants and their morphology and metabolism when using the vegetation indices GLI, EXG, VARI and traditional criteria for assessing productivity, opening up new opportunities in the development of modern approaches in the biotechnology of essential oil plants.
Evaluation of the Use of LED Lighting in Combination with the Use of γ-PGA SAP Peptide on the Growth and Development of Peppermint Plants in a Closed Biosystem
O. V. Shelepova 1, E. N. Baranova 1, K. A. Sudarikov 2, 3, L. S. Olekhnovich 1, L. N. Konovalova 1, V. V. Latushkin 2, P. A. Vernik 2, A. A. Gulevich 4
Main Botanical Garden of N. V. Tsitsin of the Russian Academy of Sciences, Moscow, Russia.
ANO Institute for Development Strategy, Moscow, Russia.
Timiryazev Moscow Agricultural Academy Russian State Agrarian University, Moscow, Russia.
All-Russian Research Institute of Agricultural Biotechnology, Moscow, Russia.
The article shows the possibility of regulating the biomass and productivity of Mentha piperita L. when grown in a closed Synergotron system. The results of the influence of modulation of light cultivation parameters and the use of treatments with low concentrations of the peptide due to changes in the intensity of growth and the formation of vegetative mass are presented. It has been established that the closed system makes it possible to identify subtle mechanisms of changes in plants and their morphology and metabolism when using the vegetation indices GLI, EXG, VARI and traditional criteria for assessing productivity, opening up new opportunities in the development of modern approaches in the biotechnology of essential oil plants.
Key words: LED lighting, vegetation indices, image processing, Mentha piperita L.
Article received: 09.07.2024
Article accepted: 05.08.2024
INTRODUCTION
Peppermint (English mint, cold mint) (Mentha piperita L.) is a perennial herbaceous plant of the Lamiaceae family, a valuable essential oil and medicinal plant. From the freshly collected above-ground mass, essential oil is obtained, which has a soothing and antispasmodic effect and is used as a refreshing and antiseptic. Menthol is extracted from essential oil, which is an anesthetic and is part of many complex preparations used in the form of oil and alcohol tinctures [1]. In addition, the leaves and inflorescences of peppermint are widely used in the confectionery and alcoholic beverage industries, as well as in the cooking of many nations as a spicy-aromatic and spicy-flavoring plant. The physiologically active substances included in its composition improve the taste of products and enhance their digestibility, have a beneficial effect on metabolism, the activity of the human nervous and cardiovascular systems [2]. The largest producers of peppermint and its processed products are farmers from India, China, Japan, North Korea, the USA, Paraguay, Thailand, Taiwan and Vietnam. India is the leader in essential oil production. The projected growth in the production of mint oil and related products, the demand for which is steadily growing, will be 3–5% per year [3].
To ensure year-round consumption of fresh mint green mass in most regions of the Russian Federation, growing plants in protected soil conditions is optimal. The development of modern agricultural technologies and the use of special equipment makes it possible to control the microclimate in terms of lighting, humidity, supply of nutrient solution and carbon dioxide, proper aeration, etc. [4]. At the same time, lighting remains the most important limiting factor, affecting both the productivity and quality characteristics of cultivated plants. A number of fundamental provisions have been established on the role of the spectrum and intensity of photosynthetically active radiation in the formation of the most important components of the production process [5,6]. The quantity and quality of light irradiation (especially intensity, spectral composition and photoperiod) affect the manifestation of the properties of a particular genotype, the expression of its genes, plant growth and metabolism, and the biosynthesis of secondary metabolites. And these indicators, in interaction with other important parameters of the cultivation environment, determine the physiological state and productivity of plants [1,7].
In the controlled conditions of closed phytotron systems, the imitation of the solar spectrum is carried out through the use of special phytolamps, the spectral composition of which has a maximum photosynthetic effect on plants and promotes the activation of the adaptive potential of plants, regulation of metabolism, which ultimately leads to optimization of the production process. [8]. It should also be noted that light modulation can increase biomass yield and improve the nutritional value of human consumption [9]. The minimum requirement for growing green crops is a mixture of blue (B) and red (R) light with wavelengths of 660 and 450 nm [10]. However, long-term illumination with exclusively red light can lead to “red light syndrome,” which is characterized by decreased photosynthetic activity, low maximum chlorophyll fluorescence quantum yield (Fv/Fm), and impaired carbohydrate accumulation leading to reduced growth [11]. The addition of blue spectrum can effectively prevent such disorders [12]. Thus, the red and blue spectra complement each other, contributing to the formation of highly productive plants. Red light favors vegetative processes, while blue light enhances the synthesis of various phytochemicals such as polyphenols, anthocyanins, vitamin C and other metabolites [13]. Currently, industrial LED phytolamps use blue and red LEDs as the main ones, which are considered the most economically advantageous [14]. However, the opinion of experts on which lighting technologies and light wavelengths are best suited for growing plants has not yet been fully formed. This is likely because photobiology studies examining the effects of different wavelengths of light on plant productivity have produced conflicting results for several decades [15].
It is believed that the most favorable results can be achieved by correcting or expanding the spectral range, using white light and a combination of R (red), B (blue), G (green) and FR (far red) [16]. Thus, the addition of 730 nm FR radiation before harvesting increases the growth rate and content of antioxidants, and the synthesis of other biologically active compounds [17].
Broad spectrum irradiation extending on the green (G) wavelength range is made possible by the use of white LEDs to increase the efficiency of photosynthesis, while UV-A radiation stimulates the production of bioactive molecules and reduces nitrates [18]. White light with complementary red light is a promising light spectrum for enhancing the photosynthetic efficiency of crops, given the key role of red light in plant growth and signaling functions. Thus, growing cabbage plants using white LEDs is more efficient than using standard blue-red LEDs [19]. A study on green onions showed that adding 3 : 1 blue light to white light was more effective than white light alone, while monochromatic blue significantly reduced photosynthetic rate and fenestrated tissue layer [20]. In general, the issue of the optimal spectral composition and types of lighting (white light, full-spectrum lighting, a combination of different types of monochromatic radiation), taking into account the individual characteristics of different crops and varieties, still remains open and requires in-depth study.
Another way to increase productivity is the use of biostimulants. Poly-γ-glutamic acid (γ-PGA) and poly-γ-glutamic acid super absorbent polymer (γ-PGA SAP) are polypeptides produced by microbial fermentation. Previous studies have reported the positive effects of using γ-PGA and γ-PGA SAP on wheat, corn, and spinach plants. Their use increased crop yields and increased plant survival under conditions of abiotic stress [21–23]. However, the use of γ-PGA SAP in essential oil crops remains limited and information on their relative effectiveness is lacking.
The aim of this study was to evaluate the effect of lighting in combination with the additional use of a biostimulant on the pigment composition of mint leaves, productivity and, as a consequence, the yield of essential oil of peppermint plants of the Aromatnoe Naslazhdenie cultivar.
MATERIALS AND METHODS
Plants of Mentha piperita L. cultivar Aromatnoe Naslazhdenie were grown in containers under two types of lighting: white light (W I and W II, respectively, with and without treatment with the γ-PGA SAP peptide) and narrow-band spectral light simulating natural light (F I and F II – with and without treatment with γ-PGA SAP peptide) with daylight hours of 16/8 and temperature conditions of 26/22 °C using the Synergotron ISR11.02.140 module (ISR, Moscow) (fig. 1, 2).
To obtain a graph of the spectral component of the lighting used, the Spectral PAR Meter PG100N was used – A portable meter that measures the range of light sources in several modes, you can create a detailed spectrum test report that will help optimize the plant growth environment through effective lighting control. With its help, the PFD, PFD and IRR indices were obtained.
During the tests of the lamp, we identified the main characteristics of the consecration affecting photosynthesis.
PPFD (Photosynthetic Photon Flux Density) measures the number of photons per second incident per square meter of surface area. It is crucial to determine the intensity of light available for photosynthesis. It is expressed in µmol/m2s.
PFD (Photosynthetic Flux Density) –measurements of the spectrum that covers PPFD and other wavelengths of light. This is important for assessing the overall illumination affecting plant growth. It is expressed in µmol/m2s.
IRR (Infrared radiation of wavelengths from 760 nm to 1 mm) refers to that part of the electromagnetic spectrum that plants do not use for photosynthesis, but which can indirectly affect plant health and growth, for example, by influencing temperature regulation. High ambient temperature, humidity and low air circulation levels can, in combination with radiant heat, cause thermal stress, potentially leading to thermal damage.
The PFD irradiation intensity for all spectral lines in the experiment and control was 955.1 in the control, and 905.5 µmol/m2s in the experiment (Table 1). The photosynthetic part of the PPFD spectrum was 765.3 and 824.5 µmol/m2s, respectively. The intensity for individual spectra is presented in Table 1.
Plants were grown in containers by five plants for each regime (W I and W II; F I and F II) and the same feeding and watering regimes were maintained throughout the experiment. Half of the mint plants at the vegetative stage using foliar spraying were treated twice (the interval between treatments was 10 days) with a solution of the γ-PGA SAP peptide at a concentration of 10–4 M. Plants were grown under controlled conditions until flowering. On the 10th day after the second treatment (1st period) and before harvesting (2nd period), the spectral characteristics of mint plants were determined.
The phenotypic characteristics of peppermint were used to determine the calculated quantitative indicators for the color of aerial organs. Intravital determination of the spectral characteristics of the aboveground organs of peppermint was carried out immediately after removal from the closed system. Three randomly selected containers containing one plant of each variant were used for evaluation. To calculate visual indices, we used the average values obtained by scanning plants based on the analysis of RGB images. To obtain images, we used the Synergotron ISR02-01 Phenoscanner (ISR, Moscow, Russia). To assess the condition of plants, indices were calculated based on those proposed earlier. To calculate condition indices, average RGB indicators were used: VARI – algorithms for remote estimation of the vegetation proportion [24]; EXG – color indicators of lighting conditions for plant identification [25]; and GLI – documenting the impact of grazing [26]. The indicated GLI, EXG and VARI indices were calculated based on the average values obtained when scanning plants based on the analysis of RGB images [27,28]. To obtain images, we used the Synergotron ISR02–01 Phenoscanner (ISR, Moscow, Russia). At the same time, a biometric analysis of glandular trichomes on mint leaves was carried out on live preparations using a Keyence VHX‑1000E digital microscope (Itasca, IL, USA). The productivity and yield of essential oil of mint plants were estimated according to a modified method [29].
When statistically processing the experimental results, Microsoft Excel and Past V 3.0 programs were used. The mean value of the indicators (M), standard errors of the mean (± SEM) and confidence interval at the 95% confidence level were determined. Differences between options were significant at P≤0.05.
RESULTS
Peppermint plants F I and W I of the original (control) lines did not have statistically significant differences in the size and habit of the aerial parts. However, W I and W II plants had slightly longer internodes and greener foliage compared to F I plants and under identical growing conditions (fig. 3). Twice foliar spraying of mint plants of both F II and W II lines with the γ-PGA SAP peptide led to some visible changes: the size of the plants increased compared to the control lines W I and F I, but this growth was not statistically significant. The most noticeable differences were changes in leaf blade color, as shown in the RGB color indices in each image.
A comparative assessment of the performance of control plants and plants treated with γ-PGA SAP peptide grown under two types of lighting, carried out using the calculation of three vegetation indices, makes it possible to reliably identify changes in the state of plants after exposure to treatment with the peptide (fig. 4). All three indicators showed significant differences between the condition of plants grown under white light and narrow-band spectrum light. Treatment of plants grown under illumination with narrow-band spectral light with γ-PGA SAP peptide improved the photochemical parameters of plants; the increase in GLI, EXG and VARI indices by the time of harvesting mint plants ranged from 57 to 71%. While in plants grown under white light, by the time of harvest, the treatment of plants with γ-PGA SAP peptide was practically leveled out, the indicators of the vegetation indices GLI and VARI remained at the original level. And only the EXG index increased by 11.5%.
The date analysis shows that the GLI and EXG indices make it possible to reliably distinguish the state of control plants and plants treated with γ-PGA SAP peptide for all parameters studied. And the VARI index is less effective for distinguishing between control and experimental plants.
If we compare changes in the spectral characteristics of plants grown under two types of lighting, as well as after treatment with γ-PGA SAP peptide, the blue spectrum turned out to be the most stable indicator, which remained virtually unchanged in all four experimental options. Intensity indicators in the red spectrum decreased in plants treated with γ-PGA SAP peptide in both W II and F II plants, and the decrease in plants grown under narrow-spectrum light was significantly greater. Control plants grown under both white spectrum and narrowband spectral light showed a higher sensitivity of color intensity in the green range, which decreased after treatment with γ-PGA SAP peptide, while the level of green color intensity of the F II variant became comparable to that of plants of variant W II. That is, mint plants treated with γ-PGA SAP peptide maintained the integrity of the photosystem structures, which contributed to the normal occurrence of biochemical processes in plants.
Essential oil is generated and stored in secretory glands in all organs of the aerial parts of mint plants (stems, leaves, calyx, corolla). Moreover, their maximum number is located on flowers, leaves of the middle and upper tiers, the minimum number is on plant stems. With the growth and increase in the size of leaves and flowers, more and more new glands are formed, and the development of the glands is a fairly rapid process. Glands of slightly smaller sizes were formed on mint leaves than on the corolla of mint flowers (Table 2). Moreover, on the abaxial side of the leaf in the control plants of the F I variant, the diameter of the glands was larger than in the W I plants. Treatment of both variants with the γ-PGA SAP peptide from the mint plant leveled out this discrepancy – the diameter of the glands was generally similar.
The density of glands on the leaves of the upper tier of plants, both in the 1st period and in the 2nd period of sampling, of samples grown under narrow-band spectral light was significantly higher than in plants grown under white light. The maximum density of secretory glands with their large sizes, recorded in plants of the FI and FII variants, determined a higher yield of essential oil in mint samples ‒1.1 times compared to plants WI and WII. Treatment of mint plants with γ-PGA SAP peptide in both variants led to an increase in yield (by 9.4% in the FII variant and 7.0% in the WII variant), and an increase in the yield of essential oil by 11.6 and 11.0%, respectively.
CONCLUSIONS
According to data obtained, the use of closed biological systems makes it possible to optimize studies of the effects of optical radiation in combination with the use of biochemical preparations on the process of growing essential oil plants. Illumination of mint plants with narrow-band full-spectrum light allowed the formation of essential oil glands of larger diameter and higher density on the leaves of the upper tier, which ensured an increase in the yield of essential oil. Treatment of mint plants with γ-PGA SAP peptide also increased yield and contributed to increased plant productivity.
ACKNOWLEDGMENTS
Work on this article was carried out within the framework of the state assignment of the GBS RAS (No. 122042700002-6) (“Biological diversity of natural and cultural flora: fundamental and applied issues of study and conservation”) and ARRIAB (No. 0431-2022-0003). The results of the work were obtained using Modules Synergotron ISR11.02.140 (ANO “Institute of Development Strategy”).
AUTHORS
O. V. Shelepova, Candidate of Biological Sciences, Leading Researcher, N. V. Tsitsin Main Botanical Garden of the Russian Academy of Sciences, Moscow, Russia.
ORCID: 0000-0003-2011-6054
E. N. Baranova, Candidate of Biological Sciences, Leading Researcher, N. V. Tsitsin Main Botanical Garden of the Russian Academy of Sciences, Moscow, Russia.
ORCID: 0000-0001-8169-9228.
K. A. Sudarikov, Research Engineer, ANO Institute of Development Strategy, Moscow, Russia.
ORCID: 0009-0005-8734-1223
L. S. Olekhnovich, Candidate of Biological Sciences, Researcher, N. V. Tsitsin Main Botanical Garden of the Russian Academy of Sciences, Moscow, Russia.
L. N. Konovalova, Researcher, N. V. Tsitsin Main Botanical Garden of the Russian Academy of Sciences, Moscow, Russia.
V. V. Latushkin, Candidate of Biological Sciences, Researcher, ANO Institute of Development Strategy, Moscow, Russia.
ORCID: 0000-0003-1406-8965
P. A. Vernik, Leading Researcher, ANO Institute of Development Strategy, Moscow, Russia.
ORCID: 0000-0001-5850-7654
A. A. Gulevich, Candidate of Biological Sciences, Leading Researcher, All-Russian Scientific Research Institute of Agricultural Biotechnology, Moscow, Russia.
ORCID: 0000-0003-4399-2903
CONFLICT OF INTEREST
The authors state that they have no conflict of interest. All the authors took part in writing the article and supplemented the manuscript in part of their work.
CONTRIBUTION OF THE MEMBERS
OF THE AUTHOR’S TEAM
The article is based on the work of all members of the author’s team.
O. V. Shelepova 1, E. N. Baranova 1, K. A. Sudarikov 2, 3, L. S. Olekhnovich 1, L. N. Konovalova 1, V. V. Latushkin 2, P. A. Vernik 2, A. A. Gulevich 4
Main Botanical Garden of N. V. Tsitsin of the Russian Academy of Sciences, Moscow, Russia.
ANO Institute for Development Strategy, Moscow, Russia.
Timiryazev Moscow Agricultural Academy Russian State Agrarian University, Moscow, Russia.
All-Russian Research Institute of Agricultural Biotechnology, Moscow, Russia.
The article shows the possibility of regulating the biomass and productivity of Mentha piperita L. when grown in a closed Synergotron system. The results of the influence of modulation of light cultivation parameters and the use of treatments with low concentrations of the peptide due to changes in the intensity of growth and the formation of vegetative mass are presented. It has been established that the closed system makes it possible to identify subtle mechanisms of changes in plants and their morphology and metabolism when using the vegetation indices GLI, EXG, VARI and traditional criteria for assessing productivity, opening up new opportunities in the development of modern approaches in the biotechnology of essential oil plants.
Key words: LED lighting, vegetation indices, image processing, Mentha piperita L.
Article received: 09.07.2024
Article accepted: 05.08.2024
INTRODUCTION
Peppermint (English mint, cold mint) (Mentha piperita L.) is a perennial herbaceous plant of the Lamiaceae family, a valuable essential oil and medicinal plant. From the freshly collected above-ground mass, essential oil is obtained, which has a soothing and antispasmodic effect and is used as a refreshing and antiseptic. Menthol is extracted from essential oil, which is an anesthetic and is part of many complex preparations used in the form of oil and alcohol tinctures [1]. In addition, the leaves and inflorescences of peppermint are widely used in the confectionery and alcoholic beverage industries, as well as in the cooking of many nations as a spicy-aromatic and spicy-flavoring plant. The physiologically active substances included in its composition improve the taste of products and enhance their digestibility, have a beneficial effect on metabolism, the activity of the human nervous and cardiovascular systems [2]. The largest producers of peppermint and its processed products are farmers from India, China, Japan, North Korea, the USA, Paraguay, Thailand, Taiwan and Vietnam. India is the leader in essential oil production. The projected growth in the production of mint oil and related products, the demand for which is steadily growing, will be 3–5% per year [3].
To ensure year-round consumption of fresh mint green mass in most regions of the Russian Federation, growing plants in protected soil conditions is optimal. The development of modern agricultural technologies and the use of special equipment makes it possible to control the microclimate in terms of lighting, humidity, supply of nutrient solution and carbon dioxide, proper aeration, etc. [4]. At the same time, lighting remains the most important limiting factor, affecting both the productivity and quality characteristics of cultivated plants. A number of fundamental provisions have been established on the role of the spectrum and intensity of photosynthetically active radiation in the formation of the most important components of the production process [5,6]. The quantity and quality of light irradiation (especially intensity, spectral composition and photoperiod) affect the manifestation of the properties of a particular genotype, the expression of its genes, plant growth and metabolism, and the biosynthesis of secondary metabolites. And these indicators, in interaction with other important parameters of the cultivation environment, determine the physiological state and productivity of plants [1,7].
In the controlled conditions of closed phytotron systems, the imitation of the solar spectrum is carried out through the use of special phytolamps, the spectral composition of which has a maximum photosynthetic effect on plants and promotes the activation of the adaptive potential of plants, regulation of metabolism, which ultimately leads to optimization of the production process. [8]. It should also be noted that light modulation can increase biomass yield and improve the nutritional value of human consumption [9]. The minimum requirement for growing green crops is a mixture of blue (B) and red (R) light with wavelengths of 660 and 450 nm [10]. However, long-term illumination with exclusively red light can lead to “red light syndrome,” which is characterized by decreased photosynthetic activity, low maximum chlorophyll fluorescence quantum yield (Fv/Fm), and impaired carbohydrate accumulation leading to reduced growth [11]. The addition of blue spectrum can effectively prevent such disorders [12]. Thus, the red and blue spectra complement each other, contributing to the formation of highly productive plants. Red light favors vegetative processes, while blue light enhances the synthesis of various phytochemicals such as polyphenols, anthocyanins, vitamin C and other metabolites [13]. Currently, industrial LED phytolamps use blue and red LEDs as the main ones, which are considered the most economically advantageous [14]. However, the opinion of experts on which lighting technologies and light wavelengths are best suited for growing plants has not yet been fully formed. This is likely because photobiology studies examining the effects of different wavelengths of light on plant productivity have produced conflicting results for several decades [15].
It is believed that the most favorable results can be achieved by correcting or expanding the spectral range, using white light and a combination of R (red), B (blue), G (green) and FR (far red) [16]. Thus, the addition of 730 nm FR radiation before harvesting increases the growth rate and content of antioxidants, and the synthesis of other biologically active compounds [17].
Broad spectrum irradiation extending on the green (G) wavelength range is made possible by the use of white LEDs to increase the efficiency of photosynthesis, while UV-A radiation stimulates the production of bioactive molecules and reduces nitrates [18]. White light with complementary red light is a promising light spectrum for enhancing the photosynthetic efficiency of crops, given the key role of red light in plant growth and signaling functions. Thus, growing cabbage plants using white LEDs is more efficient than using standard blue-red LEDs [19]. A study on green onions showed that adding 3 : 1 blue light to white light was more effective than white light alone, while monochromatic blue significantly reduced photosynthetic rate and fenestrated tissue layer [20]. In general, the issue of the optimal spectral composition and types of lighting (white light, full-spectrum lighting, a combination of different types of monochromatic radiation), taking into account the individual characteristics of different crops and varieties, still remains open and requires in-depth study.
Another way to increase productivity is the use of biostimulants. Poly-γ-glutamic acid (γ-PGA) and poly-γ-glutamic acid super absorbent polymer (γ-PGA SAP) are polypeptides produced by microbial fermentation. Previous studies have reported the positive effects of using γ-PGA and γ-PGA SAP on wheat, corn, and spinach plants. Their use increased crop yields and increased plant survival under conditions of abiotic stress [21–23]. However, the use of γ-PGA SAP in essential oil crops remains limited and information on their relative effectiveness is lacking.
The aim of this study was to evaluate the effect of lighting in combination with the additional use of a biostimulant on the pigment composition of mint leaves, productivity and, as a consequence, the yield of essential oil of peppermint plants of the Aromatnoe Naslazhdenie cultivar.
MATERIALS AND METHODS
Plants of Mentha piperita L. cultivar Aromatnoe Naslazhdenie were grown in containers under two types of lighting: white light (W I and W II, respectively, with and without treatment with the γ-PGA SAP peptide) and narrow-band spectral light simulating natural light (F I and F II – with and without treatment with γ-PGA SAP peptide) with daylight hours of 16/8 and temperature conditions of 26/22 °C using the Synergotron ISR11.02.140 module (ISR, Moscow) (fig. 1, 2).
To obtain a graph of the spectral component of the lighting used, the Spectral PAR Meter PG100N was used – A portable meter that measures the range of light sources in several modes, you can create a detailed spectrum test report that will help optimize the plant growth environment through effective lighting control. With its help, the PFD, PFD and IRR indices were obtained.
During the tests of the lamp, we identified the main characteristics of the consecration affecting photosynthesis.
PPFD (Photosynthetic Photon Flux Density) measures the number of photons per second incident per square meter of surface area. It is crucial to determine the intensity of light available for photosynthesis. It is expressed in µmol/m2s.
PFD (Photosynthetic Flux Density) –measurements of the spectrum that covers PPFD and other wavelengths of light. This is important for assessing the overall illumination affecting plant growth. It is expressed in µmol/m2s.
IRR (Infrared radiation of wavelengths from 760 nm to 1 mm) refers to that part of the electromagnetic spectrum that plants do not use for photosynthesis, but which can indirectly affect plant health and growth, for example, by influencing temperature regulation. High ambient temperature, humidity and low air circulation levels can, in combination with radiant heat, cause thermal stress, potentially leading to thermal damage.
The PFD irradiation intensity for all spectral lines in the experiment and control was 955.1 in the control, and 905.5 µmol/m2s in the experiment (Table 1). The photosynthetic part of the PPFD spectrum was 765.3 and 824.5 µmol/m2s, respectively. The intensity for individual spectra is presented in Table 1.
Plants were grown in containers by five plants for each regime (W I and W II; F I and F II) and the same feeding and watering regimes were maintained throughout the experiment. Half of the mint plants at the vegetative stage using foliar spraying were treated twice (the interval between treatments was 10 days) with a solution of the γ-PGA SAP peptide at a concentration of 10–4 M. Plants were grown under controlled conditions until flowering. On the 10th day after the second treatment (1st period) and before harvesting (2nd period), the spectral characteristics of mint plants were determined.
The phenotypic characteristics of peppermint were used to determine the calculated quantitative indicators for the color of aerial organs. Intravital determination of the spectral characteristics of the aboveground organs of peppermint was carried out immediately after removal from the closed system. Three randomly selected containers containing one plant of each variant were used for evaluation. To calculate visual indices, we used the average values obtained by scanning plants based on the analysis of RGB images. To obtain images, we used the Synergotron ISR02-01 Phenoscanner (ISR, Moscow, Russia). To assess the condition of plants, indices were calculated based on those proposed earlier. To calculate condition indices, average RGB indicators were used: VARI – algorithms for remote estimation of the vegetation proportion [24]; EXG – color indicators of lighting conditions for plant identification [25]; and GLI – documenting the impact of grazing [26]. The indicated GLI, EXG and VARI indices were calculated based on the average values obtained when scanning plants based on the analysis of RGB images [27,28]. To obtain images, we used the Synergotron ISR02–01 Phenoscanner (ISR, Moscow, Russia). At the same time, a biometric analysis of glandular trichomes on mint leaves was carried out on live preparations using a Keyence VHX‑1000E digital microscope (Itasca, IL, USA). The productivity and yield of essential oil of mint plants were estimated according to a modified method [29].
When statistically processing the experimental results, Microsoft Excel and Past V 3.0 programs were used. The mean value of the indicators (M), standard errors of the mean (± SEM) and confidence interval at the 95% confidence level were determined. Differences between options were significant at P≤0.05.
RESULTS
Peppermint plants F I and W I of the original (control) lines did not have statistically significant differences in the size and habit of the aerial parts. However, W I and W II plants had slightly longer internodes and greener foliage compared to F I plants and under identical growing conditions (fig. 3). Twice foliar spraying of mint plants of both F II and W II lines with the γ-PGA SAP peptide led to some visible changes: the size of the plants increased compared to the control lines W I and F I, but this growth was not statistically significant. The most noticeable differences were changes in leaf blade color, as shown in the RGB color indices in each image.
A comparative assessment of the performance of control plants and plants treated with γ-PGA SAP peptide grown under two types of lighting, carried out using the calculation of three vegetation indices, makes it possible to reliably identify changes in the state of plants after exposure to treatment with the peptide (fig. 4). All three indicators showed significant differences between the condition of plants grown under white light and narrow-band spectrum light. Treatment of plants grown under illumination with narrow-band spectral light with γ-PGA SAP peptide improved the photochemical parameters of plants; the increase in GLI, EXG and VARI indices by the time of harvesting mint plants ranged from 57 to 71%. While in plants grown under white light, by the time of harvest, the treatment of plants with γ-PGA SAP peptide was practically leveled out, the indicators of the vegetation indices GLI and VARI remained at the original level. And only the EXG index increased by 11.5%.
The date analysis shows that the GLI and EXG indices make it possible to reliably distinguish the state of control plants and plants treated with γ-PGA SAP peptide for all parameters studied. And the VARI index is less effective for distinguishing between control and experimental plants.
If we compare changes in the spectral characteristics of plants grown under two types of lighting, as well as after treatment with γ-PGA SAP peptide, the blue spectrum turned out to be the most stable indicator, which remained virtually unchanged in all four experimental options. Intensity indicators in the red spectrum decreased in plants treated with γ-PGA SAP peptide in both W II and F II plants, and the decrease in plants grown under narrow-spectrum light was significantly greater. Control plants grown under both white spectrum and narrowband spectral light showed a higher sensitivity of color intensity in the green range, which decreased after treatment with γ-PGA SAP peptide, while the level of green color intensity of the F II variant became comparable to that of plants of variant W II. That is, mint plants treated with γ-PGA SAP peptide maintained the integrity of the photosystem structures, which contributed to the normal occurrence of biochemical processes in plants.
Essential oil is generated and stored in secretory glands in all organs of the aerial parts of mint plants (stems, leaves, calyx, corolla). Moreover, their maximum number is located on flowers, leaves of the middle and upper tiers, the minimum number is on plant stems. With the growth and increase in the size of leaves and flowers, more and more new glands are formed, and the development of the glands is a fairly rapid process. Glands of slightly smaller sizes were formed on mint leaves than on the corolla of mint flowers (Table 2). Moreover, on the abaxial side of the leaf in the control plants of the F I variant, the diameter of the glands was larger than in the W I plants. Treatment of both variants with the γ-PGA SAP peptide from the mint plant leveled out this discrepancy – the diameter of the glands was generally similar.
The density of glands on the leaves of the upper tier of plants, both in the 1st period and in the 2nd period of sampling, of samples grown under narrow-band spectral light was significantly higher than in plants grown under white light. The maximum density of secretory glands with their large sizes, recorded in plants of the FI and FII variants, determined a higher yield of essential oil in mint samples ‒1.1 times compared to plants WI and WII. Treatment of mint plants with γ-PGA SAP peptide in both variants led to an increase in yield (by 9.4% in the FII variant and 7.0% in the WII variant), and an increase in the yield of essential oil by 11.6 and 11.0%, respectively.
CONCLUSIONS
According to data obtained, the use of closed biological systems makes it possible to optimize studies of the effects of optical radiation in combination with the use of biochemical preparations on the process of growing essential oil plants. Illumination of mint plants with narrow-band full-spectrum light allowed the formation of essential oil glands of larger diameter and higher density on the leaves of the upper tier, which ensured an increase in the yield of essential oil. Treatment of mint plants with γ-PGA SAP peptide also increased yield and contributed to increased plant productivity.
ACKNOWLEDGMENTS
Work on this article was carried out within the framework of the state assignment of the GBS RAS (No. 122042700002-6) (“Biological diversity of natural and cultural flora: fundamental and applied issues of study and conservation”) and ARRIAB (No. 0431-2022-0003). The results of the work were obtained using Modules Synergotron ISR11.02.140 (ANO “Institute of Development Strategy”).
AUTHORS
O. V. Shelepova, Candidate of Biological Sciences, Leading Researcher, N. V. Tsitsin Main Botanical Garden of the Russian Academy of Sciences, Moscow, Russia.
ORCID: 0000-0003-2011-6054
E. N. Baranova, Candidate of Biological Sciences, Leading Researcher, N. V. Tsitsin Main Botanical Garden of the Russian Academy of Sciences, Moscow, Russia.
ORCID: 0000-0001-8169-9228.
K. A. Sudarikov, Research Engineer, ANO Institute of Development Strategy, Moscow, Russia.
ORCID: 0009-0005-8734-1223
L. S. Olekhnovich, Candidate of Biological Sciences, Researcher, N. V. Tsitsin Main Botanical Garden of the Russian Academy of Sciences, Moscow, Russia.
L. N. Konovalova, Researcher, N. V. Tsitsin Main Botanical Garden of the Russian Academy of Sciences, Moscow, Russia.
V. V. Latushkin, Candidate of Biological Sciences, Researcher, ANO Institute of Development Strategy, Moscow, Russia.
ORCID: 0000-0003-1406-8965
P. A. Vernik, Leading Researcher, ANO Institute of Development Strategy, Moscow, Russia.
ORCID: 0000-0001-5850-7654
A. A. Gulevich, Candidate of Biological Sciences, Leading Researcher, All-Russian Scientific Research Institute of Agricultural Biotechnology, Moscow, Russia.
ORCID: 0000-0003-4399-2903
CONFLICT OF INTEREST
The authors state that they have no conflict of interest. All the authors took part in writing the article and supplemented the manuscript in part of their work.
CONTRIBUTION OF THE MEMBERS
OF THE AUTHOR’S TEAM
The article is based on the work of all members of the author’s team.
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