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Project titleEarly remote diagnosis of stress photosynthetic response of agricultural plants under the influence of adverse factors

KeywordsNPQ, photochemical reflectance index, remote plant status diagnostics, xanthophyll cycle, adverse factors, plant stress response, photosynthesis

Annotation
The way to highly productive and environmentally friendly agriculture is based on the rational use of chemical and biological protection equipment for agricultural plants, which requires the development of systems for remote monitoring of their condition. In this case, early diagnosis of the development of stress conditions in the plant under the action of biotic (diseases and pests) and abiotic factors (adverse temperature, drought, etc.) becomes especially important, since the use of protective and preventive methods in the early stages of damage development is most effective. The remote character of the diagnosis of the state of plants and the high speed of its carrying out are of great importance either since this allows monitoring the state of plants in large areas. Photosynthesis plays a key role in the productivity of agricultural plants and has a great sensitivity to the action of adverse factors, therefore the evaluation of photosynthetic processes is a promising tool for diagnosing the stress response of plants. However, the problem of remote diagnosis of stressful photosynthetic responses in the field remains far from the solution. Currently, a number of indices based on the parameters of reflected light are actively used and characterize, in particular, the overall photosynthetic biomass of plants (for example, the vegetative index is NDVI). However, changes in such indices under the influence of unfavorable factors occur with significant damage to plants developing in the diurnal time range, and therefore their applicability to early diagnosis of plant stress response is limited. Another direction is associated with the registration of fluorescence, which is realized either by passive detection of fluorescence induced by sunlight, or by active excitation. The second way is the most informative, in particular, it allows to evaluate non-photochemical quenching of the fluorescence of photosystem II (NPQ), the increase of which is a reliable indicator of the stress photosynthetic response. However, registration of fluorescence requires complex and expensive equipment, and a method based on active excitation of fluorescence is not currently implemented as a remote monitoring system. Thus, there is an urgent need for a method that, based on measurements of reflected light, will show rapid stress responses of the photosynthetic apparatus and will become the main one for remote diagnosis of the condition of agricultural plants. A promising case of this method is the registration of the "photochemical reflectance index" (PRI), which is calculated on the basis of reflection values at a wavelength of 531 and 570 nm, which shows stress transitions in the xanthophyll cycle, and is apparently closely related to NPQ. Registration of PRI is actively used in environmental studies, however its use for agriculture is very limited. It can be expected that the use of PRI will reveal the rapid stress responses of photosynthesis (in the minute, and possibly in the second range) when adverse factors of biotic and abiotic nature act on agricultural plants. The aim of the proposed project is to develop a method for early remote diagnosis of the stressful photosynthetic response of agricultural plants to the action of adverse factors of a different nature that relies on the registration of the magnitude, dynamics and spatial distribution of PRI, and the creation of a prototype system that allows the developed method to be implemented. The following general tasks are supposed to be solved: (1) to find out how effective is the measurement of PRI in various agricultural plants and to assess the prospects for using such an indicator for different species; (2) to identify and quantitatively describe the relationship between PRI and NPQ under the action of adverse factors of a different nature; (3) to develop and technically implement a system for remote recording of dynamics and spatial distribution of PRI, and also to carry out its testing in laboratory and field conditions; (4) to assess the possibility of diagnosing the nature and intensity of the adverse factor on the basis of analysis of the dynamics and spatial distribution of PRI, and in the case of the existence of this possibility, develop methods for such diagnosis. To solve the tasks in the 1st year of the project implementation the simultaneous registration of PRI using a spectrometer and registration of NPQ using a PAM-fluorimeter in laboratory conditions will be performed. After the detection of optimal PRI and NPQ measurement modes, a number of agricultural plants will be analyzed for the value of PRI and its relationship to the NPQ value under conditions of varying illumination intensity estimation. Such a series of experiments will allow to evaluate the relationship between PRI and NPQ in plants of different species, to evaluate the prospects of used PRI registration and to select "model" objects for further processing of the method. Further in the laboratory, an analysis will be made of the relationship between PRI and NPQ under the influence of adverse abiotic factors (primarily drought and elevated temperature), as well as an analysis of the dynamics of changes in the studied parameters and an assessment of the overall damage to plants. Based on the experimental results obtained in the first year of the project, a regression or dynamic model will be developed connecting the values of PRI and NPQ. Within the second year of the project implementation, first of all, the development and technical implementation of the system for recording and visualizing the spatial distribution of PRI, as well as its subsequent approbation in the laboratory, will be carried out by comparing the parameters of PRI and NPQ under conditions of varying illumination intensity. Under laboratory conditions, the temporal and spatial characteristics of the changes in PRI and NPQ will be investigated under the influence of unfavorable abiotic factors; An assessment will be made of the possibility of identifying the nature and strength of the factor from the measured indicators and, if this possibility exists, methods for such diagnostics are developed. In addition, the experimental results of the second year of research will be used to verify and refine the regression (or dynamic) model of the PRI and NPQ communication developed at the previous stage. During the 3rd year of the project implementation, the developed system will be tested in open ground conditions, including the assessment of the dynamics and spatial distribution of PRI under the influence of adverse abiotic (primarily drought) and biotic (pests and / or diseases of the plants) factors. An additional assessment will be made of the feasibility of diagnosing a particular type of adverse factor for temporal and spatial characteristics of PRI. At the end of the project, the results will be summarized and the technical implementation of the final prototype of the system for remote diagnostics of the stressful photosynthetic response of agricultural plants, including both the technical component and the program complex that manages the operating modes of the system, processing and visualization of the results obtained, is carried out. In addition, an assessment will be made of the prospects for using the developed complex to use for field monitoring using unmanned aerial vehicles.

Expected results
The most common result of the proposed project is the development of a method for early remote diagnosis of the stressful photosynthetic response of agricultural plants to the action of adverse factors of a different nature, which relies on the registration of magnitude, dynamics and spatial distribution of PRI, and the creation of a prototype system that allows the developed method to be implemented. Such a result will exceed the world level of research in this field, since, despite a large number of publications in high-ranking scientific journals (for example, Global Change Biology, IF = 8.444, or Remote Sensing of Environment, IF = 5.881) on the use of PRI registration in Research of natural plant communities, such systems are currently lacking. The practical importance of the development of such a system will also be great, since it will combine the relative simplicity and cheapness of systems based on the registration of reflected light and a high sensitivity to the development of a stressful photosynthetic response, which is usually characteristic for the use of the fluorescence detection method. Further prospects for the development of the system will be its implementation on an unmanned aerial vehicle and use for rapid remote monitoring of significant field areas. The intermediate results of the project, which also have high scientific significance and correspond to the world level of research, include: - Identification of PRI features in various agricultural plants, since, despite the high applied importance of the task and the large number of plant studies in natural communities, this issue is currently being studied only in a very limited number of works; - correlation analysis of PRI and NPQ under the influence of adverse factors, since the majority of ecological works are aimed at the development and refinement of methods for assessing the efficiency of photosynthetic processes in natural plant communities, and the development of stress photosynthetic responses by the PRI registration method has been studied on a very limited scale; - Identification of temporal and spatial features of the change in PRI under the influence of adverse factors, abiotic and biotic nature. This question remains practically undeveloped and at the same time its solution, at least, can give a method for identifying stressful photosynthetic at very early stages of its development. In addition, such studies open up the potential for early diagnosis not only of the presence of adverse effects, but also of its nature and intensity, which is of great fundamental and applied importance. - Development of a regression or dynamic model connecting the value of PRI to the value of NPQ under various conditions, since in most studies it used to be limited to analyzing the correlation between the values of PRI and NPQ. The development of such a model will make it possible to convert the value of PRI into a corresponding value of the standard indicator of the stressful photosynthetic response, which is NPQ, which will facilitate the analysis and interpretation of the data obtained in the PRI study. In particular, such a model will be the basis for their comparison with the results of a very large number of studies examining the influence of adverse factors and environmental conditions on NPQ.

Annotation of the results obtained in 2019
The first task that was solved at the third stage of the Project was the modification and improvement of the software of the developed system for measuring the spatial distribution of the photochemical reflectance index (PRI) in plants (PRI-imaging system). As part of this modification, a version of the Pri 2.0 program, in which a number of new features were implemented, was developed. First of all, a calibration procedure was implemented to minimize the technical error associated with the different spatial locations of the studied plants. Secondly, the procedure for reducing the error due to stochastic heterogeneity of the sensitivity of the camera matrix pixels was implemented. For this, the possibility of spatial averaging of the results by the moving average method was realized in the new version of the program. Three options were implemented - without averaging, averaging over a 3x3 square and averaging over a 5x5 square. Thirdly, a number of new features related to the analysis of the resulting images were implemented. In particular, Pri 2.0 provides the ability to set the ROI on the PRI spatial distribution obtained by the system, estimate average values and standard deviations of PRI in such ROIs, and obtain the temporal dynamics of the studied values. The results can be presented in the form of a graph or a table in the program; it is also possible to save them as separate files. The second task was aimed at a detailed analysis of the mechanisms and prospects of the applied application of PRI changes induced by illumination in the second range. Pea plants were used as a model object. As part of the solution to this problem, it was shown that light-induced changes in PRI can be divided into three components: slow, fast, and ultrafast. Slow changes develop in the minute range of lighting; their relaxation in such a time range is absent. The dynamics of changes in this component show that it is apparently due to convertions in the xanthophyll cycle. Rapid PRI changes develop and relax within a few tens of seconds. The dynamics of such changes strongly correlate with the dynamics of changes in light transmission at a wavelength of 535 nm in the range of tens of seconds, which reflects changes in light scattering by chloroplasts at a wavelength of 530-545 nm associated with the acidification of the lumen of chloroplasts. Ultrafast changes developed within a few seconds of illumination; they included a rapid decrease in PRI (500-1000 ms) and subsequent complete or partial relaxation of its value. Ultrafast PRI changes correlated with the development of the electrochromic shift and were apparently associated with changes in the electric potential gradient on the thylakoid membrane. Considering that the ultrafast components of the PRI change can be caused by illumination of plants with the yellow-green measuring light of the system for several seconds, from a technical point of view, such components were the most promising for use in assessing the state of plants. An analysis of the influence of measurement conditions on the registration of an ultrafast component of changes showed that such changes can be measured under various conditions (presence/absence of spatial fixation of leaves, controlled/natural measurement conditions). At the same time, the amplitude of ultrafast PRI measurements was slightly higher under dark conditions. Subsequent analysis of the possibility of using the ultrafast component of the PRI change to assess plant damage during drought showed that the development of water stress cause significant changes in the amplitude of such a component: a decrease in amplitude during moderate drought and an increase in amplitude during severe drought. At the same time, the magnitude of such changes was relatively small, which limits the possibility of using this parameter in remote monitoring. The third task was aimed at adapting the application methods of the developed PRI-image system for assessing stress changes in plants during drought in open ground and natural light. Pea plants were used as a model object. First of all, the solution to this problem made it possible to identify some technical problems and additional possibilities with this type of analysis. It was shown that the main factor causing errors to the measurement of PRI in field conditions are gusts of wind, causing faster fluctuations in the spatial arrangement of leaves and stems. To solve this problem, we used a short series of PRI measurements (11 repetitions), among which we chose the result with the lowest standard deviation for the resulting image for further analysis. It was also revealed that PRI analysis in an array of plant shoots that form a fairly dense vegetation cover allows the use of a standard location of the zones for analysis (ROI). This makes it possible to avoid the manual or automated search for leaves and the location of ROI on them, i.e. greatly simplifies the analysis. The study of the effectiveness of detecting stress changes during the development of drought in open ground and natural light using the developed PRI-imaging system showed that the absolute values of PRI decrease and the standard deviations of the index within the studied ROI increase with the development of drought. Changes in both parameters begin to develop in the early stages of drought and reach significant values when the relative water content in plants declined by 10% or more. It is important to note that the most effective for detecting drought is the joint use of two criteria - a decrease in the absolute value of the PRI below the threshold level and an increase in the standard deviation of the PRI above the threshold level (at least one of these criteria was sufficient to identify the drought). The fourth task was aimed at summarizing the results of the Project. In its framework, it was shown that the developed system can be used to obtain four groups of parameters. In this case, the first three groups can be obtained without the use of additional blocks. Firstly, it is a measurement of the absolute value of PRI. Such a measurement is effective in the analysis of drought-induced stress changes at the level of vegetation cover (for example, peas); however, it is less effective in the analysis of leaves with a fixed position in space. Apparently, the main field of application of the PRI absolute value is monitoring the state of plants in open ground and, possibly, in the greenhouse. Secondly, this is a change in the standard deviation of the PRI. This standard deviation was associated with the development of stress changes during drought in all types of experiments (presence/absence of spatial fixation of leaves, controlled/natural measurement conditions). Apparently, this parameter can be considered as the most universal indicator of the development of stress changes that can be used with various options for monitoring the state of plants (laboratory, greenhouse, open ground). Thirdly, these are ultrafast PRI changes that developed when illuminating plant objects with measuring yellow-green light for several seconds. Apparently, the ultrafast component of the changes in PRI can be used to evaluate the light-induced changes in the electric potential on the thylakoid membrane; however, the magnitude of such changes during the development of drought is relatively small. Thus, ultrafast PRI changes can be used more possibly in laboratory conditions (scientific research, high-performance phenotyping). Fourth, these are PRI changes caused by actinic illumination in the range of tens of seconds and minutes. The measurement of such changes requires an additional source of actinic light with a controlled intensity and a low level of background lighting; i.e. can be implemented in laboratory conditions or in a greenhouse. The implementation of such a system in open ground is quite complicated. Changes in PRI in the second and minute range are an effective tool for evaluating photosynthetic parameters; in particular, they can be used to determine the non-photochemical quenching of chlorophyll fluorescence (NPQ). Quantitative relationships between NPQ and PRI changes were described in the framework of the Project by linear regression models. The field of application of such changes in PRI can be scientific studies of photosynthetic processes in the laboratory, high-performance phenotyping and, possibly, early detection of stress changes in the photosynthetic apparatus when growing plants in open ground. According to the results of the Project, an application for a patent in the Russian Federation for “A system for measuring the photochemical reflectance index PRI in plants” was prepared and sent for consideration. A number of scientific articles have been published in journals indexed by the Web of Science and Scopus databases, including journals in Q1.

Publications

1. Mudrilov M., Katicheva L., Ladeynova M., Balalaeva I., Sukhov V., Vodeneev V. Automatic determination of the parameters of electrical signals and functional responses of plants using the wavelet transformation method Agriculture, V.10. N. 1. Article 7 (year - 2020) https://doi.org/10.3390/agriculture10010007

2. Sukhova E., Sukhov V. Relation of photochemical reflectance indices based on different wavelengths to the parameters of light reactions in photosystems I and II in pea plants Remote Sensing, V. 12, N. 8. Article 1312 (year - 2020) https://doi.org/10.3390/rs12081312

3. Sukhova E., Yudina L., Gromova E., Nerush V., Vodeneev V., Sukhov V. Burning-induced electrical signals influence broadband reflectance indices and water index in pea leaves Plant Signaling & Behavior, V. 15, N. 4. Article e1737786 (year - 2020) https://doi.org/10.1080/15592324.2020.1737786

4. Yudina L., Sukhova E., Gromova E., Nerush V., Vodeneev V., Sukhov V. A light‑induced decrease in the photochemical reflectance index (PRI) can be used to estimate the energy‑dependent component of non‑photochemical quenching under heat stress and soil drought in pea, wheat, and pumpkin Photosynthesis Research, - (year - 2020) https://doi.org/10.1007/s11120-020-00718-x

5. Gromova E.N., Sukhova E.M., Khlopkov A.D., Yudina L.M., Nerush V.N., Vodeneev V.A., Sukhov V.S. Анализ связи между нефотохимическим тушением флуоресценции хлорофилла и фотохимическим индексом отражения (PRI) у высших растений Сборник научных трудов VI Съезда биофизиков России. Краснодар: Полиграфическое объединение «Плехановец», 2019, Т. 2, с. 339-340 (year - 2019) https://doi.org/10.31429/SbR6.2019.001

6. Sukhov V.S. Вызванный электрическими сигналами системный фотосинтетический ответ растений: феноменология, механизмы, физиологическая значимость и перспективы практического использования IX Съезд общества физиологов растений России «Физиология растений – основа создания растений будущего» (Казань, 18–24 сентября 2019 г.): тезисы докладов. Казань: Издательство Казанского университета, 2019., с. 420 (year - 2019) https://doi.org/10.26907/978-5-00130-204-9-2019-420

7. Sukhov V.S., Sukhova E.M., Yudina L.M., Gromova E.N., Vodeneev V.A. Дистанционное зондирование быстрых стрессовых ответов фотосинтетического аппарата у растений Сборник научных трудов VI Съезда биофизиков России. Краснодар: Полиграфическое объединение «Плехановец», 2019, Т. 2, с. 140 (year - 2019) https://doi.org/10.31429/SbR6.2019.001

8. Yudina L.M., Gromova E.N., Khlopkov A.D., Nerush V.N., Vodeneev V.A., Sukhov V.S. The measurement of photochemical reflectance index (PRI) as an indicator of the local and systemic plants photosynthetic response 10th International Conference Photosynthesis and Hydrogen Energy Research for Sustainability. Abstracts and Programme. Eds. Suleyman Allakhverdiev, Ilya Naydov. Saint Petersburg, Russia., P. 149. (year - 2019)

9. - Essential tool for precision farming: new method for photochemical reflectance index measurement EurekAlert!, NEWS RELEASE 7-MAY-2019 (year - )

Annotation of the results obtained in 2017
This Project was performed in collaboration with the laboratory of biophotonics of Institute of Applied Physics (IAP RAS). In the first stage of the Project, a method of simultaneous registration of a photochemical reflectance index (PRI) and nonphotochemical quenching of fluorescence (NPQ) in plant leaf was tested. This system included PAM-fluorimeter, spectrometer and source of light. The two variants of a light source were used. The first light source was made on the basis of a white luminodiode and broadband color filters (yellow and yellow-green). The second light source was made on the basis of a halogen lamp. The first lamp illuminated a plant by yellow-green light; portion of photosynthetically active radiation (PAR) was small. Simultaneously the plant was illuminated by red actinic light of PAM-fluorimeter. The yellow-green light was periodically switched to exclude influence of actinic and background light on PRI measurement. The second lamp illuminated plant by broadband light with significant PAR. This lamp was used without the additional source of actinic light; the lamp illuminated plant permanently. It should be additionally noted that the testing of light sources showed that the combination of two type of luminodiodes (with maximums about 531 and 570 nm) was not effective light source for measurement of PRI. Further an analysis of an efficiency of PRI application for detection of photosynthetic stress in agricultural plants was performed. Dependencies of PRI and NPQ on light intensity were shown in pea, wheat and pumpkin. In particular, the increase in intensity of red actinic light caused decrease in PRI and increase in NPQ; changes of these physiological parameters were closely related. Moreover changes in PRI were observed even under weak intensity of the yellow-green light. This result showed that three investigated plants could be used as model plants for analysis of PRI changes under stress conditions. It is important that values of PRI in different plants were varied; as a result, significant differences were shown in analysis of ΔPRI only (the value of change of PRI relatively on dark level of index). Furthermore, it was shown that changes in PAR intensity induced transitory processes in photosynthesis of pea. These processes could cause a decrease of efficiency of PRI application for detection of NPQ under natural light, however, this influence, probably, was not strong. Further, changes in PRI in plants under stress conditions (high temperature, soil drought) were investigated. The influence of local damage-induced electrical signals was additionally analyzed. It was shown that short-term heating induced increase of absolute value of ΔPRI in pea, wheat and pumpkin. These changes were significantly correlated with NPQ increase in the leaf. The heating could also induce decrease of the photochemical reflectance index; however this phenomenon was not always observed and it was weakly related with changes in NPQ. Measurement of Normalized Difference Vegetation Index (NDVI), which is widely used in monitoring of plants, did not show significant changes. The investigation of influence of soil drought in pea showed initial decrease of PRI; however, further this effect was not significant. On the other hand, the increase of absolute values of ΔPRI was observed for all investigated period. This increase was closely related with increase of nonphotochemical quenching. The analysis of NDVI showed that the drought caused decrease of this index; however the decrease of NDVI started later that initiation of changes of PRI. Thus the increase of absolute values of ΔPRI is good indicator of the photosynthetic stress under the high temperature and soil drought. Additionally, detailed analysis of influence of propagating electrical signals on photosynthesis was performed. It was shown that electrical signals increased absorption of light by photosystem II and caused transitory increase of electrons flow. Probably, these changes were related with decrease of pH in the chloroplast lumen. Therefore electrical signals should influence on PRI. Really, the further analysis showed that electrical signals caused transitory decrease of PRI, the magnitude of this change was significantly correlated with magnitude of NPQ increase. This result showed that changes of PRI can by used for monitoring of photosynthetic response induced by stress signals. Experimental data for three plant species (pea, wheat and pumpkin) under different conditions were used for development of the regression model of relation between PRI and NPQ. It was shown for these three species that ΔPRI was linearly correlated with NPQ and its fast (energy-dependent) component. Significant linear correlation was also observed at common analysis of all results for these three species. In contrast, the relation between PRI and NPQ was weak and was not described by regression model. Series of additional experiments were performed at the first stage of Project. Firstly, a meta-analysis of literature data was performed. In this work it was shown that relation between PRI and NPQ depended on conditions of measurements and distribution of level of photosynthetic stress among investigated plants. Secondly, it was shown that drought caused significant changes in NPQ distribution in leaves. This result showed that investigations of spatial distribution of photosynthetic stress level and PRI values in leaf can be effective tool for analysis of photosynthetic stress. Thirdly, preliminary technical solutions for development of a system of measurement and visualization spatial distribution of PRI in plant were proposed in collaboration with IAP RAS. Thus results of first stage of Project showed that changes in the photochemical reflectance index were a good indicator of the photosynthetic stress induced by excess light, heating, soil drought and propagation of electrical signals. An important result was significant efficiency of ΔPRI in comparison with PRI for detection of the photosynthetic stress. This result showed necessity of investigations of spatial distribution of PRI (including analysis of ΔPRI between different region of same plant) and/or investigations of PRI changes under different light intensity (including analysis of ΔPRI under different light conditions). Three articles were published or accepted for publication in journals indexed by Web of Science and Scopus, including two journals from Q1. Results were also reported in conferences.

Publications

1. Sukhov V.S., Gromova E.N., Sukhova E.M., Surova L.M., Nerush V.N., Vodeneev V.A. Анализ связи показателей световой стадии фотосинтеза с фотохимическим индексом отражения (PRI) в условиях кратковременного освещения листа гороха Биологические мембраны, - (year - 2018)

2. Sukhova E., Mudrilov M., Vodeneev V., Sukhov V. Influence of the variation potential on photosynthetic flows of light energy and electrons in pea Photosynthesis Research, Volume 136, Issue 2, pp 215–228 (year - 2018) https://doi.org/10.1007/s11120-017-0460-1

3. Sukhova E., Sukhov V. Connection of the photochemical reflectance index (PRI) with the photosystem II quantum yield and nonphotochemical quenching can be dependent on variations of photosynthetic parameters among investigated plants: A meta-analysis Remote Sensing, V. 10. N. 5. Article 771 (year - 2018) https://doi.org/10.3390/rs10050771

4. Gromova E.N., Surova E.M., Nerush V.N., Sukhova E.M., Sukhov V.S. Влияние засухи и электрических сигналов на нефотохимическое тушение и фотохимический индекс отражения (PRI) у гороха «Биосистемы: организация, поведение, управление» 71-я Всероссийская с международным участием школа-конференция молодых ученых. Тезисы докладов, Н. Новгород, Университет Лобачевского. 2018. С. 70 (year - 2018)

5. Sukhov V., Vodeneev V. Electrical responses and photosynthesis in higher plants: a theoretical problem and practical perspectives 8th International Conference “Photosynthesis and Hydrogen Energy Research for Sustainability-2017” in honor of Agepati S. Raghavendra, William A. Cramer, and Govindjee”, Hyderabad, 2017. P. 139 (year - 2017)

6. Sukhova E., Nerush V., Sukhov V. A photochemical reflecting index as perspective method for remote monitoring of plant photosynthesis under changeable conditions: meta-analysis of literature data 8th International Conference “Photosynthesis and Hydrogen Energy Research for Sustainability-2017” in honor of Agepati S. Raghavendra, William A. Cramer, and Govindjee”, Hyderabad, India, Hyderabad, 2017. P. 186 (year - 2017)

7. Sukhova E.M., Khlopkov A.D., Ratnitsina D.A., Sukhov V.S. Влияние интенсивности падающего света на развитие нефотохимического тушения на примере гороха посевного: Экспериментальный анализ и математическое моделирование. «Биосистемы: организация, поведение, управление» 71-я Всероссийская с международным участием школа-конференция молодых ученых. Тезисы докладов, Н. Новгород, Университет Лобачевского. 2018. С. 222 (year - 2018)

8. Sukhova E.M., Sukhov V.S. Влияние вариабельного потенциала на фотосинтетические процессы высших растений: Экспериментальный анализ и математическое моделирование «Биосистемы: организация, поведение, управление» 71-я Всероссийская с международным участием школа-конференция молодых ученых. Тезисы докладов, Н. Новгород, Университет Лобачевского. 2018. С. 221 (year - 2018)

9. - В Нижнем Новгороде жгли горох для определения его реакции на стресс ТАСС-Чердак, - (year - )

Annotation of the results obtained in 2018
Main tasks of the second stage of the Project was (i) development of the system for imaging of the photochemical reflectance index (PRI) and estimation of its efficiency; (ii) adaptation of the system for estimation of the non-photochemical quenching of fluorescence (NPQ); (iii) revealing of properties of changes in NPQ and PRI under action of stressors (drought and heating), including analysis of spatial distribution of these changes; (iv) analysis of fast shifts in PRI under short illumination and estimation of possibility of application of these for revealing of the stress responses in plants. The first task was solved in collaboration with limited liability company “Laser Center of Nizhny Novgorod”. The system of PRI imaging was developed and tested; the primary software for this system was also developed. The system of PRI imaging includes two digital cameras with synchronization, which are equipped by spectral interference filters (light transmission at 531 and 570 nm), beam splitting plate for single “input” for imaging, green-yellow LED, controller and other components. The important feature of the system is the using of pulses of the green-yellow measuring light; the method minimizes errors induced by background light. Maximal visualization field is 30x22 cm2, minimal time between measurements is 5 s, maximal number of measurements in the series is 9 999. The system of PRI-imaging was used for solution of other tasks. It was shown on basis of simultaneous measurements of spatial distribution of PRI (the system) and NPQ (the standard system of the NPQ imaging) that the developed system can efficiently estimate NPQ on basis of measurements of light-induced changes in PRI (ΔPRI) in minutes range in plants with large leaves (pea, pumpkin). In contrast, efficiency of estimation of NPQ on basis of ΔPRI in small leaves (e.g. in wheat leaves, which are narrow) was not high. Linear regressions were used for description of connection between NPQ and ΔPRI; the regressions were similar with the linear regressions, which described connection of NPQ and ΔPRI at measurements without imaging. After that the system of PRI imaging was used for estimation of changes in PRI under soil drought and heating, which are important stressors for agriculture. The first, it was shown that the light-induced changes in PRI in the minutes range is the sensitive indicator of photosynthetic stress under these conditions; moreover, ΔPRI was strongly linearly connected with NPQ. This result shows that analysis of the light-induced changes in PRI in the minutes range is perspective approach for detection of stressors-caused changes in photosynthetic machinery in green-house or laboratory. In contrast, using of the ΔPRI for monitoring of the plant physiological state in fields is strongly limited (illumination by actinic light for minutes is very difficult at field investigations). As a result, the developed system of PRI imaging was used for analysis of alternative approaches for revealing of the plant stress. We showed that variability of PRI in investigated areas (a standard deviation, a difference between maximal and minimal values of PRI) notably increases with development of soil drought. This increase is strongly correlated with development of NPQ and is probably tobe connected with water stress. However, the similar variability after short term temperature increase was not detected. Thus, this variability is specific for soil drought, but not for elevated temperature. It is important to note that this variability can be detected without using a white calibration surface because this parameter is perspective for remote sensing of plants in fields. The alternative parameter for monitoring can be fast shift of PRI in second range which was shown with using of different durations of plant illumination by the measuring green-yellow light. In particular, this shift of PRI was decreased under soil drought and almost completely suppressed under heating. It is important, that this effect, which is dependent on the type of stressor, can be used for plants monitoring in fields. Additionally, it is important, that the analysis of spatial NPQ distribution in leaves showed specific features in this distribution as well as in the dynamic of the distribution under drought and temperature action. However, the measurements of spatial PRI distribution in different parts of leaflet had high errors and this method could not be used on basis of PRI imaging. Thus, our results show that the developed system for PRI imaging can measure PRI and dynamic of its changes. The PRI variability can be used for stress detection in agricultural plants. Development and improving of proposed approaches are common tasks of the next stage of the Project.

Publications

1. Sukhova E., Sukhov V. Analysis of Light-Induced Changes in the Photochemical Reflectance Index (PRI) in Leaves of Pea, Wheat, and Pumpkin Using Pulses of Green-Yellow Measuring Light Remote Sensing, V. 11, N. 7, Article 810 (year - 2019) https://doi.org/10.3390/rs11070810

2. Sukhova E.M., Yudina L.M., Vodeneev V.A., Sukhov V.S. Анализ связи изменений фотохимического индекса отражения (PRI) и закисления люмена хлоропластов листьев гороха и герани в условиях кратковременного освещения Биологические мембраны, Т. 36, № 3, с. 218–228 (year - 2019) https://doi.org/10.1134/S0233475519030083

3. Vladimir Sukhov , Ekaterina Sukhova , Ekaterina Gromova , Lyubov Surova , Vladimir Nerush , Vladimir Vodeneev The electrical signals-induced systemic photosynthetic response is accompanied with changes in photochemical reflectance index in pea Functional Plant Biology, V. 46, N. 4, P. 328-338 (year - 2019) https://doi.org/10.1071/FP18224

4. Vladimir Sukhov, Ekaterina Sukhova, Vladimir Vodeneev Long-distance electrical signals as a link between the local action of stressors and the systemic physiological responses in higher plants Progress in Biophysics & Molecular Biology, - (year - 2019) https://doi.org/10.1016/j.pbiomolbio.2018.11.009

5. Sukhov V.S., Sukhova E.M., Gromova E.N., Surova L.M., Nerush V.N., Grinberg M.A., Vodeneev V.A. Фотохимический индекс отражения – как инструмент мониторинга стрессовых фотосинтетических ответов растения на локальном и системном уровне Годичное собрание Общества физиологов растений России "Механизмы устойчивости растений и микроорганизмов к неблагоприятным условиям среды". Сборник материалов. Часть I., 749-751 (year - 2018) https://doi.org/10.31255/978-5-94797-319-8-749-751

6. Sukhova E.M., Sukhov V.S. Моделирование световой зависимости нефотохимического тушения флуоресценции хлорофилла и ее перспективы для создания оптической модели листа Годичное собрание Общества физиологов растений России "Механизмы устойчивости растений и микроорганизмов к неблагоприятным условиям среды". Сборник материалов. Часть I., 752-754 (year - 2018) https://doi.org/10.31255/978-5-94797-319-8-752-754

7. Yudina L.M., Sukhova E.M., Gromova E.N., Nerush V.N., Vodeneev V.A., Sukhov V.S. Фотохимический индекс отражения (PRI) как инструмент мониторинга фотосинтетического стресса у сельскохозяйственных растений Сборник материалов V Международной научно-методической конференции "Роль физиологии и биохимии в интродукции и селекции сельскохозяйственных растений", Том 1, С.347-350. (year - 2019)