Plant electrophysiological information manifests the composition and nutrient transport 1 characteristics of membrane protein 2

21 Background: Almost all life activities of plants are accompanied by electrophysiological information. Plant 22 electrical parameters are considered to be the fastest response to environment. 23 Results: In this study, the theoretically intrinsic relationships between the clamping force and leaf resistance (R), 24 capacitive reactance (Xc) and inductive reactance (XL) were revealed as 3-parameter exponential decay based on 25 bioenergetics for the first time. The intrinsic resistance (IR), intrinsic capacitive reactance (IXc) and intrinsic 26 inductive reactance (IXL) in plant leaves were monitored via these relationships for the first time, and the nutrient 27 transport capacity (NTC) in plant cells based on IR, IXc and IXL was first defined. The results indicate that IXc and 28 IXL could be used to manifest the composition of surface and binding proteins in cell membrane, plant with high 29 crude proteins and crude ash had higher NTC, and which accurately revealed the nutrient transport strategies in 30 tested plants. 31 Conclusions: This study highlights that plant electrophysiological information could effectively manifest the 32 composition and nutrient transport characteristics of membrane protein in plant cells. 33


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Almost all life activities in plants, including the metabolism of substances and energy, development, stress 38 resistance and signal transduction, involve charge separation, electron movement, proton and dielectric transport, etc. 39 [1][2]. The electrical properties of plant cells are derived from the cell membrane with a double electric layer, which 40 is two electron density bands approximately 2.5 nm thick on the inside and outside of the membrane and a 41 transparent band approximately 2.5 nm thick in the middle. And membrane lipids and proteins, the mainly 42 compositions of cell membrane, can be regarded as insulating layer, have a high electrical resistivity, enabling the 43 plant cell to store electric charge [3]. Therefore, the electrophysiological information in plants is closely related to the 44 life activities, and the changes of structure, composition and ion permeability in plant cells will inevitably lead to 45 significant changes in electrophysiological information [3][4][5][6][7][8].

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Plant electrical parameters are considered to be the fastest response to environmental stimulus such as drought, salt 47 stimulation, cold stimulation, diseases and insect pests, exogenous force [7][8][9][10][11]. Previously, a traditional approach, 48 the electrical parameters in plants are measured by the insertion of two electrodes into the stem or leaf [12][13].

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However, this method is unstabitily and difficult to manipulate, and the plant electrical signals acquired lacked 50 representativeness, reproducibility and comparability needling injury, as well as different environments, users and 51 other factors. Moreover, the intrinsic or spontaneous electrical parameters in plants are not detected by previously 52 methods. Thus, can the intrinsic relationships between environmental stimulus and electrophysiological parameters 53 be feasible to obtain intrinsic electrical parameters with high reproducibility in plants or evaluate their life 54 phenomena? Can these intrinsic relationships be described by corresponding physical mechanism models? 55 Generally, a mesophyll cell can be regarded as a concentric sphere capacitor with both inductor and resistor 56 function, and many aligned mesophyll cells make up the leaf capacitor [2,14]. The ions, ion groups and electric 57 dipoles in mesophyll cells are electrolytes of leaf capacitor and most related to electrophysiological information [15]. 58 Interestingly, Guo et al. [16] reported the capacitance (C) values of maize leaves increased with clamping forces, and 59 manifested clamping forces stimuli changed the electrophysiological information in plant leaves. However, this 60 intrinsic mechanism or relationship between clamping force and the electrophysiological information of plant leaves 61 wasn't revealed. Thus, it is of great practical significance to clarify the intrinsic mechanism between clamping forces 62 and electrophysiological parameters and provide a rapid, accurate and real-time technique for monitoring the 63 physiological state of plant leaves.

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Cell is the site of all biochemical reactions, and cell membrane side is an important barrier to ensure a stable 65 environment inside the cell. It has been estimated that 15~30% of the nuclear gene encoded proteins are involved in 66 nutrient transport on the cell membrane, and the energy used by cells in nutrient transport up to two-thirds of the total 67 energy consumed by cells [1]. The nutrient transport capacity of cells is most closely related to the type and quantity 68 of surface and binding proteins in cell membrane, thus, the composition and content of membrane protein can 69 indirectly reflect the nutrient transport capacity of cells. Protein detection methods of biological samples include 70 conventional, electrochemical, molecular biology, electrophoresis and mass spectrometry methods [17]. However, 71 the detection of membrane proteins is limited to single cell or single proteins, and the existing protein detection 72 technology is difficult to accurately evaluate the composition characteristic of cell membrane protein [17][18].

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Moreover, the nutrient transport capacity ultimately affects the nutrient use efficiency of plants, and the most 74 commonly used method of plant nutrient use evaluation is the ratio of total nutrient in plants to total input nutrient 75 [19][20]. However, this nutrient use efficiency also does not directly reflect the nutrient transport capacity. To the best 76 of our knowledge, the composition and nutrient transport characteristics of membrane protein has rarely been 77 reported.

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The fully expanded leaves, which account for a high proportion of plant biomass, determine and reflect the plant 79 nutrient metabolism. Since the concentration of electrolytes in cells (ions, ion groups and electric dipoles) in leaf 80 cells is directly affected by the nutrient metabolism in plant leaves, and then it is accompanied by vigorously 81 electrical activities. In this study, it was first clarified and constructed the intrinsic mechanisms and physical models 82 between clamping forces and leaf resistance (R), capacitive reactance (Xc) and inductive reactance (XL).  118 where E= the electromotive force (V), E 0 = the standard electromotive force (V), R 0 = the gas constant (8.314570 J 120 K -1 mol -1 ), T= the thermodynamic temperature (K), C i = the concentration of the electrolytes that respond to R inside 121 the cell membrane (mol L -1 ), C o = the concentration of the electrolytes that respond to R outside the cell membrane 122 (mol L -1 ), F 0 = Faraday constant (96485 C mol -1 ), and n R = the number of transferred electrolytes (mol).

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The internal energy of the electromotive force can be converted into pressure work, and they have a direct 124 relationship, PV=a E, that is: where M= the iron block mass (kg), m= the mass of the plastic rod and the plate electrode (kg), and g= 9.8 N/kg.

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For mesophyll cells, the sum of C o and C i is certain. C i is directly proportional to the conductivity of the 132 electrolytes that respond to R, and the conductivity is the reciprocal of R. Hence, can be expressed as , where f 0 = the ratio coefficient of the conversion between C i and R, and C T = C o + C i . Therefore, 134 formula (2) was transformed into formula (4): Formula (4) was rewritten: 138 and ln 139 Formula (6) takes the exponents of both sides: 141 Further: Because d= V S , formula (8) was transformed into: 145 For the same leaf tested in the same environment, the d, a, E 0 ,R 0 ,T, n R , F 0 , C T , and f 0 of formula (9) are constant.

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Let , and the intrinsic mechanism relationships of leaf R and F was: 148 where y 0 , k 1 and b 1 are model parameters.

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When F=0, the intrinsic resistance (IR) of the plant leaves could be obtained: 150 With the same R, the intrinsic mechanism relationships of leaf Xc and F was revealed (Additional file 1): 153 where p 0 , k 2 and b 2 are model parameters.

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When F=0, the intrinsic capacitive reactance (IXc) of plant leaves could be calculated as: With the same R, the intrinsic mechanism relationships of leaf XL and F was revealed (Additional file 1): 158 where q 0 , k 3 and b 3 are model parameters.   Table 1 207 Fig. 2.

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The intrinsic electrophysiological information and the nutrient transport capacity of B. papyrifera in two 210 conditions were successful monitored using the corresponding equation parameters. As shown in Table 2, the leaf IR, IXc and IXL of B. papyrifera in the agricultural soil are significantly (p < 0.01) lower than those of that in the 212 moderately rocky desertification soil. Theoretically, the lower IXc and IXL, the more surface and binding proteins. 213 Actually, crude protein of B. papyrifera in the agricultural soil are significant (p < 0.05) higher than those of that in 214 the moderately rocky desertification soil, which is in good agreement with IXc and IXL. Moreover, for the same 215 plant, the leaf IXc is lower than IXL which shows that binding proteins is more than surface proteins. As displayed in 216 Table 2, the NTC and crude ash of B. papyrifera in the agricultural soil are significantly (p < 0.01) higher than those 217 of that in the moderately rocky desertification soil. The results showed that B. papyrifera in the agricultural soil grow 218 well under the high nutrient (crude ash) conditions, and cell membrane proteins (crude protein) were relatively much 219 which supported it higher NTC as compared to that in the moderately rocky desertification soil. 220 Table 2 221 222 Electrophysiological information and nutrient transport of the herbaceous and woody plants 223 224 As illustrated in Table 3, Table 3 230 231 Electrophysiological information and nutrient transport of S. tuberosum and C. annuum 232 233 As shown in Table 4, the leaf IR, IXc and IXL of S. tuberosum are significantly (p < 0.01) lower than those of C. 234 annuum in the same growth habitat, while NTC, crude protein and crude ash are higher. And IXc is lower than IXL 235 in same plant. The results showed that S. tuberosum with high membrane protein (crude protein) and nutrient (crude 236 ash) contents promote the efficient transport and utilization of nutrients by its membrane proteins, which made it had 237 higher nutrient transport capacity (NTC).

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Currently, the detection of membrane proteins is limited to single cell or single proteins, and the existing protein 265 detection technology is hardly evaluate the composition characteristic of cell membrane protein [17][18]. The results 266 in this study showed that IXc and IXL could be used to manifest the composition of surface and binding proteins in 267 cell membrane, that was, the lower IXc and IXL, the more surface and binding proteins. This is closely related to 268 the fact that the high content of membrane proteins promoted the nutrient elements to pass through cell 269 membrane more smoothly, thus made the cell membrane resistivity lower. In this study, plant with high crude 270 proteins had relatively lower IR, IXc and IXL, which strongly supported the feasibility of using IXc and IXL to 271 characterize the composition characteristic of membrane proteins. This study found that a phenomenon was common 272 in the all tested plants, that was, the IXc was lower than IXL in same plant. This result perfectly proves the life fact 273 that binding proteins is more than surface proteins in cell membrane [1][2].

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Due to the poor nutritional environments, plants in rocky desertification soils are more vulnerable to low nutrient 275 stress than those in cultivated soils [22][23][24]. The results showed that B. papyrifera in the agricultural soil grow well 276 under the high nutrient (or crude ash) conditions, and cell membrane protein (or crude protein) content were higher 277 which supported it higher nutrient transport capacity as compared to that in the moderately rocky desertification soil.

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The monitoring of the transport capacity of plant nutrients has rarely been reported in previous studies. In this study, 279 the nutrient transport capacity (NTC) was defined based on IR, IXc and IXL for the first time. The results showed 280 that the higher crude protein and crude ash in all tested plants, the higher NTC. The possible reason is that plant with 281 high membrane protein (crude protein) and nutrient (crude ash) contents promoted the efficient transport and

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The leaf electrophysiological parameters were measured using a LCR-6300 tester (Gwinstek, Taiwan, China) with a 322 frequency and voltage of 3 kHz and 1.5 V, respectively, as described by Zhang et al. [24]. Every mesophyll cell can 323 be regarded as a concentric sphere capacitor, many aligned mesophyll cells make up the leaf capacitor, the parallel 324 connection modes of LCR is thus applied. Firstly, the leaf was put between the two electrodes of a self-made 325 parallel-plate capacitor with a diameter of 7 mm (Fig. 3). And then leaf capacitance (C), impedance (Z) and R at 326 different clamping forces were continuously collected by adding the same quality iron blocks, and recorded 11-13 327 data each clamping force. Finally, leaf Xc and XL were respectively obtained according to formula (23) Table 2 The nutrient transport parameters of B. papyrifera in two habitats 453 Table 3 The nutrient transport parameters of four plants 454 Table 4 The nutrient transport parameters of S. tuberosum and C. annuum 455 Table 5 Growth age, habitat information, measuring conditions and sampling weather of all tested plants