An exogenous preparation for improving the heat tolerance of cucumbers and its application

Abstract

The present invention relates to the technical field of cucumber cultivation, and particularly to an exogenous preparation for improving the heat tolerance of cucumbers and its application. The present invention discovers that sucrose, chitosan, γ-aminobutyric acid, and calcium chloride have the effect of regulating the heat tolerance of cucumber seedlings. Among them, sucrose has a better effect, which can effectively improve the antioxidant enzyme activity of cucumber seedlings under heat stress, reduce the malondialdehyde content, and promote the expression of heat stress-related genes. Based on this, the present invention provides an exogenous preparation including sucrose, which can effectively improve the heat tolerance of cucumber seedlings and has important significance in the field of cucumber cultivation.

Description

Technical Field

[0001] The present invention relates to the technical field of cucumber cultivation, and particularly relates to an exogenous preparation for improving the heat tolerance of cucumbers and its application. Background Art

[0002] Cucumber (cucumis sativus L.) is a crop that likes warmth but is not heat-tolerant. The suitable temperature for its growth during the day is 25 - 30°C, and high temperatures above 35°C will have an adverse impact on its growth. Continuous high-temperature conditions will lead to a series of problems such as a decrease in the photosynthetic ability of cucumbers, a sharp increase in the content of reactive oxygen species in the body, and an increase in the degree of membrane lipid oxidation, which will further lead to a decrease in the fruit-setting rate of cucumbers, weak plant growth, affecting its yield and quality, and causing economic losses.

[0003] The heat tolerance of cucumbers is a quantitative trait controlled by multiple genes and is easily affected by the environment. The genetic laws and genetic models related to heat tolerance are not yet perfect, resulting in a long breeding cycle and low efficiency for heat-tolerant cucumber varieties. Spraying exogenous preparations is a method with quick results and low cost for plants to cope with high-temperature stress.

[0004] Existing research has found that sucrose not only serves as an important energy source and structural substance in plants, but also has a signal regulation function; sucrose can regulate the expression of transcription factors and enzyme activities to participate in plant growth and development and stress responses.

[0005] Chitosan is a product of the deacetylation of chitin. Due to its advantages such as the biological functionality, safety, and microbial degradability of natural polymers, it has been widely studied and applied in fields such as medicine, food, chemical engineering, and biomedical engineering. Summary of the Invention

[0006] In order to solve the problems existing in the prior art, the present invention provides an exogenous preparation for improving the heat tolerance of cucumbers and its application. Using sucrose as the exogenous preparation can effectively improve the heat tolerance of cucumber seedlings.

[0007] In the first aspect, the present invention provides the application of sucrose in regulating the heat tolerance of cucumbers.

[0008] Further, the application includes any one or more of the following:

[0009] i) Improving the antioxidant enzyme activity of cucumbers;

[0010] ii) Reducing the degree of membrane lipid oxidation of cucumbers;

[0011] iii) Reducing the malondialdehyde content of cucumbers;

[0012] iv) Increasing the pigment content in cucumbers.

[0013] Furthermore, the heat stress genes include: heat shock transcription factors and / or AP2.

[0014] Furthermore, regulating the heat tolerance of cucumbers means improving the heat tolerance of cucumbers.

[0015] Furthermore, the cucumbers are cucumber seedlings.

[0016] In a second aspect, the present invention provides an exogenous preparation for improving the heat tolerance of cucumbers, including sucrose; the concentration of the sucrose is 0.1 - 5 g / L.

[0017] Furthermore, the concentration of the sucrose is 0.1 - 2.5 g / L.

[0018] Furthermore, it further includes one or more of chitosan, γ-aminobutyric acid or calcium chloride.

[0019] Furthermore, the concentration of the chitosan is 0.05 - 1.5 g / L; and / or, the concentration of the γ-aminobutyric acid is 0.05 - 1.5 g / L; and / or, the concentration of the calcium chloride is 0.5 - 2 g / L.

[0020] As a preferred specific embodiment, the present invention provides an exogenous preparation, including 0.5 - 2 g / L sucrose + 0.1 - 1 g / L chitosan.

[0021] Furthermore, it further includes 0.1 - 1% Tween - 20.

[0022] The present invention further provides the application of the exogenous preparation in improving the heat tolerance of cucumber seedlings.

[0023] The present invention has the following beneficial effects:

[0024] The present invention discovers that substances such as sucrose, chitosan, γ-aminobutyric acid or calcium chloride can improve the heat tolerance of cucumber seedlings. Applying these substances during the growth period of cucumber seedlings can improve the antioxidant enzyme activity of cucumbers under heat stress conditions, reduce the degree of membrane lipid oxidation of cucumbers, reduce the malondialdehyde content of cucumbers, increase the pigment content of cucumbers, and promote the expression of heat stress-related proteins in cucumbers, thereby effectively improving the heat tolerance of cucumbers.

[0025] The technical solution provided by the present invention is simple to operate and convenient to use. After foliar spraying, the effect on improving the heat tolerance of cucumbers is significant and the effect is rapid.

[0026] The preparation provided by the present invention has a wide source of raw materials, low cost and is safe and non-toxic, and will not pose a safety hazard to plants or the human body. Description of the Drawings

[0027] Figure 1Schematic diagram of the effect of the specific reagent provided in Example 1 of the present invention on the antioxidant enzyme activity of cucumber seedlings under heat stress (Duncan's test method was used for difference analysis, and different lowercase letters indicate significant differences at the P<0.05 level, n = 3).

[0028] Figure 2 Schematic diagram of the effect of the specific reagent provided in Example 1 of the present invention on the malondialdehyde content of cucumber seedlings under heat stress.

[0029] Figure 3 Schematic diagram of the effect of γ-aminobutyric acid, chitosan, calcium chloride and sucrose provided in Example 1 of the present invention on the pigment content of cucumber seedlings under heat stress; among them, A is the effect on the chlorophyll a content, B is the effect on the chlorophyll b content, C is the effect on the carotenoid content, and D is the effect on the total chlorophyll content.

[0030] Figure 4 Schematic diagram of the effect of γ-aminobutyric acid, chitosan, calcium chloride and sucrose provided in Example 1 of the present invention on the expression of heat stress-related genes in cucumber seedlings under heat stress; among them, A is the effect on the relative expression level of HSF, B is the effect on the relative expression level of HSP20, and C is the effect on the relative expression level of AP2.

[0031] Figure 5 Schematic diagram of the effect of different concentrations of sucrose provided in Example 1 of the present invention on the antioxidant enzyme activity of cucumber seedlings under heat stress; among them, A is the effect on the POD activity, B is the effect on the CAT activity, and C is the effect on the SOD activity.

[0032] Figure 6 Schematic diagram of the effect of different concentrations of sucrose provided in Example 1 of the present invention on the malondialdehyde content of cucumber seedlings under heat stress.

[0033] Figure 7 Schematic diagram of the effect of different concentrations of sucrose provided in Example 1 of the present invention on the pigment content of cucumber seedlings under heat stress; among them, A is the effect on the chlorophyll a content, B is the effect on the chlorophyll b content, C is the effect on the carotenoid content, and D is the effect on the total chlorophyll content.

[0034] Figure 8 Schematic diagram of the effect of different concentrations of sucrose provided in Example 1 of the present invention on the expression of heat stress-related genes in cucumber seedlings under heat stress; among them, A is the effect on the relative expression level of HSF, B is the effect on the relative expression level of HSP20, and C is the effect on the relative expression level of AP2.

[0035] Figure 9Schematic diagram of the effects of different formulation combinations provided in Example 1 of the present invention on the antioxidant enzyme activities of cucumber seedlings under heat stress; among them, A is the effect on POD activity, B is the effect on CAT activity, and C is the effect on SOD activity.

[0036] Figure 10 Schematic diagram of the effects of different reagent combinations provided in Example 1 of the present invention on the malondialdehyde content of cucumber seedlings under heat stress.

[0037] Figure 11 Schematic diagram of the effects of different reagent combinations provided in Example 1 of the present invention on the pigment content of cucumber seedlings under heat stress; among them, A is the effect on chlorophyll a content, B is the effect on chlorophyll b content, C is the effect on carotenoid content, and D is the effect on total chlorophyll content.

[0038] Figure 12 Schematic diagram of the effects of different reagent combinations provided in Example 1 of the present invention on the expression of heat stress-related genes in cucumber seedlings under heat stress; among them, A is the effect on the relative expression level of HSF, B is the effect on the relative expression level of HSP20, and C is the effect on the relative expression level of AP2.

[0039] Figure 13 Schematic diagram of the growth conditions of cucumber seedlings under different reagent combinations provided in Example 1 of the present invention. Detailed implementation manners

[0040] The following examples are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0041] The cucumber materials used in the present invention are all publicly disclosed cucumber materials. The cucumber materials Xintaimici and S19096 of the present invention belong to R53 and R47 in the published article. This material has been publicly disclosed in the journal article (Liu B, Guan D, Zhai X, et al. Selection footprints reflect genomic changes associated with breeding efforts in 56 cucumber inbred lines[J]. Horticulture research 2019, 6(127).).

[0042] Unless otherwise specified, the reagents used in the embodiments of the present invention can be commercially purchased.

[0043] Example 1

[0044] 1. Test materials: Xintaimici, S19096.

[0045] 2. Test design

[0046] Take cucumber seeds with plump growth and place them in a constant temperature incubator for two days of germination. Select seeds with consistent germination and sow them in a seedling tray. The substrate is peat and vermiculite (peat:vermiculite is 2:1), and place it in a light incubator for cultivation. The growth conditions in the light incubator are set as 25°C / 12h during the day, light intensity 30000 lux; 18°C / 12h at night, light intensity 0 lux; air relative humidity 60%-80%. When the seedlings grow to the two-leaf and one-heart stage, select seedlings with consistent growth for heat stress treatment.

[0047] The heat stress conditions are set as 38°C / 9h during the day, light intensity 30000 lux; 28°C / 15h at night, light intensity 0 lux; air relative humidity 60%-80%.

[0048] 2.1 Effects of single reagent spraying on cucumber seedlings under heat stress

[0049] First, in this invention, four reagents, namely 0.5 g / L sucrose (SUC), 0.1 g / L chitosan (CTS), 0.1 g / L γ-aminobutyric acid (GABA), and 1.0 g / L calcium chloride (CaCl2), are respectively used to spray the leaves of Xintaimici seedlings under heat stress, and spraying deionized water is set as the control group (designated as CK).

[0050] Spray once one day before high temperature stress, and spray once every morning or evening during heat stress until the leaves are evenly wet.

[0051] After 2 h of heat stress, take cucumber leaves and store them in liquid nitrogen for real-time fluorescence quantitative PCR (qRT-PCR) to detect the expression of heat stress-related genes.

[0052] After 7 days of heat stress, measure the antioxidant enzyme activities (superoxide dismutase, antioxidant enzyme, catalase), malondialdehyde content, and photosynthetic pigment content (including chlorophyll a, chlorophyll b, total chlorophyll content, carotenoid) in the leaves of cucumber seedlings under different treatments;

[0053] Based on the performance of cucumber seedlings under the spraying of the four reagents in the above indicators, screen an optimal preparation and conduct subsequent concentration screening.

[0054] 2.2 Effects of spraying different concentrations of sucrose on cucumber seedlings under heat stress

[0055] Five concentration gradients of sucrose solution were set, which were 0.1 g / L, 0.5 g / L, 1.0 g / L, 2.5 g / L, and 5.0 g / L respectively; spraying deionized water was used as the control group (designated as CK). Another two cucumber varieties, Xintaimici and S19096, were selected to conduct high-temperature treatment and subsequent index determination simultaneously to explore whether spraying specific reagents has the same effect on improving the heat tolerance of cucumber seedlings of different varieties. The remaining steps (steps related to relevant detections) were the same as above.

[0056] 2.3 Effects of spraying specific reagent combinations on cucumber seedlings under heat stress

[0057] One or more reagents were selected from different exogenous preparations and combined with sucrose to set the following experimental groups, namely 1.0 g / L sucrose (SUC), 1.0 g / L sucrose + 0.1 g / L γ-aminobutyric acid (SUC + GABA), 1.0 g / L sucrose + 0.1 g / L chitosan (SUC + CTS), 1.0 g / L sucrose + 0.1 g / L γ-aminobutyric acid + 0.1 g / L chitosan (SUC + GABA + CTS); spraying deionized water was used as the control group (designated as CK). The rest was the same as above.

[0058] 3. Index determination methods

[0059] The activity of superoxide dismutase (SOD) was determined by the nitroblue tetrazolium (NBT) method, the activity of peroxidase (POD) was determined by the guaiacol method, and the activity of catalase (CAT) was determined by the ultraviolet spectrophotometry.

[0060] The content of malondialdehyde (MDA) was determined by the thiobarbituric acid method (TBA).

[0061] The chlorophyll content was determined by spectrophotometry. 0.15 g of leaf veins-removed leaves were soaked in 20 ml of 95% ethanol solution, shaken well after dark extraction for 36 h, and the optical density values of the extract at 665 nm, 649 nm, and 470 nm were measured with a Genesys180 model ultraviolet-visible spectrophotometer.

[0062] The total RNA of cucumber leaves was extracted using the Fast Universal Plant RNA Extraction Kit provided by Huayueyang Company. 1 μg of RNA sample was reverse-transcribed into complementary DNA (cDNA) using the FastKing One-Step Genomic DNA Removal and cDNA Synthesis Kit of TIANGN Company. qRT-PCR was performed using the QuantStudioTM 6 Flex System.

[0063] The reaction system was as follows: 5 μL of SYBR Green Mix, 0.5 μL of cDNA template, 4 μL of ddH2O, and 0.25 μL of each primer, and the total volume was 10 μL.

[0064] Using Ubiqutin as the internal reference gene, the relative expression level of the gene was calculated by the 2- -△CT CT method. The primer sequences are shown in Table 1:

[0065] Table 1 List of primers for measuring genes

[0066]

[0067]

[0068] 4. Data processing

[0069] The experimental data were analyzed by one-way ANOVA, principal component analysis and membership function analysis using SPSS 26.0 software, and multiple comparisons of significant differences (P<0.05) were performed using the Duncan test method; Microsoft Excel 2016 and Prism 6.0 software were used for graphing. The calculation of relevant indicators is as follows:

[0070] Principal component analysis: The principal component Cl was extracted according to the criterion that the eigenvalue is greater than 1;

[0071] Membership function value

[0072]

[0073] where x i represents the i-th comprehensive index, x min and x max represent the minimum and maximum values of the trait index scores on each principal component, respectively;

[0074] Weight w i :

[0075]

[0076] w i corresponds to the weight of the i-th principal component, p i represents the eigenvalue corresponding to the i-th principal component extracted;

[0077] Heat tolerance comprehensive value (D):

[0078]

[0079] 5. Results and analysis

[0080] 5.1 A specific reagent can improve the antioxidant enzyme activity of cucumber seedlings under heat stress

[0081] The cucumber seedlings under heat stress were sprayed with 0.1g / L γ-aminobutyric acid (GABA), 0.1g / L chitosan (CTS), 1.0g / L calcium chloride (CaCl2) and 0.5g / L sucrose (SUC) on the leaves at 7:00 am every day, and the deionized water was used as the control (CK). The SOD, POD and CAT activities were measured after 7 days of heat stress treatment.

[0082] The results are as follows Figure 1 As shown in the figure, in the four treatment groups of single spraying of four reagents, the activities of three antioxidant enzymes were all improved compared with the control group. Taking CAT enzyme activity as an example, GABA, CTS, CaCl2, and SUC increased by 90.6%, 85.6%, 59.45%, and 107.9% respectively compared with the CK group, and the activity was highest in the sucrose group. In summary, single spraying of GABA, CTS, CaCl2, and SUC can increase the antioxidant enzyme activity of cucumber seedlings under heat stress to varying degrees to respond to heat stress.

[0083] 5.2 Specific agents can slow down the degree of membrane lipid oxidation in cucumber seedlings under heat stress

[0084] High temperature stress can cause excessive accumulation of reactive oxygen in plants, aggravate the degree of cell membrane lipid oxidation, and thus lead to an increase in malondialdehyde (MDA) content. The higher the MDA content, the more serious the degree of cell membrane lipid peroxidation, and the greater the damage caused by high temperature to plants.

[0085] The results are as follows Figure 2 As shown in the figure, in the four treatment groups sprayed with exogenous agents, the MDA content decreased compared with the control group; the GABA, CTS, CaCl2, and SUC groups decreased by 23.5%, 15.5%, 5.6%, and 26.8% respectively compared with the high temperature control group; among them, the spraying of SUC, GABA, and CK showed a significant decrease. These data indicate that SUC and GABA can slow down the degree of membrane lipid oxidation in cucumber seedlings under heat stress.

[0086] 5.3 Specific agents can increase the pigment content of cucumber seedlings under heat stress

[0087] Photosynthetic pigments participate in the absorption and transfer of light energy or cause primary photochemical reactions during photosynthesis. The content of photosynthetic pigments is an internal factor that affects photosynthesis.

[0088] from Figure 3As can be seen from the results shown, when spraying γ-aminobutyric acid, chitosan, calcium chloride, and sucrose alone, the contents of chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids in cucumber leaves generally showed an upward trend compared with the high-temperature control group, and the high and low trends of different treatments were generally the same for different pigment contents. However, there were differences in the effects of spraying the four reagents on increasing pigment content. Chitosan treatment could increase the contents of chlorophyll a, chlorophyll b, and total chlorophyll; while sucrose showed the best performance in increasing the carotenoid content. Generally speaking, all four reagents could increase the pigment content of cucumber seedlings under heat stress, and the effects of different reagents on increasing pigment content were different.

[0089] 5.4 Specific reagents can promote the expression of heat stress-related genes in cucumber seedlings under heat stress

[0090] Heat shock protein (HSP) is a functional protein induced by heat stress, and its encoding gene is regulated by heat shock transcription factor (HSF). AP2 is a class of transcription factors unique to plants that participate in plant growth and development and respond to biotic and abiotic stresses. Existing studies have shown that in heat stress, the gene expression levels of this transcription factor family in cucumber increase.

[0091] The results are as Figure 4 shown. After spraying sucrose and γ-aminobutyric acid, the gene expression levels of endogenous HSF (CsaV3_2G025510), HSP20 (CsaV3_3G002770), and AP2 (CsaV3_1G022920) in cucumber increased significantly compared with other treatment groups. In addition, the expression levels of these three heat stress-related genes in cucumber were consistent, that is, in a certain treatment group, when the HSF expression level was higher, correspondingly, the expression levels of HSP20 and AP2 in its body were also relatively higher. In the single sucrose treatment group, the expression levels of the above genes in its body were also higher.

[0092] In summary, the four reagents GABA, CTS, CaCl2, and SUC all had varying degrees of effects on improving the antioxidant enzyme activity of cucumber seedlings under heat stress, alleviating the degree of membrane lipid peroxidation, increasing the photosynthetic pigment content, and promoting the expression of heat stress-related genes, and to a certain extent, they could alleviate the damage caused by heat stress to cucumber seedlings.

[0093] Based on the performance of different treatments in each index, sucrose had the best comprehensive effect on improving the heat tolerance of cucumber seedlings.

[0094] 5.5 Sucrose can improve the antioxidant enzyme activity of cucumber seedlings under heat stress

[0095] Since foliar spraying of sucrose has a significant effect on improving the heat tolerance of cucumber seedlings, five sucrose concentration gradients of 0.1 g / L, 0.5 g / L, 1.0 g / L, 2.5 g / L, and 5.0 g / L were further set, and deionized water spraying was used as a control (CK) to treat the test plants. After 7 days of heat stress treatment, the antioxidant enzyme activities among different treatments were measured under two cucumber cultivars, Xintaimici and S19096.

[0096] The results are as Figure 5 shown. Generally, the POD activities of both cultivars first increased and then decreased with the increase of sucrose concentration. The CAT activity of the Xintaimici cultivar showed fluctuations. Specifically, compared with the CK, the activities of the four treatment groups of 0.1 g / L, 0.5 g / L, 1.0 g / L, and 2.5 g / L increased by 16.0%, 41.0%, 42.9%, and 27.8% respectively; the 5.0 g / L sucrose group decreased by 10.6%; the SOD enzyme activity data showed that for both cultivars, low concentrations of sucrose promoted the increase of SOD activity, while high concentrations had no significant effect. It can be seen that too high sucrose concentration has an ineffective effect on improving heat tolerance; while appropriate sucrose concentration can significantly increase the antioxidant enzyme activities of cucumber seedlings of the two cultivars under heat stress.

[0097] 5.6 Sucrose can mitigate the degree of membrane lipid oxidation in cucumber seedlings under heat stress

[0098] As Figure 6 can be seen, in the Xintaimici cultivar, compared with the CK treatment, the MDA contents in the sucrose treatment groups of 0.1 g / L, 0.5 g / L, and 1.0 g / L decreased by 12.8%, 26.2%, and 11.0% respectively; in the S19096 cultivar under the same treatment, the MDA contents decreased by 25.9%, 26.2%, and 8.9% respectively; however, in both cultivars, there was no significant difference in the MDA contents between the 2.5 g / L and 5.0 g / L sucrose treatment groups and the CK group.

[0099] The results indicate that appropriate sucrose concentration can mitigate the degree of membrane lipid oxidation in cucumber seedlings under heat stress, while high sucrose concentration has poor effects.

[0100] 5.7 Sucrose can increase the pigment content in cucumber seedlings under heat stress

[0101] Subsequently, the present invention measured the effects of different concentrations of sucrose treatment on the contents of different photosynthetic pigments in two cucumber cultivars under heat stress.

[0102] As Figure 7 shown by the results, the effects of different concentrations of sucrose treatment on the contents of photosynthetic pigments in cucumber seedlings of the two cultivars under heat stress generally showed a trend of first increasing and then decreasing.

[0103] 5.8 Sucrose can promote the expression of heat stress-related genes in cucumber seedlings under heat stress

[0104] It is speculated in the present invention that the reason why spraying sucrose can improve the heat tolerance of cucumber seedlings may be related to the fact that sucrose can regulate the expression of transcription factors in vivo. For cucumber seedlings under heat stress treated with sucrose, various physiological indexes are better than those of the CK, and the expression levels of genes in the transcription factor family related to heat stress in their bodies also increase.

[0105] As Figure 8 can be seen, after spraying different concentrations of sucrose on the two cucumber varieties under heat stress treatment, the expression of genes HSF, HSP20, and AP2 will increase compared with the CK. This indicates that treating cucumber seedlings under high-temperature stress with sucrose can promote the expression of their heat stress-related genes.

[0106] 5.9 Comprehensive effects of different reagent treatments on improving the heat tolerance of cucumber seedlings

[0107] To comprehensively measure the index parameters and more comprehensively reflect the heat tolerance of cucumbers among different treatments, the evaluation method of the present invention combines the principal component analysis (PCA) and the membership function method. The principal component analysis can reduce the dimensions of multiple significantly correlated and information-overlapping indexes into several independent principal components that can reflect a large amount of information of the original data, and assign weights to each index; then, according to the membership function method, calculations are performed using the values calculated by the principal component analysis. Finally, a comprehensive heat tolerance value is obtained, and the comprehensive heat tolerance of cucumber seedlings under each treatment is reflected according to the level of this comprehensive heat tolerance value.

[0108] The results calculated based on this comprehensive method for the measured experimental data are shown in Table 2 and Table 3. As can be seen from Table 2, the measured heat tolerance indexes are divided into three independent principal components Cl1, Cl2, and Cl3 based on the principal component analysis, with contribution rates reaching 39.4%, 26.6%, and 21.2% respectively, and the cumulative contribution rate reaching 87.1%. As can be seen from Table 3, whether it is Xintaimici or S19096, after treatment with different concentrations of sucrose, the highest score in the comprehensive heat tolerance value is obtained with 1.0 g / L sucrose. Therefore, the comprehensive effect of treating with 1.0 g / L sucrose is the best for improving the heat tolerance of cucumbers.

[0109] Table 2 Load conditions of each index on different principal components calculated based on the principal component analysis

[0110]

[0111]

[0112] Table 3 Comprehensive heat tolerance values of cucumber seedlings under different treatments

[0113]

[0114] 5.10 Specific reagent combinations can improve the antioxidant enzyme activities of cucumber seedlings under heat stress

[0115] In this invention, the combinations of SUC with GABA and CTS were used to spray the leaves of cucumber seedlings of two varieties under heat stress. Five treatments were set up, namely 1.0 g / L sucrose (SUC), 1.0 g / L sucrose + 0.1 g / L γ-aminobutyric acid (SUC+GABA), 1.0 g / L sucrose + 0.1 g / L chitosan (SUC+CTS), 1.0 g / L sucrose + 0.1 g / L γ-aminobutyric acid + 0.1 g / L chitosan (SUC+GABA+CTS), and deionized water (CK).

[0116] From Figure 9 As can be seen from the results shown, the SOD, POD, and CAT enzyme activities of the two varieties were improved in the four treatments of SUC, SUC+GABA, SUC+CTS, and SUC+GABA+CTS compared with CK, but there were differences in the effects of different treatments on enhancing enzyme activities. For example, in Xintaimici, the POD activity increased by 47.2% after single spraying of sucrose compared with the CK group; while the POD activity of SUC+CTS increased significantly by 103.8% compared with the CK group. Another example is in S19096, the POD activities of SUC, SUC+GABA, SUC+CTS, and SUC+GABA+CTS all increased significantly compared with the CK group. In terms of SOD and CAT activities, different treatment groups also had varying degrees of increase compared with the CK group. It can be seen that specific reagent combinations can improve the antioxidant enzyme activities of cucumber seedlings under heat stress, and the effect may be better than that of single spraying.

[0117] 5.11 Specific reagent combinations can slow down the degree of membrane lipid oxidation of cucumber seedlings under heat stress

[0118] From Figure 10 As can be seen from the results shown, after spraying the combinations of SUC, SUC+GABA, SUC+CTS, and SUC+GABA+CTS on Xintaimici under heat stress, the malondialdehyde content decreased significantly by 19.8%, 21.0%, 23.8%, and 22.0% respectively compared with CK; while in S19096, SUC, SUC+GABA, and SUC+CTS also showed significant decreases compared with CK. Therefore, it is concluded that specific reagent combinations can slow down the degree of membrane lipid oxidation of cucumber seedlings under heat stress.

[0119] 5.12 Specific reagent combinations can increase the pigment content of cucumber seedlings under heat stress

[0120] By Figure 11As can be seen from the results shown, in terms of photosynthetic pigments, single spraying of sucrose and spraying of sucrose in combination with different reagents can all increase the photosynthetic pigment content of the two varieties to varying degrees. For the two varieties, after treatments of SUC, SUC+GABA, SUC+CTS, and SUC+GABA+CTS, the total chlorophyll content of cucumber seedlings increased compared with that of CK; the carotenoid content increased significantly with the treatments of SUC+CTS and SUC+GABA+CTS; among them, the total chlorophyll content and carotenoid content in the SUC+CTS group were the highest in both varieties, indicating that this combination had the best effect on increasing the pigment content of cucumber seedlings under heat stress.

[0121] 5.13 Specific reagent combinations can promote the expression of heat stress-related genes in cucumber seedlings under heat stress

[0122] From Figure 12 it can be seen that after spraying the above-mentioned specific combination of reagents on the Xintaimici variety under heat stress treatment, the relative expression levels of endogenous HSF, HSP20, and AP2 in cucumbers increased compared with those of CK, but in S19096, SUC+CTS could significantly increase the expression levels of the three heat stress-related genes in cucumbers. It can be seen that spraying the compound reagent can promote the expression of certain heat stress-related genes in cucumber seedlings under heat stress.

[0123] 5.14 Specific reagent treatments can alleviate heat stress damage to cucumber seedlings

[0124] After continuously treating cucumber seedlings with heat stress for 7 days and spraying the corresponding preparations on the leaves in this invention, the growth conditions of cucumber seedlings under different treatments were observed. The results are as Figure 13 shown. After heat stress treatment, cucumber seedlings showed varying degrees of wilting, yellowing of leaves, and drooping. Among the two varieties, the CK group had the weakest growth and the most obvious wilting degree; the other four treatment groups had better growth, with the leaves showing a small degree of wilting, but the plant body was more robust and grew faster. The results indicate that spraying specific exogenous preparations can alleviate the damage caused by heat stress to cucumber seedlings and maintain the normal growth of cucumber seedlings under heat stress.

[0125] Finally, according to the comprehensive evaluation method, the heat tolerance of the two cucumber varieties after treatment with different preparations under heat stress was comprehensively evaluated. As can be seen from Table 4, among the two varieties, the combination of sucrose + chitosan (SUC+CTS) had the highest comprehensive heat tolerance value and the best heat tolerance effect.

[0126] Table 4 Comprehensive heat tolerance values of cucumber seedlings under different reagent combinations

[0127]

[0128]

[0129] In summary, the best effect is achieved with the formulation of 1.0 g / L sucrose + 0.1 g / L chitosan, which can significantly improve the heat tolerance of cucumbers.

[0130] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made thereto based on the present invention, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection required by the present invention.

Claims

1. Application of an exogenous preparation for improving heat tolerance of cucumber in improving heat tolerance of cucumber seedlings, characterized in that, The exogenous preparation includes sucrose and chitosan; the concentration of the sucrose is 0.1 - 5 g / L, and the concentration of the chitosan is 0.05 - 1.5 g / L.

2. The application according to claim 1, wherein It further includes one or more of γ-aminobutyric acid or calcium chloride.

3. The application according to claim 2, wherein The concentration of the γ-aminobutyric acid is 0.05 - 1.5 g / L; and / or the concentration of the calcium chloride is 0.5 - 2 g / L.

4. The application according to any one of claims 1-3, characterized in that, It further includes 0.1 - 1% Tween-20.

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