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This paper mainly explores the physiological response of seedlings to PEG osmotic stress, which provides a theoretical basis for revealing the physiological mechanism of drought resistance of Gymnocarpus.
Seedlings of gymnocarpus were used as experimental materials, and PEG-6000 with different mass fractions was used for 8 h and 24 h to produce osmotic stress, and some water physiological indexes and antioxidant indexes of leaves were determined.
Under PEG stress, the relative water content of leaves of seedlings decreased significantly. At 24 h of stress, with the increase of PEG concentration, the content of bound water/free water increased significantly and then decreased.
Physiological characteristics and adaptation mechanisms of gymnocarpus
Gymnocarposprzewalskii belongs to the genus Caryophyllaceae, which is a rare and endangered plant of the ancient Mediterranean remnants, mainly distributed in most of the Hexi Corridor of Gansu Province, some areas of Xinjiang, Inner Mongolia and the central and western parts of Ningxia in mainland China.
It has the characteristics of drought resistance, wind erosion resistance to sand burial, and salt and alkali tolerance, and is of great scientific significance for the study of the evolution and climate change of xerophytes in northwest China and Inner Mongolia.
Experts predict that the precipitation in the suitable area of Gymnocarpus will be 40-200 mm in the future, indicating that Gymnocarpus has strong drought adaptability. Due to the poor habitat in the distribution area and the impact of human activities, the population of Gymnocarpus has been decreasing.
Affected by global climate change, drought has become a major problem in today's society, which has an important impact on the growth and development of plants, and is also the main factor limiting plant growth.
Experts have shown that under arid environmental conditions, plants will prevent damage to the body by adjusting their own physiological and biochemical characteristics, or initiating self-protection mechanisms, which is manifested in water metabolism, osmoregulation, and antioxidant system response.
When plants are subjected to osmotic stress, they can actively accumulate soluble sugars, prolines and soluble proteins to achieve osmotic regulation and protect cell structure and function.
This significantly increased the ability of plants in osmoregulation and adaptability to arid environment, and improved the survival ability of plants under adversity, and the changes in their content could effectively reflect the strength of plant drought resistance.
In addition, regulating the balance of reactive oxygen species through the antioxidant enzyme system is another important mechanism for plants to adapt to drought.
Therefore, studying the changes of water metabolism, osmoregulatory substance content and antioxidant enzyme system in plants can effectively understand the physiological response mechanism of plants to drought.
Polyethylene glycol, on the other hand, has a strong osmotic pressure, which causes plant cells to lose water and form an environmental state of drought stress. The osmotic stress effect of PEG-6000 was similar to that of normal plant growth and drought.
Some experts also used different concentrations of PEG-6000 solution to soak the roots of the seedlings to study the changes of physiological indexes.
Therefore, it is feasible to study the physiological response characteristics of seedlings to simulated osmotic stress by treating seedlings with different concentrations of PEG-6000 solution to produce osmotic stress.
At present, the current research on the current stage of gymnocarpus mainly involves seed germination, leaf anatomy, ecological adaptability, population structure and spatial distribution pattern.
However, there have been no reports on the physiological response of seedlings under different stress times and different stress degrees in the study of osmotic stress response.
Therefore, this study took the seedlings of gymnocarpus as the research object, analyzed their physiological responses under different PEG concentrations and different stress times, and explored their physiological adaptation mechanism to osmotic stress, so as to provide a theoretical basis for the study of drought resistance mechanism of gymnocarpus.
Seedling cultivation assay
The seeds were collected from the Anxi Extreme Arid Desert National Nature Reserve in Gansu Province, and the population of Gymnocarpus was 12 h·d-1 and the humidity was 60%.
When it grows in the artificial climate chamber for 2 months and the rhizome of the seedling is lignified, it is transplanted into 25cm×30cm pots, managed indoors, and moved outdoors in mid-May to grow under natural conditions.
Seedlings grew to August, seedlings with consistent growth were selected, the soil on the root system was washed, and treated with 0%, 5%, 10%, 15% and 20% polyethylene glycol solution, with 5 replicates for each treatment and 3 plants for each repeat.
After 8 h and 24 h of stress treatment, the leaves were collected and the physiological indexes were repeated 3 times, and the samples were taken from the leaves of the same part of the plant.
The relative water content was determined by drying and weighing, the content of bound water and free water was determined by Abbe refractometer, the content of proline was determined by sulfosalicylic acid, and the content of soluble sugar was determined by anthone colorimetric method.
The soluble protein content can also be determined by Coomassie brilliant blue G-250 staining method, malondialdehyde content by thiobarbituric acid method, and superoxide dismutase activity by nitrogen blue tetrazolium reduction method.
The peroxidase activity was determined by guaiacol method, and the catalase activity and ascorbate peroxidase activity were determined with reference to the research method.
Effects of PEG stress on the content of osmotic regulators in leaves of Gymnocarpus nugs
With the increase of stress time and stress degree, there were differences in the content of osmotic regulatory substances in seedling leaves.
The contents of Pro and SS in seedling leaves showed an increasing trend as a whole, but when the PEG concentration reached 15%, the Pro content showed a decreasing trend at 8 h and 24 h.
At 8 h of stress, the Pro content of PEG increased significantly at 5%, 10% and 20%, and at 24 h of stress, the Pro content of leaves increased first, then decreased and then increased.
However, all of them were significantly higher than those of CK, and the Pro content reached the highest under 20% PEG treatment, and with the increase of PEG concentration, the Pro content was 2.5 times, 3 times, 2.5 times and 3.5 times higher than that of CK, respectively.
Under the same PEG stress concentration, there were significant differences in leaf Pro content at 8h and 24h.
When PEG was 10% and 15%, the SS content was significantly higher than that of CK, and when the PEG concentration increased to 20%, the SS content decreased significantly.
At 24 h of stress, the SS content of leaves showed a fluctuating trend, but the SS content of all PEG stress treatments was significantly higher than that of CK, and the SS content of leaves reached the maximum when the PEG concentration was 20%, which was 48.3% higher than that of CK.
Moreover, there were differences in the response of SP content to the change of PEG stress concentration when the PEG stress time was different.
At 8h of stress, the SP content decreased with the increase of PEG concentration, and the SP content of each treatment was significantly lower than that of CK when the PEG concentration was ≥ 10%, and the SP content was the lowest when the PEG concentration was 20%, which was 40% lower than that of CK.
At 24 h of stress, the SP content of leaves increased first and then decreased, and there was no significant difference between SP content and CK in different PEG concentrations.
When the PEG concentration was 10%~20%, the SP content at 24 h was significantly higher than that at 8 h, which was 1.4 times, 1,7 times and 1.5 times higher than that at 8h, respectively.
With the increase of PEG concentration and the prolongation of stress time, the MDA content of leaves increased gradually. At 15% and 20% PEG stress for 8 h, the MDA content was significantly higher than that of CK, which was 1.7 and 1.8 times higher than that of CK.
At 24 h of stress, the MDA content under different concentrations of PEG was significantly higher than that of CK, and the content of MDA was the largest under 20% PEG treatment, which was 2.6 times that of CK.
Under the same PEG concentration, the MDA content at 24 h was significantly higher than that at 8 h, and with the increase of PEG concentration, it was 1.8 times, 1.6 times, 1.4 times and 1.5 times, respectively, and the degree of membrane lipid peroxidation was significantly increased.
With the increase of PEG concentration and the extension of stress time, the H2O2 content in leaves increased significantly1. When PEG was stressed for 8 h, there were significant differences between H2O2 content and CK at different PEG treatment concentrations.
Compared with CK, the increase was 53.3%, 51.3%, 16.8% and 59.6%, and the content of H2O2 was significantly higher than that of CK at 24 h under stress, and the highest content was higher at PEG concentration of 20%, which was 1.6 times that of CK.
The H2O2 content at 24 h was significantly higher than that at 8 h under the same PEG concentration, and with the increase of PEG concentration, it was 1.4 times, 1.5 times, 2.0 times and 1.6 times that of 8 h of stress, respectively, and reached the most significant concentration at 15% PEG treatment.
With the increase of PEG stress, the antioxidant enzyme activity of seedlings showed an overall upward trend.
At 8 h and 24 h of PEG stress, the SOD activity at each treatment concentration was significantly higher than that of CK, and the maximum value was reached at PEG concentration of 20%, which was 1.9 and 2.8 times higher than that of CK, respectively.
Under the same PEG treatment concentration, the SOD activity of leaves was significantly enhanced at 24 h compared with that at 8 h, which was 1.6 times, 1.8 times, 1.5 times and 1.5 times that of 8 h, respectively.
At 8 h of stress, the POD activity of leaves increased slowly, and when the PEG concentration was ≥ 15%, the POD activity was significantly higher than that of CK.
At 24 h of stress, the POD activity of different concentrations of PEG was significantly higher than that of CK, and the POD activity reached the maximum value of 20% PEG concentration, which was 12.9 times that of CK.
Under the same concentration of PEG stress, the POD activity of leaves was significantly higher at 24 h than at 8 h, which was 4.1, 6.9, 6.4 and 5.9 times that of 8 h, respectively.
CAT activity was significantly higher than that of CK at 8 h of stress, and was the highest at 15% PEG concentration, which was 5.7 times that of CK.
Water metabolism index is the most intuitive indicator of water status of plants when they are subjected to water stress. The higher and more stable the RWC, the stronger the drought adaptability of plants.
Studies have shown that when Va/Vs is low, it means that the metabolic activity in the plant is stronger, and vice versa, the metabolism is weaker, but the resistance is stronger.
The water deficit was more obvious when PEG was stressed for 24 h, and the leaf could significantly increase the proportion of water binding.
It actively accumulates proline and soluble sugar, improves water retention capacity, reduces osmotic potential, maintains cell turgor pressure, and adapts to a certain degree of osmotic stress.
PEG stress forced membrane lipid peroxidation to occur in the leaves of Gymnocarpus oleifice, and the excessive accumulation of H2O2 content during PEG stress for 24 h produced obvious peroxidation damage to the leaf membrane system.
The seedlings significantly enhanced the activities of SOD, POD, CAT, and APX in leaves, scavenged excessive free radicals, alleviated membrane system damage, and alleviated osmotic stress.