Highland barley (Hordeum vulgare L.), as the dominant crop on the Qinghai-Tibetan Plateau, is a typical representative of plants adapted to extreme environmental conditions. However, the harsh environment, severe salinisation and frequent freezing and thawing in the Qinghai-Tibetan Plateau are main limiting factor for crop growth in this region. The physiological response of highland barley to salinisation and freeze–thaw stresses was studied in this paper. Under the combined stresses of 60 mmol/L NaCl·60 mmol/L NaHCO3 and freeze–thaw cycles (10, −5, and 10°C), the changes in the relative moisture content, relative electrical conductivity, soluble protein, malondialdehyde (MDA) and photosynthetic indices Pn and E in seedling leaves of eight groups of treatments (CK, S, A, S-A, CK (FT), S (FT), A (FT), and S-A (FT)) were analysed. Results showed that a single stress did not cause a change in the MDA content. All of the combined stresses in S-A, CK (FT), S (FT), A (FT), and S-A (FT) treatments increased the MDA content of barley seedlings, and the MDA content of S-A (FT) reached 28.438 at T2 (−5°C) μmol/g. During the freeze–thaw cycle, the cell membrane of seedlings was damaged more seriously by alkali stress, which showed a significant increase in relative conductivity. The relative moisture content value of seedlings was more than 100% because the seedlings could absorb more moisture due to mechanical injury. The protein content of osmoregulatory substances in highland barley seedlings increased with increasing stress, indicating resistance to stress. Moreover, the effect of freeze–thaw stress on photosynthesis was more significant. The changes in indices proved that an appropriate amount of salt stress could improve the resistance of the plant cell membrane. Alkali stress had a significant effect on the growth of highland barley seedlings. Freezing and thawing can aggravate the damage of saline–alkali stress to highland barley seedlings, resulting in changes in the biological membrane permeability and photosynthesis of seedlings. The fluctuation of osmoregulation substance content confirmed that highland barley seedlings had a certain degree of stress resistance. Freeze–thaw cycles will aggravate the damage of land salinisation to highland barley seedlings. To better reduce the impact and loss of land salinisation and freeze–thaw disasters on agriculture in the Qinghai-Tibetan Plateau, priority should be given to solving freeze–thaw stress in the process of grain production.
Background Qinghai-Tibet Plateau is known for characteristics of high altitude, low rainfall and varying temperature, and the crops in this area are susceptible to abiotic stresses such as drought, basic salt and freeze-thaw that caused damages in different perspectives such as the permeability of biological membrane, osmotic adjustment, and antioxidant enzyme system. Hordeum vulgare L. is an indispensable crop in plateau and plays an important role in agricultural ecosystem as well.Result In this experiment, H. vulgare L. was used as experimental material and the physiological characteristics soluble protein (SP) content, malondialdehyde (MDA) content, antioxidant enzyme activity and relative water content (RWC) of seedlings were examined under freeze-thaw condition combined with drought and alkali stress.Conclusion Research results indicated that under the combined stresses of basic salt and drought, H. vulgare L. seedlings were damaged by lipid peroxidation, weakened superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities, while enhanced osmotic adjustment ability in plants cell. It was suggested that, in agricultural management, the simultaneous occurrence of two stresses, basic salt and drought, should be avoided in the early stage of H. vulgare L. planting to reduce the physiological stress on plants.
The freeze–thaw and allelopathy from alien giant ragweed (Ambrosia trifida L.) and artemisinin have led to a serious stress to plants, influencing the agricultural quality and crop yield in north-east China. Yet, little is known how allelopathy affect plants under the freeze–thaw process. In this study, the characteristics in winter rye (Secale cereale L.) seedlings were investigated by laboratory simulation. The results showed that during the freezing process, application of artemisinin and A. trifida extract significantly increased the soluble protein content and accelerated lipid peroxidation, while they significantly inhibited antioxidant enzymes, photosynthesis and respiration (P < 0.05). During the thawing process, the freezing pressure decreased, and activities of antioxidant enzymes were significantly improved to mitigate artemisinin and A. trifida extract induced stress (P < 0.05). In addition, the sensitivity of the investigated metabolic processes in winter rye seedlings were highest to artemisinin and A. trifida extract in the freezing process. This study suggested that the stress response induced by artemisinin and A. trifida extract on winter rye seedlings in the freezing process was greater than that in the thawing process.
Secale cereale L. (rye) as an overwinter forage usually harvested in the autumn, widely grows in the northeastern China, where the temperature varies widely from day to night. In this area, the crop is confronted with not only freeze–thaw stress, but also the soil salinization. In this study, the rye seedlings under alkaline salt (AS) stress were subjected to both cutting treatment (CT) after growing for 7 days and freeze–thaw (FT) stress(10/−5°C) after 6 days regrowth. The changes of soluble protein (SP), malondialdehyde (MDA), relative water content (RWC), catalase (CAT) and superoxide dismutase (SOD) activities in seedlings were studied to analyze the physiological effects of FT and AS stress with CT. The results indicated, under the combined stress, the enzyme activity and RWC decreased and the soluble protein and MDA content increased. Cutting treatment led to the accumulated of MDA, increase of enzyme activity and decrease of RWC in seedlings. The finding from the study indicates that the CT could aggravate the membrane peroxidation under the combined stress of FT and AS and enhance the osmotic adjustment ability of rye and activated the antioxidant enzyme system. The rye having been cut is more sensitive to the compound stress.
In Qinghai-Tibet Plateau, crops are commonly subjected to freeze–thaw and salt stress factors simultaneously, and allelopathy is common, which affects the growth of highland barley (Hordeum vulgare L.), the largest food crop in Tibet. In order to explore the effects of artemisinin, salt and freeze–thaw (FAS) stress on physiological characteristics of highland barley seedlings, hydroponic experiment was carried out with the addition of 20 mg/L artemisinin and 150 mM NaCl as well as the simulation of freeze–thaw environment. The results suggested that under combined stress, the soluble protein content in combined stresses of artemisinin, FAS increased by 97.8%, the variation of relative conductivity in FAS group was lower than that in combined salt and freeze–thaw stress (FS), the relative water content decreased significantly (P < 0.05), the malondialdehyde (MDA), H2O2 and soluble sugar content in FAS group accumulated but less than those in FS group, and the superoxide dismutase (SOD) activity in combined artemisinin and freeze–thaw stress (FA) and FAS groups decreased. In addition, after freeze–thaw treatment, photosynthesis was weakened, and internal CO2 conentration (Ci) in FAS group significantly decreased (P < 0.05). This study proved that appropriate amount of artemisinin can alleviate the damage of salt and freeze–thaw stress on barley seedlings.
Crops are commonly subjected to freeze-thaw and salt stress factors simultaneously in Qinghai-Tibet Plateau. In the agricultural field, potassium fulvic acid can not only promote plant growth and increase crop yield but also enhance plant resistance to stress. In this study, the changes of osmotic adjustment substances, antioxidant enzyme activities and photosynthetic characteristics of barley seedlings under alkaline salt and freeze-thaw stress were investigated by laboratory simulation. The results showed that under single alkaline salt stress, the soluble protein content increased significantly (P < 0.05), and the malondialdehyde (MDA) content of seedlings increased by 63.1%; however, antioxidant enzymes activities and photosynthetic rate of barley seedlings decreased. Under combined stresses of alkaline salt and freeze-thaw, the soluble protein content, antioxidant enzyme activities, and photosynthetic rate of barley seedlings decreased; in contrast, the MDA content of seedlings increased. With the addition of potassium fulvic acid, the soluble protein content of seedlings increased, MDA content decreased significantly (P < 0.05), and enzyme activities tended to be stable. This study revealed that the addition of a proper amount of potassium fulvic acid could mitigate the damage of alkali salt and freeze-thaw stress on barley seedlings.
Increasing levels of sodium carbonate are major causes of grassland alkalinization in the Song-Nen Plain of northeast China. In winter-spring alternation, plants are often subjected to double stresses of alkaline salt and freeze-thaw. Here, Medicago sativa CV. Zhongmu No.1 seedlings were used to study the effects of laboratory-simulated basic salt (BS) and freeze-thaw (FT) stresses on the contents of osmoregulatory substances, biological membrane permeability, and antioxidant enzyme activity. The results showed that under individual BS-or FT-stress, the soluble protein in seedlings decreased by 9.6-20.2%, proline and MDA contents increased by 18.4-48.1 and 7.8-37.7%, respectively. Furthermore, the activities of SOD and POD increased by 6.2-24.9 and 4.8-30.3%, respectively. During the freezing and thawing cycles, both proline and MDA contents initially increased and then decreased; these observations contrasted with those for soluble protein content. Activities of SOD and POD increased in attempts to resist reactive oxygen species (ROS). Moreover, M. sativa CV. seedlings under combined stress of BS and FT showed significantly higher physiological responses than those under individual stress (BS-or FT-stress). The results of this study demonstrate the molecular basis for BS-and FT-stress tolerance by M. sativa. In turn, this could lead to strategies for further enhancement of these tolerances in the plant.
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