| Low temperature is a critical factor in restricting the regional distribution and seasonal growth of plants in the North of China.Cold injury,especially freezing injury,always brings huge loss for the plant production related industries.Low-temperature stress also influence the production of landscape plants and output of crops.The stress mechanism and the plant resistance mechanism have always been a research focus.As a perennial shade herbage,Oreorchis patens is greatly cold-resistant and can resist the low temperature of-40℃ under natural conditions different from most of the other Orchidaceae plants,Oreorchis patens grows new leaves in summer and keeps evergreen in winter,so it is the excellent undergrowth greening cover plant in Northeastern region.In this paper,the blade structure and physiological and biochemical winter-resistance mechanism of Oreorchis patens were researched to reveal the winter-resistance mechanism of Oreorchis patens and promote its wide application in landscaping by observing its structure changes,determining indexes such as photosynthetic system and stress-resistance substances.The low-temperature injury of plants is manifested in the destruction of the leaf cell structure,the increase of membrane permeability and ion leakage,the enhancement of membranous peroxidation,and the weakening of photosynthesis.In severe cases,it will causes plant injury or death.During the temperature declined,the MDA content increased first and then decreased,and the difference was significant(P<0.05),furthermore,it was always lower than other plants,indicating that the biomembrane of Oreorchis patens hadn’t been seriously damaged,which was inconsistent with the results of transmission electron microscope observation in this experiment.It might be caused by the relatively large temperature span of the test conditions below zero degree.In normal situations,the enzyme and non-enzyme substances within the plant cells constitute the free radical scavenging system.The generation and scavenging of intracellular free radicals is a dynamic balance process.The free radicals in plant cells are usually at a low level and aren’t sufficient to cause intracellular damage.The experimental results showed that the activity of SOD and CAT increased first and then decreased with significant differences(P<0.05),and the activity of CAT was maintained at a relatively high level,which might be due to the fact that low temperature stress activates the antioxidant system of tissues and cells to improve the low-temperature stress capacity of tissues and cells.The resistance to cold stress increased.However,as temperature gone further down,the leaves of Oreorchis patens entered a dormant state,and the activity of the enzyme decreased;The activity of POD was lower than that of other plants,and the activity was slightly increased during the temperature declining.so that POD didn’t play an important role in the winter-resistance of Oreorchis patens.Under low temperature stress,as the temperature declined,the palisade tissue thickness and spongy tissue thickness of the leaves of Oreorchis patens became smaller,the cytoarchitecture compactness was decreased,while the intercellular space was extended.The ultrastructure of the leaf cells of Oreorchis patens was severely damaged under the low-temperature stress and the deformed cell walls can be observed clearly,it means that as the low-temperature stress intensified,the integrity of the cell membrane was severely damaged,the electrolyte penetration increased and winter injury occurred. |
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