| Purple Majesty is the gold medal winner chosen in 2003 by All America Selections (AAS) who has the good reputation of "Oscar" of world breeding industry, which is highly valuable in scientific researches and ornamental. In recent years, Purple Majesty has been promoted to the garden construction in various cities because of its excellent ornamental, and Purple Majesty will most likely be an important green plant in the city. Drought stress, high temperature stress and the double stress were simulated in the experiment to research the correlative physiological and biochemical indexes of Purple Majesty,at the same time, salicylic acid’s mitigating the negative effects of temperature stress on Purple Majesty was also studied. By this study, we hope to elucidate a series of response mechanisms of Purple Majesty on drought stress, high temperature stress and the double stress and achieve the goal of further increasing the resources of the landscape ground cover plants in Chongqing. The flowing is the results:1.Root vigor and root ratio will increase when the area and root volume increase,as the stress time extend, drought stress on the Purple Majesty at the early time of seeding can promote seedling root growth, so that the material content of fresh roots, total root length, root surface total root length, root surface area, root volume and root-shoot ratio decreased root activity is also reduced. Drought stress,high temperature stress and the double stress can inhibit the root growth of Purple Majesty seedlings, while reduce the fresh root material content of seedlings, total root length, root surface area and root volume, the number of root tips. SA treatment can increase Purple Majesty seedings roots fresh matter content, total root length, root surface area, root volume, root activity and root-shoot ratio caused by the drought stress, high temperatures stress and drought, high temperature double stress. This proved that SA treatment can slow down the root injury because of drought, high temperatures and the double stress, and then promote the root growth of seedings.2.Drought stress,high temperature stress and the double stress treatment significantly reduced the number of chloroplast grana, grana of stacking was not obvious, and the grana lamellae arranged in a loose, indicating that drought stress, high temperatures stress and drought, high temperature double stress treatment can make varying degrees of damage on membrane structure of chloroplasts.At the condition of drought stress, high temperatures stress and drought, high temperature double stress,0.5mmol·L-1 of SA treatment on the Purple Majesty seedlings can make Chloroplast membrane structure relatively complete, grana lamellae more closely, indicating that SA can effectively protect the chloroplast membrane structure. Drought stress, high temperature stress and the double stress treatment reduced the chlorophyll a, chlorophyll b, total chlorophyll content and Car content of Purple Majesty seedlings, while SA treatment can increase the chlorophyll a, chlorophyll b, total chlorophyll content and Car content of Purple Majesty seedlings under drought stress, high temperature stress and the double stress treatment at each treatment period.3.Drought stress, high temperature stress and the double stress treatment reduced the photosynthetic capacity of the leaves of Purple Majesty seedlings, making the net photosynthetic rate, stomatal conductance, transpiration rate decreased, while SA treatment can increase the photosynthetic capacity of the leaves of Purple Majesty seedlings,in this way, making the net photosynthetic rate, stomatal conductance, transpiration rate increased in varying degrees.In the drought stress,high temperature stress and the double stress treatment, Fo andΦPSⅡof Purple Majesty seedlings leaves was significantly lower than the control, SA treatment can effectively increase the Fo andΦPS II of Purple Majesty seedlings under drought stress,high temperature stress and the double stress treatment; In the drought stress and high temperature double stress, Fv/Fm of Purple Majesty seedlings leaves was significantly lower than the control, SA treatment can effectively increase Fv/Fm of Purple Majesty leaves under drought stress,high temperature stress and the double stress treatment, indicating that drought and high temperature stress on PSII damage was less than the double stress of drought, heat damage to PSII.4.The ability difference to generate hydroxyl radicals was not significant between heat stress and control in 3-7 days,but in the 9th day, the content increased rapidly and significantly higher than the control;The ability to generate hydroxyl radicals of Purple Majesty seedlings increased rapidly as time goes by under drought stress and double stress,and the ability to generate hydroxyl radicals in stress treatment was higher than the control in all the time; SA treatment can reduce the ability to generate hydroxyl radicals under drought stress,high temperature stress and the double stress treatment. Compared to the control, the anti-superoxide anion radical activity unit under the drought stress, high temperature stress and the double stress treatment reduced a little, while after the SA treatmen, anti-superoxide anion radical activity unit were higher than the coressponding stress treatment.Hydrogen peroxide levels were all somewhat higher than control under drought stress, high temperature stress and the double stress treatment, while after SA treatmen,it will be somewhat lower than the corresponding stress theatment, indicating that SA treatmen had some role in mitigation under the drought stress,high temperature stress and the double stress treatment.5.The relative conductivity and MDA content of Purple Majesty seedling leaves increased if drought stress, high temperature stress and the double stress treatment was significant or very significant, With the stress treatment time, the relative conductivity and MDA content had a increasing trend,and relative conductivity rate of increase in drought stress and drought,heat double stress is greater than the single heat stress treatment. The SA treatment can reduce the relative conductivity and MDA content of Purple Majesty seedling leaves because of drought stress, high temperature stress and the double stress treatment, playing a protective role on the membrane structure.The soluble protein in the Purple Majesty seedling leaves firstly increased and then decreased under drought stress and the drought,high temperature double stress.In the 5th day of the drought,high temperature double stress, the soluble protein content reached the maximum,while in drought stress treatment,it did not reach the maximum until the 7th day.But in the high temperature stress, the soluble protein content in the Purple Majesty seedling leaves was first increased and then decreased,but in the last it increased again. In the drought stress,high temperature stress and the double stress treatment, the soluble protein content in the Purple Majesty seedling leaves were significantly lower than control (P<0.05),except in the 5th day under the the high temperature stress. SA treatment can increase the soluble protein content in the Purple Majesty seedling leaves under the drought stress, high temperature stress and the double stress treatment, In various periods of stress treatment, the soluble protein content in the Purple Majesty seedling leaves were higher than the same stress and lower than the same control.The soluble sugar content in the Purple Majesty seedling leaves was not significantly different between the high temperture and the control;Under the drought stress, the soluble sugar content in the Purple Majesty seedling leaves firstly increased and then decreased,in the third day、5th day and 7th day three periods of drought stress, the soluble sugar content was higher than the control of the same period.In 4 hours under double stress, the soluble sugar content was significantly or very significantly higher than the same period control. Salicylic acid pre-treatment can step to increase the soluble sugar content in the Purple Majesty seedling leaves under the drought stress, high temperature stress and the double stress treatment.The Pro content in the Purple Majesty seedling leaves under the control, drought stress, high temperature stress and the double stress treatment increased first and then decreased,in the 7th day reached to the maximum. In pre-heat stress treatments,the Pro content was significantly higher than room temperature and the difference was significant, post-heat stress treatments, the Pro content was a little higher than the control.,but the difference was not signicant, SAtreatment reduced the Pro content of all periods under high temperture stress. The Pro content in the Purple Majesty seedling leaves under drought stress and double stress wereboth signicantly or very signicantly higher than that in the control, SA Treatment reduced the Pro content in the Purple Majesty seedling leaves under drought stress and drought, heat double stress.6.The POD and APX activity of Purple Majesty seedling leaves increased rapidly, significantly higher than the control at 3-5 days under drought stress, but in 7-9 days of drought stress, POD and APX activity decreased rapidly and significantly lower than the control. SA pre-treatment can increase the POD and APX activity of Purple Majesty seedling leaves under drought stress. High temperature and high temperature, drought double stress significantly reduced the POD and APX activity of Purple Majesty seedling leaves, but POD activity changed little in high-temperature and high temperature, drought double stress treatment. SA pre-treatment can significantly increase the POD and APX activity of Purple Majesty seedling leaves under high temperature and high temperature, drought double stress. Drought stress, high temperature stress and the double stress treatment decreased the SOD and CAT activity of Purple Majesty seedling s, SA pretreatment can improve SOD and CAT activity of Purple Majesty seedling leaves under drought stress, high temperature stress and the double stress treatment.7.In the early period (3、5d) of drought and high temperature stress,IAA content was higher than the control,but as the time went on,it would have an decreased trend,in the late time (7、9d),IAA content was lower than the control.After the drought,heat double stress,IAA content were always the highest levels in all treatments. SA treatment can increase the IAA content in the Purple Majesty seedling leaves under drought stress,while the IAA content in the 5d、7d、9d of Purple Majesty seedling leaves under high temperature stress also increased.The ABA content in the control was always at a low level, drought stress, high temperature stress and the double stress treatment can significantly increase the ABA content, SA Treatment reduced the ABA content under the drought stress,high temperature stress and the double stress treatment.The JA content in the 3d and 5d of the Purple Majesty seedling leaves was about the same as the control; After that, the JA content increased rapidly,and significantly higher than the control.But after the high temperature stress,the difference was not significant from the control.In the 3d of drought,heat double stress treatment,the JA content was a little lower than the control,and then increased rapidly,which were higher than the Corresponding control. SA treatment can decrease the JA content of the Purple Majesty seedling leaves under the drought stress, high temperature stress and the double stress treatment. |
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