| Azaleas are the any plant of in Ericaceae. Being one of the top ten most famous flowers in China, it was spent with a high ornamental value and landscape value. However, Rhododendron L. plants grow naturally in high altitude areas of southwestern China, where its cold-moisture-like nature can be fit.So high temperature is the major stress factor affecting plant on domestication and utilization. In order to illuminate the responsive mechanism of Rhododendron L. under high temperature stress, four-year-old seedlings of R. jinggangshanicum and R. simiarum were planted in artificial climate chamber and physiological and biochemical changes of them were determined under different degree of high temperature (22℃,30℃,38℃). Meanwhile R. mucronatum, R. moulmainense, R. molle, R. chihsinianum and R. rubiginosum in different subgenus were determined the physiological response to high temperature stress. It expect to provide theoretical point to the introduction domestication, protection, nourishing and landscape value of Rhododendron L. plant.1. Under high temperature stress, physiological and biochemical indexes of R. jinggangshanicum and R. simiarum changed similarly in trend. However, the degree of increasing or decreasing showed a significant correlation to the heat resistances between them.(1) The activities of four kinds of defensive enzymes increased as the temperature rising; R. jinggangshanicum's SOD, POD, APX activities increased significantly lower than R. simiarum's, whereas R. jinggangshanicum's CAT activity increased greater than R. simiarum's, but this index was reverse under three temperature conditions. It implies that the increase of antioxidative enzyme's activities under high temperature stress is an important system for plants to resistant high temperature oxidation injury, and R. simiarum with stronger heat resistance enjoys a greater defensive enzymes activity or increase rate than R. jinggangshanicum with weak heat resistance.(2) The AsA contents decreased as the temperature rising; The AsA content of R. jinggangshanicum decreased much more significant than the same index in R. simiarum, and the decrease of AsA content go against the elimination of active oxygen species. We consider that the great decrease of AsA is a major reason for the oxidative damage of R. jinggangshanicum under high temperature stress.(3) The proline and soluble protein contents of two plants all increased as the temperature rising;The proline content of R. jinggangshanicum increased a lower degree while its soluble protein increased much greater (209.44% higher than reference) than R. simiarum's when temperature was 38℃; under high temperature stress, R. jinggangshanicum with weaker heat resistance accumulated comparatively fewer Pro but massive soluble protein. It is because Pro accumulation is the protective reaction to high temperature whereas the massive soluble protein accumulation may be the injury reaction.(4) The H2O2 and MDA contents all increased as the temperature rising; H2O2 of R. jinggangshanicum increase more than R. simiarum, and the MDA increase of R. jinggangshanicum under 30℃is greater than R. simiarum while things are reverse when it is 38℃.(5) Principal component analysis implies that APX, CAT, MDA and H2O2 are major indexes for heat resistances in R. jinggangshanicum and R. simiarum; membership function analysis shows the heat resistance in R. simiarum is stronger than R. jinggangshanicum; this conclusion is consistent with natural reality.2. Azaleas are dramatic difference among different subgenus's genetic mechanism. Under high temperature stress, the physiological response mechanisms of the five Rhododendrons L. plants, though not identical, still have some certain rules.(1) When treated at 30℃, the SOD activity of the five Rhododendrons L. plants all increased compared with comparison, but with temperature increasing, activity declined; Rhododendron with strong heat-resistance had big growth and small drop in SOD. The CAT activity of the five Rhododendrons L. plants all strengthened as temperature increasing, with its growth size basically consistent with strong or weak heat-resistance. In general, the APX activity of the five Rhododendrons L. plants strengthened with temperature enhancing, but its variation was due to specific species. (2) Proline contents of the five Rhododendrons L. plants all increased with temperature growing, and it had negative correlation with the heat-resistance of different species when treated at 30℃(May be caused by stress of low-intensity), but positive correlation at 38℃.(3) H2O2 and MDA contents of the five Rhododendrons L. plants all increased as stress temperature growing, with overall trend of small increase in species with strong heat-resistance and large increase in weak ones.(4) The result of principal component analysis displayed that malondialdehyde content, hydrogen peroxide content, proline content and APX, CAT activity were important in high temperature stress exaluation for the seedlings of Rhododendron L. plants. The capacity of high temperature resistance of five Rhododendron L. plants was gauged as follow:R. mucronatum＞R. moulmainense＞R. chihsinianum＞R. rubiginosum＞R. molle.Under heat stress, the balance between the production and scavenging of reactive oxygen is broken, but the rhododendron is able to start emergency defense mechanism, mainly through promoting the activity of protective enzyme and Pro content to enhance its ability to adapt to heat stress. Compared with the R. molle, under high temperature, AsA content in R. jinggangshanicum decreased greatly, meanwhile SOD activity and Pro content increased comparatively small, and H2O2 and soluble protein mass accumulated, as a result, plants suffered serious injuries. It showed that physiological response is consistent with its heat-resistant strength. The physiological vulnerability performed under high temperature stress is one of genetic mechanisms why R. jinggangshanicum is narrowly distributed and increasingly endangered, and also an important reason to restrict its garden application.
|
PDF Full Text Request