ALTITUDINAL VARIATION OF ANTIOXIDATIVE SYSTEM IN LEAVES OF RHODIOLA QUADRIFIDA AND R. GELIDA
四裂红景天与长鳞红景天叶片中抗氧化系统随海拔梯度的变化

Alpine environments are characterized by rapid changes in climate, and leaves of alpine plants are routinely exposed to high light intensities at low temperatures. The fact that there seems to be no impairment of photosynthesis by high light and low temperatures under field conditions indicates a very well regulated system of carbohydrate turnover together with a functional system of antioxidants. To study the mechanisms of adaptation of alpine plants, we investigated the antioxidative defense capacity in leaves of two alpine plants, Rhodiola quadrifida and R. gelida. Field investigations were carried out on the slopes of Tianshan Mountain near the Tianshan Glacier NO. 1. Along this slope, R. quadrifida was found between 3 500 and 3 805 m and R. gelida was found between 3 805 and 4 010 m. The two species coexisted at 3 805 m. Plant specimens used in this experiment were collected at 50 m intervals from 3 610 to 3 900 m. Our results showed that the malondialdehyde (MDA) content in leaves of R. gelida was significantly greater than that in R. quadrifida, suggesting that R. gelida might suffer more serious oxidative stress compared to R. quadrifida. The fact that R. gelida can survive and maintain normal metabolism at high elevations suggests that it might be an adaptive mechanisms to endure serious oxidative stress in this harsh environment. The increase in the activities of antioxidative enzymes, such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) as well as the contents of reduced glutathione (GSH) and ascorbic acid (AsA), in the leaves of R. gelida suggested a combined and balanced enhancement of antioxidants to improve stress resistance in alpine plant leaves. Among all the antioxidative enzymes examined, peroxidase (POD) was quite distinct from others. Activity of POD was below the limits of detection in leaves of R. quadrifida collected from elevations lower than 3 805 m, but enhanced activity was observed in leaves of R. gelida as altitude increased implying that POD might play an important role in plant adaptation to alpine environments. Given the inverse relationship between growth rate and peroxidase activity demonstrated in many plant developmental systems, in-depth studies on the role of peroxidases in adaptation of R. gelida to high altitudes are warranted.