Physiological Response Of Brassica Napus L.to Continued NaCl Stress With Different Concentrations

As the over-cultivation and use of land and the rapid development of industry, the area of avaible arable land in our country reduced significantly. Coupled with the pressuure of expansion, food shortage will be an urgent problem for a long time. So the development and utilization of saline and alkalied soil will be one of the useful ways to solve this problem. Brassica campestris L.(Crucifera, Brassica) is the third kind of largest oil crop in the world and the first largest oilseed and fifth largest field crop in China, which has high nutritional value and economic value. Among them, Brassica napus L. is recognized as a more salt-tolerant crop,In this study,2varieties of Brassica napus L. seedlings, Zheshuang6and Yangyou9, were treated with different concentrations of NaCl solutions, then the changes of relative water content, relative conductivity, free proline content, soluble sugar content, MDA content, antioxidant enzyme (SOD, POD, CAT) activities, chlorophyll content, chlorophyll fluorescence parameters, photosynthetic rate in leaves and K/Na in different parts of root, stem and leaf were determined. The results were as follows:1. Under continued NaCl stress, the relative water content in leaves almost not affected under low salt concentration, and inhibited with the increase of NaCl concentration. Besides, the relative water content reduced with the increase of stress time. RWC in Yangyou decreased earlier and quicker than in Zheshuang under the same NaCl stress.2. Under continued NaCl stress, the relative conductivity and MDA content in leaves raised with the increase of NaCl concentration. During the entire treatment, relative conductivity in Yangyou increased quicker than in Zheshuang, and the MDA content was also higher. 3. Under continued NaC1stress, the free proline and soluble sugar content in leaves raised in general with the increase of NaC1concentration and treat time. And the accumulation of these2substances in Yangyou was higher than in Zheshuang.4. At the early stage of NaC1stress, the reactive oxygen species (ROS) in leaves of Zheshuang was removed mainly through SOD, POD and CAT together, then through POD and CAT and SOD activity decreased at the later stage. In leaves of Yangyou, the ROS was also removed together by SOD, POD and CAT in the early and by mainly POD in the later. Obviously, the balance and coordination of this3enzymes in Zheshuang was better than in Yangyou.5. Under continued NaCl stress, the changes of chlorophyll fluorescence parameters (Fv/Fm、 Fv/Fo、ΦPSⅡ) in leaves of Zheshuang and Yangyou was consistent, which dropped with the increase of NaC1concentration and stress time. The chlorophyll fluorescence parameters in Yangyou decreased earlier and quicker than those in Zheshuang.6. With the increase of NaCl concentration and stress time, the relative chlorophyll content and photosynthesis rate all decreased both in Zheshuang and Yangyou. But the rate of descent in Zheshuang was less than that inYangyou, and the time of significant decrease was also later in Zheshuang than in Yangyou.7.14d after NaCl treatment, relative content of K and K/Na in different parts of stem and leaf dropped with the increase of NaC1concentration, while the relative content of Na increased. And the changes of elements in Zheshuang was smaller than in Yangyou. Besides, the K/Na ratio in root of Zheshuang increased and declined in that of Yangyou. Which indicated that the ability of ion balance in Zheshuang was better than in Yangyou.In conclusion, these results indicated that under continued NaC1stress with different concentration, Zheshuang and Yangyou both had salt resistance in some extent. By contrast, salt tolerance of Zheshuang was stronger than Yangyou, and Zheshuang was easier to adapt to salt stress.