Cultivar Differences In Growth Of Cotton And Their Cadmium And Nutrient Uptake Under Various Cadmium Levels

Green house pot and hydroponic experiments were conducted over the period of two growing seasons (2001-02), using three (0,0.1, and 1 uM Cd) and four (0,0.1, 1 and 10 uM) Cd levels, respectively, on Huajiachi campus, Zhejiang University, Hangzhou, China. The pot experiment was carried out in 2001 to select the relatively Cd- sensitive and resistant cultivar, respectively. The preliminary 7 cultivars used for the experiment were as follows: Simia3, Zhongmial2, Zhongmial6, Zhongmial6-2 (glandless isogene line of Zhongmia16), Caixuan 3 (natural colored cotton with green fiber), Caixuan 2 (natural colored cotton with brown fiber) and Zhemia 9 (glandless). After analyzing the results it was determined that Simia3, and Zhongmial6, Zhongmial6-2 were the Cd-sensitive and Cd-resistant cultivars, respectively.A second, more in-depth, hydroponic experiment was conducted during the second growing season to investigate the effects of Cd toxicity on yield, yield components, and mineral uptake and distribution, and Cd, Cu, Fe and Zn concentration and chlorophyll content in functional leaves during ontogenesis of three different Cd-tolerant cultivars obtained in pot experiment. The results showed that Cd concentration in vegetative organs increased with increases of Cd concentration in the nutrient solution. Meanwhile, Cd concentration in different vegetative organs is in order as follows: root> petiole> xylem> fruiting branch, leaf> phloem. In addition, Cd concentration in xylem of main stem was significant higher than that in phloem, indicating that xylem translocation maybe the main way for Cd translation from root to shoot and leaf. Cadmium concentration in different reproductive organs is in order as follows: seed coat, seed nut> boll shell >fiber. On the other hand, there was significant difference in Cd concentration between cultivars at 1 ji M Cd treatment, and Simia 3 showed higher Cd concentration and greatest reduction in lint yield than other 2 cultivars. For example, lint yield decreases at 0.1 and luM Cd treatments were found in Simia 3 by 4.74% and 35.41% over control, respectively. However, the lint yield of Zhongmial6 exposed to O.ljiM Cd increased by 69.69% in comparison with control, while at 1 uM Cd a decrease of 9.7% was observed, respectively. Meanwhile, a sharp decrease in boll number per plant was found in the 3 cultivars at 1 uM Cd treatmentCadmium concentration in both functional leaves and petioles increased with increasing Cd concentrations in the culture medium, and remained high throughout the growth period. Meanwhile, in 10 uM Cd treatments the cultivars differed significantly in Cd concentrations of functional leaves and petioles, the highest concentration was recorded in Simia 3. On the other hand, petiole Cd concentration was significantly higher, and along with greater increase with external Cd levels, than that in functional leaves throughout the growth period, indicating that petiole Cd concentration may aid in developing an effective procedure to identify and characterize new metal-tolerant cultivar in cotton.There was no significant difference in Zn, Cu and Fe concentrations of functional leaves and petioles between 0, 0.1 and 1 uM Cd treatments. However, a significant increase in Zn, Cu and Fe concentrations of functional leaves and petioles was observed in 10 uM Cd treatments, when compared with controls. On the other hand, the highly significant difference (p<0.05) in Zn, Cu and Fe increase was also found in plants among 3 cultivars at 10 |iM Cd level. For instance, Zn increase in 10 uM Cd treated plants, at 21 days Cd exposure, ranged from 33.0% in Zhongmia 16 to 359.1 % in Simia 3 in petioles compared with controls, respectively.Cotton plants exposed to 0.1 fiM Cd showed a slight but not statistic significant increase (p>0.05) in SPAD values relative to control and a slight decrease in chlorophyll contents, respectively, whereas exposure to 1 uM Cd induced a slight decrease in SPAD values. Increasing Cd concentration in medium to 10 uM induced a sharp decline (p<0.05) i...