Studies On Absorption And Accumulation Of Chromium In Pumpkin

The absorption and distribution of chromium (Cr) were studied in Cr-gathering pumpkin(C. maxima)and common pumpkin by using 51Cr tracer and nutrient culture technique,and the subcellular distribution of chromium in roots,stems and leaves,it's effects to some physiological characteristics with the relationship of pumpkin's endurance at the seedling stage of pumpkin were also studied. Main results are as follows:1.The result showed that in the aboveground parts of plant, 51Cr of 64.4% accumulated in the leaves, 30.2% in the stemsand only 5.4% in the flowers at seedling stage. Moreover, the metal mainly localized in the leaves and stems close to root parts. At fruit stage, the distribution rate of 51Cr was 51.1% in the fruits, 41.6% in the leaves, 4.8% in the stems and 2.4% in the flowers, respectively. A large quantity of chromium was concentrated mainly in fruit and middle leaves of the plant. Pumpkin absorbed and transported more tagged Cr during the fruit stage than the seedling stage. 10 days after the application of 51Cr, the activity of 51Cr were counted. It is found that during the seedling stage the activities in the unlabelled leaves were the highest, while during fruit stage those in stems were the highest. In addition, the specific activities in the roots were higher than that in other parts of pumpkin during flowering and seedling stage. The specific activities of different parts of leaves and stems were relevant with the distance of tagged leaves. The distribution ratio of 51Cr in pumpkin fruits reached 9 %。2. The 51Cr activity in aboveground parts of pumpkin after root's application at seedling stage was 4.55KBq,at fruits stage it had reached 8.28 KBq;and if we applied to leaves,the 51Cr activity in aboveground parts of pumpkin after root's application at seedling stage is 26.59 KBq, at fruits stage reached118.39,these results showed that 51Cr activity might bear a relation with transport length.3. The nutrient culture experiments had showed that lower concentration Cr(VI) could stimulate plant growth, and the results of chlorophyll content and soluble protein content were higher than control had proved. With the increase of concentration of Cr6+, activities of superoxide dismutase (SOD) varied little, but peroxidase (POD) varied obviously. The chlorophyll content and soluble protein content increased first but then decreased.By contrast, the activity of actalase (CAT) decreased steadily, also root's activity ncreased first but then decreased the membrane lipid peroxidation and MDA contents in hypocotyls increased obviously These changes differed between Cr-gathering pumpkin and common pumpkin.Whileat the condition of higher concentration Cr(VI), Cr-gathering pumpkin showed higher chlorophyll content and soluble protein content and lower cell membrane permeability,which indicated Cr-gathering pumpkin was more patient with Cr.4. Chromium accumulated mainly in cell wall and soluble fraction. The distribution ratio of chromium in cell organs was higher in common pumpkin than in rich-chromium pumpkin.Also,Cr contention in roots would be higher than stems and leaves,in Cr-gathering pumpkin or common pumpkin.