Chemical Forms And Subcellular Distribution Of Cd In Different Organs Of Hybrid Rice Under Cd Stress

In recent years, industrial waste hasn't been dealt properly, and pesticide and chemical fertilizer (Cd included) have been used unreasonably. Owing to that, a great deal of paddy soil has been contaminated by Cadmium, not only the growth and development of rice were inhibited, yield and quality were reduced, but also human health was threatened greatly. At present, the study about the mechanism of hybrid rice under Cd stress from the viewpoint of chemical forms and subcellular distribution have been reported seldom. Taking one hybrid rice cultivar with low Cd accumulated in grain and three hybrid rice cultivars with high Cd accumulated in grain as study materials, a hydroponic experiment was carried out to study the chemical forms and subcellular distribution of Cd and the effect of Cd on Ascorbate acid and soluble sugar in different organs of hybrid rice, and further to reveal the tolerance mechanism of hybrid rice under Cd stress. The main results are as follows:(1) The Cd content in grain of D83A/R527 was lower than FuYou838,D You498,II You892 under Cd stress. Compared with the treatment of 0.5mg/LCd, the amplification of Cd content in grain of D83A/R527 in the four varieties was the smallest under the treatment of 1mg/LCd. And contrasted the content under the treatment of 3mg/L and 1mg/LCd, although the amplification of D83A/R527 was higher than II You892 by 16%, the content in grain of D83A/R527 was also the lowest. It showed there was low Cd accumulated in grain of D83A/R527.(2) In root, crown, stem, leaf sheath, leaf and uppermost internode of four hybrid rice cultivars, increased Cd level in the medium caused a significant increase of Cd concentration in total Cd content and chemical forms. The contents of Cd were different in each organ, and on the whole, and the order was: root>crown>stem>leaf sheath>leaf> uppermost internode. In root, crown, leaf sheath, leaf and uppermost internode, the greatest amount of Cd was found in extraction solution of NaCl, followed by HAC. But in stem, the extraction of ethanol was higher than HAC. The proportion of ethanol and H₂O extractable-Cd in stem was the highest, then were leaf sheath, leaf, uppermost internode, and next were root and crown, it proved the different Cd content in every organ was in correlation with the difference of chemical forms. Compared with other three cultivars with high Cd accumulated in grain, total Cd content and each extractable-Cd content of D83A/R527 were lower, and it was lower in proportion of H₂O and ethanol extractable-Cd, but higher in proportion of HAC and HCl extractable-Cd. It suggested that Cd in D83A/R527 was hard to mobile, and leaded to low accumulation of Cd in grain.(3 ) In crown, leaf sheath and uppermost internode of four cultivars, increased Cd level in the medium caused a significant increase of Cd concentration in all fractions and total Cd content. Most Cd was distributed in F₁(cell wall fraction), followed by F3(soluble fraction) and F2(organelle fraction) except in crown in Tillering stage, F₃>F₁. The subcellular distribution of Cd in different organs was different, on the whole, the Cd content of crown was higher than leaf sheath and uppermost internode, and the proportion in cell wall of crown was lower than leaf sheath and uppermost internode, but the proportion in soluble fraction was higher, it revealed the difference of Cd content in each organ was in correlation with the difference of subcellular distribution. The Cd content in all fractions and total Cd content of D83A/R527 was the lowest, then were D You498 and II You892, FuYou838 was the highest. And D83A/R527 had higher Cd proportion in the cell wall but lower in the soluble fraction and organelle fraction, this was the mechanism of D83A/R527 low accumulation of Cd in grain.(4) Ascorbate acid content of leaf in tillering and booting stage increased when the four hybrid rice cultivars subjected to 0.5mg/LCd stress, but it was inhibited when subjected to 1mg/L and 3mg/LCd stress. However, in filling stage, ascorbate acid content of leaf decreased significantly under Cd stress. And ascorbate acid content of stem decreased significantly under Cd stress in the three growth stages. Compared with other three cultivars with higher Cd accumulated in grain, D83A/R527 had higer ascorbate acid content and the rangeability was small. There were significant and negative correlation between Ascorbate acid content and each extractable-Cd content and also the total Cd content, the results indicated the influence of the extractable-Cd content on ascorbate acid content was significant.(5) Compared with the contrast, Soluble sugar content of leaf and stem in hybrid rice increased significantly and showed rising trend with the increase of Cd concentrations. Compared with the other three cultivars with high Cd accumulated in grain, D83A/R527 had lower soluble sugar content and accumulating speed. There were significant and positive correlation between soluble sugar content and each extractable-Cd content and total Cd content, and the results further showed the effecct of the extractable-Cd content on soluble sugar content was significant.