Effect Of Aluminum Toxicity On Polysaccharide Of Cell Wall Of Rape (Brassica Napus L.)

Aluminum (Al) toxicity is an important factor determining the distribution of plant species and ecotypes in natural habitats and crop productivity on acidic soils. Aluminum primarily affects root growth by interfering with processes critical for the regulation of growth in the root apex. Despite a large research effort for years, the mechanism of Al-induced inhibition of root growth and the reasons for the spatial differences in Al sensitivity between apical root zones are still not well understood. Evidence has accumulated supporting the hypothesis that the root apoplast (cell wall) plays an important role in the expression of Al toxicity and Al resistance recently. However, how cell wall-binding sites and cell properties such as polysaccharides, enzymes play a role in Al expression and resistance is not clear. The object of the present study is to investigate the relationships between the response of rape (Brassica napus L.) roots to Al toxicity and cell wall composition in root segments, the effects of Al on the amount of cell wall polysaccharides in the root apex cell wall cultivars of rape (Brassica napus L.) to investigate Al toxicity mechanisms in rape. The main results of this study are as follows:Exposured to 25, 75, 250, 500μmol/L AlCl₃ solution, elongation of rape roots were inhibited severely, which were 63.6%, 71.1%, 58.4%, 68.4% repectively after 24h treatment. The callose content of root 0-10mm of rape (Brassica napus L.) was higher than other treatment. It indicated that rape (Brassica napus L.) was sensitive to 75μmol/L AlCl₃.The callose content of root 0-10mm of rape (Brassica napus L.) was highest when treated by 0, 75, 500μmol/L AlCl₃ for 24h, 48h, 72 h, but it was highest when treated by 500μmol/L AlCl₃ for 3-12 h. Callose increased with the increase of time indicated that inhibition of root growth occured rapidly after exposure to Al, and especially at higher concentration. Lower concentration of Al inhibited elongation of rape roots when they were treated for longer times.The results of the uronic acids and KDO content in cell wall shown that pectin uronic acid and KDO content in cell walls of 0-10 mm root segments was significantly higher than those of control at AlCl₃ treatment , indicating that much Al was binding with RG-II of cell wall.The uronic acids and total sugar content in pectin, hemi-cellulose and cellulose were higher than contrast when treated by 75 and 500μmol/L AlCl₃ for 12h and obviously for 24h. The uronic acids and total sugar content was higher at 75μmol/L AlCl₃ than at 500μmol/L AlCl₃ after treating for 24h compared to 12h. These results suggested that Al modified the metabolism of cell wall components and thus made the cell wall thick and rigid, therefore inhibited the root growth of rape (Brassica napus L.).The uronic acid and KDO concentration in pectin of root segment and content of pectin,hemi-cellulose, cellulose and callose was significantly increased at Al stress which indicated the change cell wall properties facilitated Al binding thus inhibited root growth and elongation.