Al-Detoxification Mechanisms Of Compound Orgacnic Acids Under Al Stress And The Regulation Of H～+-ATPase On The Secretion Of Organic Acids In Rye

The secretion of citrate and malate from rye roots could be induced by Al stress. In order to elucidate the Al detoxification mechanisms by compound organic acids (citrate and malate) in rye, five-day-old Al-sensitive wheat( Jin mai 47) roots were objected to study the effects of these organic acids on root elongation, root cell membrane osmosis, activities of catalase (CAT), peroxidase (POD) and H⁺-ATPase of root apices by water-cultivated method. It showed that Al induced increasing in electrolyte of roots was suppressed by the addition of both citrate and malate, while an increase in both root elongation and activities of CAT, POD and H⁺-ATPase were found in the treatments with both citrate and malate under 50μmol·L^-1 Al stress. These effects of compound organic acids were increased with the increasing of their dose (25～200μmol·L^-1) . Al-detoxification effect of compound organic acids was more significant as the increasing rate of citrate/malate from 1:2 to 1:1 in the certain concentration of malate (50, 100μmol·L^-1). However, there had no distinct Al-detoxifcation effect of compound organic acids on wheat with doubled the concentration of malate in the certain concentration of citrate. These results indicated that Al-induced secretion of both citrate and malate was an effective mechanism for rye to deal with Al toxicity and Al-induced secretion of compound organic acids was an Al resistant mechanism for rye.On the other hand, in order to investigate the regulation of H⁺-ATPase on Al-induced secretion of organic acids from rye roots, five-day-old rye(King) and wheat(Jin mai 47) roots were objected to study the relationship between H⁺-ATPase and the secretion of organic acids by treating with abscisic acid (ABA) and indoleacetic acid (IAA), anion inhibitors 4,4'-diisothio-cyanostilbene-2,2'-disuifonic acid (DIDS), niflumic acid (NIF), anthracene-9-carboxylic acid (9-AC) and plasma membrane ATPase inhibitor (SV). These results showed that H⁺-ATPase activity of rye root apices was higher than that in wheat after exposure of roots to 10,30,50μmol·L^-1 AI solution for 24 h. Under Al stress, H⁺-ATPase activity was stimulated by low concentration IAA (1μmol·L^-1) treated, while the secretion of organic acids was increased. However, H⁺-ATPase activity was significantly inhibited by ABA (1,25μmol·L^-1) and high concentration IAA (25μmol·L^-1), while the amount of Al-induced organic acids was decreasing. Oneμmol·L^-1 IAA and 1μmol·L^-1ABA respectively exerted stimulatory and inhibitory effects on the H⁺-ATPase activities and secretion of organic acids. These results suggested that H⁺-ATPase of root apices would involve in the regulation of Al-induced secretion of organic acids from rye roots.In addition, H⁺-ATPase activity and the secretion of organic acids were inhibited by treatments with 10μmol·L^-1 NIF, 9-AC, DIDS solution which contained 1μmol·L^-1 IAA. Moreover, the inhibitory effect of 1μmol·L^-1ABA on the activity of root apices H⁺-ATPase and Al-induced secretion of organic acids from rye roots was strengthened by NIF, 9-AC and DIDS. These results implied that H⁺-ATPase seemed to involve in activating anion channels to allow organic acids efflux.Furthermore, the secretion of organic acids and H⁺-ATPase activity were inhibited by SV, which is a plasma membrane ATPase inhibitor. It suggested that plasma membrane H⁺-ATPase would be an important regulated factor of cells in Al-induced secretion of organic acids.