INDUCTION OF MICROSOMAL MEMBRANE-PROTEINS IN ROOTS OF AN ALUMINUM-RESISTANT CULTIVAR OF TRITICUM-AESTIVUM L UNDER CONDITIONS OF ALUMINUM STRESS

Three-day-old seedlings of an Al-sensitive (Neepawa) and an Al-resista nt (PT741) cultivar of Triticum aestivum were subjected to Al concentr ations ranging from a to 100 mu M for 72 h. At 25 mu M Al, growth of r oots was inhibited by 57% in the Al-sensitive cultivar, whereas root g rowth in the Al-resistant cultivar was unaffected. A concentration of 100 mu M Al was required to inhibit root growth of the Al-resistant cu ltivar by 50% and resulted in almost total inhibition of root growth i n the sensitive cultivar. Cytoplasmic and microsomal membrane fraction s were isolated from root tips (first 5 mm) and the adjacent 2-cm regi on of roots of both cultivars. When root cytoplasmic proteins were ana lyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, no changes in polypeptide patterns were observed in response to Al stres s. Analysis of microsomal membrane proteins revealed a band with an ap parent molecular mass of 51 kD, which showed significant accumulation in the resistant cultivar following Al exposure. Two-dimensional gel a nalysis revealed that this band comprises two polypeptides, each of wh ich is induced by exposure to Al. The response of the 51-kD band to a variety of experimental conditions was characterized to determine whet her its pattern of accumulation was consistent with a possible role in Al resistance. Accumulation was significantly greater in root tips wh en compared to the rest of the root. When seedlings were subjected to At concentrations ranging from 0 to 150 mu M, the proteins were eviden t at 25 mu M and were fully accumulated at 100 mu M. Time-course studi es from 0 to 96 h indicated that full accumulation of the 51-kD band o ccurred within 24 h of initiation of AI stress. With subsequent remova l of stress, the polypeptides gradually disappeared and were no longer visible after 72 h. When protein synthesis was inhibited by cyclohexi mide, the 51-kD band disappeared even when seedlings were maintained i n Al-containing media. Other metals, including Cu, Zn, and Mn, failed to induce this band, and Cd and Ni resulted in its partial accumulatio n. These results indicate that synthesis of the 51-kD microsomal membr ane proteins is specifically induced and maintained during Al stress i n the Al-resistant cultivar, PT741.