PLANT PHYSIOLOGY , Vol 104, Issue 3 1007-1013, Copyright © 1994 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Induction of Microsomal Membrane Proteins in Roots of an Aluminum-Resistant Cultivar of Triticum aestivum L. under Conditions of Aluminum Stress
A. Basu, U. Basu and G. J. Taylor
Department of Botany, University of Alberta, Edmonton, Alberta T6G 2E9, Canada
Three-day-old seedlings of an Al-sensitive (Neepawa) and an Al-resistant
(PT741) cultivar of Triticum aestivum were subjected to Al concentrations
ranging from 0 to 100 [mu]M for 72 h. At 25 [mu]M Al, growth of roots was
inhibited by 57% in the Al-sensitive cultivar, whereas root growth in the
Al-resistant cultivar was unaffected. A concentration of 100 [mu]M Al was
required to inhibit root growth of the Al-resistant cultivar by 50% and
resulted in almost total inhibition of root growth in the sensitive
cultivar. Cytoplasmic and microsomal membrane fractions were isolated from
root tips (first 5 mm) and the adjacent 2-cm region of roots of both
cultivars. When root cytoplasmic proteins were analyzed by sodium dodecyl
sulfate-polyacrylamide gel electrophoresis, no changes in polypeptide
patterns were observed in response to Al stress. Analysis of microsomal
membrane proteins revealed a band with an apparent molecular mass of 51 kD,
which showed significant accumulation in the resistant cultivar following
Al exposure. Two-dimensional gel analysis revealed that this band comprises
two polypeptides, each of which is induced by exposure to Al. The response
of the 51-kD band to a variety of experimental conditions was characterized
to determine whether its pattern of accumulation was consistent with a
possible role in Al resistance. Accumulation was significantly greater in
root tips when compared to the rest of the root. When seedlings were
subjected to Al concentrations ranging from 0 to 150 [mu]M, the proteins
were evident at 25 [mu]M and were fully accumulated at 100 [mu]M.
Time-course studies from 0 to 96 h indicated that full accumulation of the
51-kD band occurred within 24 h of initiation of Al stress. With subsequent
removal of stress, the polypeptides gradually disappeared and were no
longer visible after 72 h. When protein synthesis was inhibited by
cycloheximide, the 51-kD band disappeared even when seedlings were
maintained in Al-containing media. Other metals, including Cu, Zn, and Mn,
failed to induce this band, and Cd and Ni resulted in its partial
accumulation. These results indicate that synthesis of the 51-kD microsomal
membrane proteins is specifically induced and maintained during Al stress
in the Al-resistant cultivar, PT741.
