PLANT PHYSIOLOGY , Vol 106, Issue 1 151-158, Copyright © 1994 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Differential Exudation of Polypeptides by Roots of Aluminum-Resistant and Aluminum-Sensitive Cultivars of Triticum aestivum L. in Response to Aluminum Stress
U. Basu, A. Basu and G. J. Taylor
Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada
Cultivars of Triticum aestivum differing in resistance to Al were grown
under aseptic conditions in the presence and absence of Al and polypeptides
present in root exudates were collected, concentrated, and analyzed by
sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Upon exposure to
100 and 200 [mu]M Al, root elongation in Al-sensitive cultivars was reduced
by 30 and 65%, respectively, whereas root elongation in resistant cultivars
was reduced by only 15 and 30%. Accumulation of polypeptides in the growth
medium increased with time for 96 to 120 h, with little additional
accumulation thereafter. This pattern of exudation was virtually unaffected
by exposure to 100 [mu]M Al in the Al-resistant cultivars Atlas 66 and
Maringa, whereas total accumulation was reduced in sensitive cultivars.
Changes in exudation were consistent with alterations in root elongation.
Al-induced or Al-enhanced polypeptide bands were detected in Atlas 66 and
Maringa after 72 h of exposure to Al. Increased accumulation of 12-, 22-,
and 33-kD bands was observed at 75 [mu]M Al in Atlas 66 and 12-, 23-, and
43.5-kD bands started to appear at 50 [mu]M Al in Maringa. In the
Al-sensitive cultivars Roblin and Katepwa, no significant effect on
polypeptide profiles was observed at values up to 100 [mu]M Al. When root
exudates were separated by ultrafiltration and the Al content was measured
in both high molecular mass (HMM; >10 kD) and ultrafiltrate (<10 kD)
fractions, approximately 2 times more Al was detected in HMM fractions from
Al-resistant cultivars than from Al-sensitive cultivars. Dialysis of HMM
fractions against water did not release this bound Al;digestion with
protease released between 62 and 73% of total Al, with twice as much
released from exudates of Al-resistant than of Al-sensitive cultivars. When
plants were grown in the presence of 0 to 200 [mu]M Al, saturation of the
Al-binding capacity of HMM exudates occurred at 50 [mu]M Al in Al-sensitive
cultivars. Saturation was not achieved in resistant cultivars. Differences
in exudation of total polypeptides in response to Al stress, enhanced
accumulation of specific polypeptides, and the greater association of Al
with HMM fractions from Al-resistant cultivars suggest that root exudate
polypeptides may play a role in plant response to Al.
