Abstract
Shooting stage roots of cereal plants varying in Al tolerance: rye (Secale L.), triticale (Triticale), barley (Hordeum L.) and four wheat (Triticum L.) varieties grown at pH 7 (controls) and stressed during 10 days at pH 4 with aluminium concentrations ranging from 0 to 40 mg dm−3 were back titrated with NaOH. Back-titration data were used for estimation of variable surface charge vs. pH dependencies and apparent surface dissociation constants distribution functions. Roots grown at pH 4 without Al addition had apparently the same charge properties as the control roots. With the increase of the concentration of the aluminium treatment, the variable surface charge of the roots decreased, beginning at 5 mg Al dm−3 for barley, at 10 mg Al dm−3 for wheat and triticale (20 mg Al dm−3 for acid resistant wheat Inia), and at 40 mg Al dm−3 for rye, and a weakening of root surface acidity was deduced from the decrease in average surface dissociation constant of the root surface. The latter was connected with an increase of the relative number of weakly acidic surface sites and a simultaneous decrease in surface groups of medium and strong acidity. During Al stress the density of variable surface charge of the roots decreased markedly. Changes in surface charge properties of Al-tolerant species were less intensive than for Al-sensitive ones.
Published Version
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