K. Tan et al., EVALUATING THE CONTRIBUTION OF MAGNESIUM-DEFICIENCY IN THE ALUMINUM TOXICITY SYNDROME IN 12 SORGHUM GENOTYPES, Plant and soil, 149(2), 1993, pp. 255-261
The contribution of Mg deficiency to Al stress in twelve different sor
ghum (Sorghum bicolor (L.) Moench) genotypes was investigated in nutri
ent solution culture under conditions of low Mg supply (between 50 and
1000 muM) at two pH values. At pH 4.2, 30 muM Al strongly inhibited M
g uptake When dry matter yield was plotted as a function of the plant
Mg concentration, similar response curves were obtained in the absence
and the presence of Al with three genotypes. With many other genotype
s dry matter yields of the control (without Al treatment) and Al-stres
sed plants were remarkably different at similar internal Mg concentrat
ions, suggesting that growth had been suppressed not by Mg deficiency
but by another factor, i.e. Al-induced root damage. At pH 4.8, 30 muM
Al hardly induced root damage but reduced Mg uptake and Al-induced Mg
deficiency could almost completely account for the growth reaction of
all genotypes. Therefore, at this pH the efficiency of uptake or use o
f Mg in different genotypes was the basis of their respective suscepti
bility to Al toxicity. When specific root length surpassed a certain c
ritical range below 80-100 m per g dry root, growth control by Al-indu
ced Mg deficiency was nearly abolished. The pH and Al concentration wh
ere this range was reached depended on the Al sensitivity of the genot
ypes.