Effect of aluminium and 6‐benzylaminopurine on the growth of the epicotyl in mungbean seedlings

Abstbact

Aluminium (Al) toxicity was studied for mungbean (Phaseolus aureus Roxb.) seedlings under controlled environmental conditions in a growth chamber. Ten‐day‐old seedlings or cuttings (root removed) grew in dilute nutrient solution (pH 4.1) with Al levels and 6‐benzylaminopurine (6‐BA) concentrations for six days. Results showed that Al concentrations less than 2 mM had no significant effect on the length of the epicotyl in mungbean seedlings. Elongation of the epicotyl of intact seedlings was inhibited by 5 mM Al. The decrease in dry weight of the epicotyl was more evident than that in dry weight of hypocotyl, root, and primary leaves, indicating that epicotyl damage was greater than other organs by Al toxicity. No significant difference was found in the length of epicotyl between seedlings with and without 6–3A treatment. But there was a marked decrease in length of the epicotyl when cuttings were treated with 1 mM and 5 mM Al. Addition of 6‐BA to the nutrient solution significantly increased the elongation of the epicotyl in cuttings treated with 0.05 mM and 1 mM Al. but only slightly in the cuttings treated with 5 mM Al. When the Al concentration was greater than 1 mM, the concentration of soluble protein in epicotyl of seedlings was increased by the Al treatment. 6‐BA significantly increased the concentration of soluble protein in the epicotyl of the seedlings with 0.05 mM or 1 mM Al treatment. The present results indirectly indicated that high concentrations of Al inhibited elongation of the epicotyl in mungbean seedlings not by the shortage of endogenous cytokinin export from the root tips to the shoots but by other toxicity mechanisms.