Effect of aluminum on δ-aminolevulinic acid dehydratase (ALA-D) and the development of cucumber (Cucumis sativus)

Aluminum is one of the most abundant elements on the planet. The effects of its toxicity to plants include inhibition of the growth of the root system and inhibition of enzymes of plant metabolism causing a delay in development. The objective of the present study was to analyze the effects of aluminum on the activity of the enzyme δ-aminolevulinic acid dehydratase (ALA-D), responsible for the formation of the monopyrrole porphobilinogen that is part of the chlorophyll molecule, as well as the cytochromes, in cucumbers. Plant growth was also monitored and the roots were submitted to histological analysis. The concentrations of Al2(SO4)3 used in the growth medium ranged from 1 to 2000 μmol/L. Cucumber (Cucumis sativus) was chosen because it is a good bioindicator of metal pollution. Results demonstrated that aluminum inhibits this enzyme and also greatly impairs plant growth. Histological analysis of the roots indicated a delay in the development of the vase elements, alterations in cell shape and cellular lesions. ALA-D inhibition may be due to the fact that aluminum present in the growth medium can compete with Mg2+ or reduce the expression of ALA-D. Probably, Al3+ forms complexes with nucleotides, with the cell wall and with other biomolecules, reducing the growth and development of the plant.