MAGNESIUM-DEFICIENCY RESULTS IN INCREASED SUBERIZATION IN ENDODERMIS AND HYPODERMIS OF CORN ROOTS

The composition of the aliphatic components of suberin in the stele and cortex of young corn (Z. mays L.) roots was determined by combined GLC/mass spectrometry of the LiAID4 depolymerization products. .omega.-Hydroxy acids were the major class of the aliphatic components of both the hypodermal (35%) and endodermal (28%) polymeric materials with the dominant chain length being C24 in the former and C16 in the latter. Nitrobenzene oxidation of the roots generated p-hydroxybenzaldehyde and vanillin with much less syringaldehyde. EM examination of the hypodermal and endodermal cell walls from roots of corn plants grown in a Mg2+-deficient (0.03 mM) nutrient solution showed that these walls were more heavily suberized than the analogous walls of roots from plants grown in normal (2 mM) Mg2+ levels. Analysis of the LiAID4 depolymerization products of the suberin polymers from these roots showed that the roots grown in low Mg2+ had 3.5 times as much aliphatic suberin monomers on a weight basis as the roots from plants grown in nutrient with normal Mg2+ levels. Roots from plants grown in Mg2+-deficient nutrient solution released 3.8 times the amount of aromatic aldehydes upon nitrobenzene oxidation as that released from normal roots. As the degree of Mg2+ deficiency of the nutrient solution was increased, there was an increase in the aliphatic and aromatic components characteristic of suberin. Thus, both ultrastructural and chemicl evidence strongly suggested that Mg2+ deficiency resulted in increased suberization of the cell walls of both hypodermis and endodermis of Z. mays roots. The roots from Mg2+-deficient plants also had a higher amount of peroxidase activity when compared to control roots.