CHAREST, CHRISTIANE & K. S. SUBRAMANIAN.
Department of Biology, University of Ottawa, PO Box 450 STN A, Ottawa, ON, K1N 6N5 CANADA.
The effect of the arbuscular mycorrhizal (AM) fungus (Glomus
intraradices Schenck & Smith) colonization on nitrogen assimilation
in maize under drought conditions was examined.
Maize plants (cv "Tuxpeno sequia", C0 drought-sensitive & C8 drought-resistant)
were exposed or not to drought for 3 wks (45-65 DAS). After these 3 wks, root
and shoot samples were analyzed for nitrate reductase (NR), nitrite reductase
(NiR), glutamine synthetase (GS), and glutamate synthase (GOGAT). Drought significantly
reduced all the enzyme activities in roots and shoots except NiR. In C0 roots,
drought caused reductions in NR, GS, and GOGAT activities by 52%, 63%, and 5%,
respectively. Drought-stressed AM-roots of both cultivars had higher NR (C0,
45%; C8, 26%), GS (C0, 76%; C8, 33%) and GOGAT (C0, 41%; C8, 53%) activities
than non-AM controls. These activities were comparable to the ones in well-watered
plants. Higher N enzyme activities were also detected in shoots of drought-stressed
AM-plants of both cultivars. Ala, Arg, Asn, Asp, Gln and Glu were the predominant
amino acids and Gln tended to increase with AM association. In C0 roots and
shoots, the amino acid pool increased by 4.6 & 1.6 times in comparaison
to non-AM controls. The increases in N-enzyme activities and nitrogenous compounds
suggest a transfer of assimilated N from the extraradical mycelium to the AM
roots.