S. Sivasankar et A. Oaks, REGULATION OF NITRATE REDUCTASE DURING EARLY SEEDLING GROWTH - A ROLEFOR ASPARAGINE AND GLUTAMINE, Plant physiology, 107(4), 1995, pp. 1225-1231
Growth systems that either permit (wet system) or prevent (dry system)
the hydrolysis of endosperm reserves in maize (Zea mays) seedlings we
re developed to study the effect of endosperm reserves on the acquisit
ion of external nitrogen. Three-day-old seedlings treated with 5 mM KN
O3 for 24 h had higher levels of nitrate reductase (NR) activity and p
rotein in shoot and root tissues in the dry relative to the wet system
. This suggests that the induction of NR is sensitive to products of h
ydrolysis of endosperm reserves. Asparagine (1 mM) or glutamine (1 mM)
, potential products of that hydrolysis, inhibited the induction of NA
DH-dependent root NR in the dry system by about 70%. The inhibition of
the induction of NR activity in the wet system was only about 35%, su
ggesting that the enzyme in the wet system was already partially repre
ssed at 3 d. At 5 d, when asparagine and glutamine levels in the plant
tissue had decreased, the induction of root NR activity was inhibited
to a similar extent in the two growth systems by amide additions. The
shoot enzyme was less sensitive to amide additions, and 10 mM concent
rations of either amide was required for a 65% inhibition.