Table 1.

Ammonium and Nitrate Stimulate Lateral Root Development in a Complementary Manner

N SupplyMicroscopy Analysis of First-, Second-, or Third-Order Lateral Roots
Total Lateral Root Length (cm·Plant−1)
First-OrderSecond-OrderThird-Order
0.8 mM NO310.60 ± 0.45b35.83 ± 3.92b0.79 ± 0.20a
0.8 mM NH4+04.81 ± 0.49a08.01 ± 0.75a2.88 ± 0.26b
0.4 mM NH4NO311.39 ± 0.98b41.04 ± 7.71b1.42 ± 0.29a
Total Number of Lateral Root Primordia Initiated (Plant−1)
First-OrderSecond-OrderThird-Order
0.8 mM NO3nd33.83 ± 2.54a24.27 ± 2.31a
0.8 mM NH4+nd25.66 ± 1.65a49.08 ± 3.87b
0.4 mM NH4NO3nd55.88 ± 4.19b71.83 ± 8.41c
Density of Lateral Root Primordia Initiated (Number·cm−1)
First-OrderSecond-OrderThird-Order
0.8 mM NO3nd3.33 ± 0.38a0.78 ± 0.12a
0.8 mM NH4+nd5.47 ± 0.60b6.52 ± 0.54b
0.4 mM NH4NO3nd5.14 ± 0.24b2.10 ± 0.42a
  • Microscopy analysis of first-, second-, or third-order lateral roots length and total number or density of lateral root primordia initiated in Arabidopsis CYCB1:GUS plants grown under local supply of ammonium, nitrate, or ammonium nitrate in vertically split agar plates (for histochemical staining and determination of lateral root measures, see Methods). Values represent means (±se) of 12 to 21 individual plants per treatment, and different letters denote significant differences among nitrogen treatments at P < 0.05 (Tukey’s test); nd, not determined.