Table II.

Means and heritabilities for physiological traits

Trait	Mean	Heritability
Leaf NO3− content	32.03	0.69
Leaf NR activity	204.95	0.87
Leaf GS activity	525.20	0.75

Results are the mean of a 2-year greenhouse experiment (1998 and 1999). Plants were grown hydroponically on a nutrient solution containing 1 mM NO₃⁻ as described in “Materials and Methods.” GS activity is expressed as nmol mn⁻¹ mg protein⁻¹ and NR activity as μmol h⁻¹ mg⁻¹ protein. NO₃⁻ concentration is expressed in mg dry wt⁻¹.