TABLE 3.

Nitrogen-fixing activity (estimated by means of acetylene reduction) in free-living and endophytic Herbaspirillum sp. strain B501gfp1

Condition	Acetylene	Ethylene evolutiond	Acetylene reduction activity
			Total activitye	Sp act, nmol h−1 (108 cells)−1
Culturea
Modified Rennie (MR)	+	65.5 ± 4.7	65.5 ± 4.7	6.4 ± 0.5
Nutrient broth (NB)	+	NDb	NDb
Plant (Oryza officinalis W0012)c
	+	15.1 ± 3.0	14.8	7.6
	−	0.3 ± 0.1

^aEthylene evolution from free-living cells grown in semisolid MR medium at 2% (vol/vol) O₂ and in NB medium for 24 h. Values given are the means ± standard deviation for three determinations.

^bND, not detected (<0.2 nmol h⁻¹ tube⁻¹).

^cEthylene evolution from 7-day-old rice seedlings inoculated with Herbaspirillum sp. strain B501gfp1 in the presence and absence of 5% (vol/vol) acetylene gas for 24 h. Uninoculated plants emitted ethylene at a rate of 0.2 to 0.5 nmol h⁻¹ g (fresh wt)⁻¹. Values of ethylene evolution in the dark are the means ± standard deviation for three determinations. Acetylene reduction activity was calculated from the difference in ethylene evolution between rice seedlings in the presence and absence of 5% (vol/vol) acetylene gas.

^dValues for ethylene evolution for cultures are in nanomoles per hour per tube; for plants, values are in nanomoles per hour per gram (fresh weight).

^eValues for total acetylene activity are in nanomoles per hour per tube for cultures; for plants, values are nanomoles per hour per gram (fresh weight).