Am. J. Bot.
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(American Journal of Botany. 2002;89:410-416.)
© 2002 Botanical Society of America, Inc.

Physiology and Development

Weedy adaptation in Setaria spp. V. Effects of gaseous environment on giant foxtail (Setaria faberii) (Poaceae) seed germination1

Jack Dekker2,4 and Mark Hargrove3

2Weed Biology Laboratory, Agronomy Department, Iowa State University, Ames, Iowa 50011 USA; 3Department of Biochemistry and Molecular Biology, Iowa State University, Ames, Iowa 50011 USA

The effects that naturally occurring gases (oxygen, nitrogen, carbon monoxide) may cause in dormant giant foxtail (Setaria faberii) seed germination under favorable temperature and moisture conditions were investigated. The germination responses to gas mixtures supported the hypothesis that S. faberii germination behavior is regulated by the amount of oxygen taken into hydrated seed over time. Setaria faberii seed germination was markedly affected by O2 concentration (in N2) above and below that of air (20% O2): the largest increase in germination (from 37 to 60%) occurred between 20–25% O2; between 0–10% O2, germination increased from 0–30%; and surprisingly germination at 10 and 20% O2 was similar. These observations reveal an asymmetrical response to incremental changes in O2 above and below that typically found in agricultural soils. Carbon monoxide had opposite effects on S. faberii germination in air depending on concentration, stimulation, and inhibition: germination increased from 37 to 56% with the addition of 1% CO, but decreased from 37 to 14% with 75% added CO. An explanation may be that there are two separate effects of CO, each occurring in different physiological systems of dormant seeds at the same time. At high concentrations (75%) in air CO inhibited seed germination, probably by inhibiting mitochondrial respiration. But low CO concentrations (0.1 or 1%) in air stimulated seed germination. It was not apparent which physiological system(s) CO and O2 affected. It seems unlikely that CO-stimulated germination arises from effects on the respiratory apparatus, but may be a consequence of CO interactions with an as yet unknown physiological factor in the seed. We provide a model of Setaria spp. dormancy consistent with its seed morphology, the gas-germination data, and the hypothesized second physiological factor that may be involved in CO stimulated germination.

Key Words: carbon monoxide • Graminae • oxygen • respiration • seed dormancy • seed germination • Setaria faberii • soil atmosphere • soil seedbanks






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