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OXYGEN DEPENDENCY OF FLAX SEED GERMINATION AND ROOT CURVATURE.  O.A. Kuznetsov and K.H. Hasenstein, UL Lafayette, LA 70504-2451

   Respiration provides the energy requirements for the breakdown of storage compounds and germination. Therefore, oxygen content is a limiting factor for seed germination. In weightlessness the formation of a water layer around seeds and the lack of buoyancy-driven gas exchange further limits oxygen availability. In preparation for an upcoming shuttle experiment (MICRO on STS-107) we studied the oxygen dependency of germination and growth of flax (Linum usitatissimum L.) seedlings in the experimental hardware. We tested between 4 to 32 seeds glued to germination paper by 10 µl of 1% (w/v) gum guar in hermetically sealed experimental chambers (gas volume = 14 mL, O₂ = 2.9 mL). For imbibition a previously optimized amount of distilled water was dispensed. The seedlings were allowed to grow for 36 h at 27C (previously determined optimal temperature) before their root length was measured. With 32 seeds per chamber, the germination rate decreased from 94 to 69%, and the root length was reduced by 20%. The inhibition was independent of ethylene. Elimination of the guar glue improved germination and growth. Experiments in controlled oxygen levels (3.6, 7.2, 9.2, 10.5, 13.9 and 21.6% O₂) showed that oxygen concentrations above 10% are able to support germination. At 3.6% O₂ no germination occurred but the seeds remained viable and 85% germinated within 24 h after transfer to 21% O₂. Interestingly, within 3 h of gravistimulation the curvature of primary roots increased at lower O₂ concentrations. At 9.2% O₂ partial removal of the seed cover improved germination from 59% to 81% and root growth (from 3.6±0.4 to 7.9±1.0 mm), suggesting that at low O₂ concentrations seed coat and glue impede oxygen diffusion to the embryo. However, the gas volume in the fligh hardware is sufficient to support normal seed germination and growth for the duration of the experiments.

(Supported by NASA grant NAG10-0190).

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