ASGSB 1999 Annual Meeting Abstracts

IMPROVING GERMINATION FOR ‘SUPER DWARF‘ RICE J.M. Frantz and B. Bugbee, Department of Plants, Soils, and Biometeorology, Utah State Univ., Logan, UT.

‘Super-Dwarf‘ rice (Oryza sativa L.) is a short (20-cm-tall) rice cultivar that lacks  hydroxylase, the enzyme responsible for conversion of gibberellic acid 20 (GA₂₀ inactive) to GA₁ (active). Under aerobic conditions, GA₁ activates amylase, a necessary step in rice germination. Consequently, ‘Super Dwarf ‘ has poor germination. Seeds germinated in microgravity is difficult because adhesion of water to seeds and porous media can cause hypoxic conditions. These low O₂ conditions prevent germination in almost all species, which is probably due to alpha-amylase not being activated in starchy seeds. In rice, activation of -amylase still occurs under anoxic conditions, thereby allowing rice to germinate. The ability to germinate suggests either GA is active in rice under anoxia, or there is an alternative pathway for amylase activation under anoxia. We examined germination under anoxic and hypoxic conditions by passing humidified N₂ or N₂/air mixtures through germination boxes. Surprisingly, germination was improved from 70% to 95% by anoxic conditions. Germination was also improved by 2.3% per C from 20 to 33C. While rice has long been known to tolerate anoxic conditions, ‘Super Dwarf‘ requires anoxia for full germination. This surprising finding not only makes ‘Super Dwarf‘ rice an excellent crop for studies in microgravity, but suggests an alternative mechanism for GA-mediated -amylase activation.

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