ASGSB 1999 Annual Meeting Abstracts

INFLUENCE OF MICROGRAVITY ON ULTRASTRUCTURE AND STORAGE RESERVES IN SEEDS OF BRASSICA RAPA L. A. Kuang, Y. Xiao, and M. E. Musgrave. Dept. of Plant Pathology & Crop Physiology, Louisiana State University, Baton Rouge, LA

Growth of higher plants in the microgravity environment of orbital platforms has been problematic. Plants typically developed more slowly in space and often failed at the reproductive phase. Short-duration experiments on the Space Shuttle showed that early stages in the reproductive process could occur normally in microgravity, so we sought a long-duration opportunity to test gravity's role throughout the complete life cycle. During a 122-day opportunity on the Mir space station, full life cycles were completed in microgravity with Brassica rapa L. in a series of three experiments in the Svet greenhouse. Here we focus on analysis of seeds produced and dried in space, comparing them to material preserved in the same way during a high-fidelity ground control. Dried seeds were imbibed on moist filter paper for 1 hr, then dissected to yield individual cotyledons. The inner cotyledons were macerated with chromic acid to determine cell number, while the outer cotyledons were fixed for light and electron microscopy. Following dehydration, embedding, and sectioning, staining of thin sections with aniline blue-black and periodic Schiff's reagent was used to localize protein and polysaccharides. Seeds produced on the Mir station had less than 20% of the cotyledon cell number found in the seeds harvested from the ground control. Cytochemical localization of storage reserves in the mature embryos showed that starch was retained in the spaceflight material, whereas protein and lipid were the primary storage reserves in the ground control seeds. Ultrastructural analysis of cotyledon tissues showed a difference in the size and density of protein bodies between the seeds produced during spaceflight and the ground control seeds. While gravity is not absolutely required for any step in the plant life cycle, seed quality in Brassica is compromised by development in microgravity.

 Supported by NASA grant NAG2-1020 to MEM.

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