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Development and Growth of Several Strains of Arabidopsis Seedlings in Microgravity1

Growth and development of dark‐grown Arabidopsis thaliana seedlings were studied in microgravity during space shuttle mission STS‐84. The major purpose of this project was to determine if there were developmental differences among the four ecotypes studied—Wassilewskija (Ws), Columbia (Col), Landsberg erecta (Ler), and C24—and to evaluate whether particular ecotypes are better suited for spaceflight experimentation compared with others. A secondary goal was to study the growth of three starch‐deficient strains of Arabidopsis by extending the observations made in a previously published report. For all strains, seed germination was not affected by microgravity, but seedlings were smaller in the spaceflight samples compared with the ground controls. The starch‐deficient strains continued to exhibit vigorous growth until the termination of the experiment at 121 h after imbibition of seeds. However, ethylene effects, i.e., reduced growth and exaggerated hypocotyl hooks, were observed in all strains studied. Nevertheless, the Ler and C24 ecotypes seem to be more suitable for spaceflight research, compared with the other two ecotypes, based on measurements of their relative and absolute growth. This type of information should aid in the design of plant experiments for the International Space Station.