Induced compression wood formation in Douglas fir (Pseudotsuga menziesii) in microgravity

In the microgravity environment of the Space Shuttle Columbia (Life and Mic rogravity Mission STS-78), were grown 1-year-old Douglas fir and loblolly p ine plants in a NASA plant growth facility. Several plants were harnessed ( at 45 degrees) to establish if compression wood biosynthesis, involving alt ered cellulose and lignin deposition and cell wall structure would occur un der those conditions of induced mechanical stress. Selected plants were har nessed at day 2 in orbit, with stem sections of specific plants harvested a nd fixed for subsequent microscopic analyses on days 8, 10 and 15. At the e nd of the total space mission period ( 17 days). the remaining healthy harn essed plants and their vertical (upright) controls were harvested and fixed on earth. All harnessed (at 45 degrees;) plant specimens, whether grown at g or in microgravity, formed compression wood. Moreover, not only the camb ial cells but also the developing tracheid cells underwent significant morp hological changes. This indicated that the developing tracheids from the pr imary cell wall expansion stage to the fully lignified maturation stags are involved in the perception and transduction of the stimuli stipulating the need Fur alteration of cell wall architecture. It is thus apparent that, e ven in a microgravity environment, woody plants can make appropriate correc tions to compensate for stress gradients introduced by mechanical bending, thereby enabling compression wood to be formed. The evolutionary implicatio ns of these findings are discussed in terms of "variability" in cell wall b iosynthesis. (C) 2001 Published by Elsevier Science Ltd. All rights reserve d.