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TEMPORARY DELAY OF COTTON FIBER INITIATION, ELONGATION, AND CELLULOSE BIOSYNTHESIS BY COLD TEMPERATURE.  D.S. Johnson^1,2 and B.A. Triplett². ¹McNair Scholars Intern  Program, Xavier University;    ²USDA-ARS, Southern Regional Research Center, New Orleans, LA.

     Cotton fiber growth is an ideal model for investigating microgravity effects on plant gene expression.  Individual fiber cells in culture will attain lengths greater than 1.3 cm in less than two weeks.  Deposition of a secondary cell wall composed almost exclusively of cellulose also occurs in vitro beginning approximately 12 days after culture initiation and continues for at least 16 more days. We have proposed to examine the effects of microgravity on gene expression during all developmental phases using this model plant system, however, flight duration on Space Shuttle missions may involve shorter intervals.  For this reason we have examined during the flight definition phase of our investigation whether development can be temporarily delayed by cold temperature exposure without deleterious effects on subsequent fiber/seed development.  Replicate cultures were initiated using day-of-anthesis cotton ovules.  On the day of culture initiation and five or ten days after culture initiation, cultures were transferred to 4 C for 1 or 2 days.  After cold temperature treatment, cultures were returned to standard culture conditions of 32 C.  Ovule fresh weight, ovule dry weight and cellulose content of the fiber were measured for all treatments.  Delaying or interrupting normal culture conditions of ovule cultures by 1 or 2 day exposure to cold temperature appears to have no major or lasting effect on any of the stages of fiber development.  Therefore, it is feasible to examine simultaneously microgravity effects on fiber at three distinct developmental stages.

     (Supported by NASA: 99-HEDS-02.)