NASTIC CURVATURES OF WHEAT COLEOPTILES THAT DEVELOP IN TRUE MICROGRAVITY

Dark-grown wheat coleoptiles developed strong curvatures within 5 h of being transferred in orbit from a 1 g centrifuge to microgravity duri ng an experiment flown on the IML-1 shuttle mission. The curving tende ncy was strongest in seedlings that were immature, with coleoptiles sh orter than 10 mm at the time of transfer, The curvature direction was non-random, and directed away from the caryopsis (the coleoptile face adjacent to the caryopsis becoming convex), The curvatures were most m arked in the basal third of the coleoptiles, contrasting with phototro pic responses, which occur in the apical third. We interpret these cur vatures as being nastic, and related to the curvatures commonly report ed to occur during clinostat rotation treatments.