Poster: Tropisms

Abs # 403: The Onset of Gravisensitivity in Flax (Linum usitatissimum) Roots

Presenter:	Ma, Zhong , zxm1769@louisiana.edu
Authors	Ma, Zhong  (A)   Hasenstein, Karl  (A)
Affiliations:	(A): University of Louisiana at Lafayette, Biology Department

We determined the onset of gravisensitivity of germinating flax roots. Seeds were glued to germination paper and placed in seed cassettes in the dark, and allowed to imbibe in different orientations. Between 0.5 to 18h after imbibition seeds were clinorotated (1rpm) for the reminder of a 24h or 36h period. After clinorotation, the percentage of roots was recorded that curved in the originally downward direction i.e., in the direction of gravity vector prior to clinorotation. Root emergence occurred 22h after imbibition. However, 9h and 12h after imbibition, 64% and 91% of the roots, respectively, curved in the direction of the initial gravity vector. Extrapolation to 50% curvature response suggests an onset of gravisensing at about 8 hours after imbibition. The orientation of the flax seed affected gravidetection. When the long axis of the embryo was placed horiziontally, gravitdetection was established after 8 hours, whereas orientation of the embryo parallel to the gravity vector but upward delayed the onset of gravisensing to >12 h. Prolonged clinorotation (over 18h) reduced the number of gravi-responding roots. The dissection and analysis of the root cap development at 6, 8 and 10 hours after imbibition will reveal the structures that must be established for gravisensing to occur. Supported by NASA grant NAG10-190.