ASGSB 2003 Annual Meeting Abstracts


PHOSPHOINOSITIDE SIGNALING AND PLANT GRAVITROPISM   I.Y. Perera, C.Y. Hung, C. Randall and W. F. Boss, Dept  of Botany,  North Carolina State University, Raleigh, NC

   Many signaling molecules and second messengers such as Ca2+, inositol 1,4,5-trisphosphate (InsP3), reactive oxygen species (ROS) and changes in pH have been implicated in the early signaling events which link gravity sensing to the initiation of a differential growth response in plants.  However at present, the importance of these different signaling pathways and the interactions between them are not well understood. As an approach towards further delineating the role of InsP3 in plant gravitropism, we have generated Arabidopsis plants constitutively expressing the human type I inositol polyphosphate 5-phosphatase (InsP 5-ptase), an enzyme that specifically hydrolyzes InsP3. The transgenic plants have no obvious phenotype under normal growth conditions and no significant differences in growth and life cycle compared with wild type Arabidopsis plants.  Strong expression of the InsP 5-ptase transgene is detectable in all tissues of the transgenic plants and basal InsP3 levels are reduced by greater than 90% compared to wild type plants. Significantly, gravitropic bending of the roots and hypocotyls of the transgenic seedlings are reduced by ~ 30% compared with the wild type.  In addition, we have monitored the gravitropic responses of inflorescence stems of mature plants.  InsP3 levels increase ~ 4 fold within the first 5-15 min of gravistimulation, preceding visible bending in the wild type plants, while levels in the transgenic plants show little detectable change. Furthermore, gravitropic bending is compromised in inflorescence stems of transgenic plants compared to wild type. Our results indicate that InsP3 is one component of the gravity signal transduction cascade of plants.  (Funded by # NAG 2-1502 to IYP and WFB)  


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