Abstract
We have demonstrated that microgravity conditions in space resulted in automorphosis and reduction of auxin polar transport activities of epicotyls in etiolated pea (Pisum sativum L. cv. Alaska) seedlings. In addition, automorphosis was phenocopied by the application of auxin polar transport inhibitors. These results strongly suggest that automorophosis is closely related to auxin polar transport. Strenuous efforts to know the regulatory mechanisms of auxin polar transport in pea seedlings at molecular bases resulted in successful identification of PsPIN2 and PsAUX1 encoding putative carrier proteins for auxin polar transport. Significantly high homology was found on deduced amino acid sequences between AtAUX1 and PsAUX1. On the other hand, PsPIN2 showed higher homology with AtPIN3 and AtPIN4 than with AtPIN1. Based on the results of gene expression of PsPIN2 and PsAUX1 under various gravity conditions, a possible role of gravity in regulating auxin polar transport will be discussed.
