Poster: Long Distance Transport

Abs # 412: Photoperiodic Induction and the Floral Stimulus

Presenter:	Hoffmann-Benning, Susanne , hoffma16@msu.edu
Authors	Hoffmann-Benning, Susanne  (A)   Lydic, Todd  (B)   Shimojima, Mie  (B)   Kende, Hans  (C) (D)  Zeevaart, Jan AD (C) (D)
Affiliations:	(A): Michigan State University, Mass Spectrometry Facility (B): Michigan State University, Dept. of Biochem. & Molecular Biology (C): Michigan State University- DOE-Plant Research Laboratory (D): Michigan State University, Plant Biology

Physiological evidence indicates that flower formation is hormonally controlled. The floral stimulus is formed in the leaves in response to an inductive photoperiod and translocated through the phloem to the apical meristem. However, because of difficulties in obtaining and analyzing phloem sap and the lack of a bioassay, the chemical nature of this stimulus is a major unsolved problem in plant biology. Microbore HPLC and MALDI-TOF-MS were used to compare the contents of the phloem sap from flowering and non-flowering plants. This allowed us to detect proteins/peptides that were very small and present at very low levels. Of the more than 100 compounds detected in the phloem sap, we obtained sequences for 16 peptides from 1-9 kDa. Four of these peptides were specific to, modified, or increased in plants that were flowering, indicating their possible role in flower induction. The sequences of these peptides showed similarities to two purine permeases, a protein kinase, and a protein with no similarities to any known protein. We also started to analyze large proteins in Perilla phloem sap using SDS-PAGE, followed by LC-MS/MS. So far, we detected 11 proteins in the size range from 21 to 150 kDa. They show low similarity to a human reverse transcriptase homologue, a transcription factor, a peppermint transport protein, a ubiquitin-activating protein, a cell wall-plasma membrane linker protein with a unique repetitive sequence, thioredoxin H, methionine synthase, a putative disease resistance protein, and glutamate synthase. We are now trying to clone the genes for several of these peptides/proteins and to study their expression. This work was supported by the U.S. Dept. of Energy (JADZ) and the MSU Research of Excellence Fund, Plant Products and Technologies (SHB)