Le transport basipete de l'AIA-5-3H dans le coleoptile de ble

Basipetal transport of [5-3H] IAA in the wheat coleoptile 3H-IAA was applied to the tips of intact wheat coleoptiles (Triticum sativum L., var. Capitole) for 30, 60 or 120 min. The quantity of label per segment (1.5 mm), determined by liquid scintillation counting, was a decreasing exponential function of distance from the source of radioactivity. Chromatographic analysis showed that 3H-IAA was transported more rapidly than its tritiated metabolites. Antoradiographs of semi-thin sections were performed after application of 3H-IAA during 2 h and after treatment by DCC [1-(3-dimethyl-aminopropyl)-3-ethycarbodiimide hydrochloride]. The quantity of label per tissue and per cell was determined at 1.5, 3.0 and 4.5 mm from the tip. Tritiated IAA was estimated to account for 70 to 100% of the label, depending on the distance from the tip. The amount of auxin transported basipetally was greatest in the parenchyma, with lesser amounts transported in the inner and outer epidermis. Tissues of the vascular bundles did not contain more than 10% of total radioactivity of the coleoptile sections. The rate of auxin transport was greater in xylem and parenchyma than in epidermis and bundle sheath. Movement was very slow in procambium and phloem. In parenchyma and epidermis the quantity of label per cell as a function of distance from the tip agreed with the model of exponential regression. These results support the theory of polar diffusion of auxin.