Localisation par autoradiographie de l'acide [5-3H]indole-3-acétique dans le bourgeon terminal du Lycopersicum esculentum

Abstract

[3H]indoleacetic acid (AIA) was applied to the shoot tip of intact young plants of Tomato (Lycopersicum esculentum Mill.) for 10, 60, or 120 min. Autoradiograms of whole plants were prepared and liquid scintillation counts of stem segments and principal root segments were performed. Chromatographic analysis showed that 66% of the radioactivity was associated with AIA after 120 min of contact with [3H]AIA. Autoradiographs of semithin and ultrathin sections were prepared after treatment by DCC (1-(3-dimethyl-aminopropyl)-3-ethylcarbodiimide hydrochloride). The quantity of label per cell and the density of label were determined for all tissues of the apical bud. The density of label was greater for meristematic cells than for differentiated cells. The observed homogeneity of label distribution in the apical meristem shows that auxin levels do not play a prominent role in distinguishing between its lateral and axial zones. The density of label was similar in the apical and in the axillary bud of leaf 4. The cells of the rib meristem, which elongate to produce pith, were more intensely labelled than the other meristematic cells. The percentage of label was calculated for each tissue in a transverse section of the stem just below the apex. The amount of auxin was greatest in the parenchyma (axial and cortical) with lesser amounts in the procambium, phloem parenchyma, and xylem parenchyma. Vessels, which had the greatest density of label, did not contain more than about 3% of total radioactivity of the stem section, while sieve tubes had only 0.5%. Pathways of auxin transport and the role of AIA in regulating meristematic activity in the apical bud are discussed.