J.PlantPhysiol. Vol. 140.pp. 75-83{1992} Introduction Pisum sativum Epicotyls Inoculated with Agrobacterium rhizogenes Agropine Strains Harbouring Various T-DNA Fragments: Morphology, Histology and Endogenous Indole-3-Acetic Acid and Indole-3-Acetamide Content E. PRINSEN!, J. BERCETCHE 2 , D. CHRIQUl 2 , and H. VAN ONCKELEN! 1 University of Antwerp (UIA), Department of Biology, Universiteitsplein 1, B-2610 Wilrijk, Belgium 2 Universite P. M. Curie, Lab. CEMV, Bat. N2, 4, Place Jussieu, F-75252 Paris Cedex OS, France Received September 16, 1991 . Accepted December 4, 1991 Summary In the present paper we correlate endogenous IAA and lAM levels with morphological and histological changes of decapitated Pisum sativum epicotyls after inoculation with pA-303,dl6Agrobacterium derived strains. Callus and subsequent root formation in the infected region are correlated with endogenous IAA accumulation as a result of expression of the TR aux genes, concomitant with lAM accumulation. Ir- respective of the bacterial strain analyzed IAA synthesis by the bacteria themselves was found to be constitutive and therefore not related to root proliferation. Inoculation with strains harbouring the aux genes (TR or TR + TL) induced callus formation, root initiation and histological changes such as tracheid differentiation and development of cribrovascular nodules surrounded by cambial-like layers. The pres- ence of TL largely abolished the geotropic growth of the neoformed roots. Inoculations with strains har- bouring only TL DNA or the Eco15 fragment covering orfl0 to 12 lead to limited histological effects and root initiation. Morphology and growth pattern of root clones obtained from inoculations with the wild type A4 pA-303,dI60culations with strains containing either TL or TR alone differed greatly and could be related to varying endogenous IAA levels. High endogenous IAA and lAM levels were found in root clones obtained after inoculation with bac- terial strains carrying only TL DNA. Key words: Agrobacterium rhizogenes, Pisum sativum, auxin, fAA, lAM Abbreviations: aux = auxin encoding loci; IAA = Indole-3-acetic acid; lAM = Indole-3-acetamide; orf = open reading frame; rol = rooting locus; T-DNA = transferred DNA; TL = Left transferred DNA; TR = right transferred DNA. Agrobacterium rhizogenes causes the hairy root disease (Riker et al., 1930). Virulence is due to a large extrachro- mosomal plasmid (Ri) carrying a transferable DNA fragment (T-DNA) (White et al., 1982), which is introduced into the plant genome (Chilton et al., 1982). Hairy roots show hormone autotrophic growth in vitro (for review see Tempe and Casse-Delbart, 1989). The Ri-plasmids of the agropine type strains contain two independently transferable T-DNA regions: TL and TR (Huffman et aI., 1984; Jouanin, 1984) whereas mannopine and cucumopine type strains only have one T-DNA region displaying significant homology with the TL region of the agropine type Ri plasmids (Filetici et al., 1987; Brevet and Tempe, 1988). Among the 18 genes iden- tified so far on the TL-DNA, only three, rotA, Band C, cor- responding to the open reading frames 10, 11 and 12 (White et al., 1985), seem to playa fundamental role in the induc- © 1992 by Gustav Fischer Verlag, Stuttgart