Roles of Auxin and Ethylene in Adventitious Root Formation by a Flood-resistant Tomato Genotype

Abstract

The relative contributions of auxin and ethylene (C2H4) in stimulating the initiation of adventitious root primordia (ARP) and their subsequent development into adventitious roots (ARs) by flooded tomato (Lycopersicon esculentum Mill. PI 406966) seedlings were evaluated using TIBA and STS. Flooded plants treated with STS (F + STS) produced ≈ 40% as many emerged ARs as plants that were flooded only (F). Only 7% of the ARP initiated by F + STS plants developed enough to emerge through the epidermis by 120 hours of treatment compared with 95% emerged for F plants. A band of TIBA applied below the lowest leaves of flooded plants (F + TIBA) virtually eliminated AR formation. Plants with two or four leaves below the TIBA band produced 16- and 35-fold more ARs, respectively, than those with no leaves below the TIBA band. Relative to nonflooded (NF) plants, F + STS plants exhibited a nearly 40-fold increase in C2H4 evolution, while F and F + TIBA plants exhibited about a 5-fold increase in C2H4 production. These results suggest that auxin accumulation at or above the floodline is essential for ARP initiation and that auxin action is not mediated through C2H4. Ethylene may be required for elongation of flood-induced ARP leading to their emergence as ARs. Chemical names used: 2,3.5 -triiodobenzoic acid (TIBA): silver thiosulphate (STS).