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- Author or Editor: Steven T. McNamara x
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).
Tomato accessions PI 128644 (Lycopersicon peruvianum var. dentatum Mill.) and PI 406966 (Lycopersicon esculentum Mill.) were identified in preliminary screening trials as being relatively nonresistant and resistant to 120 hr of flooding, respectively. Many adventitious roots (AR) developed on the lower stems of flooded PI 406966 seedlings, while few formed on flooded PI 128644 plants. Root formation by flooded PI 406966 seedlings depended on de novo initiation rather than emergence of preformed initials. Hypocotyl porosity of PI 406966 plants increased from between 3% and 6% to 8% by 36 and 72 hr of flooding, respectively. Porosity of PI 128644 hypocotyls was unchanged by 72 hr of inundation. Flooding did not affect the secondary root porosity of either accession. The limited capacity of PI 128644 seedlings to develop AR and aerenchyma was not related to an inability to synthesize 1-aminocyclopropane-l.carboxylic acid or ethylene in response to hypoxia. Chemical name used: 1-aminocyclopropane-1-carboxylic acid (ACC).
Abstract
Tomato accessions PI 128644 (Lycopersicon peruvianum var. dentatum Mill.) and PI 406966 (L. esculentum Mill.) were identified in preliminary screening trials as being relatively nonresistant and resistant to root-zone flooding, respectively. A comparative study of these accessions was undertaken to examine adaptive responses to inundation. Root and shoot growth of both accessions were inhibited by 120 hr of flooding. Aerobic respiratory capacity of secondary roots of both accessions decreased to a similar extent after 24 hr of inundation. Flooding did not significantly affect anaerobic root respiration rate of either accession. Stomatal conductance decreased after 24 hr of flooding for both accessions, with some recovery by PI 406966 after 168 hr of treatment, coinciding with development of adventitious roots on lower stems. Few adventitious roots formed on flooded PI 128644 plants. Leaf water potential of both accessions initially increased as a result of flooding, but declined to near control level by 120 hr of treatment. Total phenol content of PI 128644 roots decreased with 72 hr of flooding, while that of PI 406966 roots was not significantly affected. Factors underlying the greater resistance of PI 406966 to flooding remain unclear, but may include a lower root respiratory requirement for O2 and greater ability to sequester or eliminate toxic substances during inundation.
Little is known about asexual propagation of Maackia amurensis Rupr. & Maxim. (Amur maackia), a N2-fixing tree species with potential for increased use in the landscape. Terminal cuttings were collected from 20 trees (10 at the Minnesota Landscape Arboretum and 10 in the Washington, D.C., area) at two times in 1992. Cuttings were treated with either 0 or 2500 mg·kg-1 IBA and held in a humidified greenhouse for 12 weeks. Primary and secondary roots were counted, and a subjective rooting score was assigned at harvest. The rooting percentage of the genotypes ranged from 19 to 92, and the number of roots and the rooting scores of the genotypes also varied significantly. Collection date and IBA had relatively minor effects on rooting. We conclude that M. amurensis can be propagated from softwood cuttings, but the usefulness of this method varies with genotype.