Regulation of Root Length and Lateral Root Number in Trifoliate Orange Applied by Peroxide Hydrogen and Arbuscular Mycorrhizal Fungi
AbstractRoot system morphology (RSM) in plants plays a key role in acquiring nutrients from the soil and is also altered by abiotic or biotic factors including soil microorganisms and signal molecules. The present study was made to evaluate the effects of an arbuscular mycorrhizal fungus (AMF, Glomus versiforme) and exogenous peroxide hydrogen (H2O2, 0, 1 and 100 μM) on root length, lateral root number and activities of polyamine-metabolized enzymes in trifoliate orange (Poncirus trifoliata) seedlings. After 5 months of inoculation with AMF, root mycorrhizal colonization was significantly increased by application of 1 μM H2O2, but markedly restrained by 100 μM H2O2. Inoculation with AMF significantly increased the taproot length and the number of second- and third-order lateral roots under 1 and 100 μM H2O2application. The AMF infection significantly increased 0-1 cm classed root length and total root length, regardless of H2O2 concentration. In general, inoculation with AMF increased arginine decarboxylase (ADC) and ornithine decarboxylase (ODC) activity of roots under 0, 1 and 100 μM H2O2, increased diamine oxidase (DAO) activity of roots under 0 μM H2O2 and decreased DAO activity of roots under 1 and 100 μM H2O2. Root polyamine oxidase (PAO) activity was similar between AMF and non-AMF seedlings, irrespectively of H2O2concentration. Results suggest that lower concentration of H2O2(1 μM) might be regarded as a signal to stimulate mycorrhizal and lateral root development through increase of ADC and ODC and decrease of DAO, while high concentration of 2O2 (100 μM) as a toxic compound of reactive oxygen species restricted AMF colonization.
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