Polyamines Participate in Mycorrhizal and Root Development of Citrus (Citrus tangerine) Seedlings

Abstract

A pot experiment was conducted to study the effects of difluoromethylornithine (DFMO, an irreversible inhibitor of putrescine (Put) formation) alone or combination with Put on mycorrhizal and root development of Citrus tangerine seedlings inoculated with Glomus mosseae. DFMO significantly inhibited plant growth (plant height, stem diameter, leaf number per plant, shoot and root dry weights), mycorrhizal (root colonization and the number of entry point, vesicle and arbuscule) and root development (total length, total projected area, total surface area and total volume), chlorophyll content, photosynthesis (photosynthetic rates, transpiration rates and stomatal conductance) and soluble protein, whereas the inhibition was partly or completely reversed by Put application to DFMO treatment. DFMO applied to mycorrhizal seedlings showed the decrease of P contents of leaves and roots, the decrease of acid, neutral and alkaline phosphatase activities of rhizosphere and the increase of available P content of rhizosphere, whereas application of exogenous Put to DFMO treatment partly unchained the effects of DFMO. DFMO strongly inhibited the allocation of glucose to root but stimulated the allocation of sucrose to root and guaiacol peroxidase (G-POD) activity of root, but these effects were reversed to a certain extent when Put was included in DFMO treatment. This study thus indicates that endogenous polyamines regulate mycorrhizal development of citrus seedlings through altering the allocation of carbohydrates to root, and also participate in root development, which is negatively related to root G-POD and may be due to inducing new protein synthesis.