Exogenous polyamines influence root morphogenesis and arbuscular mycorrhizal development of Citrus limonia seedlings

To investigate the influence of exogenous polyamines (PAs) on the root morphogenesis and arbuscular mycorrhizal development of Citrus limonia Osbeck seedlings, experiments were carried out in pots or specially designed containers. Analysis using WinRHIZO^® sofware indicated that exogenous PAs significantly reduced the average root diameter, which was due to the increased percentage of fine roots and the decreased percentage of coarse roots. Root length and the 1st lateral number were also slight increased. The increase in the mitotic index of root tip cells revealed using hydroponic culture indicated the involvement of the mitosis process in the PA-induced changes in root morphogenesis. These changes finally led to the increases in the relative chlorophyll contents (SPAD) and the biomass of seedlings. Moreover, exogenous PAs affected the mycorrhizal colonization in a concentration-dependent manner, with low concentration (0.2 × 10^?4 M) increasing but high concentration (1.0 × and 5.0 × 10^?4 M) decreasing it. These results suggest that exogenous PAs can affect positively the growth of C. limonia seedlings via the pathway of altered root morphogenesis and mycorrhizal development.