Phosphor eflux from maize roots in highly localised to the root tip

Wien

2014

S. 6

Artikel aus einer ZeitschriftUnselbständiges Werk

200189731

In addition to phosphorus influx, efflux is regarded an important component of P uptake by plant roots. Several studies demonstrated that generally both, apical as well as basal root parts contribute to P influx. However, data on the localization of efflux is hardly available in literature. In previous studies we observed high concentrations of P in closely confined regions around root tips of soil-grown Brassica napus L. and Zea mays L. plants. Supported by numerical simulation we hypothesized P efflux as a potential cause for these P hotspots. To clarify the nature of our observation, we labelled the shoot P of Z. mays plants grown in soil-filled rhizotrons by puncturing the coleoptile and placing a droplet containing 33P on the lesion. Phosphorus is phloem-mobile, therefore the radioactive spike is readily redistributed in the whole plant after labelling. Using a 2D sampling and imaging technique for P, we acquired images of the distribution of 33P release by the maize roots. After a sampling period of 48 h the efflux images showed that P release from maize roots is highly confined to the apical region of the root, with only negligible contribution of more basal root axes. Although the roots were actively growing during the sampling period and efflux localization at the mm scale is complicated, our data indicate that the route of P efflux is mainly via the apoplastic phloem-soil continuum at the initial, unsuberised phloem. We conclude that P influx and efflux are not co-localized in maize roots and discuss the consequences on root ion uptake and rhizosphere ecology.