52Fe Translocation in Barley as Monitored by a Positron-Emitting Tracer Imaging System (PETIS): Evidence for the Direct Translocation of Fe from Roots to Young Leaves via Phloem

Abstract

The real-time translocation of iron (Fe) in barley (Hordeum vulgare L. cv. Ehimehadaka no. 1) was visualized using the positron-emitting tracer 52Fe and a positron-emitting tracer imaging system (PETIS). PETIS allowed us to monitor Fe translocation in barley non-destructively under various conditions. In all cases, 52Fe first accumulated at the basal part of the shoot, suggesting that this region may play an important role in Fe distribution in graminaceous plants. Fe-deficient barley showed greater translocation of 52Fe from roots to shoots than did Fe-sufficient barley, demonstrating that Fe deficiency causes enhanced 52Fe uptake and translocation to shoots. In the dark, translocation of 52Fe to the youngest leaf was equivalent to or higher than that under the light condition, while the translocation of 52Fe to the older leaves was decreased, in both Fe-deficient and Fe-sufficient barley. This suggests the possibility that the mechanism and/or pathway of Fe translocation to the youngest leaf may be different from that to the older leaves. When phloem transport in the leaf was blocked by steam treatment, 52Fe translocation from the roots to older leaves was not affected, while 52Fe translocation to the youngest leaf was reduced, indicating that Fe is translocated to the youngest leaf via phloem in addition to xylem. We propose a novel model in which root-absorbed Fe is translocated from the basal part of the shoots and/or roots to the youngest leaf via phloem in graminaceous plants.

A Transporter at the Node Responsible for Intervascular Transfer of Silicon in Rice

“…Intervascular transfer is also required for other minerals to be selectively delivered to the grains. For example, redirection at the node from the xylem stream to newly developing organs, apical meristems, young leaves, or inflorescences, independent of the transpiration stream, has been observed for Zn (Obata and Kitagishi, 1980a, 1980b), Fe (Tsukamoto et al, 2009), and Cd (Kashiwagi et al, 2009). However, the transporters involved in these processes have not been identified.…”

Nicotianamine Functions in the Phloem-Based Transport of Iron to Sink Organs, in Pollen Development and Pollen Tube Growth in Arabidopsis

“…Especially during the development of leaves, flowers, and seeds, these young organs act as sinks, and the requirement for phloem transport of micronutrients to these sinks is high. A recent study provided evidence that young leaves of barley (Hordeum vulgare) receive Fe primarily from the phloem, while older leaves receive Fe from the xylem (Tsukamoto et al, 2009). The conclusion that sink organs rely on a NA-dependent phloem pathway for obtaining adequate levels of Fe is supported by our finding that Fe accumulated in the phloem in the absence of NA.…”

“…Generally, NA is needed for the unloading process and remobilization of Fe from the phloem in A. thaliana, which is especially important in the sink organs. In graminaceous species like barley, the situation might be different, and NA and phytosiderophores might be more generally involved in long-distance transport (Tsukamoto et al, 2009;Nishiyama et al, 2012).…”

Fe isotope fractionation caused by translocation of iron during growth of bean and oat as models of strategy I and II plants

“…The mechanisms of iron transport in plants, once taken up by the roots, are less clear. It has recently been suggested that younger leaves receive their iron primarily from the phloem whereas older leaves receive iron from the xylem (Tsukamoto et al 2009). In the xylem iron is transported as Fe(III)-citrate (Tiffin 1966), in the phloem as Fe(III)-ITP (Iron Transporter Protein) or Fe-nicotianamine (NA) (Kruger et al 2002;Curie et al 2009).…”