Fe 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

Tsukamoto, Takashi*; Nakanishi, Hiromi*; Uchida, Hiroshi*; Watanabe, Satoshi; Matsuhashi, Shimpei; Mori, Satoshi*; Nishizawa, Naoko*

The real-time translocation of iron (Fe) in barley ( L. cv. Ehimehadaka no.1) was visualized using the positron-emitting tracer Fe 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, Fe first accumulated at the basal part of the shoot. Fe-deficient barley showed greater translocation of Fe from roots to shoots than did Fe-sufficient barley. In the dark, translocation of Fe to the youngest leaf was equivalent to or higher than that under the light condition, while the translocation of Fe 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, Fe translocation from the roots to older leaves was not affected, while Fe translocation to the youngest leaf was reduced. 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.