⁵²Mn translocation in barley monitored using a positron-emitting tracer imaging system

Abstract

Until now, the real‐time uptake and movement of manganese (Mn), an essential plant nutrient, has not been documented in plants. In this study, the real‐time translocation of Mn in barley (Hordeum vulgare L. cv. Ehimehadaka no. 1) was visualized using the positron‐emitting tracer 52Mn and a positron‐emitting tracer imaging system (PETIS). PETIS allowed the non‐destructive monitoring of Mn translocation in barley under various conditions. In all cases, 52Mn first accumulated in the discrimination center (DC) at the basal portion of the shoot, suggesting that this region may play an important role in Mn distribution in graminaceous plants. Manganese‐deficient barley showed greater translocation of 52Mn from roots to shoots than did Mn‐sufficient barley, demonstrating that Mn deficiency causes enhanced Mn uptake and loading into vascular bundles. In contrast, the translocation of 52Mn from roots to shoots was suppressed in Mn‐excess barley. In these plants, the uptake of Mn may be suppressed or Mn may accumulate in the intercellular organelles of root cells, resulting in low rates of Mn translocation to shoots. In Mn‐sufficient barley, the dark treatment did not suppress the translocation of 52Mn to the youngest leaf, suggesting that the translocation of Mn to the youngest leaf is independent of the transpiration stream. When 52Mn was supplied to the cut end of an expanded leaf, 52Mn was transported to the DC within 27 min and then retranslocated to roots and other leaves. Our results show that the translocation of Mn from the roots to the DC depends passively on water flow, but actively on the Mn transporter(s).

Tracing Cadmium from Culture to Spikelet: Noninvasive Imaging and Quantitative Characterization of Absorption, Transport, and Accumulation of Cadmium in an Intact Rice Plant

“…Compared with these substances, Cd showed 1/200th to 1/9th lower velocities in this study, although rice plants at a similar growth stage were tested. Interestingly, Tsukamoto et al (2006) reported that the velocity of transport of 52 Mn in the shoot from the shoot base was 3.6 cm h 21 in a 3-week-old manganesedeficient barley plant, which was very similar to our results with Cd. It is known that interactions take place between cationic solutes and negatively charged groups in the cell walls of the xylem vessels along the pathway from the roots to the leaves (Marschner, 1995), and organic chelating compounds including citrate affect these interactions (Senden et al, 1992).…”

The node, a hub for mineral nutrient distribution in graminaceous plants

“…In graminaceous plants, this preferential distribution seems to occur in the nodes, as shown by previous physiological studies. Several radioisotope tracer studies revealed that mineral elements, including Zn, Mn, and Fe, newly taken up by the roots are primarily accumulated in the nodal parts and then translocated to the developing tissues, with much lower allocation to older leaves in rice [3][4][5][6] or barley (Hordeum vulgare) [7,8]. A few recently identified mineral element transporters localized in the nodes have provided new insights into the molecular mechanisms of nutrient distribution in graminaceous plants.…”

A node-based switch for preferential distribution of manganese in rice

“…Previous physiological studies have shown that plants are able to change the distribution pattern in response to environmental changes. For example, the Mn distribution pattern in barley changes with Mn supply conditions 9 . Under Mn-sufficient condition, Mn taken up by the roots was distributed to expanded leaves.…”

“…Under Mn-sufficient condition, Mn taken up by the roots was distributed to expanded leaves. Under Mndeficient condition, Mn was rapidly accumulated at the shoot basal region and then preferentially distributed to the youngest leaf 9,10 . However, molecular mechanisms underlying different distribution patterns in response to environmental changes are poorly understood.…”