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Published on: May 11, 2019
Cadmium transport characteristics in the phloem of sweet potato
Zanming Chen1, Xinyu Zhao1, Shiyuan Zhang2
1Sanya Institute of Nanjing Agricultural University, Sanya, 572024, China; College of Life Sciences, Nanjing Agricultural University, Nanjing, 210095, China.
Abstract:
Cadmium (Cd) pollution in farmland soil poses serious threats to human health. The Cd transport and accumulation in the aboveground tissues of sweet potato (Ipomoea batatas L.) variety "Fu Cai 18″ and the characteristics of phloem-mediated Cd transport were elucidated in this study. Sweet potato seedlings grown in hydroponics were analyzed. The scanning through μ-XRF revealed that Cd was mainly distributed in cortex cells and vascular tissues of the stem; in leaves, it was mainly distributed in veins. The root regeneration and leaf smearing tests revealed that Cd accumulated in the stem can be redistributed to new growth sites and leaves; Cd accumulated in leaves can be transported to roots and young tissues through the phloem. Hence, Cd, transported to the aboveground tissues, can be re-transported in specific directions through the phloem. The leaf phloem exudate collection test demonstrated that the presence of Cd diminished calcium and zinc levels. Analysis of exudate via molecular sieve chromatography revealed that 50-70 % of Cd in the phloem of sweet potato may chelate with small-molecule compounds. Moreover, the contents of lysine, proline, and some carbohydrates (terpinetriose, lactose, stachyose, glucosamine, sorbitol, and maltose) significantly increased in the phloem exudate, suggesting that these substances participated in Cd transport in the phloem of sweet potatoes. These results highlight the critical function of phloem-mediated Cd transport, likely involving its chelation with small molecules and specific elements and metabolites. These results can potentially provide a theoretical basis for understanding the mechanism underlying heavy metal transport in sweet potato.
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