Blommaert Hester, Aucour Anne-Marie, Wiggenhauser Matthias, Moens Claudia, Telouk Philippe, Campillo Sylvain, Beauchêne Jacques, Landrot Gautier, Testemale Denis, Pin Serge, Lewis Caleb, Umaharan Pathmanathan, Smolders Erik, Sarret Géraldine
Université Grenoble Alpes, Université Savoie Mont Blanc, CNRS, Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD), Université G. Eiffel, Institut des Sciences de la Terre (ISTERRE), Grenoble, France.
Université de Lyon, Université Lyon 1, Ecole Normale Supérieure (ENS) de Lyon, Centre National de la Recherche Scientifique (CNRS), Unité Mixte de Recherche (UMR) 5276 Laboratoire de Géologie de Lyon - Terre, Planète et Environment (LGL-TPE), F-6922, Villeurbanne, France.
Front Plant Sci. 2022 Dec 2;13:1055912. doi: 10.3389/fpls.2022.1055912. eCollection 2022.
The research on strategies to reduce cadmium (Cd) accumulation in cacao beans is currently limited by a lack of understanding of the Cd transfer pathways within the cacao tree. Here, we elucidated the transfer of Cd from soil to the nib (seed) in a high Cd accumulating cacao cultivar. Here, we elucidated the transfer of Cd from soil to the nib (seed) in a high Cd accumulating cacao cultivar through Cd stable isotope fractionation, speciation (X-Ray Absorption Spectroscopy), and localization (Laser Ablation Inductively Coupled Plasma Mass Spectrometry). The plant Cd concentrations were 10-28 higher than the topsoil Cd concentrations and increased as placenta< nib< testa< pod husk< root< leaf< branch. The retention of Cd in the roots was low. Light Cd isotopes were retained in the roots whilst heavier Cd isotopes were transported to the shoots (Δ Cd = 0.27 ± 0.02 ‰ (weighted average ± standard deviation)). Leaf Cd isotopes were heavier than Cd in the branches (Δ Cd = 0.18 ± 0.01 ‰), confirming typical trends observed in annual crops. Nibs and branches were statistically not distinguishable (Δ Cd = -0.08‰ ± 0.06 ‰), contrary to the leaves and nibs (Δ Cd = -0.25‰ ± 0.05 ‰). These isotope fractionation patterns alluded to a more direct transfer from branches to nibs rather than from leaves to nibs. The largest fraction (57%) of total plant Cd was present in the branches where it was primarily bound to carboxyl-ligands (60-100%) and mainly localized in the phloem rays and phelloderm of the bark. Cadmium in the nibs was mainly bound to oxygen ligands (60-90%), with phytate as the most plausible ligand. The weight of evidence suggested that Cd was transferred like other nutrients from root to shoot and accumulated in the phloem rays and phelloderm of the branches to reduce the transfer to foliage. Finally, the data indicated that the main contribution of nib Cd was from the phloem tissues of the branch rather than from leaf remobilization. This study extended the limited knowledge on Cd accumulation in perennial, woody crops and revealed that the Cd pathways in cacao are markedly different than in annual crops.
目前，由于对可可树体内镉（Cd）转移途径缺乏了解，限制了关于减少可可豆中镉积累策略的研究。在此，我们阐明了镉在一个高镉积累型可可品种中从土壤转移至可可豆仁（种子）的过程。在此，我们通过镉稳定同位素分馏、形态分析（X射线吸收光谱法）和定位分析（激光烧蚀电感耦合等离子体质谱法），阐明了镉在一个高镉积累型可可品种中从土壤转移至可可豆仁（种子）的过程。植株中的镉浓度比表土中的镉浓度高10 - 28倍，且随着胎盘＜可可豆仁＜种皮＜荚壳＜根＜叶＜枝条的顺序增加。镉在根中的保留率较低。轻镉同位素保留在根中，而重镉同位素则转运至地上部分（ΔCd = 0.27 ± 0.02‰（加权平均值±标准偏差））。叶片中的镉同位素比重于枝条中的镉同位素（ΔCd = 0.18 ± 0.01‰），这证实了在一年生作物中观察到的典型趋势。可可豆仁和枝条在统计学上无显著差异（ΔCd = -0.08‰ ± 0.06‰），与叶片和可可豆仁的情况相反（ΔCd = -0.25‰ ± 0.05‰）。这些同位素分馏模式表明，镉从枝条到可可豆仁的转移比从叶片到可可豆仁的转移更直接。植株总镉中最大比例（57%）存在于枝条中，在枝条中镉主要与羧基配体结合（60 - 100%），且主要定位于树皮的韧皮射线和栓内层。可可豆仁中的镉主要与氧配体结合（60 - 90%），植酸盐是最可能的配体。有力证据表明，镉像其他养分一样从根转移到地上部分，并积累在枝条的韧皮射线和栓内层中，以减少向叶片的转移。最后，数据表明可可豆仁中镉的主要来源是枝条的韧皮组织，而非叶片的再转运。本研究扩展了关于多年生木本作物中镉积累的有限知识，并揭示了可可中的镉转移途径与一年生作物明显不同。
