Department of Life Sciences, School of Agriculture, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, Kanagawa, 214-8571 Japan.
Life Sciences Program, Graduate School of Agriculture, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, Kanagawa, 214-8571 Japan.
Plant Cell Physiol. 2021 Jul 17;62(3):515-527. doi: 10.1093/pcp/pcab017.
Zinc (Zn) is nutritionally an essential metal element, but excess Zn in the environment is toxic to plants. Autophagy is a major pathway responsible for intracellular degradation. Here, we demonstrate the important role of autophagy in adaptation to excess Zn stress. We found that autophagy-defective Arabidopsis thaliana (atg2 and atg5) exhibited marked excess Zn-induced chlorosis and growth defects relative to wild-type (WT). Imaging and biochemical analyses revealed that autophagic activity was elevated under excess Zn. Interestingly, the excess Zn symptoms of atg5 were alleviated by supplementation of high levels of iron (Fe) to the media. Under excess Zn, in atg5, Fe starvation was especially severe in juvenile true leaves. Consistent with this, accumulation levels of Fe3+ near the shoot apical meristem remarkably reduced in atg5. Furthermore, excision of cotyledons induced severe excess Zn symptoms in WT, similar to those observed in atg5.Our data suggest that Fe3+ supplied from source leaves (cotyledons) via autophagy is distributed to sink leaves (true leaves) to promote healthy growth under excess Zn, revealing a new dimension, the importance of heavy-metal stress responses by the intracellular recycling.
锌（Zn）是一种必需的营养金属元素，但环境中的过量锌对植物是有毒的。自噬是负责细胞内降解的主要途径。在这里，我们证明了自噬在适应过量锌胁迫中的重要作用。我们发现，与野生型（WT）相比，自噬缺陷型拟南芥（atg2 和 atg5）在过量锌诱导的黄化和生长缺陷方面表现出明显的症状。成像和生化分析表明，自噬活性在过量锌下升高。有趣的是，在培养基中补充高水平的铁（Fe）可以缓解 atg5 的过量 Zn 症状。在过量锌下，atg5 中的铁饥饿在幼叶中尤为严重。与此一致的是，在 atg5 中，茎尖分生组织附近 Fe3+ 的积累水平显著降低。此外，子叶的切除会在 WT 中引起严重的过量 Zn 症状，类似于在 atg5 中观察到的症状。我们的数据表明，自噬从源叶（子叶）供应的 Fe3+ 通过自噬被分配到汇叶（真叶），以促进在过量 Zn 下的健康生长，揭示了一个新的维度，即细胞内再循环对重金属胁迫反应的重要性。
