砷是一种有毒的类金属元素，环境中的砷进入植物体后，不仅会影响植物生长发育，还会通过食物链进入人体，威胁人类生命安全。因此，了解植物体内砷耐性的调控机制对于缓解砷对植物的毒害、减少砷向人体的迁移至关重要。乙烯是一类天然产生的植物激素，在植物的胁迫应激反应中发挥重要作用。有研究表明乙烯可由重金属胁迫诱导合成，并促使植物产生防御反应。但是，乙烯调控植物砷耐性的机制尚不明确。本实验以拟南芥（Arabidopsis thaliana）为实验材料，通过分析砷胁迫下野生型和乙烯相关突变体的根系相对伸长等砷耐性表型来初步确定乙烯对拟南芥砷毒害的缓解作用，并进一步从三个方面探究乙烯提高拟南芥砷耐性的机制。主要研究结果如下：

1. 与Col-0相比，乙烯过量合成突变体eto1-1的根系相对伸长增加，乙烯不敏感突变体ein2-5减少；砷胁迫下，外源ACC增加了Col-0的相对根伸长。砷胁迫下拟南芥幼苗的生物量、根系活力、根系生长和光合色素合成均受到抑制，eto1-1所受抑制最低。除此之外，eto1-1的脯氨酸和可溶性蛋白含量显著高于野生型，丙二醛含量显著低于野生型，而ein2-5结果则相反。以上结果表明乙烯参与调控拟南芥砷耐性。
2. 实验发现，拟南芥幼苗砷积累量依次为：ein2-5 > Col-0 > eto1-1。与Col-0相比，eto1-1的砷转运系数显著降低。另外，三个株系的砷外排速率和根系细胞壁砷含量没有显著差异。这说明乙烯能够减少拟南芥砷积累，并将大部分砷隔离在根部，减少砷由根系向地上部的转运，但乙烯不参与砷的外排和细胞壁富集。
3. 乙烯能够促进拟南芥砷还原和区隔化。As(V) 胁迫下，拟南芥地上部和根系As(III) 占总砷百分比依次为：eto1-1 > Col-0 > ein2-5。与Col-0相比，砷胁迫下eto1-1的谷胱甘肽和植物螯合肽（PCs）含量显著升高，半胱氨酸含量显著降低；eto1-1和ACC处理后的Col-0中γ-ECS、GSH2、PCS1、ABCC1和ABCC2基因表达量上调，砷胁迫下上调更显著。这表明乙烯能够促进砷与非蛋白巯基螯合，并促进砷的液泡区隔化进程。此外，外源添加ACC能够提高Col-0的砷耐性，但不影响PCs合成缺失突变体（cad1-3、pad2-1）和ABCC液泡膜转运蛋白双突变体（abcc1abcc2）的砷耐性，这表明乙烯对拟南芥砷耐性的提高可能依赖于砷的螯合和液泡区隔化途径。
4. 与Col-0相比，砷胁迫下eto1-1的活性氧（过氧化氢和超氧阴离子）含量显著减少，抗氧化酶（过氧化物酶和超氧化物歧化酶）活性显著增强。这表明，乙烯能够减少砷胁迫下拟南芥的活性氧积累，增强其抗氧化酶系统的活力。

综上分析，乙烯能够缓解拟南芥砷毒害，促进砷的还原、植物螯合肽的合成及ABCC基因的表达，从而促进砷的液泡区隔化，提高拟南芥的砷耐性。本研究对深入探索乙烯调控植物砷耐性的机制，提高植物的砷耐性提供了基础和依据。

Arsenic (As), a toxic metalloid element, not only inhibits the growth and development of plants, but also threatens human health through the food chain. Therefore, understanding As tolerance mechanisms of plants is very important to alleviate As toxicity to plants, and reduce As translocation to human body. Ethylene is a kind of natural plant hormone, which plays an important role in stress response of plants. Previous studies have shown that ethylene can be induced by heavy metal, and thus promote the defense response of plants. However, the mechanisms of ethylene regulating arsenic tolerance in plants is still unclear. In this study, the relative root elongation was used to evaluate As tolerance of Arabidopsis thaliana wild-type (Col-0) and ethylene-related mutants, to preliminarily testify ethylene play roles on As resistance of Arabidopsis. Therefore, the mechanisms of ethylene to improve As tolerance in Arabidopsis was further explored. The main results of this study are as follows:

1) Compared with Col-0, the relative root elongation of ethylene overproduction mutant eto1-1 increased and ethylene insensitive mutant ein2-5 decreased significantly under As stress. Exogenous ACC increased the relative root elongation of Col-0, and alleviated As toxicity to Arabidopsis. Arsenic reduced Arabidopsis biomass, root vigor, root growth and photosynthetic pigment contents, the inhibition rate was lower in eto1-1 than ein2-5 and Col-0. Furthermore, the proline contents and soluble protein in eto1-1 were higher than Col-0, while malondialdehyde was lower than Col-0 significantly. The reversed trend in ein2-5 was found. These results indicated that ethylene improved As tolerance in Arabidopsis.

2) The highest concentration of As was found in ein2-5, while the lowest concentration was in eto1-1. Compared with Col-0, the As translocation factors of eto1-1 was lower significantly. There was no significant difference in As efflux rate and As concentration in cell wall between wild-type and two mutants. These results showed that ethylene reduced the accumulation of As and inhibited the translocation of As from root to shoot in Arabidopsis, but it does not influenced As efflux and accumulation in the cell wall.

3) Ethylene promoted As reduction and compartmentation in vacuole. Under As(V) stress, the proportion of As(III) in shoot and root of Arabidopsis was higher in eto1-1 than Col-0 and ein2-5. Compared with Col-0, the glutathione and PCs contents of eto1-1 increased and the cysteine content decreased significantly under As stress. The genes of γ-ECS, GSH2, PCS1, ABCC1 and ABCC2 in eto1-1 were up-regulated compared with Col-0, especially under arsenic stress. The same results were found in Col-0 when exogenous ACC was supplied. These indicated that ethylene promoted the chelation of As with non-protein thiols and vacuole compartmentalization. Moreover, the addition of ACC improved As tolerance of Col-0, but did not affect As tolerance of cad1-3, pad2-1 and abcc1abcc2, which implied that the improvement of As tolerance by ethylene may depend on As chelation and compartmentalization in vacuole.

4) The contents of hydrogen peroxide and superoxide anion decreased and the activities of peroxidase and superoxide dismutase increased in eto1-1 compared to Col-0 under As stress. The results showed that ethylene could reduce the accumulation of reactive oxygen species and enhance the activity of antioxidant enzyme system in Arabidopsis.

In conclusion, ethylene can alleviate arsenic poisoning and improve arsenic tolerance of Arabidopsis by promoting vacuole compartmentalization. This study provides the basis for further exploring the mechanism of ethylene regulating plant arsenic tolerance.