| Copper (Cu) is the essential transition metal in the process of growth and development of higher plants and even all living creatures, which is involved in many physiological processes and exists with a variety of oxidation states in plants. In physiological conditions, Cu has two molecular forms, Cu+and Cu2+. Cu2+is combined with N in the side chains of histidine, whereas Cu+often reacts with methionine or cysteine. As a structural element of some metal proteins, copper is a cofactor for many enzymes involved in electron transmission in mitochondria and chlproplasts and the oxidative stress-induced reactions of plants. Copper in high concentration has toxic effects on organisms, which can lead to protein functional inactivation or structural destruction. To protect themselves from the high-concentration copper stress, plants have a complex metal transport network to adjust to changes of the concentration of copper ions in vivo timely and appropriately. But its potential epigenetic mechanism has not been fully elucidated. EDDS (Ethylene diamine acid) is a biodegradable metal chelating agent which is able to be completely degraded in the soil easily and quickly. It is an effective amendment to remove heavy metals in soil. In recent years, it has become a frequently used soil ameliorant to absorb heavy metal ions due to its significant chelates ability as well as the promotion to plants’absorption of the metal. Common plants could survive in heavy metal-contaminated soils with EDDS applied.The metals in soil can be transferred and enriched in plants, and thus be removed by harvesting plants. In this study, we use rice, one; of the most widely sown crop and classic model plants, as the experiment material. We observe a variety of physiological and biochemical changes induced by high-concentration copper stress and the addition of EDDS, revealing that EDDS could enhance tolerance potential of rice to excess Cu toxicity. We treat rice with200μM copper and Cu plus EDDS for3days to test copper content and pHysiological and biochemical changes in rice to study an antagonistic action to EDDS under excess Cu stress. The results were as follows:1. With only copper treatment, we detected apoptosis in rice root cells by TUNEL and PI double staining in flow cytometry and found more significant changes in rice roots treated with200μM copper compared to those treated with100μM. Initially according to pHenotypic pHenomenon, in both treatments rice roots undergonecrosis apoptosis. Therefore, the copper concentration of200μM was selected.2. Rice seedling growth was inhibited with the rate of electrolyte leakage relatively increased, SOD activity increased, CAT activity reduced and plasma membrane H+-ATP enzyme activity decreased. It is critical for plants to maintain the integrity of membrane structure under heavy metal stress. The results above indicated that heavy metal copper broke through this defense and came into the cells, but EDDS played a protective role in the defense.3. The chlorophyll and carotenoid content was markably decreased and the level of the mRNA of Cytochrome P450gene,OsHMA9, the sulpHate transporter gene and the metallothionein-like protein gene were observed increased in response to Cu stress. However, these expression levels return normal with the presence of EDDS.4. Cu treatment also induced a global epigenetic response which is associated with cell nucleus condensation.These physiological, genetic and epigenetic responses of rice seedlings’exposure to excess copper were modified by the addition of EDDS, suggesting that the supply of EDDS in medium containing high concentration of Cu ions could enhance plants’ tolerance potential to excess Cu toxicity through antagonizing Cu-induced poisonous effects at various levels. |
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