| 摘要: |
| 以绿豆幼苗为材料，研究了外源一氧化氮（NO）处理对Cd2+胁迫3天和8天时幼苗叶片和根系DNA含量、DNA链间交联程度以及叶片光合参数的影响。结果表明：单独Cd2+胁迫导致叶片和根系DNA含量降低，DNA链间交联程度增加，叶片净光合速率、气孔导度和胞间隙CO2浓度降低，气孔限制值升高；与单独Cd2+胁迫相比，NO和Cd2+复合处理提高了叶片和根系DNA含量，降低了DNA链间交联程度，同时使叶片净光合速率和气孔导度升高，而使胞间隙CO2浓度和气孔限制值降低。结果说明，NO能缓解Cd2+胁迫对绿豆幼苗DNA结构及其代谢的影响；Cd2+胁迫抑制绿豆幼苗光合作用的主要原因是气孔因素，而NO主要通过提高幼苗叶片非气孔因素缓解了Cd2+胁迫对幼苗光合作用的抑制。 |
| 关键词: 一氧化氮 镉胁迫 绿豆幼苗 DNA 光合作用 |
| DOI：10.7515/JEE182034 |
| CSTR：32259.14.JEE182034 |
| 分类号: |
| 基金项目:国家自然科学基金项目（31570397）；陕西省自然科学基础研究计划项目（2016JZ008）；商洛市科学技术研究发展计划项目（SK-2013-15） |
| 英文基金项目:National Natural Science Foundation of China (31570397); Natural Science Research Plan of Shaanxi Province of China (2016JZ008); Science and Technology Research and Development Project of Shangluo City (SK-2013-15) |
|
| Effects of NO on DNA and photosynthesis of mung bean seedlings under Cd2+ stress |
|
LI Huimin, LUO Fenlan, HE Junmin
|
|
1. School of Life Sciences, Shaanxi Normal University, Xi’an 710062, China
2. Shangluo Vocational and Technical College, Shangluo 726000, China
|
| Abstract: |
| Background, aim, and scope With the acceleration of the industrialization process, heavy metal pollution has become one of the hot issues in the world. Cd2+ is a more common heavy metal pollutant, so the effect of Cd2+ stress on plants has been widely concerned. Previous studies have shown that Cd2+ stress has toxic effects on many aspects of plant growth and development, including plant DNA and photosynthesis. So, it is important to explore the safe and effective methods to alleviate the toxic effects of Cd2+ pollution on plants, but the researches on these topic are still less. Nitric oxide (NO) acting as a new signaling molecule plays an important role in plant growth and development, defence responses and stress resistance. Previous studies have shown that NO can alleviate the toxic effects of some stresses on plants, such as drought stress, salt stress, hot stress and low temperature stress. However, whether and how NO alleviates the toxic effects of heavy metal stresses on plants are still less known. The aim of this paper is to explore whether and how NO alleviates the toxic effects of Cd2+ stress on plant DNA and photosynthesis. Materials and methods In this study, seedlings of mung bean (Phaseolus raditus L. cv. Qindou-20) were used as plant materials, grown in plant growth chambers under a 14 h photoperiod (300 — 3500 μmol ∙ m−2 ∙ s−1), at a day/night temperature cycle of (25 ± 2)℃ / (20 ± 2)℃ and a relative humidity of 75% and incubated in 1/2 Hoagland solution. After 33 h of seedling growth, all the seedlings were divided into four groups and transferred to 1/2 Hoagland solution alone (CK), 1/2 Hoagland solution containing 50 μmol ∙ L−1 NO donor sodium nitroprusside (SNP), 1/2 Hoagland solution containing 5 μmol ∙ L−1 CdCl2 (Cd2+) or 1/2 Hoagland solution containing 50 μmol ∙ L−1 SNP and 5 μmol ∙ L−1 CdCl2 (SNP + Cd2+), respectively. When seedlings were treated for 3 d and 8 d, the net photosynthetic rate (Pn), stomatal conductance (Gs), and intercellular CO2 concentration (Ci) were measured with a portable CIRAS-2 type photosynthesis system (PP Systems) and stomatal limitation (Ls) was calculated with the formula Ls = (Ao − Ai)/Ao×100%, where Ao is the Pn when Ci is equal to the atmospheric CO2 concentration, and Ai is the Pn at the atmospheric CO2 concentration. DNA contents and DNA hyperchromicity were measured with TU-1800s UV spectrophotometer. Results Compared to CK, Cd2+ stress alone reduced DNA content, enhanced the degree of cross-linking between DNA chains in leaves and roots, decreased Pn, Gs and Ci and increased Ls in leaves. Compared to Cd2+ stress alone, the combined treatment of exogenous NO and Cd2+ increased DNA content and decreased the cross-linking between DNA chains in leaves and roots, while Pn and Gs were increased, and Ci and Ls were decreased in leaves. Discussion In consistent with the results of previous studies, our results in this paper also show that Cd2+ stress has the toxic effects on plant DNA and photosynthesis. Furthermore, our results clearly show that exogenous NO can effectively alleviate the toxic effects of Cd2+ stress on plant DNA and photosynthesis. In addition, although previous studies have paid much attention on the inhibitory mechanisms of Cd2+ stress on photosynthesis, it is still unclear which factor between stomatal and nonstomatal limitations plays more important role during different stages of Cd2+ stress-inhibited photosynthesis. Our results in this paper indicate that the stomatal limitation plays a more important role during the early stage of Cd2+ stress-induced inhibition of photosynthesis. Combined with the previous results, we suggest that under Cd2+ stress, the inhibition of photosynthesis in mung bean leaves is the results of both stomatal and nonstomatal limitations, but the stomatal limitation is dominant during early stage, nonstomatal limitation becomes the dominant one during late stage. Moreover, our results also show that exogenous NO alleviates the inhibitory effects of Cd2+ stress on photosynthesis mainly by improving the photosynthetic activity of seedling mesophyll cells. Conclusions (1) Exogenous NO can effectively alleviate the toxic effects of Cd2+ stress on DNA and photosynthesis in mung bean seedlings; (2) Stomatal limitation plays a more important role during the early stage of Cd2+ stress-inhibited photosynthesis; (3) NO alleviates the inhibitory effects of Cd2+ stress on photosynthesis mainly by improving the photosynthetic activity of mesophyll cells. Recommendations and perspectives Although our results show that NO can effectively alleviate the toxic effects of Cd2+ stress on DNA and photosynthesis, the detailed mechanisms underlining these processes are still unclear, which should be studied in the future. |
| Key words: NO Cd2+ stress mung bean seedlings DNA photosynthesis |
