Lin Qingqi, Chen Siyuan, Chao Yuanqing, Huang Xiongfei, Wang Shizhong, Qiu Rongliang
School of Environmental Science and Engineering, Sun Yat-sen University, 135 Xingang Xi Road, 510275 Guangzhou, China.
School of Environmental Science and Engineering, Sun Yat-sen University, 135 Xingang Xi Road, 510275 Guangzhou, China; Guangdong Provincial Key Lab of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University, 135 Xingang Xi Road, 510275 Guangzhou, China.
Environ Pollut. 2017 Jan;220(Pt A):421-430. doi: 10.1016/j.envpol.2016.09.084. Epub 2016 Sep 30.
Uptake and accumulation by plants is a significant pathway in the migration and transformation of phthalate esters (PAEs) in the environment. However, limited information is available on the mechanisms of PAE metabolism in plants. Here, we investigated the metabolism of di-n-butyl phthalate (DnBP), one of the most frequently detected PAEs, in pumpkin (Cucurbita moschata) seedlings via a series of hydroponic experiments with an initial concentration of 10 mg L. DnBP hydrolysis occurred primarily in the root, and two of its metabolites, mono-n-butyl phthalate (MnBP) and phthalic acid (PA), were detected in all plant tissues. The MnBP concentration was an order of magnitude higher than that of PA in shoots, which indicated MnBP was more readily transported to the shoot than was PA because of the former's dual hydrophilic and lipophilic characteristics. More than 80% of MnBP and PA were located in the cell water-soluble component except that 96% of MnBP was distributed into the two solid cellular fractions (i.e., cell wall and organelles) at 96 h. A 13-20% and 29-54% increase of carboxylesterase (CXE) activity shown in time-dependent and concentration-dependent experiments, respectively, indicated the involvement of CXEs in plant metabolism of DnBP. The level of CXE activity in root subcellular fractions was in the order: the cell water-soluble component (88-94%) >> cell wall (3-7%) > cell organelles (3-4%), suggesting that the cell water-soluble component is the dominant locus of CXE activity and also the domain of CXE-catalyzed hydrolysis of DnBP. The addition of triphenyl phosphate, a CXE inhibitor, led to 43-56% inhibition of CXE activity and 16-25% increase of DnBP content, which demonstrated the involvement of CXEs in plant metabolism of DnBP. This study contributes to our understanding of enzymitic mechanisms of PAE transformation in plants.
植物的吸收和积累是邻苯二甲酸酯（PAEs）在环境中迁移和转化的重要途径。然而，关于植物中PAE代谢机制的信息有限。在此，我们通过一系列水培实验，以初始浓度10 mg/L研究了南瓜（Cucurbita moschata）幼苗中最常检测到的PAEs之一邻苯二甲酸二正丁酯（DnBP）的代谢。DnBP水解主要发生在根部，在所有植物组织中均检测到其两种代谢产物，邻苯二甲酸单正丁酯（MnBP）和邻苯二甲酸（PA）。地上部分中MnBP的浓度比PA高一个数量级，这表明由于MnBP具有亲水性和疏水性双重特性，其比PA更容易转运到地上部分。除了在96小时时96%的MnBP分布到两个固体细胞组分（即细胞壁和细胞器）中之外，超过80%的MnBP和PA位于细胞水溶性组分中。分别在时间依赖性和浓度依赖性实验中显示的羧酸酯酶（CXE）活性增加13 - 20%和29 - 54%，表明CXEs参与了植物对DnBP的代谢。根亚细胞组分中CXE活性水平的顺序为：细胞水溶性组分（88 - 94%）>>细胞壁（3 - 7%）>细胞器（3 - 4%），这表明细胞水溶性组分是CXE活性的主要位点，也是CXE催化DnBP水解的区域。添加CXE抑制剂磷酸三苯酯导致CXE活性受到43 - 56%的抑制，DnBP含量增加16 - 25%，这证明CXEs参与了植物对DnBP的代谢。这项研究有助于我们理解植物中PAE转化的酶促机制。
