Department of Plant Biology, Federal University of Viçosa, Viçosa, MG, 36570-000, Brazil.
Environ Sci Pollut Res Int. 2015 Aug;22(15):11265-74. doi: 10.1007/s11356-015-4342-9. Epub 2015 Mar 24.
Arsenic (As) is a toxic element to most organisms. Studies investigating anatomic alterations due to As exposure in plants are scarce but of utmost importance to the establishment of environmental biomonitoring techniques. So, this study aimed to investigate the effects of As on the development and initial root growth in Cajanus cajan (Fabaceae), characterize and quantify the possible damages, evaluate genotoxic effects, and identify structural markers to be used in environmental bioindication. Plants were exposed hydroponically to 0.5, 1.0, 1.5, and 2.0 mg As L(-1), as sodium arsenate. Growth parameters were measured, and in the end of the exposure, root samples were analyzed for qualitative and quantitative anatomical alterations. Arsenic genotoxicity was evaluated through analysis of the mitotic index in the root apex. Compared to the control, As-treated seedlings showed an altered architecture, with significantly decreased root length (due to the lower mitotic index in the apical meristem and reduced elongation of parenchyma cells) with darkened color, and abnormal development of the root cap. A significant increase in vascular cylinder/root diameter ratio was also detected, due to the reduction of the cellular spaces in the cortex. The secondary xylem vessel elements were reduced in diameter and had sinuous walls. The severest damage was visible in the ramification zone, where uncommon division planes of phellogen and cambium cells and disintegration of the parenchyma cells adjacent to lateral roots were observed. The high sensibility of C. cajan to As was confirmed, since it caused severe damages in root growth and anatomy. The main structural markers for As toxicity were the altered root architecture, with the reduction of the elongation zone and increase of ramification zone length, and the root primordia retained within the cortex. Our results show a new approach about As toxicity and indicate that C. cajan is a promising species to be used for bioindication of environmental contamination by As.
砷（As）是大多数生物体的有毒元素。研究砷暴露对植物解剖结构变化的影响的文献很少，但对建立环境生物监测技术至关重要。因此，本研究旨在研究砷对菜豆（Fabaceae）发育和初始根生长的影响，表征和量化可能的损伤，评估遗传毒性效应，并确定用于环境生物指示的结构标记。植物在水培条件下暴露于 0.5、1.0、1.5 和 2.0 mg As L(-1) 的砷酸钠中。测量生长参数，在暴露结束时，对根样进行定性和定量解剖结构改变分析。通过根尖有丝分裂指数分析评估砷的遗传毒性。与对照相比，砷处理的幼苗表现出改变的结构，根长明显减少（由于根尖分生组织的有丝分裂指数降低和薄壁细胞伸长减少），颜色变暗，根冠发育异常。还检测到维管束/根直径比的显著增加，这是由于皮层细胞间隙减少所致。次生木质部导管元素直径减小，壁呈正弦状。在分枝区观察到最严重的损伤，其中可见到不常见的栓内层和形成层细胞分裂面以及与侧根相邻的薄壁细胞解体。菜豆对砷的高敏感性得到了证实，因为它导致根生长和解剖结构严重受损。砷毒性的主要结构标记是改变的根结构，伸长区减少，分枝区长度增加，以及保留在皮层内的根原基。我们的结果提供了砷毒性的新方法，并表明菜豆是一种有前途的物种，可用于指示环境中砷污染。
