镉在水花生叶片中的亚细胞分布及其毒理学

以水花生为试验材料,研究了不同浓度镉(Cd)(0、0.05、0.1、0.2、0.4 mmol·L-1)胁迫下水花生叶中Cd及矿质元素的亚细胞分布、抗氧化能力、叶绿素、可溶性蛋白和植物络合素(PCs)含量的变化.结果表明:随着培养液中Cd浓度的增加,叶片内各亚细胞组分中Cd含量显著增加,但分布不均,主要积累在细胞壁,其次为可溶成分,线粒体和叶绿体中分布最少.Cd处理浓度大于0.2 mmol·L-1时,呈现Cd向水花生叶的可溶成分中分配增加、细胞壁中分配减少的趋势.矿质元素的吸收明显失衡,表现为各亚细胞组分中Ca含量显著增加且主要分布在细胞壁中,细胞壁和可溶成分中P和K含量不断降低,叶绿体中Mg和Fe的含量逐渐减少.叶绿素和可溶性蛋白含量持续下降.谷胱甘肽和抗坏血酸含量先升后降,总抗氧化能力(T-AOC)不断提高,PCs大量累积.水花生对水体中的Cd有一定耐性,且Cd在亚细胞结构中的富集量与其毒性间具有明显的剂量-效应关系;亚细胞中矿质元素的紊乱以及叶绿素和可溶性蛋白含量的显著降低,Cd在亚细胞中的积累对植物体造成了明显的毒害作用;Ca在细胞壁中的累积以及PCs和T-AOC水平的提高说明水花生具有较强的抗性;PCs的合成量与Cd对水花生的毒性变化有一定的相关性,可以作为Cd胁迫的生物标记物.

Subcellular distribution and phytotoxicity of cadmium in Alternanthera philoxeroides leaves

A hydroponic experiment was conducted to study the subcellular distribution of Cd and mineral elements in Alternanthera philoxeroides leaves and the leaves anti-oxidative capacity and chlorophyll, soluble protein, and phytochelatins (PCs) contents under the stress of different concentration (0, 0.05, 0.1, 0.2, 0.4 mmol x L(-1)) Cd. With the increasing concentration of Cd in culture medium, the Cd content in all subcellular components of A. philoxeroides leaves increased significantly, and mainly distributed in cell wall, followed by in soluble fractions, and in chloroplast and mitochondria. When the Cd concentration in the medium exceeded 0.2 mmol x L(-1), the Cd was more allocated in soluble fractions than in cell wall. Cd stress resulted in an obvious imbalance of mineral elements uptake. With the increasing concentration of Cd, the Ca content in all subcellular components, especially in cell wall, increased significantly, whereas the P and K contents in cell wall and soluble fractions as well as the Mg and Fe contents in chloroplast decreased. In the meantime, the soluble protein and chlorophyll contents showed a decreasing trend, the glutathione and ascorbic acid contents decreased after an initial increase, the total anti-oxidative capacity (T-AOC) increased progressively, and the PCs accumulated in large quantity. These results suggested that A. philoxeroides had definite resistance to the water body Cd, and there was a dosage-effect relationship between the Cd enrichment in the subcellular components of A. philoxeroides leaves and the phytotoxicity of Cd. The imbalance of the mineral elements in subcellular components and the decrease of soluble protein and chlorophyll contents in chloroplast indicated the obvious phytotoxicity of Cd, while the massive accumulation of Ca in cell wall and the increased levels of PCs and T-AOC suggested the stronger resistance of A. philoxeroides to Cd stress. There was a definite correlation between the PCs production by A. philoxeroides and the toxicity of Cd, suggesting that the PCs could be considered as a sensitive biomarker for estimating the Cd phytotoxicity.