Biosynthetic regulation of phytochelatins, heavy metal-binding peptides

Phytochelatins (PCs) are heavy metal-binding peptides that play important roles in the detoxification of toxic heavy metals and the regulation of intracellular concentrations of essential metals in eukaryotes, including higher plants, fungi, and microalgae. Recently, PC synthase genes in higher plants and fission yeast have been identified and characterized, enabling molecular biological studies to unravel the mechanisms underlying PC synthesis. Moreover, recent routine database searches have unexpectedly identified genes that are similar to plant PC synthase genes in the genomes of worms and some prokaryotes. In this review, we introduce these recent advances in our understanding of the molecular mechanisms for PC biosynthesis and functions in order to supply basic information about the unique and attractive peptides applicable to various fields.     

A tomato stem cell extract, containing antioxidant compounds and metal chelating factors, protects skin cells from heavy metal-induced damages

Heavy metals can cause several genotoxic effects on cells, including oxidative stress, DNA sequence breakage and protein modification. Among the body organs, skin is certainly the most exposed to heavy metal stress and thus the most damaged by the toxic effects that these chemicals cause. Moreover, heavy metals, in particular nickel, can induce the over-expression of collagenases (enzymes responsible for collagen degradation), leading to weakening of the skin extracellular matrix. Plants have evolved sophisticated mechanisms to protect their cells from heavy metal toxicity, including the synthesis of metal chelating proteins and peptides, such as metallothioneins and phytochelatins (PC), which capture the metals and prevent the damages on the cellular structures. To protect human skin cells from heavy metal toxicity, we developed a new cosmetic active ingredient from Lycopersicon esculentum (tomato) cultured stem cells. This product, besides its high content of antioxidant compounds, contained PC, effective in the protection of skin cells towards heavy metal toxicity. We have demonstrated that this new product preserves nuclear DNA integrity from heavy metal damages, by inducing genes responsible for DNA repair and protection, and neutralizes the effect of heavy metals on collagen degradation, by inhibiting collagenase expression and inducing the synthesis of new collagen.     

Genotypic dependent effect of exogenous glutathione on Cd-induced changes in proteins, ultrastructure and antioxidant defense enzymes in rice seedlings

Greenhouse hydroponic experiments were conducted using Cd-sensitive (cv. Xiushui63) and tolerant (Bing97252) rice genotypes to evaluate how different genotypes responded to Cd toxicity in presence of glutathione (GSH). Results showed that GSH alleviates Cd-toxicity, ameliorates Cd-induced damages on leaf/root ultrastructures. Nine proteins in roots were identified, using 2-DE coupled with mass spectrometry, whose expression were down-regulated in Xiushui63, up-regulated/unchanged in Bing97252 by Cd; coinstantaneously enhanced/unchanged in Cd + GSH over Cd alone treatment in both genotypes. They are l-ascorbate peroxidase, putative short-chain dehydrogenase/reductase, Glycolipid transfer protein, elongation factor, Os04g0652700, carbonic anhydrase, Os08g0374000, chitinase, and putative disease resistance response protein. Eight proteins in leaves with expression of increase in Bing97252 but down-regulate/unchange in Xiushui63, categorized as four groups of their functions: carbon metabolism, TCA cycle, photorespiration and RNA processing. Furthermore, we identified eight proteins with repressed expression in Cd-treated and up-regulated in Cd + GSH-treated rice leaves of Xiushui63.     

低浓度镉胁迫下2种水生植物体内植物络合素的响应

采用溶液培养方式,研究了水环境低浓度镉(Cd)(0.01～0.64 μmol/L)较长时间胁迫下漂浮植物水浮莲(Pistia stratiotes L.)和沉水植物伊乐藻(Elodea nuttallii)体内植物络合素(PCs)的响应规律.结果显示,2种水生植物对外界Cd胁迫表现出明显的吸收和积累效应,水浮莲体内PCs的响应明显强于伊乐藻.水浮莲体内的PCs诱导量与Cd处理浓度存在良好的剂量-效应关系,Cd浓度≥0.08 μmol/L水浮莲根系产生明显毒害效应并伴随根系PCs的诱导量急剧增加.回归分析显示,2种水生植物体内PCs的合成水平与Cd的生物毒性呈现一定的线性关系,表明PCs可作为重金属Cd胁迫的生物标记物指示水体中重金属的毒害程度.比较而言,水浮莲体内PCs对Cd污染更为敏感,可通过检测其根系PCs的含量来评价和预测实际水环境中Cd的污染.