Phytochelatin biosynthesis and cadmium detoxification

İnsanın endüstriyel aktivitesi sonucunda çevredeki ağır metal kirlenmesi artmakta ve ağır metal toksisitesi önemli çevresel problemlere neden olmaktadır. Cd, Hg, Cr, Pb gibi gerekli olmayan ağır metaller çok düşük konsantrasyonlarda bile oldukça toksiktir. Bitkilerdeki ağır metal detoksifikasyonu ve tolerans moleküler anlamda, metal-bağlayan bileşiklerin üretimi, vakuollerde metal birikimi, membran yapısında değişiklik, stres metabolitlerinin sentezi gibi birçok farklı mekanizmalar tarafından yürütülür. Ancak son yıllarda araştırma konusu olarak en fazla ilgi duyulan mekanizma kelat oluflumudur. Bitkilerin aşırı Cd konsantrasyonuna gösterdiği tepkilerden biri Cd-bağlayan polipeptidler, ya da bir peptid ligand grubu ile kelat meydana getiren fitokelatinlerdir (PC). PC'ler yüksek bitkiler, algler ve bazı mantarlar tarafından üretilir, PC-Cd bileşikleri oluşturulur ve serbest metal konsantrasyonu azaltılarak özellikle Cd detoksifikasyonu ile Cd toleransında önemli rol oynarlar. Bu bileşikler glutationdan (GSH) ve ilişkili tiollerden PC sentaz aktivitesi ile meydana gelirler. PC biyosentezinin genetik ve moleküler temelinin anlaşılabilmesi, kirlenmiş çevrelerin fitoremediasyonunda kullanılacak bitkilerin geliştirilebilmesi açısından büyük önem taşımaktadır. Bu derleme, PC biyosentezi ve Cd detoksifikasyonu alanındaki bilgileri özetlemektedir.

Fitokelatin biyosentezi ve kadmiyum detoksifikasyonu

Heavy metal contamination in the environment is increasing due to human industrial activity and heavy metal causes major environmental problems. Ions like Cd, Hg, Cr, or Pb are non essential heavy metals which are potentially highly toxic even at very low concentrations. Heavy metal detoxification and tolerance in plants can be achieved by a number of different mechanisms on the molecular basis. Such as the production of metal-binding compounds, metal deposition in vacuoles, alterations of membrane structures, synthesis of stress metabolites; but the mechanism which has been studied most closely in recent years is chelation. One reaction of plants to excess Cd concentration is the formation of Cd-binding polypeptides, or the chelation by a family of peptide ligands, the phytochelatins (PCs). PCs are produced by higher plants, algae and some fungi in order to detoxify Cd by sequestration to form PC-Cd complexes which play a pivotal role in heavy metal, primarily Cd tolerance by decreasing their free concentrations. PCs are derived from glutathione (GSH) and related thiols by the action of PC synthase. Understanding the genetic and molecular basis of PC biosynthesis mechanism is an important goal in developing plants for the phytoremediation of contaminated environments. This review summarizes present knowledge in the field of PC biosynthesis and Cd detoxification .

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