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Plants for proper growth and development require a certain concentration of macronutrients and micronutrients. However, high concentrations of metals , both necessary and ballast are very toxic to living organisms. Plants, as nieprzemieszczające organisms during the life cycle, generated collection mechanisms governing processing , distribution and storage of ions or other substances . In recent years in plant cells have been identified and characterized initially various systems involved in the active transport of metal ions moving across the cell membrane . We distinguish among them Integral membrane proteins from the family CACA ( called Ca2 + / Cation antiporter ) , transporting Ca2 + or other cations using the transmembrane gradient of H + or Na + . On the basis of similarity and functions, all proteins in the family CACA divided into five sub-groups: antyportery Na + / Ca2 + ( NCX ) dependent potassium antyportery Na + / Ca2 + ( NCKX and CCX ) , identified in prokaryotes transporters YRBG and transporters CAX , wherein the closest previously characterized proteins belong to the subfamily caca CAX . CAX proteins have been identified in plants , fungi and bacteria, and what is interesting gene sequences are not homologous to the genes of CAX model animal organisms , including man . Initially, all vegetable protein CAX grouped in one subfamily numbering 11 transporters ( CAX1 -11) . Then , based on more detailed analysis of the amino acid composition , sub-family divided into two groups of proteins : typical protein CAX ( CAX1 - 6 ) and the atypical protein CAX ( CAX7 -11) , showing a strong resemblance to antyporterów Na + / Ca2 + -dependent potassium . Typical CAX protein Arabidopsis thaliana and Oryza sativa further divided into two different groups: IA and IB . A single polypeptide chain protein CAX is composed of about 400 amino acids and forms a transmembrane domain (7-12) of a- helix structure . CAX transporters subfamily proteins are caca domain characteristic of this family , as well as themes specific to its type . These domains often play a key role in regulating the activity of transport proteins conditional, their transport function and determine their substrate specificity . Distinguished within the sequence of Loops 1 and c- c- 2 , which act as a filter for the selection and the corresponding binding cations autoinhibitorową domain that participates in the regulation of the activity of proteins , CaD domain , manganese domain , the domain D and amino acid motif that is likely to Transporter determine substrate specificity . Studies in heterologous systems , as well as mutants of plant CAX analysis demonstrated that the type transporters are a major component of CAX retention system calcium homeostasis in plant cells and yeast . However, further analysis showed CAX functional proteins that are transporters affinity for a wide variety of metals. CAX insertion of genes derived from various plants yeast mutants lacking specific transporters metal mutant restored the ability to transport a Cd2 + , Ca2 + , Zn2 + and Mn2 + , and thus the resistance to excess of these metals in the environment. Over time , it turned out that the functions of the proteins of this family are diverse and at the level of the whole organism indirectly determine the proper growth and development of plants . Probably , they contribute not only in the maintenance of homeostasis of metals ( Ca , Mn , Ni and Cd), but also more widely to maintain ionic equilibrium in the plant . Cax1 mutants accumulate less Zn2 + and Mn2 + , whereas in double mutants were significantly cax1/cax3 level PO43 - , Mn2 + , and Zn2 + relative to the wild plant . Also indicates the share of CAX transporters in plant responses to stress, cold and salt stress . AtCAX1 transcript level rose significantly after treatment of the plants at 4 ° C , while expression of genes AtCAX1 - 4 was stimulated in the presence of salts in the environment. Quite a number of studies also indicate interactions between CAX transporters and interactions of these proteins with other membrane proteins . Profile of gene expression CAX organ analyzed in Arabidopsis thaliana showed that each of the genes of this family are differentially expressed or the like at various stages of ontogeny plants . Biotechnological manipulation involving CAX genes can lead to a modified crop plants , which are a rich source of the necessary elements in the human diet . SCAX1 gene expression in potato , tomato and carrot caused an increase in calcium content in the edible parts of plants, and increased sequestration of this element in the central vacuole . CAX proteins can also be used in so-called process . phytoremediation or soil purification from heavy metals . Plants with increased expression of genes in higher degree CAX accumulated cadmium , manganese, and calcium in the vacuoles.

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The Editorial Board
Andrzej Łukaszyk - przewodniczący, Zofia Bielańska-Osuchowska, Szczepan Biliński, Mieczysław Chorąży, Aleksander Koj, Włodzimierz Korochoda, Leszek Kuźnicki, Aleksandra Stojałowska, Lech Wojtczak

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