Histone modification is a ubiquitous regulator of gene transcription. Arabidopsis CUP-SHAPED COTYLEDON (CUC) genes serve as a marker for shoot apical meristem initiation, but how they are regulated during shoot regeneration from in vitro culture, it is not yet understood. Here, the histone modification status of CUC1, CUC2, and CUC3 was analysed using a combination of chromatin immunoprecipitation (ChIP) and real time quantitative PCR. The activation of CUC1 and CUC2 was associated with an increased level of histone H3K4 trimethylation and/or H3K9 acetylation, as well as a reduced level of H3K9 demethylation in various parts of their promoter and coding sequences. Histone modification is suggested to play an important role in regulating CUC1 and CUC2 expression during shoot regeneration.

Histone modification is a ubiquitous regulator of gene transcription. Arabidopsis CUP-SHAPED COTYLEDON (CUC) genes serve as a marker for shoot apical meristem initiation, but how they are regulated during shoot regeneration from in vitro culture, it is not yet understood. Here, the histone modification status of CUC1, CUC2, and CUC3 was analysed using a combination of chromatin immunoprecipitation (ChIP) and real time quantitative PCR. The activation of CUC1 and CUC2 was associated with an increased level of histone H3K4 trimethylation and/or H3K9 acetylation, as well as a reduced level of H3K9 demethylation in various parts of their promoter and coding sequences. Histone modification is suggested to play an important role in regulating CUC1 and CUC2 expression during shoot regeneration.

The role of glutathione (GSH) in the adaptation of wild type Arabidopsis thaliana plants to Cd stress was investigated. The nutrient solution (control or containing 50 or 100 μM Cd) was supplemented with buthionine sulfoximine (BSO; 50, 100, 500 μM, to decrease the GSH content in plants) or GSH (50, 100, 500 μM, to increase its content in plants) in order to find how GSH content could regulate Cd stress responses. BSO application did not influence plant biomass, while exogenous GSH (especially 500 μM) reduced root biomass. BSO (500μM) in combination with Cd (100 μM) increased Cd toxicity on root growth (by over 50 %), most probably due to reduced GSH content and phytochelatin (PC) accumulation (by over 96 %). On the other hand, combination of exogenous GSH (500 μM) with Cd (100 μM) was also more toxic to plants than Cd alone despite a significant increase in GSH and PC accumulation (up to 2.7 fold in the roots). This fact could indicate that the natural content of endogenous GSH in wild type A. thaliana plants is sufficient for Cd-tolerance. A decrease in this GSH content led to decreased Cd-tolerance of the plants but an increase in GSH content did not enhance Cd-tolerance, and it showed even toxic effect on the plants.

The role of glutathione (GSH) in the adaptation of wild type Arabidopsis thaliana plants to Cd stress was investigated. The nutrient solution (control or containing 50 or 100 microM Cd) was supplemented with buthionine sulfoximine (BSO; 50, 100, 500 microM) to decrease the GSH content in plants or GSH (50, 100, 500 microM) to increase its content in plants in order to find how GSH content could regulate Cd stress responses. BSO application did not influence plant biomass, while exogenous GSH (especially 500 microM) reduced root biomass. BSO (500 microM) in combination with Cd (100 microM) increased Cd toxicity on root growth (by over 50 %), most probably due to reduced GSH content and phytochelatin (PC) accumulation (by over 96 %). On the other hand, combination of exogenous GSH (500 microM) with Cd (100 microM) was also more toxic to plants than Cd alone despite a significant increase in GSH and PC accumulation (up to 2.7 fold in the roots). This fact could indicate that the natural content of endogenous GSH in wild type A. thaliana plants is sufficient for Cd-tolerance. A decrease in this GSH content led to decreased Cd-tolerance of the plants but an increase in GSH content did not enhance Cd-tolerance, and it showed even toxic effects on the plants.

The role of glutathione (GSH) in the adaptation of wild type Arabidopsis thaliana plants to Cd stress was investigated. The nutrient solution (control or containing 50 or 100 μM Cd) was supplemented with buthionine sulfoximine (BSO; 50, 100, 500 μM, to decrease the GSH content in plants) or GSH (50, 100, 500 μM, to increase its content in plants) in order to find how GSH content could regulate Cd stress responses. BSO application did not influence plant biomass, while exogenous GSH (especially 500 μM) reduced root biomass. BSO (500μM) in combination with Cd (100 μM) increased Cd toxicity on root growth (by over 50 %), most probably due to reduced GSH content and phytochelatin (PC) accumulation (by over 96 %). On the other hand, combination of exogenous GSH (500 μM) with Cd (100 μM) was also more toxic to plants than Cd alone despite a significant increase in GSH and PC accumulation (up to 2.7 fold in the roots). This fact could indicate that the natural content of endogenous GSH in wild type A. thaliana plants is sufficient for Cd-tolerance. A decrease in this GSH content led to decreased Cd-tolerance of the plants but an increase in GSH content did not enhance Cd-tolerance, and it showed even toxic effect on the plants.

Natural accessions of Arabidopsis thaliana exhibit a clinal variation in freezing tolerance following temperature changes across the natural habitat. Here we performed molecular evolution and population genetic analyses of homologous INDUCER OF CBF EXPRESSION1 (ICE1) and ICE2 genes, the master regulators of plant cold response. A study of ICE genes polymorphism was performed using 60 A. thaliana ecotypes grouped according to their geographic origin. The genetic diversity of ICE2 was characterized by a high number of haplotypes and an overall high diversity. The levels of nonsynonymous nucleotide polymorphism increased from a northern group southward. On the contrary, the ICE1 gene sequence was less diverse and there was no clinal variation in the sequence polymorphism. Thus, different selection forces acting on the ICE2 gene might be one of the reasons of clinal variation in freezing tolerance. This clinal variation also indicates that ICE2 is more important for a cold response than ICE1. The study of the ratio of numbers of nonsynonymous to synonymous substitutions (Ka/Ks) between A. thaliana paralogs shows that the sequence diversification and emergence of two new ICE2-specific motifs could contribute to the functional diversification of the duplicates. The Ka/Ks for ICE2 of A. thaliana and A. lyrata orthologs was an order of magnitude greater than that for the ICE1 orthologs, which suggests that the protein sequence of ICE2, an early duplicate, evolved under a weaker selective constraint. A relaxed selection on ICE2 in southern populations and more stringent in northern populations also confirmed its role in a cold resistance. The selection pressure on ICE1 might be caused by its role in the control of more essential than cold response functions.

Natural accessions of Arabidopsis thaliana exhibit a clinal variation in freezing tolerance following temperature changes across the natural habitat. Here we performed molecular evolution and population genetic analyses of homologous INDUCER OF CBF EXPRESSION1 (ICE1) and ICE2 genes, the master regulators of plant cold response. A study of ICE genes polymorphism was performed using 60 A. thaliana ecotypes grouped according to their geographic origin. The genetic diversity of ICE2 was characterized by a high number of haplotypes and an overall high diversity. The levels of nonsynonymous nucleotide polymorphism increased from a northern group southward. On the contrary, the ICE1 gene sequence was less diverse and there was no clinal variation in the sequence polymorphism. Thus, different selection forces acting on the ICE2 gene might be one of the reasons of clinal variation in freezing tolerance. This clinal variation also indicates that ICE2 is more important for a cold response than ICE1. The study of the ratio of numbers of nonsynonymous to synonymous substitutions (Kₐ/Kₛ) between A. thaliana paralogs shows that the sequence diversification and emergence of two new ICE2-specific motifs could contribute to the functional diversification of the duplicates. The Kₐ/Kₛ for ICE2 of A. thaliana and A. lyrata orthologs was an order of magnitude greater than that for the ICE1 orthologs, which suggests that the protein sequence of ICE2, an early duplicate, evolved under a weaker selective constraint. A relaxed selection on ICE2 in southern populations and more stringent in northern populations also confirmed its role in a cold resistance. The selection pressure on ICE1 might be caused by its role in the control of more essential than cold response functions.