Transcriptional and posttranscriptional regulation of chloroplast gene expression by heavy metals in barley seedlings

The effects of Cd, Cu, and Ni ions on chloroplast gene expression were studied in 7-day-old barley (Hordeum vulgare L.) seedlings. Toxicity of heavy metals (HM) was estimated from their effects on root and shoot growth and from the accumulation of HM in roots and leaves of seedlings grown in roll culture. Root growth was affected by HM to a higher extent than shoot growth. A statistically significant inhibition of root growth was observed at concentrations of all studied HM ≥100 μM. Leaf growth was inhibited by Cu and Ni at concentrations ≥400 μM, while the inhibitory effect of Cd on leaf growth was observed at concentrations ≥100 μM. The translocation of Cu from roots to shoots of barley seedlings proceeded slower than the accumulation of Cu in roots. Unlike Cu, Ni was actively accumulated by shoots in addition to its strong absorption by roots. Using the run-on transcription and RT-PCR (reverse transcription-polymerase chain reaction), we showed that HM at a concentration of 100 μM regulated the expression of individual chloroplast genes. The presence of either Cd, Cu, or Ni ions in the plant growth solution enhanced transcription of rpl16, rpl23, and rpl12 genes encoding ribosomal proteins, and of ndhA encoding the subunit 1 of plastid NADH-plastoquinone oxidoreductase. Transcription of sixteen other studied plastid genes was not affected by HM. The activation of transcription of the studied genes was not always accompanied by an increase in the transcript copy number. Northern blot analysis showed that Cd impaired the splicing of rpl16, a chloroplast gene that contains an intron. Thus, this study proves that HM regulate not only the transcriptional activity of chloroplast genes but also the splicing of rpl16 transcripts. © 2011 Pleiades Publishing, Ltd

Transcriptional and posttranscriptional regulation of chloroplast gene expression by heavy metals in barley seedlings

The effects of Cd, Cu, and Ni ions on chloroplast gene expression were studied in 7-day-old barley (Hordeum vulgare L.) seedlings. Toxicity of heavy metals (HM) was estimated from their effects on root and shoot growth and from the accumulation of HM in roots and leaves of seedlings grown in roll culture. Root growth was affected by HM to a higher extent than shoot growth. A statistically significant inhibition of root growth was observed at concentrations of all studied HM ≥100 μM. Leaf growth was inhibited by Cu and Ni at concentrations ≥400 μM, while the inhibitory effect of Cd on leaf growth was observed at concentrations ≥100 μM. The translocation of Cu from roots to shoots of barley seedlings proceeded slower than the accumulation of Cu in roots. Unlike Cu, Ni was actively accumulated by shoots in addition to its strong absorption by roots. Using the run-on transcription and RT-PCR (reverse transcription-polymerase chain reaction), we showed that HM at a concentration of 100 μM regulated the expression of individual chloroplast genes. The presence of either Cd, Cu, or Ni ions in the plant growth solution enhanced transcription of rpl16, rpl23, and rpl12 genes encoding ribosomal proteins, and of ndhA encoding the subunit 1 of plastid NADH-plastoquinone oxidoreductase. Transcription of sixteen other studied plastid genes was not affected by HM. The activation of transcription of the studied genes was not always accompanied by an increase in the transcript copy number. Northern blot analysis showed that Cd impaired the splicing of rpl16, a chloroplast gene that contains an intron. Thus, this study proves that HM regulate not only the transcriptional activity of chloroplast genes but also the splicing of rpl16 transcripts. © 2011 Pleiades Publishing, Ltd

Effect of Photosynthetic Electron Transport Inhibition in vivo on the Chloroplast Genes Transcription in Arabidopsis

Transcription of both nuclear and plastid genes encoding components of photosynthetic apparatus is subjected to redox regulation. The origin of redox signals mediating this regulation is chloroplast electron transport chain (ETC) itself. Up to date the effects of redox state of individual ETC components on chloroplast genes transcription rate was demonstrated only for some selected genes and only in isolated chloroplasts. In the present work ETC inhibitors was used for in vivo modulations in plastoquinone pool redox state, and run-on transcription approach was used to evaluate the plastid genes transcription rate. We have demonstrated that plastoquinone redox state has impact on transcription rate of wide range of Arabidopsis chloroplast genes. Treatment by DCMU (plastoquinone pool is oxidized) lead to increase of transcription rate of the majority of plastid genes studied. Treatment by DBMIB (plastoquinone pool is reduced) lead to decrease of plastid genes transcription rate. Simultaneous treatment by one of photosynthesis inhibitors and KCN (mitochondrial respiratory complex IV inhibitor) lead to decrease of transcription rate of plastid genes in most cases. Our results suggest probable participation of mitochondria in the redox regulation of plastid genes expression in Arabidopsis