Subcellular Redistribution of Root Aquaporins nduced by Hydrogen Peroxide

Aquaporins are water channel proteins that mediate the fine-tuning of cell membrane water permeability during development or in response to environmental stresses. The present work focuses on the oxidative stress-induced redistribution of plasma membrane intrinsic protein （PIP） aquaporins from the plasma membrane （PM） to intracellular membranes. This process was investigated in the Arabidopsis root. Su- crose density gradient centrifugation showed that exposure of roots to 0.5 mM H2O2 induces significant depletion in PM fractions of several abundant PIP homologs after 15 rain. Analyses by single-particle tracking and fluorescence correlative spectroscopy showed that, in the PM of epidermal cells, H2O2 treat- ment induces an increase in lateral motion and a reduction in the density of a fluorescently tagged form of the prototypal AtPIP2;1 isoform, respectively. Co-expression analyses of AtPIP2;1 with endomembrane markers revealed that H2O2 triggers AtPIP2;1 accumulation in the late endosomal compartments. Life- time analyses established that the high stability of PIPs was maintained under oxidative stress conditions, suggesting that H2O2 triggers a mechanism for intracellular sequestration of PM aquaporins without further degradation. In addition to information on cellular regulation of aquaporins, this study provides novel and complementary insights into the dynamic remodeling of plant internal membranes during oxida- tive stress responses.

The AFB1 auxin receptor controls the cytoplasmic auxin response pathway in Arabidopsis thaliana

The phytohormone auxin triggers root growth inhibition within seconds via a non-transcriptionalpathway.Among members of the TIR1/AFB auxin receptor family,AFB1 has a primary role in this rapidresponse. However, the unique features that confer this specific function have not been identified.Here we show that the N-terminal region of AFB1, including the F-box domain and residues thatcontribute to auxin binding,is essential and sufficient for its specific role in the rapid response. Substitutionof the N-terminal region of AFB1 with that of TIR1 disrupts its distinct cytoplasm-enriched localizationand activity in rapid root growth inhibition by auxin. Importantly, the N-terminal region of AFB1 isindispensable for auxin-triggered calcium influx, which is a prerequisite for rapid root growth inhibition.Furthermore, AFB1 negatively regulates lateral root formation and transcription of auxin-induced genes,suggesting that it plays an inhibitory role in canonical auxin signaling. These results suggest that AFB1may buffer the transcriptional auxin response, whereas it regulates rapid changes in cell growth thatcontributeto rootgravitropism.

Distinctive and complementary roles of E2F transcription factors during plant replication stress responses

Survival of living organisms is fully dependent on their maintenance of genome integrity,being permanently threatened by replication stress in proliferating cells.Although the plant DNA damage response(DDR)regulator SOG1 has been demonstrated to cope with replication defects,accumulating evidence points to other pathways functioning independent of SOG1.Here,we report the roles of the Arabidopsis E2FA and EF2B transcription factors,two well-characterized regulators of DNA replication,in plant response to replication stress.Through a combination of reverse genetics and chromatin immunoprecipitation approaches,we show that E2FA and E2FB share many target genes with SOG1,providing evidence for their involvement in the DDR.Analysis of double-and triple-mutant combinations revealed that E2FB,rather than E2FA,plays the most prominent role in sustaining plant growth in the presence of replication defects,either operating antagonistically or synergistically with SOG1.Conversely,SOG1 aids in overcoming the replication defects of E2FA/E2FB-deficient plants.Collectively,our data reveal a complex transcriptional network controlling the replication stress response in which E2Fs and SOG1 act as key regulatory factors.

Arabidopsis FtsZ2-1 and FtsZ2-2 Are Functionally Redundant, But FtsZ-Based Plastid Division Is Not Essential for Chloroplast Partitioning or Plant Growth and Development

FtsZ1 and FtsZ2 are phylogenetically distinct families of FtsZ in plants that co-localize to mid-plastid rings and facilitate division of chloroplasts. In plants, altered levels of either FtsZ1 or FtsZ2 cause dose-dependent defects in chloroplast division; thus, studies on the functional relationship between FtsZgenes require careful manipulation of FtsZ levels in vivo. To define the functional relationship between the two FtsZ2 genes in Arabidopsis thaliana, FtsZ2-1 and FtsZ2-2, we expressed FtsZ2-1 in an ftsZ2-2 null mutant, and vice versa, and determined whether the chloroplast division defects were rescued in plants expressing different total levels of FtsZ2. Full rescue was observed when either the FtsZ2-1 or FtsZ2-2 level approximated total FtsZ2 levels in wild-type （WT）. Additionally, FtsZ2-2 interacts with ARC6, as shown previously for FtsZ2- 1. These data indicate that FtsZ2-1 and FtsZ2-2 are functionally redundant for chloroplast division in Arabidopsis. To rigorously validate the requirement of each FtsZ family for chloroplast division, we replaced FtsZ1 with FtsZ2 in vivo, and vice versa, while maintaining the FtsZ level in the transgenic plants equal to that of the total level in WT. Chloroplast division defects were not rescued, demonstrating conclusively that FtsZ1 and FtsZ2 are non-redundant for maintenance of WT chloroplast numbers. Finally, we generated ftsZtriple null mutants and show that plants completely devoid of FtsZ protein are viable and fertile. As plastids are presumably essential organelles, these findings suggest that an FtsZ-independent mode of plastid partitioning may occur in higher plants.

Estimation of cytotoxic potency by brine shrimp lethality bioassay application of Clerodendrum infortunatum Linn.

Objective:To learn a scientific and systematic knowledge of anticancer,antimicrobial and pharmacological activities of natural products and estimate cytotoxic potency by using ethanol and chloroform extracts of root,leaf and stem of Clerodendrum infortunatum(Verbenaceae)due to its random use in customary and traditional medicine to cure common ailments such as intestinal disorder,diarrhea,tuberculosis and respiratory problems etc.Methods:The in vitro application was carried out with the bench-top bioassay method by using brine shrimp lethality bioassay.Results:All of the crude extracts were found to be lethal and effective.The LC50 value of ethyl alcohol fraction of root was 20.845 mg/L compared to the standard drug tetracycline of 14.675 mg/L to brine shrimp nauplii,indicating that the extracts were biologically active.Conclusions:The cytotoxic study of LC50 value showed that a good correlation with the antibiotic tetracycline.From the comparative correlation error bars and percentage,we understood that ethyl alcohol fraction of root extract was very effective.This study serves as a basis for further research to lead compounds to be isolated so that it may be as a template for the implications of these results for bioactivity and drug discovery potential of herbal products.