Abstract. We have generated a series of plectin deletion and mutagenized cDNA constructs to dissect the functional sequences that mediate plectin's interaction with intermediate filament (IF) networks, and scored their ability to coalign or disrupt intermediate filaments when ectopically expressed in rat kangaroo PtK2 cells. We show that a stretch of ~50 amino acid residues within plectin's carboxy-terminal repeat 5 domain serves as a unique binding site for both vimentin and cytokeratin IF networks of PtK2 cells. Part of the IFbinding domain was found to constitute a functional nuclear localization signal (NLS) motif, as demonstrated by nuclear import of cytoplasmic proteins linked to this sequence. Site directed mutagenesis revealed a specific cluster of four basic amino acid residues (arg4277-arg 428°) residing within the NLS sequence motif to be essential for IF binding. When mutant proteins corresponding to those expressed in PtK2 cells were expressed in bacteria and purified proteins subjected to a sensitive quantitative overlay binding assay using Eu3+-labeled vimentin, the relative binding capacities of mutant proteins measured were fully consistent with the mutant's phenotypes observed in living cells. Using recombinant proteins we also show by negative staining and rotary shadowing electron microscopy that in vitro assembled vimentin intermediate filaments become packed into dense aggregates upon incubation with plectin repeat 5 domain, in contrast to repeat 4 domain or a mutated repeat 5 domain.

Highlights• Cancer is second deadly disease after cardiovascular diseases.• There is a tremendous need to discover novel safer and more effective anticancer agents.• Plants serve as a basis for promising therapeutic agents for cancer treatment.• Important plant derived anticancer agents have been discussed here.• Some potential plant derived lead molecules have also been discussed. *Corresponding author:Centre for Microbial Ecology and Genomics, Graphical abstract

Brassinosteroids have been extensively used to overcome various abiotic stresses. But its role in combined stress of salt and excess copper remains unexplored. Seeds of two cultivars (Rocket and Jumbo) of Cucumis sativus were grown in sand amended with copper (100 mg kg(-1)), and developed seedlings were exposed to salt stress in the form of NaCl (150 mM) at the 30-day stage of growth for 3 days. These seedlings were subsequently sprayed with 0 or 0.01 μM of 24-epibrassinolide (EBL) at the 35-day stage. The plants exposed to NaCl and Cu in combination exhibited a significant decline in fresh and dry mass of plant, chlorophyll content, activities of carbonic anhydrase, net photosynthetic rate and maximum quantum yield of the PSII primary photochemistry followed by NaCl and Cu stress alone, more severely in Jumbo than in Rocket. However, the follow-up treatment with EBL to the stressed and nonstressed plant improved growth, chlorophyll content, carbonic anhydrase activity and photosynthetic efficiency, and further enhanced the activity of various antioxidant enzymes viz. catalase, peroxidase and superoxide dismutase and content of proline at the 40-day stage of growth, and the response of the hormone was more effective in Rocket than in Jumbo. The elevated level of antioxidant enzymes as well as proline could have conferred tolerance to the NaCl- and/or Cu-stressed plants resulting in improved growth, water relations and photosynthetic attributes. Furthermore, antioxidant enzyme activity and proline content were more enhanced in Rocket than in Jumbo cultivar.

Brassinosteroids (BRs) and polyamines, well-established growth regulators, play a key role in abiotic stress response in plants. In the present study, we examined the role of 24-epibrassinolide (EBL, an active BR) and/or putrescine (Put) in the salt-induced stress in cucumber. The 15-d-old plants were exposed to 100 mM NaCl and they were subsequently treated by exogenous EBL and/or Put. The salt stress reduced significantly plant growth and gas-exchange parameters, and increased proline content and electrolyte leakage in the leaves. Toxic effects induced by salt stress were completely overcome by the combination of EBL and Put. EBL and/or Put treatments improved the growth parameters of the NaCltreated plants, such as shoot length, root length, fresh and dry mass. Our data also indicated that applications of EBL and Put upregulated the activities of the antioxidant enzymes, such as catalase, peroxidase, and superoxide dismutase under salt stress.