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#plant cell biology

17 public questions tagged with this topic.

Plant tissue culture 2

Cybridization is mainly useful for transfer of:

Cybridization primarily useful for transfer of cytoplasmic traits encoded by mitochondrial or plastid genomes which are generally maternally inherited and cannot be introgressed through nuclear hybridization alone. Key agricultural examples include cytoplasmic male sterility CMS caused by chimeric mitochondrial open reading frames atp6 orf138 orf79 interfering with pollen development essential for hybrid seed production in maize rice sunflower Brassica onion; triazine herbicide resistance due to psbA D1 protein mutation in chloroplast photosystem II; and traits like cold tolerance linked to mi

Ref: Bravo & Evans 2011 cybrid CMS; Kumar et al., Front Plant Sci cytoplasmic traits.

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Plant tissue culture 2

Fusion of cytoplasm of two cells with nucleus from one parent is called:

Fusion product containing cytoplasm of two cells but nucleus from only one parent is termed cybrid cytoplasmic hybrid, distinction from true somatic hybrid which contains both nuclei yielding allotetraploid. Cybrids arise when protoplasts of two sources fuse forming heterokaryon with two nuclei and mixed organelles followed by selective loss or inactivation of one nucleus. Inactivation can be engineered by pre treating one partner with gamma irradiation X ray or metabolic inhibitor iodoacetate that damages nucleus while preserving cytoplasm viability. During subsequent mitosis heterokaryon res

Ref: Sidorov et al., 1981 cybrid concept; Gleba 1979 Cytoplasmic inheritance.

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Plant tissue culture 2

Electrofusion induces fusion by:

Electrofusion induces protoplast fusion by applying controlled electrical pulses that create reversible membrane breakdown at points of contact allowing lipid bilayers to merge and cytoplasms to coalesce, offering higher fusion frequency viability and selectivity than chemical PEG method. Protocol consists of two electrical phases: first low strength high frequency alternating current 50 to 200 kilohertz field causes dielectrophoresis polarizing protoplasts forming induced dipoles aligning them in pearl chains bringing membranes into intimate contact at poles. Second short high intensity direc

Ref: Zimmermann & Vienken 1982 electrofusion; Tempelaar et al., Plant Sci electroporation.

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Plant tissue culture 2

Common fusogen used for induced protoplast fusion is:

Common chemical fusogen employed to induce protoplast fusion is polyethylene glycol PEG polymer with molecular weight typically 1500 to 6000 daltons applied at concentration 15 to 40 percent weight per volume combined with calcium ions 50 millimolar and alkaline pH 9 to 10. PEG induces fusion through multiple mechanisms: it is highly hydrophilic binding water molecules dehydrating intermembrane space reducing hydration repulsion between negatively charged phospholipid bilayers, promotes close apposition of membranes via calcium bridging between phosphate head groups and creates molecular disor

Ref: Kao & Michayluk 1974 PEG fusion; NCBI protoplast fusion review.

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Plant tissue culture 2

Dead protoplasts are stained red by:

Dead protoplasts are stained red by propidium iodide PI nucleic acid intercalating fluorescent dye that distinguishes membrane compromised cells. PI is cationic molecule unable to cross intact lipid bilayer of viable protoplasts due to charge and size exclusion, so viable population excludes dye remaining unstained. In dead cells membrane integrity lost through enzymatic damage or physical stress, PI diffuses entering cytoplasm nucleus where it intercalates between double stranded DNA and RNA base pairs with strong affinity, enhancing red fluorescence emission at 617 nm when excited green ligh

Ref: Jones 1987 PI dead staining; Molecular Probes Handbook viability dyes.

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Plant tissue culture 2

Viable protoplasts fluoresce green when stained with:

Viable protoplasts fluoresce bright green when stained with fluorescein diacetate FDA, vital fluorescent dye used routinely for viability assessment before fusion or transformation to ensure batch quality above 80 percent. FDA itself is non fluorescent lipophilic molecule that diffuses across intact plasma membrane permeable only to living cells with intact barrier. Inside cytoplasm active non specific esterases present exclusively in living cells hydrolyze ester bonds releasing fluorescein highly fluorescent polar molecule that accumulates inside membrane intact vesicle because its negative c

Ref: Widholm 1972 FDA viability; Larkin 1976 fluorescein diacetate Plant Physiol.

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Cell Organelles

Which of the following plastids is involved in pigment synthesis?

Plastids constitute a family of interrelated organelles arising from undifferentiated proplastids, with interconversion regulated by light, developmental cues and nuclear-encoded transcription factors like GLK. Leucoplasts are non-pigmented plastids predominantly found in roots, seeds, tubers and non-green tissues, serving as biosynthetic hubs rather than photosynthetic factories. Unlike chloroplasts and chromoplasts, they lack extensive thylakoid grana and photosynthetic apparatus but retain double envelope and stromal enzymes for fatty acid, amino acid, starch and secondary metabolite synthe

Ref: Taiz et al., Plant Physiology and Development, 6th ed., Chapter 1: Plastid Types and Terpenoid Synthesis.

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Protein Sorting and Trafficking

What signal is required for targeting proteins to the thylakoid lumen?

Final intra-chloroplast sorting thylakoid lumen after stroma entry requires crossing thylakoid membrane barrier maintaining proton gradient ATP synthesis. Lumenal precursors plastocyanin copper OE16 OE23 photosystem II oxygen evolving complex Rieske iron-sulfur PetC transport stroma lumen. Precursors carry bipartite targeting sequences N-terminal chloroplast transit peptide TOC-TIC entry second thylakoid transfer domain 30-70 residues positively charged N-region hydrophobic core C-region cleavage thylakoid processing peptidase. Two distinct pathways recognize transfer domain: Sec pathway trans

Ref: Cline & Theg, Mol Membr Biol 2007: Twin-arginine RR motif for Tat pathway to thylakoid lumen.

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Protein Sorting and Trafficking

Which pathway is involved in the targeting of thylakoid proteins?

Thylakoid membrane harbors photosynthetic machinery requiring insertion light-harvesting polytopic proteins after chloroplast envelope import stroma. Four conserved pathways inherited cyanobacterial ancestor: Sec pathway unfolded proteins SecYEG translocase SecA ATPase, SRP pathway specialized highly hydrophobic light-harvesting chlorophyll a/b binding proteins LHCPs pigments. Stromal chloroplast SRP cpSRP54 GTPase homologous bacterial SRP54 NG M domains binding signal sequence GTP, unique cpSRP43 chaperone absent bacteria three chromodomains four ankyrin repeats specifically binding L18 motif

Ref: Schuenemann, Annu Rev Plant Biol 2007: cpSRP pathway targets proteins to thylakoid membrane.

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Protein Sorting and Trafficking

What is the main function of the TIC complex in chloroplasts?

Chloroplast envelope encloses two translocon systems tandem importing majority organelle proteome 3000 proteins despite plastid genome about 100. Precursors synthesized cytosol N-terminal transit peptide enriched hydroxylated serine threonine positively charged amphipathic not hydrophobic distinct mitochondrial presequence. First receptor TOC outer envelope: Toc159 large 159 kDa GTPase selectivity filter photosynthetic versus housekeeping via acidic A-domain, Toc34 small 34 kDa regulatory, Toc75 Omp85 beta-barrel superfamily 14-strand channel 3 nm pore translocating polypeptide. After outer me

Ref: Soll & Schleiff, Nat Rev Mol Cell Biol 2004: TIC imports proteins across chloroplast inner envelope.

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Mitochondria Plastids Ribosomes and Other Organelles

The thylakoid system of a chloroplast is extensively damaged, but the stroma and chloroplast envelope remain intact. Whi

Chlorophyll occurs in the thylakoids, and stacks of thylakoids form grana, which are the sites of light reactions. Circular DNA, ribosomes and enzymes for carbohydrate and protein synthesis occur in the stroma and may remain present.

Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Mitochondria Plastids Ribosomes and Other Organelles

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