Plant tissue culture 2

Plant tissue culture 2

Somatic embryogenesis is especially important in genetic engineering because it enables:

Somatic embryogenesis holds exceptional importance in genetic engineering pipelines because it enables rapid regeneration of uniformly transformed plants from single cell origin reducing chimerism and accelerating transgenic event recovery. Transformation methods Agrobacterium co cultivation particle bombardment or ribonucleoprotein delivery introduce DNA into many cells; if regeneration proceeds via organogenesis from multicellular meristem shoot, transformed sectors may coexist with non transformed cells producing chimera requiring extensive segregation analysis. Embryogenic systems initiate

Ref: Birch 1997 transformation; Rao et al., Plant Cell Rep single-cell regeneration transgenics.

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Plant tissue culture 2

Which of the following is NOT a fusogen?

Colchicine is not considered fusogen, unlike true fusogenic agents that promote membrane merging of protoplasts. Legitimate fusogens include polyethylene glycol PEG high molecular weight polymer that dehydrates membrane interface creating calcium bridges neutralizing negative charge inducing lipid mixing upon dilution, high concentration calcium ions at alkaline pH around 10.5 similar mechanism reducing electrostatic repulsion, and inactivated Sendai virus bearing fusogenic HN and F glycoproteins that merge animal and plant membranes albeit rarely used now due to biohazard handling. Electrical

Ref: Anne & Harada 1991 fusogens list; Kao 1977 colchicine not fusogen.

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Plant tissue culture 2

Colchicine is used in plant tissue culture mainly to:

Colchicine is used in plant tissue culture mainly to induce polyploidy and chromosome doubling rather than as fusogen or wall digesting agent. Alkaloid isolated from Colchicum autumnale binds tubulin dimers preventing polymerization into microtubules forming mitotic spindle fibers during metaphase. Without functional spindle, sister chromatids fail to separate at anaphase, nuclear membrane reforms enclosing doubled chromosome complement leading to endoreduplication tetraploid or doubled haploid formation. Application involves treating haploid plantlets derived from androgenesis gynogenesis or

Ref: Blakeslee & Avery 1937 colchicine polyploidy; Dhooghe et al., Plant Methods antimitotic.

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Plant tissue culture 2

Somatic hybridization can transfer:

Somatic hybridization can transfer extensive genetic material ranging from blocks of linked genes to entire chromosomes or whole genomes, contrasting with single gene transformation using plasmid vectors. When two protoplasts fuse, initial heterokaryon contains cytoplasm of both parents and nuclei that may fuse producing allotetraploid somatic hybrid carrying full complement of chromosomes from both species, allowing introgression of polygenic quantitative trait loci QTL controlled by multiple genes interacting for disease resistance, abiotic stress tolerance, quality attributes that cannot be

Ref: Helgeson 1979 potato somatic hybrid; Bhat & Bhat 2011 gene blocks transfer.

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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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Plant tissue culture 2

Osmotic stabilizers such as mannitol are required to:

Osmotic stabilizers such as mannitol sorbitol glucose at 0.3 to 0.7 molar act as essential protectants preventing protoplast bursting after cell wall removal because wall normally provides mechanical resistance counterbalancing internal turgor pressure generated by high intracellular solute concentration. Without rigid wall plasma membrane alone insufficient to resist water influx driven by lower external water potential, protoplasts swell and lyse within minutes, destroying preparation. Non metabolizable sugar alcohol mannitol provides iso osmotic environment matching cell sap osmolarity abou

Ref: Kao & Michayluk 1975 osmotic stabilizer; Plant Cell Culture protoplast methods.

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Plant tissue culture 2

Most common tissue source for protoplast isolation is:

Fully expanded young leaves represent most common and convenient source for protoplast isolation across many species due to favorable physiological and structural attributes maximizing yield and viability. Young leaves have thin primary walls composed of cellulose hemicellulose and pectin not yet extensively lignified or suberized, allowing efficient enzymatic digestion within 4-12 hours using cellulase plus macerozyme mixture. Mesophyll cells are large highly vacuolated with minimal intercellular air spaces ensuring enzyme access, contain chloroplasts providing visual marker for intact protop

Ref: Evans & Bravo 1986 mesophyll protoplast; Bhojwani & Dantu leaf protoplast protocol.

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