Practice question

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 disorder increasing membrane fluidity and probability of lipid mixing and coalescence upon gradual dilution washing out PEG. Efficiency of heterokaryon formation ranges 10 to 30 percent depending on species and concentration exposure time 15 to 30 minutes. Although PEG causes some cytotoxicity protein denaturation requiring thorough washing after treatment, it remains cheapest most accessible method for somatic hybridization compared to electrofusion equipment requiring electroporators. Other chemical fusogens include high calcium alkaline pH alone and inactivated Sendai virus with fusogenic hemagglutinin proteins. PEG fusion nonspecifically generates multinucleate products but selection via fluorescence markers or complementation enables recovery of desired hybrids for crop improvement.