An expansin is a protein that promotes extension of a plant cell wall without requiring detectable hydrolysis of its structural polysaccharides. Wall extension and destruction of the wall are different processes: rearranging a load-bearing network can allow it to yield while leaving its components largely intact.[ref]
Two endogenous proteins that induce cell wall extension in plants by S. McQueen-Mason and others. Abstract: reconstituted wall extension without detectable hydrolytic breakdown
The motivating 1992 experiment extracted proteins from growing seedling cell walls and added the extract to isolated walls. Fractionation separated two active proteins, about and , each able to restore extension. The activity depended on conditions such as pH and was not equally effective on every tested wall type.[ref]
Two endogenous proteins that induce cell wall extension in plants by S. McQueen-Mason and others. Abstract: extraction, fractionation and reconstitution comparisons
A useful control compares equally loaded isolated walls with and without the active preparation. Extension after addition connects a measurable mechanical response to material in the preparation; measuring only the abundance of a protein in a growing stem would provide a weaker connection. The reconstitution result does not assign every change in whole-plant growth to expansin.
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