Expansins: proteins that promote cell wall loosening in plants.

It was July 7, 1912, and Harry Houdini, ir the company of a bevy of dutiful report ers, was going to perform one of his greatest escapes, from a barge floating in the middle of the East River in New York. First he was shackled in leg irons two pairs of handcuffs, and elbow irons. Then he was crammed into a sturdy wooden crate, 40 inches x 22 inches x 24 inches, and the lid was nailed shut and reinforced with steel bands. For added effect, the box was given a further wrapping of stout ropes and fitted with 200 pounds of lead weights. Following the obligatory hype and fanfare, the completely sealed crate, with the manacled Houdini inside, was lowered over the side of the barge. Even the skeptics on board must have been silenced as the box slowly sank out of sight into the murky depths below. Seconds passed. Predictably, just when the frantic onlookers were about to demand that the box be raised, the smiling magician broke the surface, leaving his gaping admirers to wonder how on earth he did it (1). A similar, but even more baffling, conundrum on a microscopic scale has been vexing plant physiologists for over half a century. Plant protoplasts are born swaddled inside tiny boxes called cell walls. These walls are quite rigid by any standard, able to resist internal hydrostatic pressures of up to 10 atmospheres. The strength of cell walls arises from their peculiar composition: tough, slender rods of crystalline cellulose microfibrils embedded in a glue-like matrix of pectins, hemicelluloses, and proteins. Indeed, the cell walls of plants can be thought of as the prototype for modern advanced composites such as fiberglass and graphite fiber-reinforced resins which are widely used as lightweight substitutes for steel. Yet despite this formidible barrier, plant cells manage to expand 10 to 100 times their original size during normal development. For decades, plant physiologists have wondered how on earth they do it.