Woolly Plants

Woolly covering on leaves of alpine plant may serve a protective function.

Bright green leaves in florets with woolly-looking white fuzz coating leaves.

Leaf buds of Dionysia tapetodes.

Matthieu Bourdon

Dionysia tapetodes is a small, cushion-like, high-altitude plant with yellow flowers and leaf rosettes covered in a down of soft, white fibers. A new study has identified the com­position of these fibers, which emerge directly through the walls of specialized leaf cells. 

A team of plant biologists led by Matthieu Bourdon and Raymond Wight­man at the University of Cambridge used Raman microscopy and a variety of chromatography, mass spectrometry, and nucle­ar magnetic resonance spectroscopy techniques to identify the chemical makeup of the fibers, commonly referred to as woolly farina. Closely related Primula plants usually have a powdery, rather than fibrous, fa­rina made up of flavone, which is part of a group of anti-inflammatory and antioxidant chemicals called flavonoids. The woolly farina of D. tapetodes was found to consist of a mix of flavone and flavone derivatives called hy­droxyflavones. The research­ers hypothesize that it is the strong hydrogen bonds in the latter chemicals that allow the substance to form fibers, rather than being deposited as a powder. 

Electron microscopy showed that the fibers are, on average, only 1.6 microns wide, orders of magnitude thinner than human hairs. Cryo-scanning electron mi­croscopy (SEM), which freezes cells, preserving their size and shape, allowed the researchers to pinpoint where the fibers emerge from cells at the end of sticky hairs called trichomes. The SEM images showed that the woolly farina forms inside the cells and then pushes through tiny holes in the plas­ma membrane, cell wall, and waxy cuticle. These punctures were a surprise, Wightman said, because such perfora­tions would normally cause the cell to burst. “From a cell’s point of view, it takes remark­able precision,” he said. 

It is not yet clear what pur­pose these fine fibers might serve, though researchers think that they may provide UV protection or prevent wa­ter loss. The fibers may also protect the leaves from freez­ing temperatures, a useful trait for a plant living in the mountainous areas of Turk­menistan, Iran, Afghanistan, and Pakistan. Further research could investigate the potential for culturing cells that produce woolly farina for human use as a biomaterial. (BMC Plant Biology

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