Fruit Spray Spurs Ripening

"When applied before harvest this compound accelerates the development of fruit flavor and color," says Jiwan Palta, a plant physiologist in the College of Agricultural and Life Sciences.

Graphic: A Cranberry Bog Harvest in Wisconsin

The compound is called lysophosphatidylethanolamine, or LPE. It occurs naturally in many plant and animal cell membranes. The Wisconsin scientists are experimenting with LPE purified from egg yolks and soybeans. When the scientists sprayed LPE on apple trees and cranberry vines two weeks before harvest, the apples and cranberries ripened more quickly and developed a redder color than fruit not sprayed with LPE. The fruit sprayed with LPE before harvest also remained crisp longer in storage.

The compound may be especially important to Wisconsin cranberry growers, who are fast replacing New England as the major producers of cranberries. Cranberries that ripen sooner could translate into increased profits in Wisconsin, where early frosts often force growers to harvest the crop before the berries are completely ripe. Growers typically receive more money for berries that are fully ripened.

Palta and his colleagues have found that LPE not only accelerates ripening but also retards aging of plant tissue. In one recent experiment they  showed that immersing snapdragon flowers in an LPE solution overnight extends their life as cut flowers from about four days to about eight days.
 
"LPE is a common lipid found in plant and animal cell membranes," Palta says. "We once thought that lipids only played an important role in plants as part of the structure of cell membranes and as an energy source. It's now clear that they play an important role in regulating cell metabolism."

The researchers have dtermined that LPE can inhibit the action of phospholipase D by up to 91 percent depending on the concentration of LPE. Phospholipase D, which occurs in both plants and animals, appears to be a key enzyme that controls the breakdown of phospholipids in plant membranes during the early stages of plant aging.

"We know more about how phospholipase D works in animals than in plants," says Palta. "Scientists have found several factors that speed up the action of phospholipase D. LPE is the first compound we know of from animals or plants that strongly inhibits this enzyme in a specific manner."

Studies with LPE are now undwerway with a wide variety of fruits and vegetables including cranberries, peaches, tomatoes, grapes and even cut flowers.

The research appears in the current issue of the Proceedings of the National Academy of Sciences