CRYSTAL CITY, Va. -- A mutant bacterial enzyme could delivercrisper, lower-fat potato chips and french fries, as well as"tomatoes that don't taste like cardboard."
A crop of the transformed "lite" spuds are to be harvested nextmonth, when their increased starch content and crop yield willbe measured, Ganesh M. Kishore, Monsanto Co.'s manager ofplant science technology, told the Ninth InternationalBiotechnology Symposium meeting here. Aside from anexpected 3 percent increase in starch content, "the high-solidrusset Burbank potato lines cannot be distinguished fromnormal control lines," he said.
"Last week at the laboratory we fried up a mess of high-starchchips, which passed all taste tests," Kishore said.
Increased starch density means decreased water content,which makes for faster cooking time of french fries and lowerfat content, he said. "They will put an end to those limpy friesat McDonald's."
Monsanto is working with potato chip and french frymanufacturers. Kishore foresees commercialization within thenext couple of years.
A mutant strain of E. coli that overproduces glycogen providesthe enzyme ADP glucosepyrophosphorylase, which regulatesthe rate of starch metabolism in plants, Kishore said. UsingAgrobacterium tumefaciens, Kishore and his associates insertedthe gene into potato, tomato and tobacco cells. In tomato plants,the gene increased the number of starch granules eightfold, hesaid.
To direct such granules into the potato tuber and away fromroots, stems and leaves, the researchers hitched on anothergene, for the potato storage protein, patatin. "We can alter thestarch content to meet the needs of specific end users," Kishoresaid.
The same starch-enhancing gene works in tomatoes, increasingtheir solid content, reducing water "and maybe even enhancingtheir flavor," Monsanto said.
A separate "ripening suspension" gene also will extend thefruit's shelf life from days to weeks, Kishore said. This worksby lowering the concentration of aminocyclopropane carboxylicacid, a precursor of the plant hormone ethylene. When the fruitis picked, ethylene is switched on, and the rapid decay processstarts.
Calgene Inc.'s Flavr-Savr transgenic tomato also delaysethylene. But the Monsanto gene "metabolizes away theprecursor entirely, so none is available for ethyleneproduction," Kishore said. Calgene's tomato degrades onlypolygalacturonic acid, the precursor of pectin, which builds thecell walls.
"The ripening suspension technology is already in advancedfield testing to identify commercial lines," Kishore said. Hepredicted that "once we combine both traits -- enhanced solidsand extended shelf life -- in a single transgenic fruit, we willhave a tomato that no longer tastes like cardboard."
This new ability to manipulate agronomic traits has wideapplication to other crops, he said. "It tells us we are not usingthe efficiency of plants to the maximum. Plants have a greatercapacity to photosynthesize and fix carbon than we have reallytapped at this point in time."
The journal Science is scheduled to publish the Monsanto workwithin the next few weeks, Kishore said.
-- David N. Leff Science Editor
(c) 1997 American Health Consultants. All rights reserved.