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Photo: Light colored corn kernels expressing fluorescent protein in the endosperm layer intermixed with darker kernels that do not have the gene for fluorescence.
ARS researchers have introduced green fluorescent protein into corn lines as a marker for different tissues, which will make it easier to study nitrogen use and grain development and improve corn processing. Here the light kernels are expressing the fluorescent protein in the endosperm layer. Photo courtesy of Adrienne Moran Lauter, ARS.

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Making Fluorescent Markers for Corn Tissues

By Ann Perry
September 25, 2008

Kernels of corn are made up of three main parts: the plant embryo, the endosperm surrounding the embryo, and the hard outer pericarp. These different seed components are used in food, animal feed and industrial products. Now a group of researchers has created experimental corn lines with visible markers that can simplify sorting through these distinctive kernel tissues.

Geneticist Paul Scott works in the Agricultural Research Service (ARS) Corn Insects and Crop Genetics Research Unit in Ames, Iowa. He partnered with Iowa State University scientists Colin Shepherd, Nathalie Vignaux, Joan Peterson and Lawrence Johnson to develop tissue markers for transgenic corn lines using green fluorescent protein (GFP).

GFP was first isolated in a single species of jellyfish. It has since been cloned and used safely in a wide range of scientific investigations in plants and animals.

Corn processors currently identify and measure different grain tissues using a range of markers. However, they would benefit from tools or techniques that would allow them to measure fractionated corn seed tissues more easily and accurately.

The research team developed transgenic corn lines containing GFP as either an embryo or an endosperm marker. They checked for GFP levels by using an instrument that measures lightwave emissions from the fluorescent corn tissues.

In one line they developed, 100 percent of the GFP fluorescence was found in the endosperm. In another line, about 67 percent of the GFP fluorescence was found in the embryo.

Afterwards, the group hand-dissected about 100 grams of transgenic kernels and identified GFP concentrations in the pericarp, embryo and endosperm tissues. This gave them baseline levels to use for identifying different tissues during the fractionation processes.

The researchers then dry-milled transgenic corn and produced separate grain fractions from the pericarp, endosperm and embryo. They succeeded in determining GFP fluorescence levels for each one. But most important, they were also able to easily identify the mix of tissues in each--a process that typically is expensive and time-consuming.

These results indicate that transgenic lines of corn containing GFP could be used to optimize existing fractionation methods and improve processing techniques. They can also support a variety of corn-related research projects, including studies on nitrogen use and grain development.

ARS is the U.S. Department of Agriculture's chief scientific research agency.