LOWERING the temperature for two hours each day reduces the height of corn plants without affecting their seed yield — a technique that could be used to grow crops in controlled-environment facilities in caves and former mines, a Purdue University study has found.
Raising the crops in isolated and enclosed environments would help prevent genetically modified pollen and seed from escaping into the ecosystem and crossing with wild plants.
Purdue horticulture professor Cary Mitchell said the technique could be particularly useful for growing transgenic crops to produce high-value medicinal products, such as antibodies for the budding plant-derived industrial and pharmaceutical compound industry.
"Grains of corn could be engineered to produce proteins that could be extracted and processed into medicine, pharmaceuticals and nutraceuticals such as essential vitamins," he said. "This is a young industry, but what we've done is show that you can successfully grow these high-value crops in contained environments."
Mitchell called corn a "good candidate crop" for the industry because of the plant's bounty of seeds and well-characterized genome, which can be modified in many ways. Using plants as "factories" to generate bioactive medicines would be far cheaper than current methods that rely on cell cultures from mammals, he said.
The challenge comes with raising corn — a towering crop that needs bright light and heat — in a dark, cool, underground mine. Mitchell and then-postdoctoral researchers Yang Yang and Gioia Massa installed a growth chamber with insulation and yellow and blue high-intensity discharge lamps in a former limestone mine in Marengo, Ind., to test how corn would react to an environment in which its growing conditions — light, temperature, humidity and carbon dioxide — were tightly controlled. To their surprise, the hybrid corn responded by growing "too well," Yang said.
"We coddled the plants with such luxurious conditions that the corn was touching the lamps before it had even tasseled," he said.
To reduce the corn's height, the researchers borrowed a trick the greenhouse industry uses to dwarf Christmas poinsettias.
Using a growth chamber that mimicked the temperature conditions and carbon dioxide levels of the Marengo mine, they dropped the temperature to 60 degrees F for the first two hours of each photoperiod, the time during which the corn received light. The temperature was restored to 80 degrees F for 14 hours and then lowered to 65 degrees F for eight hours of darkness.
The temperature dip dwarfed the stalk height by 9-10% and reduced the stalk diameter by 8-9% without significantly affecting the number and weight of the seeds.
"This is a technique you could easily do in a mine or cave," Mitchell said. "It is an affordable, non-chemical means of taking genetically modified crops to harvest maturity without getting any kind of pollen or seed into the ecosystem."
He said former mines could be prime locations to grow high-value, transgenic plants because their natural coolness lessens the need to ventilate the heat produced by the lamps. The high levels of carbon dioxide in mines also promote plant growth.
"Productivity in a controlled environment is superior to that in the field, and you can raise more than one crop per year," Mitchell said. "Controlled-environment agriculture is going to be one of the big movements of the 21st century."
The study was published in Industrial Crops & Products and is available at www.sciencedirect.com/science/article/pii/S0926669013006791.