A U.S. government research agency has awarded biologists from three institutions $3.8 million for a program to gain understanding about the process by which plant cells turn light into energy. The payoff could be higher production and improved nutritional quality of essential food crops.
The National Science Foundation (NSF) has made the five-year award to researchers from Cornell, the Boyce Thompson Institute (BTI) for Plant Research on the Cornell campus and to the University of Nebraska. The investigation concerns chloroplasts, the organelles of the plant cell that harbor the chemical process by which green plants synthesize organic compounds from carbon dioxide and water in the presence of sunlight.
"Having a better understanding of how these molecular processes within the plant are regulated will allow scientists, one day, to make better, higher quality crops," said project co-investigator Thomas Brutnell, a plant scientist at BTI. "If we want to make our food more nutritious, or if we want to turn these plant chloroplasts into little factories, we should know how they work," he said.
His reference to "factories" indicates the hope that plant cells could one day produce specialty proteins such as pharmaceuticals.
The focus of the NSF-funded research is to grasp how two kinds of cells, called the bundle sheath and the mesophyll, function in maize, as a model to understanding how several species of plants developed adaptations to minimize losses to photorespiration. This is a wasteful process by which the plant cell uses oxygen and liberates carbon dioxide as cellular respiration. These flowering plants use a method of carbon dioxide uptake that forms a four-carbon molecule. Hence these plants are called C4 plants. Corn and sorghum are two of the best-known examples of C4 plants.
"We have to ask, what are the mechanisms that allow corn, for example, to adapt to dry and arid environments?" said Brutnell. "One thing unique to corn is that it has two types of leaf chloroplasts that work together to turn light and carbon dioxide into sugars. This coordination of activities is likely to involve novel and interesting communication networks."
The biologists' aim is not only to understand how plants harvest light energy more efficiently under arid conditions, but also to better understand the multitude of functions of the chloroplast.
The scientists believe that the project's greatest strength is possibly improving harvests of four-carbon plants. "As the plastid is essential for carbon fixation, lipid metabolism, starch and amino acid biosynthesis, our studies will likely impact research aimed at improving maize agronomic performance," said van Wijk, the project's principal investigator and an assistant professor in plant biology at Cornell. Chloroplasts have also been found to provide a cellular defense against pathogens by synthesizing protective nitric oxide and salicylic acid, he noted.
Chloroplasts are minute structures, the endpoint of the plastid development, present in all green-plant cells. Although plastids are found in the cells of young stems and immature fruits, leaves are the real photosynthetic factories of the plant. Leaf cells are the heart of photosynthesis output because they have hundreds of chloroplasts. It is these that one day could become a center of production of biochemical compounds and pharmaceuticals.
"With the advent of micro-array technology, proteomics [the study of all the proteins in an organism] tools and large mutant plant collections, we now have a unique opportunity to explore this dynamic organelle in corn. This is particularly relevant in light of the economic impact corn has had on American agriculture," said van Wijk.
Joining van Wijk and Brutnell in the project are David Stern, plant scientist and vice president of BTI, and Thomas Clemente, assistant professor, horticulture and botany, University of Nebraska.
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