Lake Alfred, Florida, USA
January 2021
In order to improve photosynthesis in plant leaves, two University of Florida scientists will study their roots and stems.
More specifically, Christopher Vincent and Fred Gmitter hope to find the optimal relationship between citrus tree “sources” and “sinks” so that plant breeders can select varieties — and growers can use practices — that lead to faster-growing plants.
Some crops that grow faster yield better food and get to market earlier, rather than later.
So, what are these “sources” and “sinks” the researchers are talking about? In this case, “sources” are the leaves where photosynthesis takes place to make carbohydrates – such as sugars, starches and cellulose – that are needed for all aspects of plant growth. “Sinks” are the places those carbohydrates are used – think fruits, roots and newly growing stems.
A new UF/IFAS project aims to improve plant performance and productivity by providing breeders with traits to enhance the photosynthetic ability of cultivated citrus. By understanding and quantifying the relationships between the “pull” of the sinks for carbohydrates and the “push” from their production sources, the researchers hope to find ways to speed up the growing cycles.
Vincent, an assistant professor and Gmitter, a professor, both in horticultural sciences – have received a $495,000 grant from the National Institute of Food and Agriculture, an arm of the U.S. Department of Agriculture, to study the relationships between sinks and sources within plants and hopefully use that information to improve the speed of plant growth.
They will study how this works in citrus, but their findings will apply to plants of all kinds.
“If we know the optimal relationship between leaves and sinks, breeders can select varieties and growers can select practices that lead to faster-growing plants,” said Vincent, a faculty member at the UF/IFAS Citrus Research and Education Center, where Gmitter also works.
Plants can only synthesize as much sugar as they can move out of their leaves to be used in tissues that don’t photosynthesize, said Vincent. These are called “sink tissues.” They include roots, fruits and new sprouts from a bud on a stem.
If leaves have excess sugar, they reduce their photosynthetic activity, would otherwise conserve water and nutrients. If the sinks on the plants are large, sugar moves faster and plants photosynthesize more, enabling plants to grow more rapidly.
“We plan to identify the effect of the size of sinks on how quickly sugars move out of leaves and through the phloem,” he said. “We expect plants to grow faster when this relationship is optimal.
To do this, Vincent and Gmitter will use pairs of plants that have exactly the same genes, but one will have exactly twice the number of copies of those genes. Previous research demonstrates that these differences in gene copy number can have a big impact on growth habit and other differences caused not by specific genes themselves, but by how much each gene is expressed relative to other genes.
“As far as our project goes, this is just a fortunate scenario that we will use to assess how differences in allocation affect sugar transport and photosynthesis,” Vincent said.
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