Plant sugar study could lead to more CO2 intake

By staff reporter

- Last updated on GMT

Related tags: Carbon dioxide, Photosynthesis

Scientists in the US have shed light on how sugars are transferred
from a plant's leaves to other parts of its structure, findings
that could enable genetic engineering in the future to help plants
cope with climate change.

As the world warms up finding ways to help crops deal with environmental changes including increased carbon dioxide has become a major focus for plant biologists. In a paper published in last month's Proceedings of the National Academy of Sciences, researcher from Cornell University report that they have substantiated a theory on plant sugar transportation put forward by senior author Robert Turgeon in 1991. He proposed that sucrose accumulates in the leaves as a result of photosynthesis then, together with other nutrients, travels into the tube-like phloem tissue. Here molecules of the sucrose join together to become larger, more complex sugars known as raffinose family oligosaccharides. As a result, they are too large to flow back to the leaf, and thus move on to the flowers, roots, fruits and other parts of the plant, where they are used or stored. According to the University, the new findings could allow researchers to engineer plants with increased photosynthetic rates, yields and carbon dioxide intake - abilities that could be "crucially important" in the era of climate change. Turgeon and lead author Ashlee McCaskill tested the theory using a plant called purple mullein (Verbascum phoeneceum L​), a relative of figwort. They genetically engineered it to silence two genes that are responsible for polymerising the sugars in the phloem. The result of this was that the sugars backed up into the leaves again. The leaves had a reduced capacity to export sugars during a prolonged dark period. "In plants with severe down-regulation, additional symptoms of reduced export were obvious, including impaired growth, leaf chlorosis, and necrosis and curling of leaf margins,"​ wrote McCaskill. Sugars are generated out of water and carbon dioxide during photosynthesis in normal plants. When there is an accumulation of sugar in the leaves, normal plants slow down photosynthesis and do not take in as much carbon dioxide. Photosynthesis and carbon dioxide intake pick up again when the sugars move out of the leaves. However previous research has indicated that when there is more carbon dioxide in the atmosphere, a series of feedback loops in the plant prevent it from absorbing the excess. McCaskill said that, in theory, increasing a plant's phloem-loading rate would enable increased rate of photosynthesis and yield. "Phloem loading is one of these feedbacks that have an effect on the ability of plants to intake carbon dioxide at the highest level,"​ she said. Source: PNAS 2007 104: 19619-19624 Published online before print as 10.1073/pnas.0707368104 Title: "Phloem loading in Verbascum phoeniceum L. depends on the synthesis of raffinose-family oligosaccharides."​ Authors: Ashlee McCaskill, Robert Turgeon

Related topics: Science, Cereals and bakery preparations

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