Researchers use IV to monitor flow of sugar in sweet sorghum, analysis aimed at maximizing biofuel potential

Test plots at the Texas A&M Research and Extension Center at Beaumont, in the foreground is grain sorghum, used primarily for animal feed, and in the background, sweet sorghum for the biofuels industry. Credit: Texas Agricultural Experiment Station.

Scientists at the Texas Agricultural Experiment Station are researching how sweet sorghum deals with sugars and have found that the process differs from that of sugar cane, a close relative. Their tactic to analyse the flow of sugar inside the plant is based on an 'intravenous' (IV) technique.

In Beaumont, Dr. Lee Tarpley, plant physiologist, and College Station colleague, Dr. Don Vietor, professor of crop physiology, focus their research on sweet sorghum (Sorghum bicolor (L.) Moench) because it is seen as a crop that could revolutionize the biofuels sector. Their analyses complement those of a growing group of scientists and plant breeders who are all studying and developing tropical grass species as future energy crops.

While sweet sorghum and sugarcane are close relatives, the researchers have shown that the two species have different ways of moving and storing sugar. Tracer sucrose is inserted into growing plants 'intravenously' (image, click to enlarge). Once the sucrose is inside the plants, the researchers can track the movement and distribution.

The scientists publish their findings under a creative commons licence as an open access article in the June issue of BMC Plant Biology.

They found that, due to the plant's physiology, sweet sorghum appears to be more efficient in reusing the stored sugar to support growth of other parts of the plant. The mechanisms in sugarcane, however, allow it to accumulate very high levels of sucrose.

The differences are critical, and need to be understood for breeders to develop new varieties specifically for the biofuel industry, says Tarpley. Sweet sorghum and sugarcane are both well suited for this purpose.

While sorghum is an annual and can fit well into a crop rotation, sugarcane is a suitable perennial for many areas, Tarpley adds. But to maximize the potential of sweet sorghum as a biofuel crop, breeders need to understand the physiology of the plant and not use sugarcane as a model:
energy :: sustainability :: ethanol :: bioenergy :: biofuels :: sugarcane :: sweet sorghum :: sugar :: plant biology :: plant breeding ::

There is a large body of research on sugarcane that was previously thought to apply equally well to sorghum. Instead, we need to fully understand how sorghum moves and stores sugar in order to elevate to the next level in our breeding efforts, Tarpley concludes.

Sorghums are receiving a great deal of interest from the scientific community. Most recently, sccientists from the U.S. Agricultural Research Service released new low-lignin sorghums that are ideal for biofuel and feed (previous post). Several projects are underway to develop drought-tolerant varieties, high sugar varieties and high biomass varieties (earlier post). Some sorghums promise great opportunities for use in developing countries, where they can be grown with low inputs to yield both fuel, food, fiber and fodder (more here and here).

Last month, a major breakthrough was achieved when researchers succeeded in engineering a sorghum that can grown in soils plagued by aluminum toxicity. Such acidic soils limit crop production in as much as half the world's arable land (previous post).


Picture: Researchers insert an IV into the sorghum plant as a means of infusing the tracer sucrose, so that they can track the movement and distribution of sugar within the growing plant. Credit: Texas Agricultural Experiment Station.

References:
Lee Tarpley and Donald M Vietor, "Compartmentation of sucrose during radial transfer in mature sorghum culm", BMC Plant Biology 2007, 7:33, DOI:10.1186/1471-2229-7-33.