Fructan facts and trivia

What is fructan?

Fructan is a storage polysaccharide produced by most C3, cool-season grasses and certain broadleaf plants. It’s made up predominately of chains of fructose that are longer than 10 units. Those shorter than 10 sugar units are called oligosaccharides, or Fructo Oligo Saccharides. . In plants, fructan production occurs only under certain conditions, generally when growth is limited by some sort of stress, while sunlight continues to create sugars that cannot be utilized. Some kinds of grass are better at making fructan than others, but we still need to acknowledge that environmental conditions are more important than genetic potential. Fructan is good for plants; it gives them energy stores to tap when times get hard. Mammals lack the enzymes to digest fructan, but symbiotic bacteria in the gut readily ferment it. Fructan is good for cows, providing a rapidly fermentable energy source for the microorganisms in the rumen. But cows ferment in the fore-gut, while horses ferment in the hind-gut, and this is where the problem lies.

Plant breeders think fructan is the GOOD stuff! They are purposely increasing it so cows give more milk, and the plant has better energy reserves to get through any stress. See page 2 of the following brochure:

http://www.molecularplantbreeding.com/pdfs/MPB_FactSheet-Pastures.pdf

Not all kinds of grass have fructan

C4, warm-season grasses utilize starch as a storage carbohydrate, and do not have fructan, although they can have FOS, the really short ones. . Examples of C4 grasses are Bermuda, Blue gramma, Big and little bluestem, crabgrass, kikuyu, bahiagrass and many other grasses of tropical origin. A few families of C3 cool season grasses store starch instead of fructan.

Weeds have fructan, too

Dandelions, chickory, thistles, ragweed, knapweed, sow thistles, wild oats, wild onions, and quackgrass all contain fructan. Dandelion (Taraxacum officinale) contains 2-1 linked inulin, which is the same kind of short chain FOS being used to induce laminitis in horses for clinical trials by Dr. Chris Pollitt. This work implicates broadleaf fructan producting weeds as a laminitis trigger, more than it does grass, which has a different kind of fructan.

These dandelions tested 27%dm NSC on May 15, 2005 after a period of sunny days and cold nights in Center, CO. The dandelions were higher, or as high in NSC as the grass tested at the same time.

When fructan is highest and lowest

From a global perspective, we cannot make generalizations about which season has the highest fructan level. We must exercise caution in attributing data gathered from one bioregion to other parts of the world. It has more to do with temperature and growing conditions, and those vary with season around the world. In temperate regions that freeze hard during winter (like the northern parts of the US), fructan concentration is highest spring and fall when the night-time temperatures are less than 40F or 5C, and lowest mid-summer and mid-winter when the temperatures are below freezing. In the summer, rapid growth uses up the sugar, so fructan formation is not triggered (except during drought, more on that later.) In the winter, fructan is hydrolyzed back into sugar to act as a cryoprotectant. If you see grass that is still green under subfreezing temperatures, it’s likely full of simple sugars, rather than fructan.

In subtropical regions and marine climates where the winter temperatures hover just above freezing( like Australia and the United Kingdom) improved C3 grasses will have the most fructan during mid-winter, and during summer drought. During optimum growing conditions spring and fall, fructan levels may be lowest.

In England, between morning fog and afternoon rain, it often averages only 3 hours of sunshine per day. Sunshine may be the most limiting factor for the amount of NSC in grass. The marine climate features less temperature fluctuations, so the amount of NSC will be highest during periods with higher sunshine. In areas with a no limit to sunshine, temperature may be more important.

Fructan concentration is inversely correlated with growth rate. In other words fructan concentration is lowest when the grass is growing faster. I know a lot of people say that fast growing grass is the enemy, but it was not a plant physiologist who made up that theory. This abstract agrees with the rest of the scientific literature:

http://www.ingentaconnect.com/content/urban/271/2001/00000158/00000007/art00320

Fructan formation is triggered when there is excess sugar in the plant. Excess sugar happens when there is more sugar being made than is being used to make protein, energy, and fiber. So when the plant is growing fast, there is less chance for sugar to build up. It is more accurate to say that ARRESTED growth causes fructan formation. If the sun is shining in the spring, and the grass starts growing quickly, THEN you have a few nights of night-time temperatures below 40F or 5C, that’s when high sugar and fructan happens. If the grass growth is limited due to a nutrient deficiency (frequently nitrogen ) fructan concentration will be higher.

In some species of C3 grasses, fructan can also be high under drought stress. This varies greatly between one species of grass to another. That’s because there are various mechanisms that can be utilized to get a plant through a long-term drought. Accumulating fructan is one strategy that works. Here’s an abstract describing fructan accumulation through the first 50 day of simulated drought stress on perennial ryegrass. http://www.blackwell-synergy.com/links/doi/10.1046/j.1469-8137.1999.00388.x

As the plant dries down, growth slows and stops, so sugars are not used up, fructan formation is triggered and the last act of the dying plant is to accumulate as much fructan as possible in the base of the plant to hoard energy for regrowth when the drought breaks. Then is has a rapidly available energy source to get a jump-start on the competing grasses.

Another mechanism that may be utilized by native grasses well adapted to drought is to just go quickly dormant when it gets hot and dry, and not use up precious reserves trying to grow under adverse conditions. This paper shows an example of these differing adaptations:

http://www.blackwell-synergy.com/links/doi/10.1046/j.1469-8137.1997.00728.x

This abstract http://www.publish.csiro.au/nid/102/paper/FP03230.htm shows a completely opposite response in a native species that is well adapted to drought in Australia , with fructan concentration going down and sugars going up.

In comparison, the introduced species like tall fescue and perennial ryegrass were a lot higher in fructan under drought stress than the well adatped native species: http://www.publish.csiro.au/nid/40/paper/AR02184.htm

Grasses like orchard and perennial ryegrass are not well adapted to drought. They will continue to try and grow, and will therefore accumulate a lot of sugar and fructan before they are forced into dormancy. Let’s remember that high fructan levels generally indicate a plant under stress. What is stressful to any organism is dependant on how well that organism is adapted to the particular stress, both genetically and physiologically. This is why it is impossible to just put out a list of grasses with lower genetic potential to accumulate NSC. We cannot take the fructan or NSC genetic potential of a grass out of context with the environmental conditions that produced it. If one grows orchard grass in humid, cloudy England, on a loamy soil with high moisture holding capacity, where it is well adapted, it may be low in fructan and NSC. Grow the same grass where its very dry and sunny, on a sandy soil that dries quickly, and it can be very high in NSC.