There’s nothing like a stiff cold wind to chase me indoors and topple six month’s worth of neglected paper into into my lap.
Among the detritus is a note about looking up a substance called inulin to see if it is known to play a role in winter hardiness in roses. Google turns up nothing in that regard but Wikipedia does mention it in that context with onions, banana and chicory.
Does anyone know what the main starch is in rose plants and if there has been any work done on the role of starches in winter hardiness of roses?
Well, just to put my own penny into this, Peace and Diamond Jubilee both had very white, and quite starchy piths. They both had very low salt and freeze tolerance- Hurricane Sandy and the freak snowstorm killed both of them, large plants too- while most of the other roses were unaffected to moderately stunted.
Inulin is a polymer that is not digestible by humans. It is the main polysaccharide in the composite Inula, and also jerusalem artichoke tubers. Diabetics sometimes use it. It yields fructose, not glucose so it goes through a different metabolic pathway and doesn’t stimulate insulin secretion. In the gut it is generally metabolized by bacteria and may produce gas.
I don’t think inulin is found in roses. Grasses have a lot of fructans (sort of relatives of inulin) but things in the rosacease will more likely have sorbitol as found in Sorbus, apples, pears, plums and sugarless gum. Osmoprotectants can only do so much to lower the freezing point.
Yeast uses trehalose which allows proteins to be stable in a “glass” rather than a crystal of water. This is used in molecular biology to make stable proteins for use in labs. They are freeze-dried with trehalose and can be kept a very long time in a refrigerator or freezer and taken out to dissolve as needed. Trehalose is not very common in plants, sucrose is much more abundant. Sucrose is not as good at protecting protein stability though it is rather similar to trehalose. Insects use tehalose to resist freezing. Pigs have high levels of an enzyme that breaks down trehalose, presumably because they eat insects (grubs in particular). Humans have the enzyme too.
Proline and glycine betaine are other common osmoprotectants use to protect organisms against drought or salt or freezing. Roses seem to depend on supercooling to avoid freeze damage. These various osmoprotectants may help make the supercooled state more stable by making less water available for forming ice crystals.
Having tried Jerusalem Artichokes out of curiosity, I whole heartedly agree with the historic quote contained in this excerpt from Wikipedia…
"The tubers are sometimes used as a substitute for potatoes:[9] they have a similar consistency, and in their raw form have a similar texture, but a sweeter, nuttier flavor; raw and sliced thinly, they are fit for a salad. The carbohydrates give the tubers a tendency to become soft and mushy if boiled, but they retain their texture better when steamed. The inulin cannot be broken down by the human digestive system,[10] but is metabolized by bacteria in the colon. This can cause flatulence and, in some cases, gastric pain. Gerard’s Herbal, printed in 1621, quotes the English planter John Goodyer on Jerusalem artichokes:
“which way soever they be dressed and eaten, they stir and cause a filthy loathsome stinking wind within the body, thereby causing the belly to be pained and tormented, and are a meat more fit for swine than men.”[11]"
“Pained and tormented belly” with a “filthy loathsome stinking wind” about sums it up. Feh!
These various osmoprotectants may help make the supercooled state more stable by making less water available for forming ice crystals.
So, then, within limits would the actual dehydration of a rose plant also protect against freeze damage by reducing phase expansion, freezing point depression and crystallization?
belly…wind"
Some mental images stay with you for life. I hope this won’t be one of those.