Leaf Cutin Monomers, Cuticular Waxes, and Blackspot Resistance in Rose
S. Mark Goodwin, Christopher J. Edwards, Matthew A. Jenks, and Karl V.
Wood
HortScience 2007;42 1631-1635
http://hortsci.ashspublications.org/cgi/content/abstract/42/7/1631?etoc
Link: hortsci.ashspublications.org/cgi/content/abstract/42/7/1631?etoc
Interesting article, Henry, but I’d be happy if you could sum up or simplify the following in your own words and vocabulary so that I too, may understand.
cutin monomer
leaf cuticle lipids
free circular waxes
hydroxylated carbon fatty acids
cutin profiles
adaxial surfaces
dihydroxy hexadecanoic acids, lololol
isolated abaxial & adaxial leaf cuticles
alkanes
ester proportions
The dihydroxy hexadecanoic acid is the easiest of all of them
dihydroxy means two OH- (hydroxyl functional group), hexadec=16, anoic acid = alkanoic acid (organic acid) ending in -COOH - I thought everyone knew that LOLOLOLOL
hmmm… well maybe alkanes is easiest
Maybe I can help here. The abaxial and adaxial surfaces are the bottom and top surfaces of a leaf. The top is adjacent to the stem (axis) when it first grows and unfurls. (Simple mnemonic device)
Cutin is part of a cuticle, a coating, a skin. It is a polymer, made of many small things into a giant network. The monomers are the small things that form the big network polymer. It is made of waxy molecules. Those are hydrocarbons ( hydrogen and carbon) with some alcohol (OH) groups attached. At the ends of the hydrocarbons there are carboxylic acids (COOH) groups. If an alcohol is connected to a carboxyl it forms an ester R-C=O,-OC-R where R means some hydrocarbon. When there are two OH on a hydrocarbon and also a carboxyl group, it can connect to other identical, or similar chains to form a three-dimensional network. Wax is just a simple ester of a long-chain fatty acid plus an alcohol. The cuticle has both cutin and wax.
With care you can peel off the top or bottom skin of a leaf and then extract the wax and cutin with a solvent. That gives the isolated cuticular waxes of the adaxial and abaxial surfaces. A profile is really a pattern, or list of different things found in the waxy layer. For some leaves the surface is more water-repellant than for others. That is determined by the relative amount of alkane, compared to alcohols and esters, the proportion, fraction, ratio of one kind to the other.
I didn’t read the paper yet but presume that there are different length hydrocarbons. Usually they vary from 16 -28 carbons in a row. The shorter ones make a soft wax, longer ones make a harder wax, which melts differently. Like in beeswax compared to non-drip candles.
The cross-linked polymer of cutin (in this case made up of dihydroxyhexadecanoic acid) is a plastic coating on the leaf to keep things out. But some fungi have enzymes that can eat the coating. Sooty blotch on apples and pears is caused by fungi that live on the wax coating of the fruit. Those particular ones don’t hurt the fruit underneath but they do make it look ugly.
With blackspot the lipid profile of the surface probably doesn’t have anything to do with invasion, which happens through the stomates (pores in the plastic that the plant breaths through) but it may determine whether the spores can stick to the leaf, and they might get some food from the wax while growing a germinating spore to invade the leaf.
One possible means of blackspot resistance, horizontal resistance in genetic terms, comes from having surfaces that the spores cannot stick to. Such resistance would presumably work agains most all strains or races, of blackspot. Vertical resistance is if there is a specific something that a certain strain of blackspot dislikes in a certain kind of rose, a toxic molecule or enzyme, for instance. Such resistance might only work for one or a few strains of blackspot fungus. For more details on resistance just do a google search. There are hundreds of articles for various fungi and plants.
Thank you Larry. I really appreciate the detailed explanation and feel like I understand the details a bit more now.
Yes, thank you very much, Larry. Now the article makes more sense. As per your suggestion, I conducted a search on vertical and horizontal resistance; some of the material is truly amazing.