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Post by raymondo on Sept 3, 2011 3:36:36 GMT -5
I have two questions relating to corn colour:
1. I've read that kernel colour comes from three sources: pericarp, aleurone layer and endosperm. Is there a list of what colours each layer can contribute and how the combinations end up?
2. At what stage in the development of the kernel does the colour show? I ask because I bought some coloured sweet corn seeds and the packet says to harvest while the kernels are still yellow. This implies that some of the colours at least do not appear until the cobs start drying down.
Many thanks in advance.
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Post by keen101 (Biolumo / Andrew B.) on Sept 3, 2011 5:43:47 GMT -5
I could have sworn Hristo posted a good PDF of the colors available in each corn layer, but i cant find it. Here is a link to a PDF that i've looked at before. www.grochbiology.org/CornGeneticsArticle.pdfRay, basically yes, the yellow pigments show up in the milk stage (if available), and the anthocyanins (red/purple/blue) pigments are the last to show up, and often only show up as the the corn is approaching the starchy stage. It is best to harvest the sweet corn when it has little or no anthocyanin colors, because it will not be as starchy. there was a neat discussion awhile back on the possibility of finding rare corns that had anthocyanins in the endosperm layer. But otherwise i guess the endosperm is only white or yellow?
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Post by Joseph Lofthouse on Sept 3, 2011 9:51:31 GMT -5
I have found some purples that show up very early and very vivid, even before yellow starts showing. Mostly though colors other than yellow don't start to show up until the late milk stage.
I don't know how gray/blue fits into the anthocyanins/carotenoid scheme of things, but it's often the last color to show up for me.
I have been selecting for vivid sweet corn color in the early milk stage. I have also been selecting some cobs that have muted colors in the milk stage. My thinking is that they have the machinery to make color, it just needs to be tweaked to make more of it sooner.
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Post by DarJones on Sept 3, 2011 11:54:10 GMT -5
Ray, I posted this in another thread, but it seems apropos here.
This post is to correct something that I simply did not investigate thoroughly enough in the past and therefore need to address. This is the difference between seedcoat, endosperm, embryo, pericarp, aleurone, and epidermis.
A tomato has an epidermis. It is the skin that I so much hate to eat, especially from the commercial varieties that have such thick skin. The epidermis of tomato comes in two common colors, clear, and yellow. Clear epidermis is one of the traits involved in a pink tomato. Yellow epidermis is what gives a reddish orange color to the fruit.
A tomato has a pericarp. It is the tissue just beneath the epidermis that expands to contain the seed. The pericarp is where blue tomatoes accumulate anthocyanin. When we eat a tomato, the pericarp and the seed locules are what we consume.
Most plants produce seed in one form or another. A seed is the dormant reproductive structure that most plants use to reproduce sexually i.e. with pollen and ovules. A typical seed has a seedcoat, aleurone layer, endosperm, and embryo.
The seedcoat is a thick layer of tissue intended to protect the endosperm and embryo from harm. It often contains natural chemicals that prevent germination until environmental conditions are acceptable for the seed to grow. A corn seed has a seedcoat and that is where I goofed. I confused the seedcoat with the pericarp. They are NOT the same. The corn seedcoat can contain small amounts of pigment, particulary red. Most other pigments do not accumulate in the seedcoat. I'm in fine company in this, I have books by Jugenheim and others that were published with "pericarp" used instead of "seedcoat".
Just beneath the seedcoat of many kinds of seed is a thin layer of specialized tissue called aleurone. It is responsible for regulating the release of stored sugars from the endosperm. Aleurone is a protein layer that often contains pigments. In corn, these pigments are the source of most of the color variations we can see.
Many kinds of seed contain nutrient reserves which are referred to as endosperm. This tissue is unique because it can be either haploid or triploid with either one or three complete sets of chromosomes. The endosperm contains starch and some protein that will feed the embryo as it grows. A very few seed such as some species of orchid do not have a true endosperm, and have to rely on other methods to feed the growing embryo and developing plant. Some types of seed absorb all of the endosperm into the cotyledons. Beans are an example of a seed that does not have attached endosperm, instead relying on the cotyledons to store starch and protein reserves.
Seed contain an embryo which is the part of the seed that can grow into a new plant. It is composed of lipids (fat like substances), protein, minerals, and just enough nutrients to initiate growth. The embryo in most seed pull nutrients from the endosperm in a process that involves the aleurone layer producing amylase to convert starch into sugar. Once the endosperm is exhausted, the plant usually sheds the mostly empty seedcoat.
For corn, you have the following:
Seedcoat - Mostly is semi-translucent, can be tinted red. The seedcoat is often referred to as the Pericarp though technically the term pericarp refers to the protective layers of a fruit such as a tomato or a peach. If you care to look it up, the seedcoat is further divided into 6 layers defined by the function of the layer and the type cell it is composed of.
Aleurone - Regulates seed germination, this is where the anthocyanins accumulate.
Floury Endosperm - nutrient storage, mostly starch.
Horny Endosperm - much denser starch, zein binds the starch tightly.
Scutellum - this is the shield region where the embryo attaches to the endosperm
Coleoptile - The pointed protective sheath covering the emerging shoot.
Plumule - the coleoptile protects the plumule until it emerges and produces the first leaves. Tropism causes the plumule to grow upward toward the light.
Radicle - The primary root initial is referred to as the Radicle. In most seed, it is the first part to emerge.
Mesocotyl - this is the region where the coleoptile and plumule are attached to the seed. It is a critical organ, transferring nutrients from the endosperm into the growing plumule.
Root Bud - after the plumule emerges from the seed, the root bud begins to grow producing the roots.
Primary Root - This is the root initial that emerges first and begins growth. You can pull up an emerging seedling and see that it has only one root usually lasting until the leaves unfurl, then the root buds begin to grow secondary roots.
Root Cap - this is the small area in the embryo that covers the root producing tissue.
Coleorhiza - Tissue that overlays and protects the radicle before it emerges. When the radicle begins to emerge, it pushes through the coleorhiza and the seedcoat. Tropism then causes the radicle to grow downward and outward.
Hilar Layer - This is the mostly inactive tissue that lies between the tip cap and the endosperm/embryo. It functions during seed expansion to transport nutrients from the cob into the developing seed.
Tip Cap - This is the sharp pointed tip that forms the primary attachment to the cob during seed development. There is a huge amount of variation in structure of the tip cap. Cherokee Squaw corn has some cobs where the corn seed is very firmly attached to the cob and others that are so lightly attached that you can rub them off the cob with a finger. I like the light attachment and plan to separate out some seed with the trait the next time I grow it for seed.
Now you know way too much about a corn seed.
DarJones
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Post by Joseph Lofthouse on Sept 3, 2011 12:53:32 GMT -5
The corn seedcoat can contain small amounts of pigment, particulary red. I've been finding some sweet corn that accumulates red in the seedcoat. (I call them pink). As raw cobs they are very pretty to me, and even though the color survives cooking, it is unfortunately leached out into the water.
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Post by raymondo on Sept 3, 2011 17:12:14 GMT -5
Thanks for that. Good article keen101, nice and clear. Interesting about the early appearance of the purple Joseph. Exhaustive info about seeds in general and corn in particular fusion. Thank you. Just a minor correction. The radicle is the primordial root so heads downward as a result of geotropism.
So, basic message, don't expect brilliant red kernels at harvest time for sweet corn? Pity. I got all excited when I found the coloured sweet corn.
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Post by Hristo on Sept 3, 2011 17:44:00 GMT -5
So, basic message, don't expect brilliant red kernels at harvest time for sweet corn? I will say it that way: don't expect brilliant red kernels at their prime. If it's SE (probably Sh2 too, but I have no red Sh2 variety) the quality will still be very good. But my biggest problem with the red sweets is that their beautiful red color changes in to not so beautiful dull red after boiling or even steaming, and this is big drawback for me. I find that the blue ones retain better their color.
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Post by 12540dumont on Sept 3, 2011 19:03:31 GMT -5
"Just beneath the seedcoat of many kinds of seed is a thin layer of specialized tissue called aleurone. It is responsible for regulating the release of stored sugars from the endosperm. Aleurone is a protein layer that often contains pigments. In corn, these pigments are the source of most of the color variations we can see."
Are there colors associated with more protein?
And thank you. I printed this, because I ask these questions all the time.
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Post by DarJones on Sept 3, 2011 19:49:27 GMT -5
I don't know. I've read some research associated with development of high protein corn but none that associated pigments with protein.
DarJones
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Post by Joseph Lofthouse on Sept 3, 2011 20:11:46 GMT -5
So, basic message, don't expect brilliant red kernels at harvest time for sweet corn? Pity. I got all excited when I found the coloured sweet corn. All of the photos of corn in a previous post alanbishop.proboards.com/index.cgi?action=display&board=corn&thread=4680&page=8#59668 were taken at the early milk stage, a few days before the corn reached it's best eating. I am growing similar corn in a sugary enhanced version. When I can more reliably grow brightly colored corn at the fresh eating stage, my next selection criteria will be to take a pot of boiling water out to the field with me (or some really clever labeling methods to allow me to bring tip-samples back to the kitchen) so that I can select for colors that are retained while cooking. Maybe all I need is a propane torch: Cook a sample while it's still attached to the cob, or even one or two kernels in a test tube. Even now I ain't doing bad for colors in cooked corn at the fresh eating stage: That dark purple was more red before cooking.
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Post by 12540dumont on Sept 3, 2011 21:10:33 GMT -5
Joseph, shall I send you a camp stove?
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Post by Joseph Lofthouse on Sept 3, 2011 23:18:47 GMT -5
More on anthocyanins in purple corn (Peruvian morado). Blueberries have been tested to be among the best anti-oxidant foods. The purple corn they tested in the study contained 3-8 times more antioxidant activity than blueberries. www.liebertonline.com/doi/abs/10.1089/act.2007.13210
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Post by DarJones on Sept 4, 2011 19:27:44 GMT -5
I knew there had to be more to the story of "pericarp" and "seedcoat" as applied to corn. I finally found it when I read about "caryopsis". It turns out that in Poaceae (true grasses of which corn is a member), the pericarp and the seedcoat are permanently fused. It is neither seedcoat nor pericarp but rather caryopsis with distinctive layers representing the pericarp and other layers representing the seedcoat. I also found a reference that blue corn has hgher protein content in an article on Wiki. en.wikipedia.org/wiki/Blue_cornDarJones
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Post by Deleted on Sept 5, 2011 18:07:25 GMT -5
I read on another thread that while the anthocyanin pigments in corn provide antioxidant support for humans, they tend to make the plant less vigorous and lower yielding. I'm curious, because I want to breed high producing and vigorous varieties like Hickory King and Virginia gourdseed with antioxidant-rich cultivars like Maiz Morado and Double Red Sweet for a new variety with both size and anti-cancer properties. However, if the colored genes will weaken the final product, then I'd rather not make the cross. Anyone?
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Post by Hristo on Sept 5, 2011 18:48:29 GMT -5
I grew for first time Maiz Morado about 5 years ago after I read this article: cms.herbalgram.org/herbalgram/issue65/article2779.htmlBack then Solana Seeds were my seed source. Initially I hoped it's endosperm is purple too, but it was not. Then I wanted to breed purple sweet corn, and purple tasty dry corn, so I made a few crosses. Maiz Morado itself is a vigorous late variety, as tall as Virginia Gourdseed, but dislikes high temps. I see no vigour problems in it's progeny, so as for the vigour I see nothing to worry about. As for the (grain) yield - it's not a prime goal for me, so I have no conclusive observations.
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