This series of posts will highlight the plants that help you celebrate the Yuletide season.
Happy New Year! Today’s post includes not just one plant but several plants that are a requirement for the traditional New Year’s feast in the South. We’re talking about greens and black-eyed peas. Tradition dictates that the greens will bring money and prosperity for the New Year, and black-eyed peas will good luck. There may not be much research to support these claims, but there’s lots of studies behind these Southern staples.
In my house, the green of choice was always cabbage, but over the years my tastes have expanded to accommodate many different cruciferous vegetables (collards, turnip and mustard greens). They may or may not bring you more money, but they are good for you. Of course, these foods rarely top the lists of favorite vegetables for children and let’s face it, those of many adults. Why? You’re probably already crinkling your nose, and, yes, many mandatory New Year’s servings of cabbage are eaten with pinched noses. So what’s the science behind the scent? Special metabolites that these plants make called glucosinolates (plant biology word of the day).
Glucosinolates (above) are made up of a sugar molecule attached to a sulfur and nitrogen-containing group. Plants make these as a defense system against insect herbivores. By themselves, they are not smelly or toxic. It is only when the glucosinolates are broken apart into the sugar, sulfate and other pungent molecules that they stink. Think of them as landmines within your vegetables. This is why the produce section doesn’t constantly reek of sulfurous gas. So how are these landmines set off to protect the plants from insect herbivores? Plants have a sophisticated activation system. They make the glucosinolates and store them in one cellular compartment, but the enzymes responsible for the breakdown (explosion) are stored in a separate compartment. When insects start chewing on cabbage (or the leaves of other greens), the contents of these compartments mix together and the defense system is active. The concentration of the glucosinolates is higher in younger plants and lessens as the plant matures. This protects young plants from being eaten beyond repair, then as the plant is finishing its life cycle, it doesn’t have to spend as much energy on its defense system.* This temporal regulation also works out nicely for us humans, by protecting these leafy greens as they grow, but mellowing the flavor by harvest time. Of course, no defense system is perfect. Fierce competition leads to countermeasures and some insect specialists have their own biochemical specializations that inactivate glucosinolates.
Black-eyed peas are not really peas (Pisum genus), but beans- Vigna unguiculata subsp. unguiculata. These plants originate from West Africa and do well even in very poor soils. It’s not just a lucky food for humans but is also grown for nutritious animal fodder and as a cover crop. This hardy legume is grown to fortify soils with nitrogen extracted by more demanding species. They basically make their own nitrogen fertilizer.** Black-eyed peas and other legumes don’t do this on their own, but through soil bacteria called Rhizobia. These plants and bacteria have a longstanding mutually beneficial relationship. Rhizobia have an enzyme that can convert nitrogen gas into a form (ammonium) that plants can use. The plants allow the bacteria to colonize their roots forming nodules. Legumes donate some of the sugars made by photosynthesis to them, and, in return, the bacteria share the ammonium they make with their plant hosts. This gives legumes access to the abundance of gaseous nitrogen in the air. Other plants (like corn) don’t have this special friendship with Rhizobia and must rely on ammonium and nitrates present in the soil or added there in the form of fertilizers.
Despite the food traditions we associate with these plants, they don’t have to rely on money or luck. They have elaborate biochemical systems that ensure they make it through the New Year.
Good Luck for the New Year and Geaux Tigers!
*That sounds like a smart investment, maybe there is a connection with money after all.
**Lucky trait indeed.
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