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Tea and Terps · Episode 4
Over a fifteen-year-old ripe pu'er from Bulang Mountain, Nik and Travis follow the B vitamins into the plant: not as supplements, but as working parts of its enzymes, all along the way from sunlight to a cannabinoid.
The cup
Nik's cup is a ripe pu'er, or shu: Bulang Old Tree 2011 from Tea Hong, a stone-pressed cake of spring 2011 leaf from Bulang Mountain in Xishuangbanna. That is Yunnan's far south, where China meets Myanmar and Laos, and the mountain carries the name of the Bulang people, who have grown tea in these forests for generations.
Ripe pu'er is made by wetting and heaping the leaf so that microbes ferment it. Nik calls it wet-piled compost with a remarkable craft wrapped around it. Nik puts a typical shu at 30 to 45 days in the pile; the maker says this one had about 75, and the extra time shows as a soft, mellow cup with almost no astringency. It is also very hard to brew badly. Nik has left ten grams in a liter thermos of boiling water for twelve hours, and it still did not turn bitter.
What Nik noticed
Special notes
Nik chose Jianshui for this session; his usual preference for shu is wood-fired duan ni.
Nik's account of the process. The pile does most of the work; in his experience, once the cake has rested a year or two its flavor changes little.
| Grade | The leaf | In the cup |
|---|---|---|
| Grade 0, gong ting | The finest young buds, golden and downy | Flavor up front that fades after three or four steeps |
| Grades 1 to 9 | Larger leaves from further down the shoot | Slower to open; the flavor peaks in the fifth to seventh cups |
| Huang pian | Mature yellow leaf | Gentle, and low in caffeine |
The youngest shoots hold the most caffeine, which is why a bud-heavy tea can feel quicker. Blending grades gives a tea both an opening and a long finish.
Chapter by chapter
Press any time to play the episode from that moment. While it plays, the chapter you are in lights up.
The family
Vitamin is a human word. It names molecules our bodies cannot make and have to eat, and the B vitamins were numbered as they were discovered, with gaps where compounds were later dropped from the list. Plants make nearly all of them for themselves, so for a plant the useful question is not whether it has its B vitamins, but what each one becomes inside the enzymes that use it.
Nik has two pictures for why that matters to a grower. Walking a steel beam into a finished building does not make the building stronger; the beam has to be built into the frame. And you would not bring a glass of milk to a dairy farmer with 420 cows. A vitamin that an enzyme depends on is not proof that feeding more of it will raise what the plant makes, because the plant already builds its own and puts each one exactly where it works.
I wouldn't give a glass of milk to a dairy farmer.
Nik
| Vitamin | Working form | One job in a plant |
|---|---|---|
| B1, thiamine | Thiamine diphosphate | Joins carbon pieces where the terpene pathway starts |
| B2, riboflavin | FAD and FMN | Moves electrons, colors carotenoids, makes THCA |
| B3, niacin | NAD and NADP | Carries the energy of light as NADPH |
| B5, pantothenic acid | Coenzyme A | Carries carbon groups such as acetyl and malonyl |
| B6, pyridoxine | Pyridoxal phosphate | Moves amino groups between carbon skeletons |
| B7, biotin | Biotin bound to its enzyme | Adds the carboxyl that makes malonyl-CoA |
| B9, folate | Tetrahydrofolate | Carries single carbons toward methylation |
| B12, cobalamin | None known | Flowering plants work without it |
Plants make every one of these except B12 for themselves.
B1, thiamine
Thiamine works as thiamine diphosphate, and one of its jobs is at the first step of the terpene pathway. Inside the plastids, an enzyme called DXS uses it to join pyruvate and glyceraldehyde 3-phosphate, three carbons each, into a five-carbon sugar, releasing one carbon as CO2. That opens the MEP pathway, which builds the five-carbon units behind monoterpenes, carotenoids and the terpene half of the cannabinoids. Sesquiterpenes come mostly from a second route in the cytosol, which starts from acetyl-CoA instead.
The same cofactor runs transketolase, the enzyme that reshuffles sugars in the Calvin cycle. One of the sugars it makes, the four-carbon erythrose 4-phosphate, opens the shikimate pathway toward phenylalanine, and phenylalanine supplies one of the rings of every anthocyanin. So one cofactor works near the start of two very different families, the terpenes and the anthocyanins.
Thiamine also holds a magnesium ion inside its enzyme. That is part of how the enzyme works, not a way of carrying magnesium around the plant, so it does not make thiamine a magnesium fertilizer.
B2, riboflavin
Riboflavin is yellow, and plants build it into FAD and FMN, the flavins. Nik's favorite example of what they do is carotenoid color. Phytoene, the first carotenoid, is colorless. Desaturation, which starts at an enzyme holding FAD, pulls hydrogens off its chain two at a time and hands the electrons on to plastoquinone. Each pair removed lengthens the run of alternating double bonds that absorbs light: with eleven in a row the molecule is red lycopene, and when its ends close into rings it is orange beta-carotene.
Flavins also sense light. In cryptochromes, the blue-light receptors, FAD absorbs blue light and starts a signal; it is a sensor, not part of photosynthesis. And at the far end of the cannabinoid pathway, THCA synthase and CBDA synthase both run on FAD, which the two branches below come back to.
you end up with a carotenoid that you can actually see with your eyeballs.
Nik
In the order the plant makes them. The numbers count the double bonds in the alternating run; each step of desaturation removes two hydrogens and lengthens it, shifting the light absorbed toward red. Closing the ends into rings twists the last bonds out of line, which is why beta-carotene looks orange rather than red.
Real structures
Six vitamins in the forms enzymes actually hold, rendered from real PubChem geometry rather than drawn. Pick one to read its job, then turn it in three dimensions.
Vitamin B1 with two phosphates added, the form enzymes hold. It lets DXS join two three-carbon pieces into five at the start of the terpene pathway, and lets transketolase reshuffle the sugars of the Calvin cycle.
Structure data: PubChem open chemistry database
Vitamin B2, the yellow vitamin. Plants build it into FAD and FMN, the flavins that move electrons in carotenoid desaturases and in THCA synthase, and that sense blue light in cryptochromes.
Structure data: PubChem open chemistry database
Built from vitamin B3. With one more phosphate it becomes NADP+, which light charges into NADPH in the chloroplast; the plant spends that charge to fix carbon and build terpenes, then charges it again.
Structure data: PubChem open chemistry database
What vitamin B5, pantothenic acid, becomes. The sulfur at the end of its long arm carries carbon groups such as acetyl, malonyl and hexanoyl, then lets them go, so the same carrier is used over and over.
Structure data: PubChem open chemistry database
Vitamin B6 in its working form. It holds an amino group while an enzyme moves it from one carbon skeleton to another, and in tea it runs the enzyme that turns glutamate into GABA.
Structure data: PubChem open chemistry database
Vitamin B7. Bound to acetyl-CoA carboxylase, it carries a carboxyl group from bicarbonate onto acetyl-CoA to make malonyl-CoA, and that carbon leaves again when the polyketide chain is built.
Structure data: PubChem open chemistry database
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B3, niacin
For anyone who knows the chloroplast, Nik's aha moment is that B3 makes the redox pairs. Niacin is built into NAD and NADP. When light drives electrons through the photosystems, NADP+ is loaded with a hydride, a proton traveling with two electrons, and becomes NADPH; in the mitochondrion its cousin NADH does the same job for respiration. The enzyme that does the loading holds FAD, so B2 and B3 work together.
The Calvin cycle spends NADPH to turn carbon dioxide into sugar, the MEP pathway spends it on the way to the plastid's terpenes, and in a tea leaf an NADPH enzyme, anthocyanidin reductase, makes the epicatechins that tea's catechins are built from. Every purchase empties the wallet and light fills it again. That is Nik's point about B3: its job is so central and so tightly regulated that adding more from outside is unlikely to make a plant capture more light.
It's the wallet that is opened up more often than pretty much any other reducing agent
Nik
B5, B7 and the cannabinoid
A cannabinoid is half terpene and half polyketide, and the two halves come from different pathways. The terpene half is the one B1 opens and NADPH from B3 drives, ending in GPP, ten carbons long. The polyketide half runs on coenzyme A, which is what B5, pantothenic acid, becomes. The name comes from the Greek for from everywhere, because Roger Williams, who identified it in 1933, found it nearly everywhere he looked.
Coenzyme A carries the pieces: acetyl-CoA, malonyl-CoA and hexanoyl-CoA. Biotin, B7, is bound to the enzyme that turns acetyl-CoA into malonyl-CoA, adding a carboxyl group from bicarbonate. One hexanoyl and three malonyl units then fold into olivetolic acid, and the carbons biotin added fall away again as CO2. The carriers are used again and again, so they make the cannabinoid possible without becoming part of it. A prenyltransferase joins GPP to olivetolic acid to make CBGA, and THCA synthase or CBDA synthase, each holding FAD from B2, finishes the job.
The varins, such as THCV, follow the same plan from a shorter acid, divarinic acid, so their path splits before CBGA. Ask whether B vitamins are involved in cannabinoids, Nik says, and the better question is which step you want to talk about.
They're known as terpenophenolic compounds.
Nik
The terpene half the MEP pathway, in the plastid
The polyketide half coenzyme A chemistry, in the cytosol
GPP meets olivetolic acid: CBGA
A prenyltransferase joins the two halves, with magnesium. No vitamin works at this step.
CBGA becomes THCA or CBDA
THCA synthase and CBDA synthase each hold FAD, made from B2. It takes electrons from CBGA and hands them to oxygen, which leaves as hydrogen peroxide, and the FAD is ready for the next molecule.
B2 · FADEach badge names the vitamin and the working form its enzyme holds. A step that depends on a vitamin does not show that feeding more of it raises the output: the plant makes its own, and each carrier comes out of the reaction ready for the next.
B6 and the antioxidants
B6 works as pyridoxal phosphate, and Nik places it at the step where nitrogen is passed between carbon skeletons. It holds an amino group in place while an enzyme moves it from one skeleton to another, so amino acids, organic acids and much of what is built from them trace back to it. That includes glutathione, the antioxidant no plant cell can live without, assembled from three amino acids that B6 enzymes help supply.
Antioxidants are meant to be recycled. When glutathione neutralizes an oxidant it pairs up into its oxidized form, and glutathione reductase recharges it with NADPH through its own FAD. That recharge is B3 and B2 at work rather than B6, and it is why one molecule can neutralize oxidants again and again. Anthocyanins behave the same way with light: they absorb it, shed the energy as heat and recover, which costs far less than building new pigment.
Cannabinoids may play the opposite part. Nik's idea is that they work partly as a photochemical sacrifice, absorbing some of the light the plant cannot use and breaking down in its place, like a car drifting through a corner with power to spare. That is a hypothesis, not a settled fact, and the two sit in different parts of the plant anyway: anthocyanins dissolve in the watery cell sap, while cannabinoids collect in the oily, almost waterless head of the trichome.
The antioxidants that plants produce are meant to be recycled.
Nik
| Compared | Anthocyanins | Cannabinoids |
|---|---|---|
| Dissolve in | Water, in the cell sap | Oil, in the trichome head |
| Made from | Phenylalanine and malonyl-CoA | GPP and olivetolic acid |
| In strong light | Absorb it, shed it as heat, recover | Perhaps absorb some and break down, in Nik's view |
Back to the cup
The same machinery runs in the leaf in Nik's cup. Caffeine carries three methyl groups, and each is added by an enzyme using SAM, the cell's methyl donor. Folate, B9, keeps SAM supplied by way of methionine, and in tea, as in every flowering plant, that step works without B12. B6 runs the enzyme that turns glutamate into GABA, and NADPH from B3 makes tea's epicatechins.
Then there is the word itself. Vitamin C is a vitamin only for us: people cannot make ascorbic acid, sailors without it got scurvy, and the Royal Navy's citrus ration is how British sailors came to be called limeys. Plants make it for themselves as an antioxidant. Inositol, sometimes listed as B8, is a six-carbon ring that plants make from glucose. And B12, the vitamin of the old grow-store sprays, has no known job in a flowering plant. Nik's guess is that any benefit from Cheech's B12 spray came from something other than the cobalamin, perhaps the methyl group it carries, though nobody has shown a plant can use it that way.
Vitamin C is something that plants make themselves.
Nik
| Molecule | For us | For the plant |
|---|---|---|
| Vitamin C | Must be eaten; without it, scurvy | Made from sugar, as an antioxidant |
| Inositol | Made in our own bodies | Made from glucose, a six-carbon ring |
| B12 | Essential, from animal foods and microbes | No known use in flowering plants |
Moments worth rewinding
Moments from the clip archive. Each one plays the full episode from where it starts, and the shorts play on their own.
B6 sits where the plant decides which carbon carries which nitrogen
Pyridoxal phosphate holds an amino group in place while the carbon skeleton around it moves.
Nik asks whether B vitamins are the next big additive, and where the evidence actually stands.
Three-carbon sugars build up to five, and B1 is there at the step that starts the terpenes.
Where nitrogen is passed from one carbon skeleton to another.
Glutathione is recharged rather than used up.
Nik's picture of cannabinoids as a way to spend light the plant cannot use.
Why anthocyanins stay in the plant's watery tissue and cannabinoids in the resin.
Inositol, scurvy, and why a vitamin for us is simply a molecule for a plant.
Keep listening
Episode 4 follows the B vitamins into the plant's machinery, and Episode 5 picks up the pigments they help build.
Episode 3 · The one beforeQ&A and Bing DaoListener questions and how Rooted Leaf works, over a Bing Dao pu'er.
Episode 5 · The one afterPigments and GyokuroPigments and gyokuro: the colors of a leaf, from chlorophyll to anthocyanins.
Episode 1 · Where it beganCarbon and Fenghuang OolongCarbon, the element plants are built from, over a cup of Phoenix oolong.
