Alternative theory for THC as protection from UV-B

[Nonpo]

An old study from the 80's caused quite a stir when posted on cannabis forums as it reported that exposure to UV-B light caused a proportional increase in THC production. The author of the paper hypothesized that because THC was an excellent absorber of UV radiation, and increased proportionally in response to UV-B radiation, that it's evolved biological function was to act as a sort of sunblock to protect the plant from being damaged by UV radiation. Ever since people have been adding UV lights to their grows and it does seem to increase THC as well as terpenes, but that explanation has never sat right with me.

Why does every other plant get along just fine without THC to protect it from UV? Why does cannabis itself get along just fine without this "sunblock" up until the stage where it begins to reach sexual maturity? THC is not there to protect the plant from UV, it does not increase with exposure to UV to protect the plant, it is there to help gather pollen that has been released from male plants that is riding on the wind. THC is very sticky and it is no coincidence that its flowers (the plant's sex organs) are what's covered in it, not its leaves or its stems. When you rub pollen onto the flower, it pollinates the bud and causes seeds to form. The larger the flower is, the more seeds it can produce if exposed to pollen.

Now ask yourself, what would increase the chances that the flower in question will be exposed to pollen and be able to produce seeds through sexual reproduction? Well, if the pollen is borne on the wind, then obviously the exterior of the plant would have a much better chance of getting pollen to hit it than the interior of the plant because there is better airflow, additionally possible bud sites inside the plant don't get as much light so they wouldn't be able to photosynthsize as much and form as many seeds. Therefore, cannabis would have evolved over time to dedicate its resources to areas that have good exposure to both light and wind. This is what we see, the plant puts more resources into producing flowers and THC at the tops of the plant. Budsites that are exposed to air and light produce more flowers and THC than ones deprived of either.

Now where does UV come into all of this? Well, the spectrum of light can tell the plant a lot of information. For example, if a seedling is under the shade of another plant, the spectrum of light reaching it will be different than it would be if it were in direct sunlight. Green light can pass through the canopy better as it is reflected off of chlorophyll. Far red light also passes through better because it is not absorbed by chlorophyll. Therefore if the plant is getting lots of far red and green light, it knows that it is in shade and will stretch vertically to reach the sunlight. Lots of UV, red, and blue light on the other hand tells the plant that it is getting direct sunlight.

Red light is always able to reach the plant, no matter what angle the sun is at and how much atmosphere the light has to filter through, however the shorter wavelengths of blue and UV light are scattered when the sun is at an angle and the light has to travel through more atmosphere. Therefore the proportion of blue/UV light increases as the sun gets higher in the sky and the overall irradiance increases. Only when the sun is directly overhead is the plant exposed to UV, so the plant knows that anything that is exposed to UV is not shaded at midday when the sun's intensity is at its peak and the plant's rate of photosynthesis is at its peak. It knows that it is the top of the plant in other words and therefore has the best exposure to both light and (pollen bearing) wind. This means if my theory is correct the plant would put more resources into these buds because it knows that they will have the best chances to gather pollen and have the best light exposure to photosynthesize for the seeds.

People report that UV-B is not the only spectrum that causes increased production of THC and terpenes, UV-A and blue or violet light also reportedly work which would make sense as they would all tell the plant the same thing essentially, that the part of the plant being exposed to that spectrum of light is getting full sun during mid-day when the plant's rate of photosynthesis is at its peak.

Any thoughts?

[Marine2143]

Aloha & Here is recent research from Seoul Semiconductor.https://issuu.com/amsterdamrai/docs/peter_barber.pptx

[Marine2143]

CMH HID & UV.

[unkle_psycho]

Don't really have any personal opinions on the matter. I used to think it was a stupid idea that the plant would protect itself by developing THC so late in its cycle, but while making seeds I realized the THC builds up just as the seeds mature, and it would make way more sense to protect the seeds then the plant itself. Plants making more THC when pollinated seemed in harmony with this idea.

I still feel the plant makes the THC pretty late, as it really piles on in the last two weeks of the plants life cycle... This delay would be even more pronounced if it were to collect pollen... Perhaps some kind of desperate last move as the hairs start to disappear? Next time I make seeds I can try to pollinate a bud at around week 7, when the THC starts raising fast. I would assume the plant is not very fertile at that point?

[Nonpo]

Don't really have any personal opinions on the matter. I used to think it was a stupid idea that the plant would protect itself by developing THC so late in its cycle, but while making seeds I realized the THC builds up just as the seeds mature, and it would make way more sense to protect the seeds then the plant itself. Plants making more THC when pollinated seemed in harmony with this idea.

I still feel the plant makes the THC pretty late, as it really piles on in the last two weeks of the plants life cycle... This delay would be even more pronounced if it were to collect pollen... Perhaps some kind of desperate last move as the hairs start to disappear? Next time I make seeds I can try to pollinate a bud at around week 7, when the THC starts raising fast. I would assume the plant is not very fertile at that point?

It would be very interesting to see a comparison between buds that are pollinated early vs buds that are pollinated late. I would assume it would create more when pollinated later because the flower is larger but I don't really know. Too late and it won't have time to actually produce the seeds before dying. I always thought the increase in THC at the end was a last ditch effort by the plant to put all resources into finding pollen so it could reproduce. It would just put out normal amounts at first, expecting in nature that it would be enough to get some pollen while it devotes more anabolic resources to growth of flower/stem rather than THC, but if it still hasn't gotten any when it's getting mature it would need to prioritize pollen gathering at the expense of other growth which is why you see plant growth essentially stop and THC production go into overdrive near the end. It may very well be that at this point the plant is past its peak fertility, but it's still trying to reproduce desperately and it needs pollen to do that.

[aulrich]

Could the late production of sticky resin be linked to getting the seeds distributed . Sticky seeds are more likely to get stuck a birds foot and spread the genes wider. There is no point in just dumping all the seeds in one spot.

There are native North American prairie grass seeds that need to go through the digestive system of a bison to actually germinate and by the time it has passed the seed is likely some distance away from the mother plant location and fertilized

[unkle_psycho]

Yes here in Scandinavia for example raspberries spread by birds too

Some people have suggested the function of thc is to screw the short-term memory of those who eat it, so they have less chance to find the plant to eat again. For sure many terpenes are to repel predators.

The best seeded plants in my narrow experience come in open pollination. The plant gets to make layers and layers of seeds, and will contain some immature ones if not left late.

I see many seedbanks sell small seeds, and while size varies a lot by strain, it also varies a lot by how early the plant has been pollinated. A 30g auto will produce hundreds of seeds, so if your not a cheapscate commercial producer it makes sense to pollinate early and get less but larger seeds.

If you go to check out hemp fields, you will notice that varieties with 0.1-0.2% of thc are still sticky, not sure if thc is an element in that. Interesting idea of animals transporting seeds that stuck to them - seems likely.

[Nonpo]

Actually, I've done some more reading on the subject and I think I might be wrong. It seems trichomes increase under UV exposure in a lot of plants, not just cannabis, and that the DNA in seeds is particularly fragile and needs to be protected from being destroyed or mutated. It seems that UV radiation hitting DNA causes mutations and produces photoproducts which block the transcription and replication of the damaged DNA which causes heritable mutations. Obviously not something the plant would want to expose its seeds to.

I also found that many of the secondary metabolites plants produce like flavonoids and terpenes can absorb UV and act as free radical scavengers to deal with the oxidative stress that UV exposure causes which may explain why the plants are smellier under UV. The essential oils that the plant produces around the flowers including cannabinoids and terpenes certainly are a wonderful multi-purpose protector for the seeds from many different threats, it's possible that UV certainly is one of them that I underestimated.

p.s. One interesting thing I came across recently was that trichome development can act as a sort of velcro to keep the flower bud shape growing properly and protect the seeds that will form.

[unkle_psycho]

From an evolutionary perspective when any life form has made its babies, the only evolutionary pressure left is the ability to provide some kind of advantage to that baby. As a human we stick around to provide our offspring with advantage, but many life-forms are not around to care for their babies... they still do what they can to provide safety and a good start to life to their seed. I was just showing my son a documentary on monarch butterflies, and the eggshell provides the first meal for the young. I've seen cannabis seeds sprout on the plant in autumn rain- surely a bad evolutionary move in scandinavia, perhaps not in some other area of the world.
Wonder if landrace varieties have higher THC in UV rich areas?

[QuantumMechanic]

I'm of the opinion that the "sticky" keeps the seeds protected from birds and other critters until they are mature. Birds love the mature seeds but don't seem to have much interest in removing them from the growing plant. (There's a company that makes bird repellent that's looks a bit like uncured silicone which stays sticky for a long time. Birds mess with it once and then don't come back. Apparently it's hard for a bird to clean "sticky" off its feet.)

It would make sense to protect the developing seed from UV. But the trichomes cover the whole plant, if you look close enough. And they do seem to contain a substantial amount of THC.