Hey growers, I know this may be TLDR for folks, but if you do check it out, I'd love to hear any feedback, comments or corrections. I always search out this stuff and do write ups because it is all part of the learning process. So please share and let me know your thoughts on the topic after reading the study or my review of it. Cheers!
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#ChadWestport #HighScience #CannabisGrowing #TPC
Publication: Frontier Plant Science
Peer Reviewed: Yes
Authors: Tesfamichael H. Kebrom
Published online 2017, Oct. 31
Title: A Growing Stem Inhibits Bud Outgrowth - The Overlooked Theory of Apical Dominance
Most of the growers who are aware of Apical Dominance, point to it as the impetus for why they trim or train their plant. The general understanding is that the plant sends auxins (which promotes growth) to the tallest branch, which is why we aim to get a nice level canopy on our plants. Apical dominance is also cited as a reason for topping the plant, based on the knowledge the plant will redistribute those auxins to other, lower branches and promote their growth. But what if I said it wasn’t so simple?
I was alerted to this research by BerkshireBud and it proved an interesting read.
Background:
Three theories for apical dominance have existed since the 1930s, Direct, Diversion and Indirect. Over eight decades, the first two theories have been heavily studied and were adapted to Auxin Transport Canalization and Second Messenger theories, respectively. However, neither can fully explain the phenomenon of apical dominance. The indirect theory developed in the 1930s has thus far been largely overlooked, but this study brings new insight to the inner-workings of the indirect theory.
What is the Indirect Theory?
Recent discoveries have been made indicating that “a growing stem is a strong sink for sugars, and sugar is indispensable for shoot branching, the indirect theory of apical dominance might now be explained as auxin-induced stem growth inhibits bud outgrowth by diverting sugars away from buds”.
***When they say “buds”, they are referring to new growth of lateral branches, not the big stinky green buds we all love. But it’s from their buds that we grow our buds.
How does it work?
In peas, the sugar level in a dormant bud increases when the bud is stimulated to grow by decapitation that removes a growing shoot tip. In addition, dormant buds in intact pea plants grow when directly fed with sucrose providing conclusive evidence for the significance of sugars for bud outgrowth.
Sink organs, such as the stem and newly formed leaves can limit sugar availability to buds. In the presence of strong sink organs such as a growing stem and limited sugar production in the main shoot, buds may become dormant. Auxin-induced stem growth indirectly inhibits buds by depriving sugars necessary for their growth. Size of internodes adjacent to the buds determines the sink strength of internodes for sucrose utilization and storage, and indirectly regulates availability of sugars to buds.
One of the ways for there to be limited sugar production, is by the removal of leaves and the loss of sugars generated through photosynthesis. This study states “A small reduction in photosynthetic leaf area due to disease or herbivory could result in the inhibition of bud outgrowth in particular during the early stage of plant growth and development”.
***Peas, like Cannabis are a dicot. Both monocots and dicots were used in this study, but I tend to reference the material regarding dicots.
Why is this important?
This brings more depth to the function of apical dominance, something we use as a tool to manipulate the growth of plants. Plants create sugars through photosynthesis but they are also able to absorb sugars from the rhizosphere. Using this theory, adding more sugars to the nutrient mix would increase your lateral growth when you have a healthy rhizosphere with microbial activity. The study in its summary states “Shoot branching might be an unintended consequence of source-sink relationships and result from an overflow of sugars to auxiliary buds that cannot be utilized by the main shoot”.
Key Take-aways;- Minor defoliation of a young plant could inhibit growth of lateral branches
- Sugars play a large role in the shoot growth
- Application of cytokinins directly to bud sites will encourage shoot growth
I didn’t include mention of Cytokinins, although this study does report that when cytokinin levels are higher than auxin levels, the plant will focus more on shoot development instead of root growth. Cytokinins are a PGR and I’m unaware of their systemic values and chemical stability when combusted, which is why I didn’t include much information.
One interesting note was that “buds in cytokinin deficient Arabdopsis plants (a dicot as well) grow in response to decapitation”. This shows that “factors that control shoot branching by acting outside the bud override those that act within the bud and induce or inhibit bud outgrowth”. However “cytokinins promote bud outgrowth when applied directly to the bud”.
Summary;
Keep in mind, the Indirect theory is one of three working theories on apical dominance. All environmental controls and nutrient levels are presumed to be at optimal levels. In the future, hopefully we will have similar tests using Cannabis plants, but much of plant science world has yet to take on the task.
It does however beg the question of should I be adding more sugars into the food and using microbes as the intermediary to the roots in order to promote better bud growth on my plants? “When investigating plant growth and development, sugar demand and supply should be taken into consideration”.
Link to study - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5671643/-
ChadWestport appreciate you breaking it down and dropping knowledge on folks like me who don’t have a botany PhD, thanks!
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Interesting, needs much more study! I have related trimming leaves off with lack of growth on plants many moons ago. A foliar feed may be made to promote this growth, maybe something for the roots as well. I have tried GA3, did not see much if any response.Comment
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Very welcome My friend. Do some research on the best ppm concentration i cant remember right now but it's around 100-250ppm of ga3 in the soaking water -
Just to round out the Ga3 discussion, here's the best concise advice I've found on creating Fem/Fem seed :
"I breed auto's and feminized plants but don't use colloidal silver. I use gibberilic acid which I find easier to work with. 2 grams per litre, twice a day until they have flowered and you have pollinated your females.
Not unusual to get several thousand seeds from a well grown female."
I can't remember where I collected that quote, but it has worked for me for inducing Fem plants to produce seeds. Kudos to ??? for the tip.
Knowledge is Power,
-Grouchy
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Good reading especially when it's about sugar's role that it plays in.Light: Viparspectra P2000, Viparspectra P1500, Viparspectra XS2000, KingLed 1500
Medium: organic, Fafard perlite, Fafard Urban Garden organic mix, Organic compost shrimps.
Nutrients: Alaskan Fish, Advanced Nutrients Big Bud, Advanced Nutrients Ancient Earth, Advanced Nutrients Sensi Cal Mag Xtra
Full auto grow
Grow room : 8X12X10, 2 industrial fans, 1 dehumidifier, 1 Vivosun carbon filter & controller
12 Wild Thailand Ryder from WOSComment
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Thanks Farmbuck I had to give you something in exchange for all the bud and hash cake porn
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Bienvenue ChadWestport , on the sugar subject, have you ever heard of blackstrap molasses powder ? I'm curious to find out if it is better than liquid. -
I haven't tried the powder, but the powder is going to be a derivative of the original with maybe a few other things in it. Without knowing much about it, I'd probably still go to the original liquid stuff. Whenever I use powders as top dressings, my soil tends to get a little hydrophobic after awhile. I stopped using them.
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I had to look up what TLDR meant. Lol.Comment
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Enjoyed the science, as always. I'm pretty sure I didn't understand half of what this says. Maybe I should have read this before I hacked off some fan leaves that were dragging in the dirt. How young is "a young plant"?Comment
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Great question, it wasn't defined as a particular height, leaf mass or age, but I would guess three weeks or younger. At that point there are more roots and more leaves for photosynthesis. It is a good idea to clean up any lower leaves that are touching the soil, for a variety of reasons, but I generally do that after week three when there has been additional growth to offset the loss of solar panels.Comment
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With regards to sugars that can be lost when defoliating, would it then be wise or beneficial to give molasses after defoliation to help replace any sugars that are lost? Or would it be absorbed/taken in, in a different way and so would make no difference?3'x3'x6' Secret Jardin grow tent
Fox 6" carbon filter and fan with acoustic ducting
Kocheal 2000w (actual 255w) Led
Couple of fans for airflow
First grow 2x RQS Fat Banana 1 x Silver leaf Critical crack og. All photo
Soil, plain multi purpose compost with perlite added
Nutrients - Bio Bizz Calmag, Grow and Bloom.
Yellow under blurple makes fluorescent orange 😀Comment
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I think that would be a great thing to try buds73 I personally want to set up an A & B comparison next time I clone. From what I get from the study, excess sugar that isn't used by the main stem for growth will be redistributed to bud sites and encourage growth. I'm still searching for negative effects of too much sugars in the root zone, but so far, the information doesn't jump out in search results as a red flag.Comment
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It would be interesting to see the results of a side by side comparison. Maybe the real reason why molasses are used towards the end of flowering is to replace sugars that are lost through the amount of leaf lost/colour changes and not necessarily to fatten or sweeten the taste of the buds although it seems it may just do that to which brings up another question of whether sugars provided by molasses have a greater benefit than sugars provided by the leaves/plant itself?
As for excess sugars in the root zone or in soil I do wonder whether that could be more of an invitation for pests -
I smell what you're cooking and I like it. That is a great hypothesis.
Excess sugars in the root zone could be an invite for certain pests but I think through smart management it could be avoided.
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