419 and Holding

Ah, good point penguin! I got so caught up in The Fool's questions about auxins, I forgot to go into anything else too much...


Hmm.....now you are taking me back a few semesters...(can you believe they call this stuff general biology?!?) But yes, you are correct....I forgot that cellular respiration wasn't part of the "dark" (or as you so aptly called it, "light-independant") cycle. Since you seem very educated on the processes already, I'm just going to reiterate (with some nice pics and diagrams) for those out there still curious.

Photsynthesis converts solar energy (light) into the chemical energy of a carbohydrate. This is the formula for photosynthesis:



There are 2 cycles involved in photosynthesis, as I (and penguin) stated: light-dependant reations, and light-independant reactions. BOTH of these are involved in PHOTOSYNTHESIS, as penguin pointed out. (Not what I said earlier: that the dependant reations were photosynthesis, and the independant reations were respiration.....not true).

The light-dependant reactions consists of photosystem I (cyclic phosphorylation, which produces ATP (energy)), and photosystem II (non-cyclic electron transfer, which splits water molecules to harvest electrons, and produces ATP and NADPH).

The light-independant reactions is also called the Calvin Cycle (again, as penguin pointed out), and basically uses the energy (ATP and NADPH) produced in the dependant reactions to reduce CO2 into glucose.

Check out this diagram:


This is all that happens in the "dark" cycle of plants.


Now this is where I became confused earlier. Cellular Respiration is almost like the "opposite" of photosynthesis. You can see this when you look at the formula for respiration:


You can see the reactants are the same as the products in photosynthesis, and vise versa.


Cellular respiration is where most of a plants chemical energy (ATP) is manufactured. Respiration consists of 4 phases:

Glycolysis (yields 2 ATP),
Pyruvate Oxidation (oxidation reaction; pyruvate is a product of glycolysis),
Krebs Cycle (yields 2 ATP),
Electron Transport Chain (yields 32-34 ATP)

The net ATP molecules produced from one cycle of cellular respiration is 36-38.

As you can see, the main manufactuer of ATP is the Electron Transport Chain (ETC). This is located in the cristae of mitochondria, and is a series of protien carriers. Electrons carried by NADH and FADH2 enter the ETC, and as a pair of electrons is passed from carrier to carrier, energy is released and is used to form ATP molecules by oxidative phosphorylation.

This is where plants get most of their chemical energy from. As penguin said, without photosynthesis (the formation of glucose), cellular respiration could not happen. So by keeping the lights on 24/7, we are allowing photosynthesis to occur all the time, thus allowing more energy to be manufactured quicker.

Here's a diagram of how photosynthesis and cellular respiration work together:



On the left is photosynthesis ("light" cycle at the top, "dark" cycle - the calvin cycle - at the bottom), and on the right is cellular respiration. As you can see, these two go hand in hand.



He said it.


Well, this may be accurate, but when I think of "optimizing growth", I don't factor in electrical costs and yada yada yada. To me, optimizing growth is all about the ladies. Money should play no part in how well we "optimize" their situations. When you bring electricity and other factors into the equation, I consider that to be the most efficient growth, but not optimized. To me, optimized growth and maximum growth are one in the same. We cant become ignorant and keep thinking of ourselves (money) if we want to give out girls the best. Just my opinion though.


So, in a nutshell again (and to tie it all together), photosynthesis includes both light-dependant and light-independant reactions. The outcome of photosynthesis is glucose, which is then used by cellular respiration to manufacture chemical energy for the plant (to grow). The plant then uses this energy (in conjuntion with the IAA auxins) to promote fast, healthy root and shoot growth. Neither the production of this chemical energy, nor the production/use of auxins, depends on a "dark" cycle, and thus, plants CAN be kept in 24 hours of light with no bad effects.

So there we have it. Thank you penguin for the nice point-outs of my mistakes. I like a person who makes me pick my brain! Sorry for the confusion, folks.

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-4:19
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The Fool

Wow, alot of info to soak in.

Ah, so it's not the dark that makes the IIA travel, it's the light!

I can't really say much else as you both have elaborated quite in-detail.

So, other than the fact the HID lights can't be run 24/0 (without serious damage to bulb or self), why doesn't everyone use 24/0; why is there still an arguement?

4:19 and Holding and penguin, your helpfull info has brought me to better understand my plants, as well as how to optimize their potential. Karma to ya!

So a little editing of the foundation has been made, and I can now build upon solid ground.



P.S. I read my botany material from an older book. It uses the term "terminal bud" for what you call the "apical meristem". I've just been accustomed to calling it that.

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Potheads
Against
Tobacco
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"The idea is to remain in a state of constant departure, while always arriving. It saves on introductions and goodbyes." -Bill Wise, Boat-Car Guy

PAST GROWS:
BS Sativa

CURRENT GROW STATUS: Grape Punch [Bogglegum x Lifestar] Mother Grow: Pending

419 and Holding

Well.....I don't know that HID's cant be run 24/0.....I mean I know that people DO run MH's for 24 hours...and they are HIDs. I've never heard of damage to bulb or anything, but I'm sure its a possibility.

But actually it's just a matter of preference. Alot of growers run high-wattage lights, so turning them off for 6 hours (1/4 of the day) saves them that much on electricity. Plus it gives the room time to cool off some (as well as bulb and ballast). Since there isn't a need to run the lights 24/7, alot just opt not to.
Myself personally, I do run my lights 24/7 for the whole veg. cycle. Just makes it easier (IMO) without the hassle of timers (and possible malfunctions of said timers) and whatnot. Also, having a dark period takes away from time I can potentially spend with my ladies.

So, it's not an "argument".....just a matter of preference.



Ah! Understood. In that case, the auxins don't need to "travel" from the terminal bud to the roots, because the root tips are 'terminal buds', or meristems. Meristems (terminal buds) are simply places where mitosis (and thus new growth) occurs.

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-4:19
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pearl

Preview Excellent reading material from you guys.
I certainly enjoy the theory behind any projects.
Fillabong did a great piece on Photosynthesis.

"The Fillabong Show - Photosynthesis"

Did anyone come up with the big answer ?

Is it better to go 18/6 or 24 with the little ladies ?

I like the idea of a rest period to relax and take everything in.
Just a personal preference. It just makes sense to me.
I've done no experiments or testing just a personal preference at this time.
Actually I've done it both ways. [24/7 and 18/6]

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Pearl's Drip System ~ Fall Harvest 2006 ~ Live Predators

419 and Holding

Well pearl, I don't know if this is "the big answer" you were looking for, but it's what I came up with...



As for the lighting versus root growth debate, I think we determined (someone correct me if they feel otherwise) that 24/7 was the way to go, but obviously 18/6 would work just fine too. Only minor advantages (constant light= constant photosynthesis = constant glucose creation = constant cellular respiration = constant chemical energy = constant growth!!!)
with having the light on 24 hours a day....

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-4:19
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penguin

Excellent diagrams, 419

I don't really think that the question has been settled on the basis of yield (even without regard to cost). 24/0 increases yield in some crops (e.g., lettuce, peppers) and actually hurts yield in others (e.g., tomatoes). Some crops do benefit from extended daylength, but with no difference in yield between 20/4 and 24/0.

Extended/continuous lighting does generally reduce chlorophyll count, so if very long days do increase growth rate in veg, this may come at a cost to maximum photosynthetic capacity in bloom, and therefore actually hurt yield.

The bottom line is that the impact on needs to be determined experimentally, and we can expect some variation based on genetics and style of grow. If very long days are beneficial at all, this is only likely to have a noticeable difference for plants that are given a long period of veg (e.g., ScrOG from seed), and not likely to have any measurable impact in a SOG.


penguin

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