Triggering flowering by manipulating hours of light

[Daemos]

It is true that there are other metabolic pathways that the plant uses to measure nightlenght. The phytochrome changes it state when no more excitated by certain wavelenghts of light. It is only so that the moonlight plays a strong role in the deactivation of the phytochrome. I am not known with the structure of this certain compound so I do not know how it changes on a molecular scale. It is certain though that the plant measures the night and not the day. On cloudy days the phytochrome is still activated but in a slower rate. It has to be really dark though if you want to upset the plant good eg. no full conversion of the phytochrome.

It is all about deactivation and reactivation and there are many debates on how the plant exactly does that. It is proven though that the moonlight does play a role in the proces but is not a must for the plant to operate properly.

Hope this helps

[Royal]

Daemos, Thanks for elaborating. It's nice to have a civil conversation on this topic. All too often, these subjects bring out the "I'm smarter than you" attitude. This board really is great. Keep the info coming -- I love to learn!

I want to make sure I understand what you mean. Are you saying that it is moon light that de-activates phytochrome? Does this mean that during a completely dark night, when the moon is not out, that phytochrome is still active because there is no moon light?

I was thinking about this topic over the weekend. I can see how moon phases may play a role, especially in equatorial regions where day length does not fluctuate as much seasonally. But I still tend to believe that the majority of plants, including orchids, would measure photoperiod by the presence and absence of usable light.

[Ross]

Originally Posted by RoyalOrchids

But I still tend to believe that the majority of plants, including orchids, would measure photoperiod by the presence and absence of usable light.

I tend to agree, otherwise how does one account for the plants being grown and bloomed faithfully in basements under constant 12 hours of light/no light? As a matter of fact, I have an Angraecum that may be finally starting to spike after I moved it down to orchidarium from its previous home in a south window. I'm not convinced on the "moon thing".

[Daemos]

Its actually the moonlight that plays a role but is not a must. See it in the chemical way (no I am not sure if this part accounts for the phytochrome in the same way but Ill explain anyway) Somethimes a molecule is not stable in its current state. For example there are a few sugars that change their molecular state by itself at room temperature. Plants invented clever molecules that change into the "active" state when excitated with UV radiation. When the energy is gone (the UV light). The molecule starts changing back into its most stable state "deactivates". You can say there is a equilibrium between two stable molecular states and one lies in a little bit higher energial range. Somehow moonlight katalyses this deactivation process. So with moonlight the moleculs deactivate quicker. Suppose the night lasts for about 8 hours the phytochrome will fully deactivate, with or without moonlight. With very short nights less will deactivate. The moon will make the nights simply look longer to the plant. If it is a huge difference concerning with or without is a issue. I grow all plants near a window but it would be a cool experiment to see how much it really matters.

I don't know how accurate plants are in doing this but I remember reading somewhere it is in +/- 1 hour precision and the moon makes it a little preciser.

Hope this clears things up