Regarding #1, not a myth;
"We exposed plants to T cycles ranging from 16 to 32 hr comprising a proportion of light to darkness equivalent to an 8L16D short day. ...
We monitored the effects of the same T cycles on flowering time by counting the number of primary rosette leaves at the time of flowering (Fig. 4A). The number of leaves formed before bolting is closely correlated with the number of days to flowering (25). Interestingly, T cycles shorter than 24 hr delayed flowering, suggesting that some degree of photoperiodic induction does take place under standard (8L16D) short-day conditions. How- ever, flowering was accelerated under 28-hr and 32-hr T cycles. Thus, T 28 hr short days were not perceived as inhibitory, even though the duration of the photoperiod was only 1.3 hr longer than under T 24 hr short-day cycles."
So;
Dark<16 hours of darkness pre-flowering prolongs flowering.
Flowering is accelerated by long periods of darkness; Dark>18.66 and Dark>21.33.
Link-
http://www.pnas.org/content/99/20/13313.full.pdf
For #1 - I disagree! (Nice paper and a good read though!)
You used a paper on
LONG DAY plants......AND they used a long day plant, along with mutations of this long day plant that somewhat mimic a short day plant in the actual exp.
They grew the plants for 10 days and took plants out and did RNA sampling every 2 days - with various lighting times equaling a spread of 16 to 32 hrs of lights out or Dark times - Correct? Please note that 32 hrs is all of 8 more then 24 and
hardly the 72 hrs that some have suggested here. I do agree that the initial stretch IS a good thing! In the work I looked at the other day i found suggestions that the slower progression to flowering onset
may slightly decrease
overall stretch. (I was most likely not to clear on that - I tend to keep most of my answers rather easy, or general in nature.)
How does this correlate to decreased bloom time and increased trich productions? In some extended lights out studies, you may see a somewhat faster flower ONSET (as was found in your paper)! Yet- no reduction in actual bloom time when you ADD the extended dark periods! You will also see NO increase in trichome production, through extended dark periods to induce a faster flowering onset.
I find this (taken from your paper)m as being the most telling thing in it.
These results demonstrate that the photope-riodic induction of flowering in Arabidopsis is not triggered by the absolute duration of light, because light dark cycles com-prising identical photoperiods have differential effects on flow-ering time. The photoperiodic timer does not measure the duration of darkness either, as NH cycles that comprised shorter nights or longer nights than normal 24 hr short days (NH 16 hr and NH 28 hr) both accelerated flowering. Lastly, floral responses do not reflect the relative durations of light or darkness within a cycle. Cycles comprising 50% light or 28% light (NH16 hr or NH28 hr, respectively) were more efficient at promoting flowering than conditions comprising intermediate proportions of light and darkness (40 or 33% in 20- and 24-hr NH cycles).
Does this not point to faster flowering
onset?
The paper also states that RNA and hormonal response was greatest directly after lights out! It did state that longer dark periods built up more RNA, amino's and hormones to be expressed by the plant at the rise to lights on (by "spectral release/expression" - this is a point that I supply here). I touched on this point either earlier, or in the other thread.
Again these points bring on a faster flower set, not increased trichome production or a true measurable reduction in flowering time worth mention - correct?
Now by reading down to the
"discussion" section of the paper, we find that the purpose of the paper is to
confirm the relationship of circadian oscillation to
initiate the onset of flowering......The resulting finding of faster onsets is secondary to the paper.
Here is a quote from the title and following paragraph of the second section in the discussion.
"Floral Induction Was Promoted When Subjective Night Events Coin-cided with the Light Portion of the Cycle.
Our results suggest that the photoperiodic regulation of flowering in Arabidopsis requires an interaction of the circadian system with a light dark cycle. According to the internal coincidence model, the effect of photoperiod may be to alter the timing of two or more circadian rhythms relative to each other, resulting in an inductive phase relationship."
I am enjoying this discussion quite a bit! Sometimes this place needs more in depth looks at things!
Give me a few to review the next paper and I'll comment on that in the next post!
(I'm trying not to be or come across as arrogant , and understand that I do. I simply want to have a back and forth on this topic on a science level and your doing it!)
@RM3 thoughts?
