photoperiod findings

[Grant Cramer]

Dear Netters,

Thank you for the wonderful response (I had over 10). This is a summary 
and conclusion of the response plus my investigation of most of the 
references.

To start with I must clarify my objectives a little better than I did in 
my first message. I am a physiologist interested in characterizing growth 
responses to different environmental stresses. Since Arabidopsis is so 
small I was looking for conditions that would optimize growth conditions 
to produce the greatest amount of leaf biomass for analyses. (I think 
there might be a few people out there who might also be interested in 
this). I have found that growing plants hydroponically is by far the best 
way to get big plants (no root restriction, well-watered all the time, 
ample nutrient supply). 

We are also interested in delaying flowering to get larger plants. We are 
using both the Columbia and Ler ecotypes (hence my interest in 
photoperiod). Shorter days delay flowering in our two ecotypes and 
produce much larger plants before flowering. The longer the day the 
earlier the plant will flower. The question is what is the optimum 
daylength that will delay flowering and provide optimum light to produce 
big plants. We have been using 8 h daylengths. Another person here was 
using 10 h. So we started to explore what might be the optimum. Now for 
the summary and conclusions.

First of all, there are many references regarding photoperiod effects. 
Most just choose arbitrary daylengths without reference or justification. 
I could not find any hard data on critical daylengths. However there are 
some references to it.
It is mentioned in a review by Klaus Napp-Zinn, 1985, Arabidopsis 
thaliana. In CRC Handbook of Flowering, Vol 1, pp 492-503.

There was also very useful information on the Columbia ecotype in a brief 
note by A. Corcos, Vol 18, of the Arabidopsis Information Service. It is 
reported that 8 h is required for bud formation, but indicates that 
daylengths below 5 h may restrict growth. This is the only report that I 
have found that looked at a number of different short daylengths. 
However, no data are presented.


Two other potentially useful references were either in journals we do not 
have easy access to or are in a foreign language. They are:

Gregory F.G. and Hussey G.G. 1953. Photoperiodic responses of A.thaliana. 
Proc. Linn. Soc. London 164, 137

Laibach, F. 1951. Uber sommer- und winterannuelle Rassen von Arabidopsis 
thaliana (L) Heynh. Ein beitrag zur atiolgoie der blutenbildung. Bietr. 
Biol. Pflanzen. 28:173 

If you have access to these or can make comments about these, it would be 
appreciated.

Also, if you have comments about optimum conditions, please do so. We are 
probably going with 23 C temperatures and 8 h daylength.

Thanks in advance,

Grant Cramer