If you are growing to bulk up seed, then you want them to grow rapidly and bolt (seed production). This will be achieved with the highest light level you can get (a mix of spectra) for a long day length (16hrs day/ 8hrs night). The opposite is true if you want to maintain the vegetative state (ie. the rosette). Optimum for Col-0 is between 300 and 400 umol m-1 sec-1

Remember that the higher the light level, the higher the heat load from light source (even cool fluorescent), so they will require more watering. Also, different accessions respond differently to all environmental parameters, so if some look very stressed (i.e. very small and browning or reddening of leaves) then conditions are too harsh - you may have to play around with a few of each to find out what they like). If you find that some require lower light levels, then you can stack them, growing some in shade under others.

For Arabidopsis, light saturation of CO2 fixation occurs at about 600 µmol quanta PAR m-2 s-1 (Eckardt et al., 1997).

Eckardt NA, Snyder GW, Portis Jr AR, Ogren WL (1997) Plant Physiol 113: 575-586

If you are growing to bulk up seed, then you want them to grow rapidly and bolt (seed production). This will be achieved with the highest light level you can get (a mix of spectra) for a long day length (16hrs day/ 8hrs night). The opposite is true if you want to maintain the vegetative state (ie. the rosette). Optimum for Col-0 is between 300 and 400 umol m-1 sec-1

Remember that the higher the light level, the higher the heat load from light source (even cool fluorescent), so they will require more watering. Also, different accessions respond differently to all environmental parameters, so if some look very stressed (i.e. very small and browning or reddening of leaves) then conditions are too harsh - you may have to play around with a few of each to find out what they like). If you find that some require lower light levels, then you can stack them, growing some in shade under others.

why 10 C? this is rather cool for flower and seed production

I agree with Janice, long days (16 h light) with cool fluorescent lights should be enough (in my experience) to grow healthy plants. But why 10C? a temperature between 15 and 20C is much better for Arabidopsis (and the lower the temperature, the longer the plants will take to flower). Do you need to get more dormant seeds? (low temperature during seed maturation produce seeds with a higher level of dormancy).

Hi, Timothy,

everything are dependent from your aim. If your aim is to study plants growth and get seeds production, you have to use 20-23 C, long day (16 h day/ 8 h night). Of course, you have to made vernialization at 4 C for 2 days. The light intensity which is suffucient to plants growth (at least in my condition), is 120-200 mkmol, this is enough to get rapid growth and seeds formation. But, remember, that different ecotype require different growth conditions and may require different light intensity.

Moreover, the consyruction of your greenhouse alos have a strong influence on plant growth.

Generally, white light is neough for plants growth. You do not need to combine different spectrum, if you do not plan to study effect of different ight on photomorphogenesis.

Also, despite light, nutrition is very importnat factor. You have to watering plants at least once per week with 1/2 Hoagland solution.

Good luck!

Sorry, I just realized that what I said may be misunderstood: That temperature (10C) is not low enough to be considered a vernalization treatment, that's why they will take longer to flower.

Add more Far-red (low R/Fr ratio) may accelerate flowering if you just want seeds. Some accessions may require vernalization at rosette stage. Don't know 10C is cold enough to give the vernalization if this is the reason you want to go with it.

I'm trying 10C for the first time. ABRC and the Nordborg group at GMI both adopted this temperature recently because many plants find that cold enough to overcome their vernalization requirement. Any that do not flower within 50 days get a trip to the 4C chamber for 50 days and generally bolt shortly after their return to 10C. Apparently, they look quite nice at 10C, and have fewer problems with pathogens (we do a lot of work with various pathogens so it's nearly impossible to avoid them around here).

Plants do take longer to flower but it serves to reduce the variation in flowering time. Yihai, do you think it would be good to eliminate the red bulbs and just keep the far-red?

Hi Timothy,

I think you really need to consider what Janice and Gabriela said, about your aim of research and the different ecological plasticity of different accessions.

In case you grow different 'ecotypes' you might end up with a lot of variation, still.

350 mutant or overexpressor lines in Col-0 or Ws or Ler might still grow to comparable phenotypes. It will also depend on what you are scoring afterwards.

Please condider: There are heritable differences in the plant's physiology - i.e. bad growth of the parental generation affects the offspring to respond differently! And maybe the information of 'bad growth' was not decumented, as long as your plants made at least some seeds....

I see tremendous differences between growth chamber and greeenhouse. Previously, I had the oportunty to use greenhouse plants. Now, I also need to abapt to growth chambers - and of course, many observable phenotypic differences could not be detected anymore.

Also consider that supplementing with UV-light has very positive effects on plant stature and viability. Besides light (qualities and intensities), humidity was a very very big problem (not so much temperature), which was one of the reasons why my plants grew very different in the greenhouse or the chambers.

The cool white gives you enough Blue, Green, and Red, I think you don't need to add more red bulbs. Just try with more blue and Far-red bulbs and see what's happening to the plants. If plants don't like it, you can always reduce the number of far-red bulbs. One thing that I want to point out is, more far-red will make plants really "shade-like", you may have less seeds than normal condition.

Hi, Timothy,

you expain everything very good! 10 C may be a good decision to overcome problem of insect and pathogens. But if your aim is to compare a phenotype of 350 different types, yoyu have to consider that benavour at 10C may be different form behavour at 20- 23 C.

So, you will have plant phenotyping only at 10 C.

Good luck!

I appreciate all your input - and so quickly! Let me provide a little additional background and then I will summarize what I've concluded thus far.

Background

My aim is to get enough seeds so I can send one tube to ABRC and have one for my lab. And ABRC wants their tube to contain at least 0.5 ml which will allow them to release these lines immediately. I do not plan to score phenotypes, but will collect data on how long it takes each accession to flower at 10C. These plants are part of the Regional Mapping Panel of 1,309 wild collected natural accessions (not mutants) from around the world so I know there will be tremendous variation, but we don't have a database set up yet that would allow us to predict which lines will bolt striaght away and which are going to need vernalization at the rosette stage. Some lines from the far north seem to need 8 weeks of cold, but growing them at 10C helps to satisfy that cold requirement. This round of bulking will take 6 months, so I'm going to give it my best shot and hope to get it right the first time (if any lines that fail meeans I will have to start another round this sumer and won't get seeds until next Christmas).

Summary after one intense day of activity (thanks so much)

The plants should do just fine with cool white alone - there are hints that enriching the sprectrum with red and blue can help but since it's not necessary I think I will set this up with cool white bulbs only for 18 hours/day. Taras mentioned growth chamber structure possibly causing problems so I will rotate plants twice per week to reduce positional effects.

PAR max is 600, optimum is around 300 but ABRC uses 1/2 that so I may shoot for around 200 as Taras recommends. This may ease any problems with cels drying out.

My chamber has humidity control. Dierk mentioned problems with humidity but I think I will program my chamber for 50% unless anyone has a better suggestion. I'm fortunate to have a greenhouse staff that will water my plants daily and feed them once per week. If I see plants under stress ( as Janice notes), I should have enough space to separate them and put them on a shelf under a shade cloth to reduce the light.

Gabriella mentioned cold temperatures leading to seeds with stronger dormancy. I haven't given that any thought until now; I'm trying to produce seeds that will remain viable for many years so a little stronger dormancy might be a good thing. How strong is this temperature effect on dormancy?

If heat is a problem You could use LED bulbs and pick out the colours best suited for Your purpose.

LED lighting will be added to 3 of my chambers this year but the ones I have for this planting won't get upgraded until next fiscal year. I'm really looking forward to having LEDs! Does dimming shorten LED lifespan the way it does fluorescents?

Hi, Timothy, I think you summarize all points very clear.If you really need only seeds propagation, you do not need to made any experiemnt with spectrum. White will be enough!

Please, alos consider that you can get induction of flowers in the genotype with flowering delay either by short treatemnt with hormones, or by feeding some nutrients at certain stage of development. You can also try simple method of in vitro seeds formation, you will save a lot of space, time and money, but in this case you can got less seeds (up to 400 from 2 ml of the medium).

Good luck!

Hi Timothy,

your ideas sound convincing - still, you might run into problems by reprducing data the first place. Probably, you will need to set up the entire thing several times.

You can not predict if under your conditions 50% humidity is fine or not or if 600 PAR is too much light.

My grwoth chambers were seit to 60 % humidity and 25 C growth (16 light / 8 dark) and my plant were small and full of anthocyanins due to stress.

I did similar experiments to your description recently. I am sure you are aware that bolting needs to be crrected for germination time (which is really tidious), so I checked at a 2 days period and marked each individual plant when it started germinating and bolting. To counteract individual bias, each genotype was planted 15 times in a randomized fashion. Lower numbers of plants increased variability drastically (in the grwoth chamber). Instead, replicates of 5 plants in the greenhouse grew to comparable results!

Anyway: I received Yosemite seeds from NASC, that never flowered under permissive chamber conditions (made more than 100 leaves), but flowered easily at long days in the green house. But the seeds from the greenhouse never germinated in my hands - only after GA treatment.

In addition, there are acessions where ageing will decrease germination rate (instead of increasing it).

Hi, Timothy, you have also consider that reason of the stress (as slow plant growth, antocyanin accumulations, etc) may be the combination of several factors, including soil composition, humidity, high light, temperature etc.

you can also take into account that for in vitro seeds formation system you can easy made a correction of your growth conditions to get optimal flowering time.

At least i am recommending you to use in vitro for the first 2-3 week of plant growth.

Good luck!

Dear Timothy, I understand your needs. I think low temp and white bulbs should be enough, but if you can please add some extra far-red light...it will overcome the late flowering phenotype of many accessions . Good luck!

Dear Timothy. 

Thank you for your question, I am also staring to grow Arabidopsis Col-o for bulking and later for stress related experiments. With all the responses that you obtained, they will help me a lot as well. 

Excellent Takalani,  and you remind me that I should add a project conclusion to this thread.  I ran 18 hour days at 10C but had to drop the fluorescent lighting level to 80% to keep the heat load down so the chamber could maintain 10C during the day . PAR varied a bit due to bulb age and ballast issues but was around 160-180; each shelf has 8 bulbs of cool white and I rotated flats around the chamber to vary their light and heat exposure plus flipped each flat back to front 3x per week. All accessions flowered.  Quick flowering accessions like Col-0 typically flower at ~28 days in our normal conditions of 20C, 18 hours, 300 PAR but this cooler treatment resulted in flowering times of ~40 to 50 days.  Plants from the far north or high mountains that typically require 6 to 8 weeks of vernalization flowered at ~100 days (max 140).  One benefit I found was the longer growth period produced larger plants and seed outputs ranged from 1mL to nearly 8 mL per plant!  My overall average was about 3.5 mL seeds per plant.  Once the plants initiated bolting, I bagged them and moved them to another chamber running at 'normal' growth conditions where they continued to grow vigorously while they bolted. Some of these plants were massive, I used 18 cell/flat trays so they'd have room to grow.  

I've since adopted this cool growth strategy for most of my bulkings.  I recently worked with a set of difficult plants from the mountains of Spain that turned very purple after a few months, but they greened up nicely if I gave them a warm 'vacation' of a weekend in the normal greenhouse conditions.   

Thanks to everyone for the great inputs!