Very interesting article on the blue light effect. I went back to the article by Gubler et al. to see the spectra of their LEDs. Also found a couple of refs by google that talk in more general terms about lighting sources and needs in general horticulture. this one is about the LEDs that are sold by one company. Rather pricy and intended for commercial use or research
They have good discussion of general spectral properties of some kinds of LED.Next trick is to match the LED to your phytochrome. turns out there are a lot of different brands out there. I’m afraid we have to read the fine print to get the actual spectrum emitted. then find out the intensity at various distances. Too much light is a negative thing, it saturates the response.
An additional factor is that red light may be more penetrating, less easily scattered. So maybe it actually can get through the achene to some (sufficient) extent. I don’t believe that question has ever been addressed by direct measurement.
Lots of opportunity for some real fun experiments here. Great for science fair projects.
Karl was asking what I too was wondering about. A “red” light from filtered light isn’t creating more red light than the white light. The filter is absorbing the other colors (and in fact, a small amount of the red due to inefficiency of pigment/dye in filter). If a filtered light is more efficient than a full spectrum light, then in fact the absence of other colors plays a role, since the unfiltered light has at least as much red light as the filtered…
So herein lies the explanation from the linked article, I suppose: “We found that the blue component of the light spectrum inhibits completion of germination in barley”
Chlorophyll a absorbs both red and blue light. Does this imply that the (blue absorbing) antenna pigments might play a role in the inhibitory affect? I didn’t know plants could “see” color and always assumed that all the photosynthetic pigments worked together as one unit.
(Okay… I didn’t read the full article. Not up to wading in that deep right now…)
It depends what you mean by seeing. usually that implies the whole system including the brain. Plants can sense the presence of different kinds of light. Blue light is detected by something called cryptochrome. that is somewhat like phytochrome, but was cryptic for decades. Winslow Briggs is a name that I associate with cryptochrome or the blue light receptor.
The red/far-red system is a flip=flop switch, but an imperfect one. you can’t get a red light that doesn’t affect the far-red detector. The best you can do is to get about 80 % into one form. The website that I mentioned above shows how LEDs do this. they are writing for greenhouse growers or indoor farmers. It is also important to know that you can overdo it with applying red/far-red light. Too much light just overwhelms the detectors. they are made to detect things like the intensity of the setting sun and the last afterglow of twilight, or the rising sun which goes through the same color change in the reverse of nightfall. they don’t act appreciably in daylight. that is why filtering white light with a strong red filter is OK. You actually want low intensity. And for best results you only do this in the absence of some other source of white light.
However, plants are also adaptive and respond to what they perceive as shading by other plants. So in “daylight” hours it is necessary to add some reddish light to many species to get good looking stocky plants. Too much red and they think they are in the shadow of another plant and grow tall and stringy. soybeans are an example of this. Roses in my experience do just fine with nothing but ordinary fluorescent cool white lighting. And if they are reblooming they are OK with 24 hour lighting. Many species need a night’s rest to do their best, especially if they only bloom at a certain daylength.
Plants grown under red light were substantially taller than those under other colors or white light. That’s why I’m wondering if the supposed improved germination of rose seeds under red light might be little more than elongation, rather than proper growth.
He did not study the effect of light on germination. However, in part 2 he did report some study on the effect of electricity on germination.
Thank you s_hardy. When I took my graduate biochem courses (my minor), processes had names but the actual chemical mechanisms were not understood (for many/most steps). It was the same for organic chemistry - it also was then a memorization field. It appears now that all of the life sciences are becoming “physical chemistry specialties”.
Thank you s-Hardy for finding the very nice clear colorful articles. Their author obviously has a lot of experience in teaching plant physiology. I just wish that he’d update his blue light special. Briggs and many others have taken it a long way further on the cryptochrome trail. The Zeaxanthins are cartenoids like the yellow pigments in roses. But the cryptochrome uses flavin and phytochrome pigments are much closer relatives of chlorophyll. It seems that we, and fruit flies have cryptochrome too, involved in regulation of our circadian rhythms.
Another example of warm after-ripening, this one for Rosa acicularis (Prickly rose):
Prickly rose regenerates vegetatively by means of widespread rhizomes. A single clone with 8 to 11 aboveground stems linked by a horizontal rhizome can cover 11.95 to 23.92 square yards (10-20 sq m). Results of an Alaskan study found rhizomes between 8 and 12 inches (20-30 cm) deep. This was sufficient for the rhizomes to be in the mineral soil below deep organic horizons [10]. Since rhizomes sprout after fire and other types of disturbance, prickly rose clones may live for hundreds of years [17].
Prickly rose flowers and sets seed frequently in open communities and infrequently under a canopy [46]. Seed is dispersed by small mammals, song birds, and grouse [1]. Seeds exhibit deep dormancy and require warm stratification for the initial stages of germination, followed by cold stratification for germination to continue [10,17,54,90]. While most seeds germinate following snowmelt the second spring after seed set, germination of one seed crop may spread over several years [17].
Ahlgren, Clifford E. 1960. Some effects of fire on reproduction and growth of vegetation in northeastern Minnesota. Ecology. 41(3): 431-445.
Calmes, Mary A.; Zasada, John C. 1982. Some reproductive traits of four shrub species in the black spruce forest type of Alaska. Canadian Field-Naturalist. 96(1): 35-40.
Densmore, R.; Zasada, J. C. 1977. Germination requirements of Alaskan Rosa acicularis. Canadian Field-Naturalist. 91(1): 58-62.
Lynch, Daniel. 1955. Ecology of the aspen groveland in Glacier County, Montana. Ecological Monographs. 25(4): 321-344.
Parminter, John. 1983. Fire-ecological relationships for the biogeoclimatic zones and subzones of the Fort Nelson Timber Supply Area. In: Northern Fire Ecology Project: Fort Nelson Timber Supply Area. Victoria, BC: Province of British Columbia, Ministry of Forests. 122 p.
Watson, L. E.; Parker, R. W.; Polster, D. F. 1980. Manual of plant species suitability for reclamation in Alberta. Vol. 2. Forbs, shrubs and trees. Edmonton, AB: Land Conservation and Reclamation Council. 537 p.
I couldn’t find a good, freely available summary that was up to date, so settled for one that would get readers up to speed on what was state of the art 20 years ago. Those who got through them and want to know more, should be on the lookout for more recent articles, as progress in this field is ongoing.