CarolineScott said:JUst bumping an oldie up.
LOwes has a red light .......short one ........$60. CDN
That seed starter book is absolutely correct, for positive photoblastic types of seeds. Near red light stimulates germination (in some seeds) by breaking dormancy, whereas far red prevents germination, induces dormancy. Here's the science on it.
Effect of Light:
Besides initiating many other photobiological processes, radiant energy has a profound influence on seed dormancy and germination. Among the innumerable species of plant, some are sensitive to light radiations. Based on the above said property seeds have been classified into three kinds, i.e. positive photoblastic types, negative photoblastic types and non photoblastic types.
In the case of positive photoblastic types when seeds are exposed to one or two cycles of intense source of white light, they germinate. On the other hand, the negative photoblastic varieties do not respond to white light treatment, but they germinate if they are maintained in complete dark conditions. The non photoblastic types are insensitive to light and they germinate irrespective of the presence or absence of light.
The effective spectrum of the visible light that induces dormancy or germination in light sensitive seeds is red light and far red light. The seeds of Grand Rapids and Pepper grass germinate promptly if they are exposed to red light. On the contrary, far red light inhibits their germination and seeds remain dormant. However the red and far red light effects on seed germination can be reversed. The table given below indicates that with the increase in the number of alternate cycles of red and far red light treatments ending with red light, the percentage of seed germination enhances significantly. But the treatment with far red as the last of the cycle, the percentage of inhibition is more or less 90-93%.
The effectiveness of red light and far red light in inducing or inhibiting the germination further suggests the involvement of phytochromes in this process. In fact, Ikuma and Thimann, way back, demonstrated the role of phytochromes in inducing seed dormancy or germination. However, the effectiveness of phytochromes depends upon other factors like water, temperature, pH, and age of seeds, duration of light treatment and other chemicals present in seeds.
Phytochromes, as described elsewhere, exist in two forms which are interconvertible in the presence of red and far red lights (PR and PfR).
The PfR produced under red light conditions undergoes reverse reaction in dark to produce PR form of the pigment. However, in some cases it has been found that the PR form is converted to PfR form by specific enzyme medicated reactions which require the input of energy. Furthermore, it is also known that PfR requires another unknown factor called X to be in active state. (PfR-X).
The PfR-X form of pigment complex is believed to be very effective in breaking the dormancy in red light requiring positive photoblastic seeds. The only difference between the positive photoblastic seeds and negative photoblastic seeds is that the former requires higher concentration of PfR –X complex than the latter one; where as the negative photoblastic seeds require a minimum amount of PfR complex to be highly effective. If the concentration of PfR is more in negative photoblastic seeds their do not germinate. Correspondingly, the non-photoblastic varieties germinate without light treatment, none the less PfR has a promotive effect. In spite of all these studies, the exact mechanism by which the phytochrome pigments bring about dormancy or break the dormancy is not clear.
