Fluence response
 | This article, Fluence response, has recently been created via the Articles for creation process. Please check to see if the reviewer has accidentally left this template after accepting the draft and take appropriate action as necessary.
Reviewer tools: Inform author |
Comment: I will ask WikiProject Plants to help with this draft. Roger (Dodger67) (talk) 20:11, 30 May 2017 (UTC)
- Comment: As I understand it fluence is quantified as energy per unit area, but this article uses "μmol/m2" which doesn't make sense as "μmol" is not a unit of energy. Roger (Dodger67) (talk) 10:32, 29 May 2017 (UTC)
- Comment: Found this in userspace. It looks pretty good but too technical for me to properly evaluate. Legacypac (talk) 20:15, 30 May 2017 (UTC)
Both fluence rates and irradiance of light are important signals for plants and are detected by phytochrome. Exploiting different modes of photreversibility in this molecule allow plants to respond to different levels of light. There are three main types of fluence rate governed responses that are brought about by different levels of light.
Very low fluence responses
As the name would suggest this type of response is triggered by very low levels of light and is thought to be mediated by phytochrome A.[1] They can be initiated by fluences as low as 0.0001μmol/m2 up to about 0.05μmol/m2.[2] Germination of Arabidopsis can be induced with very low levels of red light as can oat seedlings. Such low levels of light are sufficient for inducing this response since they only convert 0.02% of the phytochrome to its active form. Since the backward reaction by far red light is only 98% efficient making the conversion non-photoreversible and allowing the response to proceed.[2] VFLRs can also be induced by making up the required fluence by brief flashes of light. Since this depends on light levels and time it is know as the law of reciprocity.
Low fluence responses
These responses require at least 1μmol/m2 to be initiated and become saturated at about 1000μmol/m2. Unlike VLFRs, these responses are photoreversible. This was shown by exposing lettuce seed to a brief flash of red light causing germination. It was then shown if this red flash was followed by a flash of far red light, germination was again inhibited.[3] LFRs also follow the law of reciprocity. Other examples of LFRs include leaf de-etiolation and enhancement of rate of chlorophyll production.
High-irradiance responses
HIRs require long exposure to relatively high light levels. The degree of response will depend on the level of light. They are characterised by the fact that they do not follow the law of reciprocity and depend on the rate of photons hitting the leaf surface, as opposed to the total light levels. This means that neither long exposure to dim levels of light nor very bright flashes of light are enough to trigger these responses.[2]
References
- ^ Modes of action of phytochromes http://jxb.oxfordjournals.org/content/49/319/127
- ^ a b c Taiz and Zeiger (2010). Plant Physiology (5. ed.). Sinauer Associates Inc. ISBN 978-0-87893-565-9.
- ^ A Reversible Photoreaction Controlling Seed Germination http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1063632/