Hello everyone, would you say that higher chlorophyll content (either chl a or b or total) is directly related with lesser NPQ or higher Fv/Fm? Do other fluorescence parameters as ETR or Fv'/Fm' may be also affected? Thank you all in advance.
These parameters might be directly related, but in a very narrow range of Chl content (pale-yellow leaves) and only under optimal conditions. Normally, there is no close relationships between pigment content and (quantum) efficiency of photosynthetic apparatus. The same is generally true for NPQ. ETR might be indeed affected since its calculation contains a factor determined by Chl content (light absorptance). Still, the relationship of Chl with ETR is likely to be strongly non-linear since A% vs. [Chl] is also non-linear.
To my opinion, the short answer is "no" if we consider multiple species. For one particular species, it can happen that some combination of environmental factors leads to increase in both chlorophyll concentration and photochemical efficiency of PSII. But this is not a general rule.
In our experiment some environmental cues caused decrease in chlorophyll content of the leaf but without considerable decrease in PSII efficiency. So I think it is not always true the correlation between chlorophyll content and PSII quantum yield.
Higher chl do not mean lesser NPQ and maintenance of Fv/Fm, especially under suboptimal conditions, the parameters Fv'/Fm'and ETR have very much significant role in maintaining the stability of chlorophyll fluorescence mechanism or PS II system.
Though chlorophyll content is not directly related to PS II quantum yield there was observations in our lab that a bleached leaf with very low chlorophyll content recorded significantly less PS II than normal leaf. Similarly a plant under drought or moisture deficit condition with pale yellow or less green colored condition had small PS II photochemistry. Therefore, there is a relationship exists between chlorophyll content and PS II. However, a slight difference in chlorophyll content does not affect PS II because PS II photochemistry is depends on other factors like incident light quantum and quality, open/closed PS II reaction center or any impairment at the electron transport components across the thylakoid membrane etc. NPQ is mostly related to accessory pigments composition like carotenoids and xanthophylls. Xanthophyll cycle conversion from epoxidised to de-epoxydised condition play a crucial role in regulating the excess light energy at photosystem level through NPQ.
Annamalai Nathan
Dear Dr Annamalai Nathan
I can not be agree with this sentence "Similarly a plant under drought or moisture deficit condition with pale yellow or less green colored condition had small PS II photochemistry. Therefore, there is a relationship exists between chlorophyll content and PS II"
Under drought conditions stomatal closure occur and prolonged drought would result in decrease in photosynthesis rate due to lack of CO2. We did an experiment to simultanuously check stomata and photosynthesis under drought and we find that at the begining of drought just stomata close without change in PSII.
Also for sure very little Chl would alter all parameters related to photosynthesis but the observed correlation is due to indirect factors.
Hope it can help in clarifying the discussion.
Chlorophyll content vs. PSII quantum yield? - ResearchGate. Available from: https://www.researchgate.net/post/Chlorophyll_content_vs_PSII_quantum_yield#view=57b405475b495244f64b6566 [accessed Aug 17, 2016].
Dear Dr. Sasan Aliniaeiferd
Yes I agree with you. Under drought or soil moisture deficit condition stomatal closure result in non availability of CO2 in the initial stages. However, in a prolonged drought with high solar light conditions chlorophyll bleaching occurs due to free radicals and ROS generation. In this condition the total PS II and electron transport components are down regulated. Therefore overall PS II turn over is less in the presence of low chlorophyll. Please check this fact with an experiment in your plant.
Annamalai Nathan
Great discussion, but would you be so kind as to explain a little bit more how the xantophylle conversion release the excess of energy? Is this process heat or fluorescence emitting? Is heat emission equal to NPQ?
- Badges
- Science topic
- Similar topics
- Biological Science
- Plant Sciences