[Coral-List] about PAM question

[shashank Keshavmurthy]

Dear Listers,
Yesterday, I posted asking about PAM fluorometer question that was posted in 2007.
I thank those who replied to me in person. One lister asked me to forward all those answers that I receive and I am compiling it to be sent to that person.

Before that, let me share this ....

The reason I unearthed that old post is related to my experiment.
I am conducting heat stress experiments on corals. I want to actually obtain time-series data of PAM, if that is possible. Hence when I was searching on the net to see if someone has carried out time series PAM readings without DARK adaptation, I bumped into that question posted in 2007.

All the answers by hinted me towards dark adaptation before taking PAM readings and this is because PAM readings are dependent upon light history (answered by Dr. Ross Hill). If I can ensure that all the coral fragments that I am using in my experiment came from colonies that were exposed to similar light intensity in the field and also I make sure that all the fragments that I keep in my tank are also exposed to same light intensity, then I could use Effective Quantum Yield (EQY) as a measure of PSII photochemical efficiency......

Then again, I was suggested (Vianney Denis) both day and night measurement to assess Non-Photochemical Quenching (NPQ) 

But, dark adaptation after all may be necessary and most of the work carried on coral-physiology do use this method  to calculate Maximum Quantum Yield and most of them use diving PAM.

But when I read through Instruction Manual of DIVING PAM, it says,"DIVING-PAM is optimized to perform one particular type of measurement with the greatest ease, accuracy and reliability, namely the determination of the Effective Quantum Yield (EQY)  of photosynthetic energy conversion, delta F/Fm', the so-called Genty-parameter.

Now for quenching analysis (qP- and qN-) it is necessary to have dark adapted fluorescence readings, but again quenching analysis is not restricted to qP- and qN- determination and relevant information can also be obtained without 
Previous dark-adaptation of the samples

See also section 12.3.6 of DIVING PAM manual about Yield measurements of illuminated samples....

This is because DIVING PAM was optimized for field investigations....well, in the field one cannot always ensure same light intensity for all the readings if there are multiple sites, or multiple months or different seasons (DIVING PAM manual suggests the use of internally generated light - Halogen lamp, which is present in DIVING PAM casing)....hmm

Well, since I still did not want to dark adapt my sample, if that is possible, and wanted to see if I can still use PAM to read light adapted samples throughout my experiment (during the day) I stumbled upon this paper,

"Helbling et al (2010) Phytoplankton distribution and photosynthesis dynamics in the Chubut River estuary (Patagonia, Argentina) throughout tidal cycles. Limnol Oceanogr. 55:55-65"

What i learnt was they do not dark adapt their samples since they wanted to measure in vivo chlorophyll a fluorescence of the photosystem II. 


They have calculated photochemical quantum yield (Y) using the equation; Y=delta F / F dash m = (F dash m - Ft) / F dash m
 
Also they have calculated, duplicate electron transport rate vs. irradiance (ETR-E)

But also see this," Uthicke (2006) Photosynthetic efficiency and rapid light curves of sediment-biofilms along a water quality gradient in the Great Barrier Reef, Australia. MEPS. 322:61-73

Hence it is always not necessary to dark adapt samples and depends on the question we are asking and the problem (see Warner (2005) An overview of the interpretation and current use of chlorophyll fluorescence to understand coral bleaching. CRTC proceedings, Mexico)

I am still pondering!!!

Thanks for the help
shashank
===============================================================
Whether our efforts are, or not, favored by life, let us be able to say, when we come near the great goal,I have done what I could - Louis Pasteur


Role of Infinitely Small in Nature is Infinitely Large - Louis Pasteur
===============================================================
Keshavmurthy Shashank
Post Doctoral Research Fellow, Dr. Chen's lab
Biodiversity Research Center, Academia Sinica (RCBAS)
128 Academia Road Sec. 2, Nankang 
Taipei 115 Taiwan, ROC.
My WebPage: http://web.mac.com/coralresearch/iWeb/shashank/Welcome.html
Lab WebPage: http://coral.biodiv.tw/Default.aspx
Alt. E-mail: shashank at gate.sinica.edu.tw, coralresearch at mac.com