Measuring Photorespiration with the LI-6400/XT System

Measuring Photorespiration with the LI-6400/XT System

Introduction

Oxygen is a competitive substrate for ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco), resulting in an inhibitory effect on net photosynthesis.  Higher CO2 to O2 ratios inside the leaf decrease the Rubisco-catalyzed reactions with O2, resulting in less carbon-wasteful reactions in the light (photorespiration). Photorespiration increases on hot, dry days when evaporative stress can cause stomata to close, lowering the intercellular CO2:O2 as CO2 is assimilated. When Rubisco was evolved by plants, earth’s atmosphere had much higher concentrations of CO2 and relatively low O2.  As plants evolved and filled different environmental niches, O2 production increased and atmospheric O2 concentration rose, thereby increasing photorespiration.  C4-type plants such as maize and sugar cane evolved an active CO2-concentrating mechanism that increases the CO2 concentration near the site of the photosynthetic reactions, which suppresses photorespiration.  Scientists and plant breeders are working to transfer this ability of C4-type plants into important C3-type plants such as wheat, rice and soybeans.  One approach to studying and quantifying photorespiration is to suppress it by supplying the leaf with only 2% oxygen (instead of the normal 21% oxygen) and measure the increased rates of photosynthesis.

Experimental Setup

The diagram below shows a simple setup in which a tank of air with only 2% oxygen supplies the incoming air to the LI-6400/LI-6400XT system. To prevent the LI-6400/XT internal pump from fighting against the external tank pressure, the tank supply is fed into the LI-6400/XT air inlet port via a T-fitting. One end of the fitting is vented to the atmosphere (through the flow meter in the diagram below) while the other flows into the LI-6400/XT.  The tank air flow is adjusted so that it slightly exceeds the demand from the LI-6400/XT so that ambient air is not sucked in by the LI-6400/XT pump. Venting to the atmosphere also ensures that the system remains at atmospheric pressure. An inexpensive flow meter can be attached to the vented part of the T-fitting to check and make sure that the air flow is in excess of the demand from the LI-6400/XT pump.

The photograph below shows an actual setup with a tank of gas (air with 2% oxygen)  for supplying air to the LI-6400/XT via a vented T-fitting. A float-type flow meter (taped to the side of the supply tank) is being used to test for excess flow.

This setup was used to test the differences between the response of  Maize (a C4 species) and Bush Beans (a C3 species) to air with a 2% oxygen content and room air with the normal 21% oxygen content.

Results

The figure below shows the Bush Bean leaf (a C3 species) photosynthetic rate in response to varying Ci, the intercellular CO2 concentrations.  At ambient CO2 concentration (Ci ≈250 ppm), photorespiration was reducing the net photosynthetic rate by about 40%.

The figure below shows the photosynthetic rate of a Maize leaf  in response to varying intercellular  CO2 concentration. In Maize (a C4 species), photorespiration is already suppressed by internal mechanisms, and supplying air with only 2% oxygen did not enhance net photosynthesis.

Conclusions

The simple modifications to the LI-6400/XT system’s operating procedure given in this Technical Tip provide one way to investigate photorespiration.  The results of the basic experiment conducted to test this technique confirm that photorespiration accounts for a substantial reduction in the net photosynthetic rates of C3 plants. Efforts by scientists to transfer some of the ability of C4 species to suppress photorespiration into economically important C3 crop plants continue to hold great promise.

13 thoughts on “Measuring Photorespiration with the LI-6400/XT System

  1. Dear,
    My name Muhammad Abdul Qirom. I am a Researcher at Forest Research and Development Agency, Ministry of Forestry Indonesian.

    I am very interesting with LI-6400/XT system’s operating and Result of LI-6400/XT. I want to ask you about how much of price this tools?.

    Thank your for your information.

    Best Regards,
    Muhammad Abdul Qirom

  2. Abdul,

    Thank you for your interest in our LI-6400XT. One of our Technical Sales Associates will be contacting you directly regarding the price. Let us know if there is anything else we can help with.

  3. i am Ifeanyi ogbuzuru, with the help of this system we can be the best researchers in Nigeria

  4. My name is Eduardo Zabaleta working at Instituto de Investigaciones Biologicas, Mar del Plata, Argentina

    I am very interesting in the LI-6400/LI-6400XT system. I would like to know the price of this equipment. Is there any company here in Argentina?

    Thank your for your information.

    Best Regards,
    Eduardo Zabaleta

  5. Dear Eduardo,

    Thank you for your interest in the LI-6400XT. We do have a distributor located in Argentina that sells and support our products. One of our technical sales associates will be in contact with you shortly and provide you with the distributor information. Let us know if there is anything else we can help with.

  6. My name Ndesingo Jonde. I am a Researcher at Forest Research and Agriculture Development Agency, Ministry of Forestry & Agriculture in Kenya.

    I am very interesting with LI-6400/XT system’s operating and Result of LI-6400/XT. I want to ask you about how much of price this tools with all acccesories?.We needs about 300 units.
    We are going to holiday so Please send us your price today and how we can purchase them from your side, If posible we need direct buying from manufactures ad we will maker another request on the same total number for other reseach teams as well.
    Every thing will be paid with kenya Goverment on suport of USAID.
    Thank your for your very much we are looking forwad to hearing from you soon.

  7. Dear Jonde,

    Thank you for your interest in our LI-6400XT. One of our Technical Sales Associates will be contacting you directly regarding the price.

  8. Hello,

    I am looking to set this up. I have two questions:

    1) As the tank gas is dry it would seem that water would have to be added to it. I have seen in the literature that authors have bubbled the 2% O2/98% N2 gas through DI and then adjusted the RH using the Drierite on the 6400. Is this the most appropriate/feasible method in your experience?

    2) The tubing in the photo above appears to be ice-maker line. Is that the best tubing for this application, or do you have other tubing material recommendations?

    Thank you for any advice.

  9. Hi Nick,

    One of our Technical Support Team Members will be contacting you directly to work through the questions you have. Please let us know if you need any further assistance!

  10. Hello..
    I wanted to know the price of Li-Cor 6400 photosynthesis measuring meter..of year 2013..kindlu reply…I am from INDIA

  11. Dear Dol kar,

    Our sales team will be in contact with you shortly to provide information regarding the LI-6400XT. They will also put you in contact with our authorized distributor in India, Elron Instrument.
    If you have any further questions, please let us know!

  12. Please quote the current price of LICOR 6400XT in India in Rupees.What parameters can be studied by 6400XT Model

  13. Dear DP,

    Our sales team has sent your information on to our authorized distributor in India, Elron Instruments. They will contact you directly regarding a quotation. If you have other questions, please let us know!

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