Differences, advantages and disadvantages of photosynthesis apparatus and oxygen electrode for measuring photosynthesis rate
The current methods of measuring photosynthetic rate are the infrared CO2 gas analyzer method (photosynthesizer) by measuring CO2 absorption and the oxygen electrode method by measuring O2 release. However, which method is accurate and what method is suitable for your own experiment?
The difference between photosynthesis apparatus and oxygen electrode to determine the photosynthesis rate:
The photosynthetic rate measured with an oxygen electrode is greater than the photosynthetic rate measured with a photosynthesis instrument.
According to the total reaction formula of photosynthesis: CO2 + 2H2O * + 4.69kJ → (CH2O) + O * 2 ↑ + H2O
The photosynthetic rate should be the same whether the oxygen electrode is used to measure the release of O2 or the photosynthesis apparatus (infrared CO2 gas analyzer method) to measure the absorption of CO2. However, this is not the case.
For every O2 molecule generated during photosynthesis, four electrons will enter the electron transport chain. After passing through the electron transport process of the electron transporter, it will be transferred to NADPH. NADPH and ATP reduce a CO2 molecule. In this case, they are equal. However, not all electrons are transferred to NADPH after passing through the electron transfer chain. Some electrons are transferred to oxygen and enter the Miller reaction, and some electrons are used in nitrogen (N) metabolism and sulfur (S) metabolism and photorespiration. The proportion of electrons used for non-reducing CO2 under adverse conditions increases. Therefore, in reality, it is not that every time an O2 molecule is released, a CO2 molecule is absorbed.
Furthermore, the determination of the release of O2 by the liquid-phase oxygen electrode is carried out in NaHCO3 solution. The NaHCO3 solution provides saturated CO2 and eliminates the effect of stomatal limitation on the photosynthetic rate. Gas phase oxygen electrode measurement of O2 release is also measured under saturated CO2 conditions, and the oxygen electrode measurement of photosynthetic rate is measured under ex vivo conditions. The photosynthesis instrument (infrared CO2 gas analyzer method) for measuring the absorption of CO2 is limited by the pores and CO2 concentration, so the size of the photosynthesis rate measured by the photosynthesis instrument and the oxygen electrode is inconsistent. In general, the photosynthetic rate measured with an oxygen electrode is greater than the photosynthetic rate measured with a photosynthesis instrument.
The characteristics of photosynthesis apparatus and oxygen electrode to determine the photosynthesis rate:
Oxygen electrode
The photosynthetic rate measured by the oxygen electrode cannot truly reflect the carbon assimilation rate of plants under actual conditions. But in some studies, people need to know the oxygen release rate of plants and compare the difference between the oxygen release rate and the assimilated CO2 rate of plants to understand the distribution of photosynthetic electrons in different ways. Adding different inhibitors can study the photosynthetic electron transfer pathway. In addition to measuring the photosynthetic rate, the oxygen electrode method can also be used to determine the oxygen consumption or oxygen release reactions of various organisms and active substances. For example, it can determine the activity of certain enzymes. Active and respiratory pathway studies, and can control the reaction conditions well. Measuring the photosynthetic rate with an oxygen electrode can eliminate the effect of stomatal limitation on photosynthesis and provide powerful data support for scientific research. The important point is to use the liquid-phase oxygen electrode to measure the photosynthetic rate of some small plant materials such as algae, moss, phytoplankton, suspended cells, buds, and stems that cannot be measured by the photosynthesis apparatus.
However, as a method for measuring photosynthetic rate, the oxygen electrode method has a single measurement index, and it is impossible to measure important parameters of photosynthesis such as stomatal conductance, transpiration rate, CO2 compensation point, and CO2 saturation point.
Oxygen electrode is used to study the photosynthetic rate of plants. The current main products are Chlorolab series and Oxygraph series liquid oxygen electrodes produced by Hansatech Scientific Instruments Co., Ltd. and Leaflab series gas phase oxygen electrodes. YSI-53 produced by Yellow Springs Instruments Co., Ltd. in the United States Type biological oxygen monitor etc.
Photosynthesis
Many fresh graduate students will think that the photosynthesis instrument is to measure the photosynthesis rate. I also thought that way at the time, but in fact, the photosynthesis instrument has a wide range of uses.
Photosynthesis instrument is used to carry out related research on plant leaf photosynthesis, transpiration, respiration and so on. Measurement parameters include CO2 concentration, net photosynthetic rate, transpiration rate, intercellular CO2 concentration, stomatal conductance, atmospheric humidity, air temperature, blade temperature, vapor pressure deficit, atmospheric pressure, light intensity, Ci / Ca, etc., and pass through the system The built-in automatic measurement program measures the plant's light-photosynthetic response curve, CO2-photosynthetic response curve, temperature-photosynthetic response curve, humidity-photosynthetic response curve and other response curves, and RuBP carboxyl can be calculated from these response curves Chemical efficiency, apparent quantum yield, light compensation point, saturation light intensity, CO2 compensation point, CO2 saturation point, temperature compensation point, RuBP regeneration rate and photosynthetic stomatal limit value are some very useful physiological and ecological parameters. Through the control of the measurement conditions, we can also study the distribution of energy and photorespiration.
At present, the widely used photosynthesis apparatus generally adopts an open gas path design. The open gas path system adopts a dual gas chamber infrared instrument, so that the gas that has not passed through the assimilation chamber enters a gas chamber as a reference gas, and the gas from the assimilation chamber As the sample gas enters another gas chamber, the infrared monitor detects the CO2 concentration difference between the reference gas and the sample gas, and calculates the photosynthetic rate based on the concentration difference, the leaf area in the assimilation chamber, and the gas flow rate. Because the method is fast and accurate, and makes up for some of the shortcomings of the closed gas circuit system, the application is becoming more and more popular.
However, due to the limitation of the leaf chamber type, the photosynthesis apparatus is inconvenient to measure the photosynthetic rate of algae, mosses and small phytoplankton, suspended cells, apple peels, buds and other materials.
Common photosynthesizers include the CIRAS-3 portable photosynthesis instrument from PP Systems in the United States (formerly the United Kingdom) and the photosynthesis instrument from Licor.
references
1. Edited by Zou Qi, Plant Physiology Experiment Guide, China Agricultural Press, 2000, Beijing, PP79-81.
2. Zhao Shijie and other editors, Plant Physiology Experiment Guidance, China Agricultural Science and Technology Press, 2002, Beijing, PP72-75.
Note: If the teacher or classmate has problems during the experiment, please call or email to exchange and learn from each other.
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