Methyl purple is an introduced quinone-imide redox dye that has been shown to be an exceptionally sensitive monitor of photosystem I activity in chloroplasts.

I. Monitoring Photosystem I Activity:

1. Material Preparation:

(1) Methyl Purple dye: It is usually dissolved in an appropriate buffer solution (such as PBS) at a concentration of 10-100 μM.

(2) Chloroplasts: Isolated chloroplasts or leaf tissue.

(3) Photosynthesis equipment: Use a spectrophotometer or fluorescence spectrometer to detect the absorption or fluorescence changes of Methyl Purple.

(4) Electron transport inhibitor (optional): Photosystem II inhibitors such as DCMU can be used to evaluate PSI dysfunction.

2. Steps:

(1) Preparation of Methyl Purple solution: Dissolve Methyl Purple in an appropriate solvent or buffer to prepare a solution of the desired concentration.

(2) Sample preparation: Incubate isolated chloroplasts or leaf tissue with Methyl Purple solution, usually for 10-30 minutes, to allow the dye to interact with PSI.

(3) Activity measurement: Use a spectrophotometer or fluorescence spectrometer to measure the absorption or fluorescence changes of Methyl Purple, usually in the wavelength range of 500-600 nm.
For example, the absorption or emission spectrum of Methyl Purple can reflect the changes in the red oxygen reduction state of PSI.
(4) Result analysis: Compare the changes in the optical properties of Methyl Purple under different conditions (such as the presence or absence of electron transfer inhibitors) to understand the function of PSI.
II. Photosynthesis efficiency study
1. Material preparation:
(1) Methyl Purple dye: Same as above.
(2) Plant samples or chloroplasts: Plant samples or isolated chloroplasts.
(3) Light source: Controlled light source is used to simulate different light intensities or conditions.
(4) Oxygen or carbon dioxide monitoring system (optional): Used to more comprehensively study the photosynthesis process.
2. Steps:
(1) Sample preparation: Isolate chloroplasts or prepare plant samples.
(2) Dye application: Add Methyl Purple dye to the sample.
(3) Light treatment: Expose the sample to light of different intensities or conditions (e.g., high light intensity stress, low light, etc.).
(4) Fluorescence/absorption measurement: Measure the fluorescence or absorption changes of Methyl Purple to correlate PSI activity and photosynthesis efficiency.