Method to Estimate Phytochrome
Since there is no chemical test, the only method available to test and estimate phytochrome is the spectrophotometric method. Firstly, the difference in the absorbance between 660 and 730 nm is measured after red light irradiation (Δ OD red, No. 1.). Next, the sample is irradiated with far-red light and again the difference in Δ OD is measured (Δ OD far-red, No. 2). The content of total phytochrome is measured by subtracting the value obtained after red light irradiation from far-red light irradiated value.
Nowadays special, spectrophotometers are also available which can measure the absorption difference between two wavelengths. These are called dual wavelength spectrophotometers.