Photosynthesis is the greatest natural process on Earth, converting sunlight into chemical energy on a massive scale and maintaining life. There are basically two successive stages of oxygenic photosynthesis, of which the light-dependent reactions in photosystem II (PSII), and in photosystem I (PSI), enable the oxidation of H2O into molecular oxygen, and production of reducing power (NADPH and ATP), while CO2 assimilation is generally known to take place long after oxygen evolution and NADP+ reduction, via light-independent reactions in the stroma.