Cytochromes are proteins with characteristic strong absorption of visible light due to their iron-containing haem prosthatic groups. Like complex III (ubiquinone to cytochrome-c) of mitochondria, the cytochrome b6f in chloroplast conveys electrons from a reduced quinone a mobile-lipid soluble carrier of two electrons (Q in mitochondria, PQB in chloroplasts) to a water soluble protein thatcarries one electron (cytochrome-c in mitochondria plastocyanin in chloroplast). In the photochemical reaction of photosystem II, the excited P680 transfer an electron to pheophytin within picoseconds giving it a negative charge. The pheophytin very rapidly passes its extra electron to protein bound plastoquinone. In photosystem-I, the excited P700 loses an electron to an acceptor A0 i.e. becomes P700+ . The P700+ is a strong oxidizing agent which quickly acquires an electron from plastocyanin (a soluble Cu containing electron transfer protein). Phytochrome is an amorphous photoreceptor chromoprotein or protein pigment which exists in two states i.e., blue and yellowish green, phytochrome is active above 550nm. It regulates many developmental phenomenon in plants like germination of seeds, photomorphogenesis, photoperiodism etc.