TWO PIGMENT SYSTEMS

Two Pigment Systems: 

In result of red drop and Emerson effect it was concluded that at least two pigment systems are involved in photosynthesis. These two pigment systems are -

1. PS1 (piment system 1)

2.PS2(pigment system 2)

Presence of two such systems has been supported by studies based on chloroplast fractionation process which showed two types of particles within the chloroplast membrane. Acc . to Salisbury and Ross in 1986 smaller and lighter particles of PS I(located in non-appressed regions (stroma lamella) of  thylakoids) and larger and heavier particles of PS II(in appressed regions (grana ) of thylakoids ).

PS I complex -

• Consists of 200 chlorophylls, 50 carotenoids and  a molecule of P 700.
• Cytochrome f, one plastocyanin, two cyt-b, FRS (ferredoxin reducing substance), one or two membrane bound ferredoxin molecules etc.are also present.
• Primary electron acceptor is Fd .
• The carotenoids collect light energy for both the systems. Reduced carotenoids such as carotenes are found in PS-I. 
• It is rich in chl-a, iron and copper.  PS I controls the process of producing a strong reductant to reduce NADP into NADPH + H+.
• It involves in cyclic as well as non cyclic phosphorylation .
• It is not associated with photolysis of water .
• Main function is ATP sunthesis and production of NADPH.

Z-scheme of elctron transport chain 

Image source credit -http://www.bio.miami.edu/dana/226/226F08_10print.html

PSII complex -

• Consists of 200 chlorophylls, 50 carotenoids, a molecule of P 680, and a primary electronacceptor Q as plastoquinone, four plastoquinone equivalents four Mn++molecules bound to one or more proteins, two cyt-b6 559, one cyt-b6 and chloride. 
•  PS II is concerned with generation of strong oxidant and weak reductant coupled with the release of oxygen.
• More oxidised forms as xanthophylls, violaxanthin and neoxanthin are found in PS-II. 
• It involves in both non-cyclic phosphorylation .
• It is associated with photolysis of water.

(water molecules lyse using light energy, produces H+ ions (protons) e- (electrons) and oxygen. )

                                                 Image source credit -http://www.memrise.com/mem/2084591/photolysis-of-water/

• Main function is ATP synthesis and hydrolysis of water.

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