Process of Hatch-Slack Pathway It is a cyclic process. The primary CO2 acceptor molecule is a three- carbon molecule Phosphoenol pyruvate (PEP) and it is present in mesophyll cells. The enzyme that catalyses this CO2 fixation is PEP carboxylase or PEPcase. The mesophyll cells of C4 plants lack the enzyme RUBISCO. The four carbon Oxaloacetic acid (OAA) is formed in the mesophyll cells. It is then converted to other four-carbon compound like malic acid or aspartic acid in mesophyll cells itself.Le ee Cerner) Leda Ue ora} Come] vThus, the basic pathway that results in the formation of the sugars, the calvin pathway is common to the C3 and C4 plants. Regeneration of PEP from C3 acid requires 2 ATP equivalent. However, there is no net gain or loss of NADPH in C4 cycle. ATP consumed in C4 plants: C4 cycle- 2ATP per CO2 fixed C3 cycle- 3 ATP per CO2 fixed Total-5 ATP per CO2 fixed Thus, to form a hexose or to fix 6 CO2, 6xS ATP= 30 ATP are consumed.Importance of C4 Plants 1) They can tolerate saline conditions due to abundant occurrence of organic acids ( malic and oxaloacetic acid) in them which lowers their water potential than that of soil. 2) Can perform photosynthesis even when their stomata are closed due to presence of strong CO2 fixing enzymes i.e. PEPcase 3) Concentric arrangement of cells in leaf produces smaller area in relation to volume for better water utilisation.Crassulacean Acid Metabolism ORE Meee eDOCS RCI eee TRAM IE URN e CHRO Ke MMIC e TOR OPO E CLT POC RUSE LT RCS Ne: oem race NaI Ue eT roan ee OUR ETN MMO EL ucr Cae LCed eg rou Crassulacean acid metabolism.Cee RUT CUE ee Oo ea tC day and open at night. .CAM plants possess xerophytic characters. CAM plants use the enzyme pepco (PEP carboxylase). The CAM pathway is adapted to minimise water loss and Peden abet aT Examples: Kalamchoe, Pineapple, Opuntia, etc. — _ \e ‘e BeCertain plants called CAM plants (with CrassulaceanAcid Metabolism-CAM ) have scotoactive stomata. These plants fix CO2 during night but form sugars only during day (When RuBisCO is active). E.g., Sedum, Ranson and Thomas coined the term CAM (Crassulacean Acid Metabolism) in 19 CO2 is fixed during night (dark) to OAA using PEP carboxylase. This CO2 comes from respiration (breakdown of starch) and also from the atmosphere. Malic acid gets stored in vacuoles.PSE LE Rt During Night eee ekAMRacecattny eect Toate uta pH of the Coe This is called acidificationThe malic acid formed during night is used as a source of COE Oe NUR Mn RN mCOe Keer Rte RUT LOD UNACAM CycleCAM CycleCAM Cycle Phosphoenol Pyruvic AcidDeacidification Phase: During day NEL e ati Oem m vacuole toWhen the malate(malic acid) is removed,acidity decreases in laced Se Meee em (eee ECO) 5 Pyruvate may be re-converted to PEP and synthesize sugar by Cs cycle.acid and CO2. The reaction is catalysed by malic acid decarboxylase (malic enzyme).When the malate(malic acid) is removed,acidity decreases in red aM Mee rem erect ete Pyruvate may be re-converted to PEP and synthesize Riera SOROSDuring Day. lon of sore we ard refaation of internalIn desert plants, the stomata opens at night (scotoactive stomata), therefore cupaunuiy amount of water can be conserved.