PHOTORESPIRATIONExercise 10 CHUA, Edbelyn ABENIDO, Shannen VALEZA, John Ruben Group 1 WX-5L Energy-converting Processes • Photosynthesis light energy -> chemical form (organic compounds) • Respiration • energy released: ATP • Photorespiration • does not result to ATP intermediate products: glycine and serine . Photorespiration • light + high temperature • IN: high [O2] • OUT: CO2 • Three organelles: chloroplast peroxisome mitochondrion . 1. Reactions occurring in photorespiration (Nelson and Cox.Figure 10. 2008). . Feature C3 C4 CAM leaf structure bundle sheath cells with no chloroplasts bundle sheath cells with chloroplasts mesophyll cells have large vacuoles enzyme for fixing atmospheric CO2 Rubisco PEPCase PEPCase optimum T° 15°C – 25°C 30° – 40°C 35°C .Table 10.1. Characteristics of plant groups exhibiting photorespiration. dry C3 or C4 but allows environments plants to survive in arid conditions PEPCase reduces photorespiration because it does not bind O2 Temporal mesophyll cells fix mesophyll cells fix separation of CO2 CO2 and produce CO2.Feature C3 C4 most plants efficient at midrange T° where a majority of plants grow other characteristics CAM xerophytes more efficient in not as efficient as hot. bundle fixation and glucose sheath cells glucose produce glucose production (spatial separation) . 2. Plants exhibiting photorespiration.Table 10. C3 rice tobacco soybean C4 corn sugarcane CAM pineapple kataka-taka . OBJECTIVES • compare the response of species exhibiting high and low rates of photorespiration and relate them to changes in carbon dioxide/oxygen levels . 2. . Photorespiration set-up.METHODOLOGY Figure 10. Observation of the rice (C3) and corn (C4) plants in two separate set-ups for 5 days. + .RESULTS Table 10.C4 plant .C3 plant. CONTROL PLANT PLANT INSIDE BELL JAR DAY RICE* CORN+ RICE CORN 0 high vigor green leaves high vigor green leaves green to yellow green leaves decresing vigor high vigor green leaves 1 high vigor normal leaves high vigor normal leaves light yellow leaves decreased vigor high vigor green leaves 2 normal vigor green leaves normal vigor green leaves decreased vigor thinner stem high vigor green to yellowish leaf parts * .3. Table 10. + .C3 plant. Observation of the rice (C3) and corn (C4) plants in two separate set-ups for 5 days. (continued) CONTROL PLANT PLANT INSIDE BELL JAR DAY RICE* CORN+ RICE CORN 3 healthy plant green leaves constant vigor green leaves yellow leaves thin stem green leaves with yellow tips 4 healthy plant green leaves normal vigor green leaves yellow leaves thin stem wilting of some leaves decreased vigor 5 healthy plant green leaves with some wilted leaves healthy plant green leaves yellowing of leaves many leaves wilted thin stem wilting leaves some parts healthy * .C4 plant .3. 3. Rice and corn control set-ups (left) and rice and corn inside bell jar for photorespiration set-up (right) at day 5. .RESULTS Figure 10. DISCUSSION • increased [O2]. decreased [CO2] • presence of sunlight Photosynthesis (PS) O2 produced • inc [O2]: higher photorespiration rate in C3 C3 plants do not exhibit CO2 conc mechanism • high [O2] fixation by ribulose 1.2-bisphosphate oxygenase in C3 • no ATP = no Energy for growth and maintenance of plants wilting . DISCUSSION • C4 plants spatial separation of enzymes useful when [CO2] is low • PEPCase in bundle sheath fixation of CO2 • PS still possible and continued production of ATP source of energy for plant growth and repair . since plant continues to photosynthesize induce photorespiration since C3 do not exhibit CO2 concentrating mechanism rubisco will act as oxygenase O2 fixated.Answers to Study Questions 1. NO ATP = NO Energy low source of E for growth and maintenance . Will [O2] in the set-up increase or decrease? What effect wwould there be on C3 plants for such change in O2 level? increase. . CO2 comp pt: [CO2] in which fixation is ZERO Light comp pt: reached evident with net CO2 exchange that is ZERO because of rate of PS or CO2 uptake is balanced with Respiration Additional.Answers to Study Questions 2. CCP is the pt at w/c the light level where CO2 is released during respiration is offset by CO2 fixation during PS. Define CO2 compensation point and light compensation point. CORN (C4) – low CO2 comp pt photosynthetic efficiency PS is reduced: efficient use of CO2 due to spatial separation of enzymes bundle sheath cells – CO2 fixation mesophyll cells – PEPCase . With the decline in [CO2] in the set-up.Answers to Study Questions 3. which species would still exhibit net photosynthesis after one (1) week? Explain your answer.