Plant Physiology 2-Photosynthesis

photosynthesisPhoto means light and synthesis means to makeProcess in which plants convert carbon dioxide and water into sugars using solar energyOccurs in chloroplast

Photosynthesis: 6 CO2 + 6 H2O C6 H12 O6 + 6 O2carbon dioxide + water = sugar + oxygenTracking atomsSTARCHphotosynthetic products often stored as starchStarch = glucose polymer

features same as in Chlorophyta (green algae) 3. similar photosynthetic storage product: starch

aerobic photosynthesis more efficient than anaerobic

Fig. 10.3 Photosynthesis

Fig. 10.1

Fig. 10.2a

Fig. 10.2b

Fig. 10.2c

Fig. 10.4

Chlorophyll Absorbs red & blue lightReflects green light

Fig. 10.6

Fig. 10.8

Fig. 10.20

Fig. 10.17

RubiscoRibulose bisphosphate carboxylase oxygenase(fixes CO2 & O2)Enzyme in Calvin Cycle (1st step)Most abundant protein on EarthCa. 25% total leaf protein

PhotorespirationWhen rubisco fixes O2, not CO2Lose 1/2 C as CO2; costs 2.5 extra ATPTake up O2Only occurs in lightOccurs 1 out of 4 reactions under todays atmospheric [CO2]Rate increases with temperature

Types of photosynthesisC3The majority of plantsC4CO2 temporarily stored as 4-C organic acids resulting in more more efficient C exchange rateAdvantage in high light, high temperature, low CO2Many grasses and crops (e.g., corn, sorghum, millet, sugar cane)CAMStomata open during nightAdvantage in arid climatesMany succulents (e.g., cacti, euphorbs, bromeliades, agaves)

Fig. 10.21

Fig. 10.22

Global Environmental Change & Photosynthesis: C3 vs. C4 vs. CAMIncreasing CO2 Increasing chronic and acute temperaturesIncreasing N (vs. decreasing C:N from increasing CO2)Changes in water

CO2 effects on photosynthesisC4 > C3 at low CO2 But, C3 > C4 at high CO2

*At high CO2, C3 more efficient than C4 at all temps.(photosynthesis only, not other processes)

Photosynthetic N-use efficiencyC4 plants need (have) less leaf N than C3Photosynthesis higher per unit N in C4Humans are increasing global N, which benefits C3 more than C4Increasing CO2 decreases leaf N content, more in C3 than C4

Photosynthetic water-use efficiencyC4 plants use less water than C3(cause stomates open less)Water availability may increase or decrease in the future.

Predicting the future for plantsHow will increases in CO2, N, and chronic and acute heat stress affect photosynthesis?Who will win or lose? C3? C4?How will pollution (eg, ozone) interact?Current research in my lab an example.

Elevated CO2Increased leaf C:NDecreased Heat-shock proteins (Hsps)Decreased thermotolerance

High CO2 effects greater in C3 than C4 and CAM species.

High CO2 effects greater on induced than basal thermotolerance.

Hypothesis

Heat stress decreased Pn in all species(not the result of stomatal closure).

Elevated CO2 had negative effects on Pn of C4 species, and positive effects on C3 species.

Pre-heat shock has a positive effect on Pn.

Heat shock decreased et of all C3 and C4 speciesThere was negative CO2 effects on all species, except for wheatThere was positive Pre-HS effects on all species

SoyFACE: CO2 & ozone

features same as in Chlorophyta (green algae) 3. similar photosynthetic storage product: starch

aerobic photosynthesis more efficient than anaerobic

Fig. 10.3 Photosynthesis