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## Photosynthesis (光合成)

Mount Usu / Sarobetsu post-mined peatland
From left: Crater basin in 1986 and 2006. Cottongrass / Daylily

#### Life is woven from the air by light

That is the conversion from light energy to chemical energy (stocked into carbohydrates, represented by glucose, sucrose and starch) by green plants.
##### Equation
6CO2 + 12H2O + [solar energy] → C6H12O6 + 6O2 + 6H2O
carbon dioxide + water + [solar energy] → glucose + oxygen + water
Do not understand by the simplified equation. You can not understand why water is important, although you might learn this equation when you were in high school.

6CO2 + 6H2O + [solar energy] → C6H12O6 + 6O2

#### Characteristics of photosynthesis on terrestrial vascular plants

CO2, 6 moles = 134.4 liters at standard temperature and pressure
##### Fig. Photosynthesis for making budget
Visible light (solar radiation) → absorbed by leaves
Water → absorbed from soil (土壌) (or water) by roots ()

### Metabolism patterns on photosynthesis (光合成における代謝様式)

#### Calvin(-Benson) cycle (カルビン(=ベンソン)回路)

= reductive pentosephosphate cycle (還元的ペントースリン酸回路)
= photosynthetic carbon reduction, PCR (光合成的炭素還元回路)
= C3 cycle (C3回路)

Three molecules of CO2 fixed give a net yield of one molecule of glyceraldehyde 3-phosphate at a net cost of nine molecules of ATP and six molecules of NADPH.

ribulose-1, 5-bP (ribulose 1, 5-bisphosphate) 5C
3-P-glycerat (3-phosphoglycerate) 3C
1, 3-bP-glycerat (1, 3-diphosphoglycerate) 3C
GAP (glyceraldehyde 3-phosphate) 3C
ribulose-5-P (ribulose 5-phosphate) 5C

1950 Calvin, et al.: discovered this cycle

### Ecophysiology of photosynthesis (光合成の生理生態)

Photosynthesis requires the efficient capture of light whilst avoiding the absorption of damaging excess energy.
Light absorption can be optimised by plant growth, the movement of leaves and the movement of chloroplasts within leaves.
To grow optimally, plants must achieve a balance between the capture of light and the uptake of other resources.
Plants living in shaded conditions have adaptations to efficiently capture light including increased shoot:root ratios, thin leaves and high chlorophyll concentrations.
Both C4 and CAM involve a separation of CO2 absorption and fixation: C4 spatially and CAM temporally.
If a plant is to survive, grow and reproduce, it must make a net gain in carbon, that is, carbon gained through photosynthesis must be greater than carbon lost through respiration.
Photosynthesis makes a significant contribution to carbon uptake from the atmosphere and may go some way to offsetting atmospheric increases due to human activity.
Understanding the effects of global warming on photosynthesis is complex but necessary to fully understand the consequences of climate change.

#### Nitrogen assimilation and photosynthesis (窒素同化と光合成)

Eq. Specific leaf area, SLA = A/WL (m2/g)

the ratio of leaf area to leaf dry mass

A: the area of a given leaf (or all leaves of a plant)
WL: the dry mass of those leaves

Eq. leaf weight ratio, LWR = WL/W

= leaf mass ratio, LMR, or leaf weight fraction, LWF

Eq. Leaf mass area, LMA = 1/SLA = WL/A (g/m2)

formerly called specific leaf weight, SLW

##### Photosynthetic nitrogen-use efficiency (PNUE)
the ratio of CO2 assimilation rate to leaf organic nitrogen content

### Carbohydrate and metabolism (炭酸同化と代謝)

To reduce photorespiration, C3 plants → C4 plants
##### C3 plant (C3植物)
photorespiration present (Calvin cycle)
spinach, peanuts, cotton, wheat, rice, barley and most trees and grasses

Photosynthetic metabolism in the chloroplasts of C3 plants. 1,3BPG, bisphosphoglycerate; G-3-P, glyceraldehyde 3-phosphate; DHAP, dihydroxyacetone phosphate; F-1,6-P, fructose 1,6-bisphosphate; F-6-P, fructose 6-phosphate; X-5-P, xylose 5-phosphate; E-4-P, erythrose 4-phosphate; S-1,7-P, sedoheptulose 1,7-bisphosphate; S-7-P, sedoheptulose 7-phosphate
##### C4 plant (C4植物)
= Hatch-Slack pathway (Hatch & Slack 1966)
photorespiration absent
Table. Characteristics of photosynthetic parameters on C4 plants.
C4 plants                         Sjoa-bean Sunflower Sugar-beat Tobacco Corn
Optimal temperature (°C)      26             25               25            25       35
O2 fixation (CO2 mg/dm2/h)   35             28              25             11       55
Photorespiration (lost O2 %)  46             27              47             55        0

+ sugar cane, millet, sorghum, pineapple, daisies, cabbage, etc.

##### CAM plant (CAM植物)
= crassulacean acid metabolism
cacti, sedum, jade, orchids and agave
Instead of separating the light-dependent reactions and the use of CO2 in the Calvin cycle in space, CAM plants separate these processes in time (night and day).

____________↓CO2
Night: PEP →→→→→ oxaloacetete →→→ malate
______PEP carboxylase______________or other organic acids
_____________________________________
______←←←←←←←←←←←←←←←←←←
__________________
Day:_____________ CO2
__________________Rubisco
______________Calvin cycle
_______sugars ←↑______
_______________←←←←

#### Glyconeogenesis (糖新生)

Def. a shunt for the synthesis of sugars such as glucose and glycogen from substances other than sugars (☛ glyoxylate cycle)

carbohydrates → sugar phosphate and sugar nucleotide
GTP + UTP → UDP-glucose + PPi
ATP → ADP-glucose ⇒ synthesis of starch
GTP → GDP-glucose ⇒ synthesis of cellulose
Glucose → galactose
UDP-glucose → UDP-galactose

### Photoinhibition (光阻害)

Light-induced reduction in the photosynthetic capacity of a plant, alga, and cyanobacterium
≈ light-induced damage to PSII ∵ photosystem II (PSII) is most sensitive