can improvement in photosynthesis increase crop yield? 組別 : 第三組 指導老師 :...
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![Page 1: Can improvement in photosynthesis increase crop yield? 組別 : 第三組 指導老師 : 張孟基老師 組員 : 何佳勳 馮學謙 潘昶儒 李政錩](https://reader033.vdocuments.site/reader033/viewer/2022061506/56649c945503460f9494fec6/html5/thumbnails/1.jpg)
Can improvement in photosynthesis increase crop yield?
組別 : 第三組指導老師 : 張孟基老師組員 : 何佳勳 馮學謙 潘昶儒 李政錩
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Introduction
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The world’s most important crops and their total yield in 2004
1. Maize: 823 Mt.2. Rice: 725 Mt.3. Wheat: 555 Mt.4. Barley: 142 Mt.5. Sorgnum: 59 Mt.
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Increased use of nitrogen fertilizer and improvement management have produced remarkable increases.
The major grain crops yield rose from 1.2t/Ha in 1951 to 2.3 t/Ha in 1993.
For maize, this increase may be attributed 50% to genetic improvement and 50% to improved management.
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Monteith principle
Pn = St˙ εi˙ εc / k (1a)
Yp = Pn˙ η (1b)
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How to increase Yp ?
1.Increase εi through earlier canopy development and ground cover.
2.Select cultivars able to respond to additional nitrogen fertilization without lodging.
3.Increase CO2 concentration.
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Elevate CO2 concentration at wheat flag leaf
1.Increase photosynthesis 50%.
2.Increase grain yield 35%.
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SPECIFIC OPPORTUNITIES FOR INCREASING PHOTOSYNTHESIS
The maximum εc for two reasons:
1. leaves become light saturated : energy is wasted and efficiency drops.
the acceptor molecule of CO2 [ribulose biphosphate (RuBP)] εc at 25 °C closer to the theoretical 0.051.
2. decreasing photorespiration(光呼吸 ) Conversion of a C3 to a C4 crop would raise the maximum εc at 25 °C
from 0.051 to 0.060. If Rubisco can be engineered to be completely specific to CO2, this
would raise εc from 0.051 to 0.073
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10%
100%
1%
1400700
75°
52° lat & 25°C
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Modifying crop canopies to increase εC
Photosynthetic photon flux densities (PPFD) : C3 about one-quarter
PPFD would be amount required to saturate photosynthesis (Fig. 1c). → other leaves is wasted
the upper leaves are more vertical and the lowermost leaves are horizontal, as plant Y (Fig. 1a) (Nobel, Forseth & Long 1993).
leaf with a 75° light energy would be 700 μmol m−2 s−1, just sufficient to saturate photosynthesis
plant Y would have over double the efficiency of light energy use than plant X at midday in full sunlight (Ort & Long 2003).
This example oversimplifies : overhead , tropics , sun angle
Older varieties( horizontal leaves such as plant X ) have been replaced by newer varieties ( vertical leaves such as plant Y )(Nobel et al. 1993).
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10%
100%
1%
1400700
75°
52° lat & 25°C
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Relaxing the photoprotected state more rapidly to increase εC
As PPFD increases, photosynthesis saturates. (Fig. 1b)
This additional energy exceeds the capacity for photosynthesis will cause photooxidative(光氧化 ) damage →photosystem II (PSII )
induced increase in thermal dissipation of energy via the formation of epoxidated xanthophylls(葉黃素 ) (Long, Humphries & Falkowski 1994; Havaux & Niyogi 1999; Baroli & Niyogi 2000).
Photoprotection(光保護作用 ) it decreases the maximum quantum yield of PSII (Fv/Fm) and CO2 uptake (ΦCO2)( Zhu et al. 2004a)
Photoprotection(光保護作用 ) is at the level of the cell, not the leaf, light is simulated for small points of 104 μm rather than as an average for a leaf.
Temperature is important because it decreases photosynthetic capacity and rate of recovery from the photoprotected state. (chilling-tolerant←→ chilling-susceptible)
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Relaxing the photoprotected state more rapidly to increase εC
Much larger losses from photoprotection result when photosynthesis is decreased by stresses (Long et al. 1994).
Photoprotection(光保護 ) fulfils a necessary function of oxidative damage to PSII, and replacement of the proteins before efficiency can be restored.
In the longer term , a continued excess of excitation energy would lead to irreversible photooxidation(光氧化 ) (Long et al. 1994).
Falkowski and Dubindky (1981) identify algae(海藻 ) associated with corals(珊瑚 ) can withstand 1.5 × full sunlight of maximum photosynthetic efficiency
Increased biomass product the ‘super-high yield’ rice cultivars. (Wang et al. (2002)
Xanthophyll(葉黃素 ) cycle capacity, including the epoxidation associated with recovery (Long et al. 1994) : photoprotection is feasible in rice.
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Photorespiration
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Photorespiration
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Photorespiration
30% carbonhydrate lost in C3 photosynthesis(phs) through photorespiration(PR).
Dissipate excess excitation energy.
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Photorespiration
Xanthophyll - more effeciency in dissipating ecxess energy than PR.
How to block PR?
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Photorespiration
Lower O2 or Higher CO2 can inhibit PR enzymes activity.
Growers - increase CO2 in greenhouse. Global [CO2] increacing - other negtive effect
s.
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C4 - Kranz anatomy
Sugarcane
http://www.botany.hawaii.edu/faculty/webb/bot311/bot311-00/PSyn/PsynDark2.htm
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C4
http://www.steve.gb.com/science/photorespiration.html
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C4
QuickTime™ and a decompressor
are needed to see this picture.
Long, 2006
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C4
Steady-state biochemical models of C3 and C
4. Canopy radiation transfer models.
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C4
QuickTime™ and a decompressor
are needed to see this picture.
Long, 2006
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C4 to C3 ?
Overexpression C4 genes in C3.
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C4
Single cell form
Red dot: Rubisco
http://www.photosynthesisresearch.org/picture_gallery.html
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Regeneration of RuBP
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Ribulose1,5-bisphosphate(RuBP)
3-phosphoglycerate(PGA)
Glyceraldehyde 3-phosphate
regeneration
reduction
carboxylation
ATP
ADP
ATP+NADPH
ADP+Pi
+NADP+
CO2+H2O
Rubisco carboxylation rate
Jmax (RuBP regenerative capacity)
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Two points in this chain limit Jmax
(1) Electron transport chain - cytochrome b6/f complex
(2) Calvin cycle – sedoheptulose-1,7-bisphosphatase (SBPase)
strongly control the rate of RuBP synthesis
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(Raines C. A., 2003)
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Increased SBPase activity intransgenic tobacco plants stimulates photosynthesisand growth
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(Lefebvre et al. 2005)
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Overview of opportunities and barriers
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Conventional plant breeding-needed several years, several generations to introduce changes
Molecular transformation -> a single gene transformation -> saving conventional breeding time
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direct effect of elevated [CO2]
suppress oxygenation and photorespiration
higher photosynthesis and yield
[CO2] negative effect (increase temperature, decrease soil moisture)
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Increase C3 εc
-> decreasing photorespiration -> increased Rubisco specificity for CO2
-> engineering C4 photosynthesis into C3 crops
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engineering C4 photosynthesis into C3 crops
introduction of the C4 photosynthetic cycle Kranz leaf anatomy associated differential expression of photosynthetic protein
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conclusion
Increase the theoretical maximum εc of C3 or C4 crops do not appear realizable on a 10-20 years
Conventional breeding – require introduction of foreign genetic material
Both environmental stress and respiration improve the tolerance of εc to stress
decrease respiration to increase εc
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預備用
QuickTime™ and a decompressor
are needed to see this picture.