5# Plant Phy Fact Aff Photosyn

7/30/2019 5# Plant Phy Fact Aff Photosyn

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Factor affecting photosynthesis

Mochammad Roviq


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Light absorption

Absorption spectra of chlorophyll a, chlorophyll b, b-caroteneand fucoxanthin (a carotenol/ xanthophyll). Maximal energy ofsunlight lies in the green and yellow regions of the spectrum, the

minimum region of absorption by chlorophylls and carotenoids.Adapted from Goodwin & Mercer (1972).


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Photosynthetic Active Radiation (PAR)

Chlorophyllmengabsorbsicahayamerah (660nm) dan biru (450

nm) Kedua cahaya

tersebut disebutPhotosynthetic

Wavelength of Lightatau disebut juga:PhotosyntheticActive Radiation

(PAR)


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Light Utilization

The efficiency of energyutilization at differentwavelengths in leaves of 8species of crop plants grownin the field (A), and 20 species

grown in a growth chamber(B).

The efficiency is expressed asquantum yield, i.e. amount ofC fixed for the same numberof quanta, setting the

maximum yield at unity. From McCree (1972).

Elsevier Science.


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Levels of irradiance and rates of

photosynthesis

Light saturationcurves ofphotosynthesis forplants of Sinapis

alba grown eitherunder strongillumination, light(sun) plants

(dashed lines), orweak illumination,shade plants(solid lines).


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C3 and C4

Photosynthesis


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Irradiance level

The light value on the X-axis through which the linepasses is called the "lightcompensation point."

Where the curves cut thex-axis is the lightcompensation point,below which respirationexceeds photosynthesis(negative CO2 uptake =CO2 output); this point

lies at a lower irradiancefor the shade plants.


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The carbon dioxide need

The amount of carbon dioxide constantly being taken fromthe atmosphere during daylight hours by all green plants isenormous.

Just four-tenths of a hectare (1 acre) of corn (10,000 plants)

accumulates more than 2,500 kilograms (5,512 pounds) ofcarbon from the atmosphere during a growing season.

Over 10 metric tons (11 tons) of carbon dioxide are neededto furnish this much carbon.

It also has been calculated that the total present

atmospheric supply of carbon dioxide (more than 2.2 billionmetric tons or about 50 metric tons over each hectare ofthe earths surface) would be completely used up in about22 years if it were not constantly being replenished.


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CO2 Content

Glycine max(soybean)leaf was excised fromexperimental-gardengrown plant and then lightacclimated at 1500 molm-2 s-1 (saturating) in a lab

The intercellular CO2 (Ci)at which photosynthesistransitions from VC-limitedto J-limited is 216 molCO2 mol

-1 air.

Stomatal limitation to

photosynthesis (l) is theeffect of the stomataresistance restrictingphotosynthesis decreasingCO2 available forphotosynthesis at growthCO2 concentration


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Internal CO2


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CO2

The response of net photosynthesis (A) to CO2 concentration.

The curved solid line shows the biochemical response of net

photosynthesis to CO2 concentration. The rate of net photosynthesisis a function of the CO2 concentration in the chloroplasts (Cc).

The decrease in CO2 concentration from the atmosphere (Ca) tochloroplasts (Cc) is a function of the sum of stomatal and internalconductances (dashed lines).


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CO2


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CO2


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CO2 Content

Ambient

Elevated


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Temperature and CO2

In the atmosphere, theconcentration of carbondioxide ranges from .03 to.04 %. However, it is foundthat 0.1% of carbondioxide in the atmosphereincreases the rate of

photosynthesissignificantly. This isachieved in thegreenhouses which areenclosed chambers whereplants are grown undercontrolled conditions. The

concentration is increasedby installing gas burnerswhich liberate carbondioxide as the gas burns


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Temperature and CO2

Jurik et al. (1984) exposed bigtoothaspen leaves to atmospheric CO2concentrations of 325 ppm and1935 ppm and measured theirphotosynthetic rates at a numberof different temperatures.

At 25C, where the netphotosynthetic rate of the leavesexposed to 325 ppm CO2 ismaximal, the extra CO2 of thisstudy boosted the netphotosynthetic rate of the foliage

by nearly 100%; and at 36C, wherethe net photosynthetic rate of theleaves exposed to 1935 ppm CO2 ismaximal, the extra CO2 boostedthe net photosynthetic rate of thefoliage by a whopping 450%.


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Temperature

In C3 plants, quantumyield ofphotosynthesisdecreases as

temperaturesincrease, whereas inC4 plants, thequantum yield ofphotosynthesis is not

significantly affectedby temperaturefluctuations between10C and 40C.


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Temperature

An optimum temperatureranging from 25oC to 35oCis required for a good rate.At temperatures around0oC the enzymes stopworking and at very hightemperatures the enzymesare denatured.

Since both the stages ofphotosynthesis requireenzyme activity, the

temperature has an affecton the rate ofphotosynthesis.


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Leaf temperature

Thephotosynthetictemperatureresponse followsa broad, bellshaped curve,with theconsequence thatplants reach> 80 % ofmaximumphotosynthesisover a broadrange oftemperatures


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Leaf temperature

Net photosynthesisas a function of leaftemperature in

sweet orange leafdiscs excised fromplants grown underdifferent conditions

in relation to theenvironmentaltemperature.


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Chlorophyll

Chloroplasts of most plants contain two majorkinds of chlorophyll associated with thethylakoid membranes.

Chlorophyll a is blue-green in color and hasthe formula C55H72MgN4O5.

Chlorophyll b is yellow-green in color andhas

the formula C55H70MgN4O6. Usually, a chloroplast has about three times

more chlorophyll a than b.


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Kadar klorofil

Klorofil merupakan pigmen yang menangkap energi cahaya danmengubah energinya menjadi energi kimia

Klorofil terdapat dalam kloroplas adalah 20-100 kloroplas / selmesophyll dalam daun

Klorosis adalah menguningnya daun karena kekurangan klorofil

Jika klorofil berkurang, maka laju fotosintesis juga akan menurun Penyebab khlorosis:

Penyakit

Kekurangan Nutrisi

N dan Mg merupakan bagian dari molekul klorofil

K diperlukan untuk aktivasi enzim dalam produksi klorofil Defisiensi nutrisi yang lain juga dapat menyebabkan klorosis juga

mereduksi laju fotosintesis


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Chlorophyll

The figure showsphotosynthesisdeclining wellbefore chlorophyll

is lost from leavesof meadowfescue. Theinteresting

behaviour of astaygreen mutantis also presented.


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The rate of photosynthesis changes similarly

with change of irradiance whether expressed

per unit of leaf area or unit of chlorophyll,

showing that the differences in ratesbetween sun and shade plants do not just

result from a difference in total chlorophyll

per unit area of leaf.


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Physiology characteristics Leaf Age

Total protein

Rubisco

Non rubiscoprotein

Chlorophyll

Photosynthesis Respiration


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Leaf age on male and female plant

Photosynthetic light response curves for Siparuna grandiflora leavesof four ages on male and female plants. Each curve was fit to the

data from four leaves


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Water supply

Less than 1% of all the water absorbed by plants is used in photosynthesis;most of the remainder is transpired or incorporated into cytoplasm,vacuoles, and other materials.

The water used is the source of electrons involved in photosynthesis, andthe oxygen released is a by-product, even though carbon dioxide alsocontains oxygen.

This has been demonstrated by conducting photosynthetic experimentsusing either carbon dioxide or water containing isotopes of oxygen.

When the isotope is used only in the water, it appears in the oxygen gasreleased.

If, however, it is used only in the carbon dioxide, it is confined to the sugarand water produced and never appears in the oxygen gas, demonstrating

clearly that the water is the sole source of the oxygen released. If water is in short supply, it may indirectly become a limiting factor in

photosynthesis; under such circumstances, the stomata usually close andsharply reduce the carbon dioxide supply.

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5# Plant Phy Fact Aff Photosyn