physiology of organisims- photosynthesis and photorespiration

photosynthesis paved to life on earth

o2 at least 2-3.5 billion years (i.e cyanobacteria) → consumed by weathering of iron and other chemicals in rocj

primary producers

plant and Algae

photosynthetic bacteria

plant dry mass in carbon

40%

production of carbohydrates

-energy storage

-structural components

-source of energy to produce ATP in cellular respiration

Anoxygenic photosynthesis

-anerobic respirationd

-purple and green sulphur bacteria

-use hydrogen sulphide, sulphide ions, hydrogen, ferrous ions, organic substrates

shorter wavelength light means

higher the energy the longer the wavelength light

light dependent reaction

thylakoids

light dependent

stroma

chloroplast important roles

-photosynthesis

-C,N,S reduction and assimilation

-biosynthesis of AA, fatty acids, chlorophyll and carotenoids

-production of phytohormones

chloroplast key locations

-Thylakoid

-lumen

-stroma

land plants have distinctive grana stacks in the thylakoids

membranes at the margins are non-appressed (green) and those within the grana stacks (red) and those appressed vs non-appressed regions of the thylakoids

excited chlorophyll energy can be released in several ways

-photochemistry

-flurorescene

-it can convert to a damaging triplet state

The fate of captured energy and photosynthetic efficency

depends on many factors including temperature, water avalibility, nutrient avalibility, nutrient avalibility, stress, etc.

cyclic electron transport

-involves psi

does not involve psii

-involves the electron transport chain

-results in ATP production

-Does not liberate o2

-Does not produce NADPH

Low light intensities

photosynthesis is light limited as as more photons are absorbed more co2 is fixed

mitochondria

respires and consumes o2 and producing co2. in the light thet are net co2 consumers, but in the dark production is greater than consumption.

plant growth under natrual light conditions provide highly flexible short-term acclimation properties toward high light stress

•Typical characteristics of HL (or sun) acclimated plants in comparison with LL (or shade) acclimated plants are:

•(1) Increased thickness of leaves with more cell layers and larger cells

•(2) Increased number of chloroplasts per cell with reduced grana stacking

•(3) Higher Chl a/b ratio and increased β-carotene and xanthophyll cycle pigment levels

•(4) Higher photosystem II (PSII)/PSI ratio and smaller PSII antenna size

•(5) Higher electron transport rates, higher CO₂ assimilation rates and higher light compensation points

•(6) Higher energy dissipation capacity

excess excitation energy can lead to photo-oxidative damage

photon excitex chlorophyll forms excited singlet chlorophyll

chlorophyll can return to its ground state by:

-photochemistry

-flurorescene

-dissipation

alternative transport energy

it can convert to the excited triplrt state 3chl which can transfer energy to oxygen to produce singlet oxygen with subsequent damage due to reactive oxygen species

There are protective strategies to avoid high light induced damage

-decrease light incidence through dynamic changes to antenna complex

-release excess energy as heat or fleurorescene

-detoxify reactive oxygen side-products of excess excitation energy

movements to optimize light interception

-chloroplasdts move to sides of cells to decrease light interception

leaf reorientation

the curling of adaptations to minimise light damage. can also decrease heat damage.

low light

more light harvesting complexes

high light

greater photosynthetic capacity

production of carbohydrates

-atmospheric co2 producing carbohydrates

-in stroma of chloroplast

-15 chemical reactions

-carboxtlation

-reduction

-regeneration

-catalyzed by enzyme RUBISCO

rubisco in red algae

is more specific but slower than that in plants

in many organisims

cannot be both fast and specific

Rubisco in cyanobacteria algae

faster but less specific in plants

calvin benson cycle has 3 cycles

-fixation

-reduction

-regeneration

chloroplast stroma

RuBP reacts with o2 glycolate is formed

glycolate

diffuses into peroxisome where it is convered to glycline

glycline

moves the to the mitochondrion and is converred to serine releasing co2

serine

moves back to the peroxisome and is converted to glycerate

glycerate

moves to the chloroplast where it is convered into 3PG and enters the calvin cycle

when is photorespiration problem?

high temperatures

high temperatures

when stomata are closed on a hot, dry day to prevent water loss co2 levels drop as co2 is consumed in the calvin cycle but o2 increases due to the same reactions. under these conditions increased internal leaf increases the rate of photorespiration

c3 plants

-3-carbon molecule as 1st product of co2, fixation: 3 phosphoglycerate

-plants showing this form of p/s are reffered to c3 plants

-these plants include rice, wheat, barley, oats and soybeans

-the c3 pathway is the evolutionary the oldest plant carbonfixation pathway, and may be considered as the basic or fundemental c-fixation mechanism

c4 plants

-7600 plants (3%) including sugarcane and corn use this pathway.

-note low number of species → recent evolution

-4 carbon molecule: oxaloactate

-An extra enzyme: phosphoenolpyruvate carboxlase

-higher affinity to co2 even at v. low

-no oxygenase activity

-different leaf anatomy

corn

is the most economically important crop plant

sugar cane

is the second most economically important c4 plant and the 6th most economically important crop plant

most c4 plants have Kranz

in plants with kranz anatomy bubdle sheath cells form a ring arounf the vascular tissue and mesophyll cells form a ring around them

c4 plants- spatial

PEP carboxxylase in cytosol of mesophyll cells, fixes co2 to produce 4c oxaloacetate

c3 plants in colder temepratures

has a slight advantage because there is additonal carboxylation steps of c4 require energy

photorespiration increases at high temperatures

-rubidco selectivly decreases

-the realitive soulibility of co2 to o2 decreases

what causes photorespiration supression?

the increase of co2

CAM plants

-found among some succulent plnats, cacti, pineapple, and several other plant families associated with arid regions

plants are open to storma

they store co2 during the night and perform photosynthesis during the day when stomata are closed

-similar to c4: first compound is 4c

-co2 fixation and calvin cycle are seperate in TIME.

crassulacean acid metabolism

1. co2 uptake at night (less water is lost through open stoma at night )

2. HCO3 is fixed by PEPC

3. CO2 is stored as c4 acids in the vacuole

4. Daytime decarboxylation releases co2

5. Rubisco fixes co2 during the day even though stomata is closed

Tequila

made from agave tequiliana and other agave species are grown for fibers and some potentially hold bioenergy crops.

effects of rising co2 on plants

-for much of plant evolution history atmospheric co2 levels were above 1000ppb and not limiting for growth of most plants

-currently atmospheric co2 levels are in the midst of a rapid and dramatic increase, starting with the industrial evolution

-co2 concentration mechanisms in plants envolved within the last 65 million years in response to decreasing levels of atmospheric co2

C₃ plants are expected to benefit more than C₄ or CAM plants from elevated CO₂

This is due to them being able to concentrate co2 carbon-fixation in c4 plants saturates at a lower than ambient co2 levels

-in c3 plants carbon-assimillation increases with increasing co2

the combination of drought and heat is particulary challenging

-drought decreases carbon assimilation by decreasing the uptake of co2 thereby lowering ci (internal concentration of co2)

-heat deactivates rubisco

-drought + heat stress combine to severly inhibit photosynthesis

plants grown in elavated co2 often show a decrease protein and nutrient content

results of a meta analysis show that when plants are grown in elavated co2 they (and the food they produce) contains more c but less n (protein) and other macro and micro nutrients essential for human health.