Plant Functions Adapted from Slide presentation of Dr Yann Guisard

Lecturer Production HorticultureSchool of Agriculture and Wine Sciences

Orange, NSW, 2800

The Story Of Water

Transpiration

loss of water from leaf surfacesvia ‘stomata’

Source: http://remf.dartmouth.edu/images/botanicalLeafSEM/source/16.html *License on site: http://remf.dartmouth.edu/imagesindex.html |Date=12-18-07)77

Transpiration

Helps regulate leaf temperature

Some plants have modified leaves to control rate of transpiration

Leaves with waxy surface ‘cuticle’ reduce water loss

Plants transpire 98% of water absorbed by roots

The cross section of a root

Water absorption by roots

Water moves in root via apoplast and symplast

Apoplast – water moves through the cell without crossing any membranes

Symplast – water travels from one cell to the next via the plasmodesmata

Impatiens – blue dye

• Stomata = Small opening surrounded by guard cells• Grapevines stomatal density = 80 – 400 / mm2

C3 C4

The cross section of a leaf

Stomata open carbon dioxide is absorbed and oxygen released, opening controlled by guard cells

Ratio of water (g) lost per gram CO2 fixed is Water Use Efficiency low ratio = more water efficient plant

Movement of water through stomata creates transpiration pull due to water tension

Upward movement assisted by osmosis, which also draws nutrients and soluble salts

• Physics– Cohesion– Adhesion– Capilarity– Evaporative demand = transpiration pull

• Plant role– Regulation:

• Stomata is a valve• Plants can sense the tension (water potential)

Role players in Transpiration

The story of lightLight Dependent Reactions

http://www.wunderground.com/data/wximagenew/m/Madrid/228.jpg

Photosynthesis (light-powered synthesis)

carbon dioxide (CO2) and water (H2O) are converted into carbohydrates and oxygen is released

Photosynthesis = two distinct processes

Light dependent reaction

Convert light energy into chemical energy in the form of ATP and NADPH

Use water and give off oxygen

Light independent reaction (dark reaction)

Take carbon atoms from atmospheric carbon dioxide and form organic compounds this process, carbon fixation, powered by ATP and NADPH

Photosynthesis = two distinct processes

Light dependent reaction

Convert light energy into chemical energy in the form of ATP and NADPH

Use water and give off oxygen

Light independent reaction (dark reaction)

Take carbon atoms from atmospheric carbon dioxide and form organic compounds this process, carbon fixation, powered by ATP and NADPH

Capture of the energy of light(aka Light Dependent Reactions)

• It all happens in the chloroplasts

Chloroplasts contained within plant cells, responsible for capturing light energy

Sun/light energy absorbed by thylakoid membranes

0.5-3.5% of total light energy used in photosynthesis

Remainder lost in heat and evaporation of water

Stroma

Grana

Thylakoid stacks

Hydrolysis

On the grana of the chloroplast

Split waterCreate E

Review – Light Dependent Reactions

H2O2H++2e-+O

PS2ATP

PS1NADPH

The story of carbon capture and fixation:

Light independent reactions

In the stroma of the chloroplast

3 turns 1 PGAL (3C)6 turns 2 PGAL (6C) 1 glucose (6C)

Most abundant enzyme in the world.

The C3 (Calvin) cycle

Photosynthesis in C3 plants is inefficient:Photorespiration

• C3 plants = 85% of all plants• Competition with photosynthesis for

RuBP• Inefficiency of C3 plants• Uses up oxygen

C4 plants (Corn, Sugarcane, Sorghum)• First detectable molecule formed by CO2

fixation is a 4 C molecule (C4)

C4

• Oxaloacetate is found in very high concentration in the mesophyll cells

• Environment is saturated with CO2

• Very rare to observe photorespiration

CAM (Pineapple, Cacti)

• Crassulacean Acid Metabolism

• Stomata open during night times and fix CO2 in the vacuoles (4 C compound, Malic Acid)

• Stomata closed during daytime (to save water) and C3 pathway is used

C3 – named due to first stable compound formed in dark reactions is a 3-carbon compound (stomata opened during day)

C4 – carbon is incorporated into 4-carbon compound, before dark reactions (stomata open or closed during day)

CAM – similar to C4 (stomata opened during night)

C3 – carbon dioxide absorbed during day with stomata open with glucose formed in the dark reactions

Stomata open all day can increase respiration during times of heat stress and drought

Limited by excess light exposure and high temperatures

C4 – carbon dioxide absorbed before it enters dark reactions

Stomata can be closed during day while carbon dioxide is captured by internal respiration, rather than carbon dioxide from outside

Photosynthesis can occur under conditions of moisture stress, when C3 plants would be limited

Despite C3 limitations, majority of world food production comes from such C3 plants as rice and wheat

CAM (crassulacean acid metabolism) photosynthesis

Similar to C4 photosynthesis

Stomata closed during day and opened at night

Loss of moisture reduced

Carbon dioxide stored and processed during day in dark reaction

CAM plants sacrifice growth and photosynthetic rates in exchange for tolerance of extreme conditions

C3 plants – cotton, grapevines, serrated tussock

represent approx. 90% earths plant biomass

grow better in cooler weather, good soil moisture

C4 plants – maize, sugar cane, mostly in grasses, i.e., PoaceaeKangaroo grass

represent approx. 3% earths plant biomass

are more tolerant of drought, heat and nitrogen deficiency

CAM plants – cactus, agave, hopbush (native to Australia)

Open stomata at night to avoid increased transpiration during heat of day

Carbon dioxide stored at night converted to carbohydrates with radiant energy during day

Comparison of C3, C4 and CAM photosynthesis pathways

C3 C4 CAM

Optimum temp. (°C)

15-30 30-45 30-35

Max. growth rate (g/dm2/day)

1 4 0.02

Stomata Open day, closed night

Open or closed day, closed night

Closed day, open night

Translocation

transfer of food materials or products of metabolism throughout plants

sugar produced in photosynthesis is the primary metabolite that is translocated from leaf to fruit, roots and grains

most translocation occurs in the phloem, up and down movement

Xylem

Thick secondary cell walls, often deposited unevenly in a coil-like pattern so that they may stretch

Dead at functional maturity (wood)

Involved in conduct of water and ions in the plant

Phloem

Involved in transport of sucrose, other organic compounds, and some ions

Living at functional maturity

Carbon Movement :Translocation

Pressure flow theory