plant functions
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Plant Functions. Adapted from Slide presentation of Dr Yann Guisard Lecturer Production Horticulture School of Agriculture and Wine Sciences Orange, NSW, 2800. - PowerPoint PPT PresentationTRANSCRIPT
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