L23 Temperature as a Limiting Factor in PS and Crop Production Flashcards
what are the main factors limiting primary production?
water and temperature stress
light and mineral elements in soil
what metabolic solutions have plants evolved to temperature and water stress?
temp - generating internal heat
water - closing stomata during the day
how much of the 100% solar radiation is actually used by plant?
24%
how much solar energy is used to produce carbohydrate sugars?
19% of solar energy is lost during metabolism
5% goes towards making carbohydrates
why are solar panels ‘more efficient’ at absorbing/ using solar energy?
they use less ~11-15% and they only prodce hydrogen as a by-product not complex carbohydrate
what causes decreased yields in crop production?
plants not being accurately adapted to their introduced climate and soil conditions (temp and water stress)
where is the highest concentration of cholorophyll/ rate of photosynthesis/ primary production observed?
less extremes in temperature (10-20degrees) and maximum rainfall
what plant can grow at low temps -5 to 5 degrees?
ice algae
what plant can grow at mid temps 10 to 40 degrees?
maize
what plant can grow at high temps 45 to 50 degrees?
thermophilic algae
what environmental signals turn plant metabolism off?
day length shortening and temperature decrease
how do plants survive freezing temperatures?
1) remove water from cytoplasm in pre-dormancy period (cellular structures cannot freeze and will not be damaged)
2) flood cytoplasm vacuole with carbohydrate and proteins which lower freezing point
what are ‘anti freeze molecules’ in plants?
carbohydrate storage in vacuoles
when do heat shock proteins become activated?
in stress conditions - extreme temperatures
what are heatshock proteins?
they are chaperones that control the aggregation and misfolding of proteins
what are the weight classes of heat shock proteins?
HSP100, HSP90, HSP70 and HSP 60
what 2 processes share a common pathway?
photosynthesis and transpiration
where does gaseous diffusion occur in the plant?
stomata openings
what gradient helps with CO2 diffusion into the plant?
water within the plant versus outside of the plant - this is because when stomata are open water is lost
what abiotic factor influences opening and closing of stomata?
temperature
how much water is lost during photosynthesis?
250-500 moles
when water is lost from the leaves what else happens?
heat loss
what happens during the Calvin cycle?
CO2 is converted into sugar
Describe C3 plants
they have a low water use efficiency
why can water loss/ transpiration be beneficial to plants?
it is a means of heatloss
what enzyme converts CO2 into sugar during Calvin cycle?
rubisco
Describe rubisco
large mass - 560kDa
very slow acting
what happens if we add more rubisco enzymes to plants?
no effect
what happens if oxygen is used in photosynthesis instead of CO2?
we get 2 carbon acid instead of a 3 carbon sugar, metabolic dead end because it cannot enter calvin cycle
what is produced when rubisco breaks down CO2?
2 phosphoglycerate molecules (3 carbon sugars) that can enter calvin cycle
where does the rubisco and CO2 carboxylation reaction occur?
choroplast with help of proxy zone and mitochondria
what is produced when rubisco reacts with oxygen during oxygenation?
phosphoglycerate and phosphoglycollate (can’t enter Calvin Cycle)
what occurs during ‘photo respiration’?
- carboxylation and oxygenation
- ruBP acts on CO2 to make 2 phosphoglycerate molecules
- ruBP acts on O2 to make 1 phosphoglycerate and 1 phosphoglycollate
how do you inactivate photorespiration pathway?
increase O2 production
how do C4 plants overcome photorespiration?
they increase CO2 concentration at active site of rubisco enzyme
what enzyme is more efficient than rubisco and why?
phosphoenol pyruvate carboxylase (PEPco), produces 4 carbon acids while knocking off photo respiration allowing high rates of sugar production
what is photorespiration?
a respiratory process in which plants take up oxygen in the light and give out some carbon dioxide, contrary to the general pattern of photosynthesis
what are C3 plants?
plants that use C3 pathway to convert CO2 into 3-phosphoglycerate for Calvin Cycle
what are C4 plants?
plants that use C4 pathway to produce oxaloacetic acid for Calvin Cycle
examples of C3 plants
oats, ryes, wheats, rice, cotton, sunflower
examples of C4 plants
maize, sugar cane, desert succulents
what is the relationship between heat generation and respiration in the spadix?
linear - as rate of respiration increases, rate of thermogenesis increases
how can respiratory systems support high rates of thermogenesis when limiting in ADP?
ADP is uncoupled from cellular respiration
how can we measure the rate of photosynthesis?
monitoring dissolved oxygen
what initiates oxygen reduction to H2O in photosynthesis?
succinate
what does SHAM inhibit?
cyanide resistant pathway in photosynthesis
what does cyanide inhibit?
electron flow through ETC cytochromes
what does addition of ADP do?
facilitates formation of proton gradient - oxygen is uptaken/ decreases significantly
rate of respiration doubles
what allows plants to generate heat quickly?
uncoupling respiration ETC from ATP and using alternative oxidase which is cyanide insensitive but sensitive to SHAM
