crop sci le 2 Flashcards
- In photosynthesis, it was seen that energy from the light reaction was used in the dark or Calvin reaction in producing the glucose
- In organisms, glucose is utilized in the presence of oxygen and broken down to carbon dioxide, water and energy. This is achieved through the process of respiration
Respiration is the apparent opposite of PS but there are salient differences in the 2 processes
- give the formula for photosynthesis and aerobic respiration
PS:
6co2+6h2o+energy (energy in) => c6h12o6+6o2
RS:
c6h12o6+6o2 (oxidation)=> 6co2+6h2o+energy (energy out)
- Respiration is also called dark respiration–The enzymatic breakdown of glucose in the presence of oxygen to produce cellular energy or ATP
- The main product of respiration is ATP, the energy currency that is required for cellular and metabolic processes in the plant
- Not the same as photorespiration!!!
- Dark respiration also occurs in the LIGHT!!
THREE Stages of Dark Respiration
- Glycolysis
- Kreb’s cycle, also known as:
a) Tricarboxylic acid cycle
b) Citric acid cycle - Electron transport system (ETS)
glycolysis
- starting materials
- products
- Glucose from photosynthesis and breakdown/ conversion of sugars; H2O
- Pyruvate or pyruvic acid; ATP (by substrate-level phosphorylation)
kreb’s cycle
- starting materials
- products
- Pyruvic acid
- CO2; NADH2 and FADH; ATP (by substrate-level phosphorylation)
electron transport chain
- starting materials
- products
- NADH2 and FADH
- ATP by oxidative phosphorylation
Energy yield for the complete oxidation of 1
glucose molecule
theoretical yield; 36-38 atp
more realistic yield; 30 atp
one of the two component of respiration
- Gross photosynthesis (P)
- Energy for converting products of photosynthesis into plant material
- k varies: 0.12 and 0.45 with plant species and plant tissues
- Rg as the source of energy
Growth Respiration (Rg)
one of the two component of respiration
- Dry mass (W)
- Energy comes protein breakdown and respiratory processes to produce CO2
- (Rm) is for Cellular functionality
Maintenance Respiration (Rm)
formulas including the two component of respiration
- k and c are coefficents for _____ respectively
R = Rg + Rm
R = kP + cW
- photosynthesis and weight
Factors That Increase Respiration Rates
- _____
- More active, younger, higher moisture content, damaged - _____
- _____
- Limited levels (hypoxia)
- Absence (anoxia)
- - Flooding is detrimental to plants due to loss of respiration - _____
- Feedback inhibition
- Accumulation of product inhibits the forward reaction
- - Storage under high CO2 decreases respiration and increases shelf life
- Age and nature of tissues
- Higher Temperature
- Increased availability of Oxygen
- Decreased levels of carbon dioxide
- Process where water moves in liquid form in plants, and
released in vapor form through aerial parts, but mostly in
leaves, to the atmosphere - Energy dependent process
- The transformation of liquid to gas phase involves use of
energy - 97-99.5% of water taken up is lost in transpiration
- formula conversion of h2o from liquid to gas
Importance of Transpiration
1. Keeps cells hydrated
2. Maintains favorable turgor pressure for the transport of nutrients absorbed by the roots from the soil
3. Cools the plant
– heat load is dissipated in the process due to the high heat of vaporization of water
– If transpiration is extremely high 🡪 dehydration and desiccation 🡪 death
*** daily water loss
–– large, well-aerated, tropical plant: 500 L
–– corn plant : 3-4 L day-1 (99% of the water absorbed by a corn plant) during its growing season is lost in transpiration)
–– tree-size desert cactus loses less than 25 mL day-1
Types of Transpiration
Based on the avenue of exit of water vapor
- Cuticular transpiration
❑ Loss of water through cuticle
❑5-10% of the water loss
❑Lenticular transpiration
- Lenticels - pores in the outer layer of a woody plant stem
❑In deciduous species (trees which sheds off leaves) and in some fruits, water
loss through lenticels may be quite substantial.
- Stomatal transpiration
❑Through the stomata
❑As much as 90% of the water lost from plants.
What affects diffusion of water from leaf to
atmosphere?
- Relative humidity (RH) (%)
❖actual water vapor in the air: water vapor pressure in leaf
❖In leaves 100% RH; in atmosphere, RH rarely exceeds 90%
❖water diffuses out from the plants to the atmosphere
- Vapor pressure deficit (VPD) (pascal (Pa))
❖Actual water vapor pressure - water vapor pressure at saturation at the same temperature
❖when VPD is 0 Pa (i.e. when RH of the atmosphere is 100%), there is no net
movement of water
❖when the RH of the atmosphere is low, the VPD is high, and the rate of transpiration is faster
Soil-Plant-Air Continuum of Water
1. Movement of water from the soil to the root xylem
a. Extracellular or apoplastic route - water moves through non-living parts,
- e.g. capillary spaces of the cell walls and intercellular spaces
b. Intracellular route
1) symplastic pathway - plasmodesmata
2) transmembrane or transcellular pathway - vacuolar membrane (tonoplast) and the plasma membranes
2 . Movement of water from root xylem to leaf xylem
- transpiration-cohesion-adhesion theory
3. Movement of water from leaf xylem to the air
- influenced by RH and VPD
- Towards lower water potential (Ψ; expressed in megaPascal, MPa)
Movement of water from root xylem to
leaf xylem
The transpiration cohesion-adhesion theory
- water vapor leaves the air spaces of the plant via the stomates
- this water is replaced by evaporation of the thin layer of water that clings to the mesophyll cells
- tension (pulling) on the water in the xylem gently pulls the water toward the direction of water loss
- the cohesion of water is strong enough to transmit this pulling force all the way down to the roots
- adhesion of water to the cell wall also aids in resisting gravity
Factors that Affect Transpiration
I. Plant Factors
1. Efficiency of evaporative surface
2. Efficiency of water absorption.
3. Other surface/stomatal modifications
4. Phytohormones
5. Canopy structure.
II. Environmental Factors
1. Edaphic (soil) factors
2. Atmospheric factors
* Light
* Relative humidity
* Temperature
* Wind velocity
* Oxygen and carbon dioxide concentrations
How Plant and Environmental Factors Affect
Transpiration
* Leaf number: more leaves, more transpiration
* Number, size, position of stomata: more and large, more transpiration, under leaf, less transpiration
* Cuticle: waxy cuticle, less evaporation from leaf surface
* Light: more gas exchange as stomata are open
* Temperature: high temperature, more evaporation, more diffusion
* Humidity: high humidity, less transpiration
* Wind: more wind, more transpiration
* Water availability: less water in soil, less transpiration (e.g. in winter, plants lose leaves)
If TRANSPIRATION is the transport of water and nutrients from soil thru roots and xylem, then
TRANSLOCATION is the movement of assimilates (sugars and other chemicals) from the leaf through the phloem to other areas for storage, utilization and consumption by the plant
Why need a transport system
in plants?
- so that cells deep within the plant tissues can
receive the nutrients they need for cell processes - In fact:
- roots can obtain water, but not sugar,
- leaves can produce sugar, but can’t get water from the air
- Sugars required for metabolism
– all the time, in all tissues - Sugars produced only
– by source tissues
– in light period - Translocation occurs
– source to sink over short term
– from storage tissues to young tissues over long term
Sucrose
* is principal photosynthetic product
– accounts for most of CO2 absorbed
– Glucose, as initial product of photosynthesis, is converted to sucrose which is the major form for transport or translocation
* important storage sugar
– tap root of carrots and sugar beet (up to 20% dry weight)
– and in leaves, eg 25% leaf dry weight in ivy
* major form for translocation of carbon
– from photosynthetic leaves (source leaves)
– in germinating seedlings after starch or lipid breakdown
Direction of translocation:
- From Source: a part of the plant that releases sucrose to the phloem e.g. leaf
- To Sink: a part of the plant that removes sucrose from the phloem e.g. root
- A plant part can act as source or sink depending on its developmental stage: for example- young leaves act as sink, but later their predominant role would be as source, once they are active in photosynthesis
ALLOCATION
* The channelling of fixed carbon into various metabolic pathways within an organ or tissue
* In a source organ:
– Metabolic utilization within the chloroplast
– Synthesis of starch within the chloroplasts
– Synthesis of sucrose for export to sink
* In a sink organ
– Metabolic utilization and growth processes
– Storage
PARTITIONING
* DISTRIBUTION of assimilates to competing sinks
– Lower mature leaves feed mainly the roots
– Higher mature leaves feed mainly the young leaves and shoot apex
* SOURCE LEAVES
– Preferentially supply sink organs with which they have vascular connection
* Flower or fruit nearest to them (directly above or below them)
- Basis for flower and fruit thinning
Mechanism of translocation of photosynthates
1. Mass or bulk flow (Münch pressure flow hypothesis)
2. Diffusion- slow
3. Cytoplasmic streaming- within the cytoplasm through plasmodesmatal connections between cells
4. Others
1. Facilitated diffusion
2. Active transport across membranes
Mechanism of assimilate translocation:
The Münch pressure flow hypothesis of assimilate transport from source to sink
xylem (vessel) - for transpiration of water
phloem (sieve tube) - for translocation of source, transportation of products of photosynthesis (sugar) thru translocation
APOPLAST PATHWAY
* sucrose is loaded into the phloem with the help of active transport. A sucrose transporter protein is used to co-transport H+ and sucrose across the cell membrane.
* the apoplast path utilizes ATP to pump H+ against the concentration gradient.
* ATP is reduced to ADP+Pi which expels energy that enable H+ to be pushed against the gradient.
* The H+ proton that is pumped against the gradient is then used by the sucrose transporter protein to move sucrose through the membrane.
* The sucrose accumulated in the companion cell is able to flow down its concentration
gradient via the plasmodesmata and into the phloem.
SYMPLAST PATHWAY
* sucrose travels in the plasmodesmata which are connections between cells.
* Therefore, the sucrose is able to flow down the sucrose concentration gradient into the phloem which has a lot of concentration of sucrose.
Plants are:
✔ Capable of making all necessary organic compounds from inorganic compounds and elements in the environment (autotrophic)
✔ Supplied with all the carbon, hydrogen, and oxygen they could ever need (CO2, H2O)
✔ Required to obtain all other elements from the soil so in a sense plants act as soil miners.
Nutrient
* any substance that can be metabolized by an
organism to give energy and build tissue
* growth and development
* source of nourishment, especially a nourishing
ingredient in a food
* providing nourishment
Categories of Plant Nutrients
* Based on Function
❖Essential
❖Beneficial
* Based on amount required by crop
❖Macroelements
❖Microelements
* Based on capability to move from one part of the plant to another
❖Mobile
❖Immobile
CRITERIA OF ESSENTIALITY
1. If the nutrient is absent, then the plant is unable to complete its life cycle
2. The function of the nutrient must not be replaceable by another element
3. The nutrient must act directly in the metabolism of the plant
