Lecture 26 - Plant Nutrition (part 1) Flashcards
(116 cards)
1
Q
What did plant evolution result from?
A
adaptations to obtain food
2
Q
What are the 2 systems that land plants have?
A
- above ground shoot system
2. below ground root system
3
Q
above ground shoot system
A
absorb light for photosynthesis
4
Q
below ground root system
A
water and minerals
5
Q
Plant ancestors absorbed nutrients directly from their…
A
aquatic environment
6
Q
Over time as plants moved onto land…
A
competition for resources resulted in taller plants, with broader leaves (more SA) for more light absorption
7
Q
What is the cost of plants moving onto land?
A
More SA for light also means more SA for water loss
• Larger plants also need larger roots for anchorage
• Greater distance to transport nutrients between the root and shoot systems
8
Q
What are the 2 vascular tissues that made the move to land all possible for plants?
A
- Xylem
* Phloem
9
Q
Xylem
A
transports water and nutrients from roots to shoots
10
Q
Phloem
A
transports photosynthates from source to sink
11
Q
What varies greatly amongst land plants?
A
shoot architecture (i.e. morphology)
12
Q
What are examples of shoot architecture (i.e. morphology) that varies greatly amongst land plants?
A
- Stem length and widths
* Branching pattern
13
Q
What does stem length and widths allow for?
A
allows plants to grow tall
14
Q
What does branching pattern allow for?
A
allows better light harvesting
15
Q
What is the function of stems?
A
support leaves and act as conduits for water and nutrient transport
16
Q
Leaves vary in size & structure & account for much of the diversity we see in land plants so DESCRIBE THIS
A
- Various adaptations for specific habitats, PREVENTING water loss and MAXIMIZING photosynthesis
- Most large leafed plants are tropical, smaller leafed plants are temperate, and very small leafed plants occur in harsh habitats
17
Q
Phyllotaxy
A
is the arrangement of leaves on a plant
18
Q
What is Phyllotaxy determined and genetically controlled by?
A
the SAM
19
Q
1 leaf per node –>
A
alternate, spiral
20
Q
2 leaves per node –>
A
opposite
21
Q
Multiple leaves per node –>
A
whorled
22
Q
What does total leaf area affect?
A
the productivity of each plant
23
Q
How does total leaf area affect the productivity of each plant?
A
- Leaves can SHADE other leaves on the same plant
* Plants can SELF-PRUNE leaves (and branches!)
24
Q
Leaves can shade other leaves on the same plant…
A
reducing photosynthetic capacity (ie. They respire more than photosynthesise!)
25
Plants can self-prune leaves (and branches!)...
to optimising leaf area index
26
Leave orientation also affects...
photosynthetic capacity
27
In low light -->
horizontal leaves are best
28
In high light -->
vertical leaves prevent water loss and burning
29
What is the photosynthesis - water loss compromise?
* Broad leaves absorb more light, have more stomata
| * Stomata open to exchange gas, but there is water loss!
30
What is the roots function?
maximize morphology & growth to absorb nutrients
31
Roots won't branch in areas of _______. But branches more in areas of _______.
low N availability
high nutrient loads, makes more proteins to take up more nitrogen
32
Roots associate with...
mycorrhizae to increase surface area of more nutrient uptake
33
What are the 2 main "compartments" of plant systems?
1. Apoplast
| 2. Symplast
34
Apoplast
everything external to the plasma membrane (including cell walls and internal
spaces of dead tracheids and vessels)
35
Symplast
consists of the cytosol, plasmodesmata, & cytoplasmic interconnections
36
What are 3 main transport "routes"?
1. Apoplastic
2. Symplastic
3. Transmembrane
37
Apoplastic
water and solutes move along the cell walls and extracellular spaces (like water through a sponge)
38
Symplastic
water and solutes move through the cytosol
39
Transmembrane
water and solutes move out of one cell, across the cell walls, and into the next cell
40
Both ____ & _____ transport occur in plant cells
active
passive
41
Primary Active Transport
Uses H+ for membrane potentials resulting from proton pumps
| • Animals used Na+
42
Secondary Active Transport
H+ is also co-transported in plants (ex. sugar in phloem cells)
• Animals co-transport Na+
43
What does gated ion channels produce?
produces electrical signals similar to action potentials in animals
• K+ ions for the opening/closing of guard cells
44
What absorption or loss of water occurs by...
Osmosis (passive transport)
45
Water potential
(solute concentration + pressure) will direct the flow of water
46
Free water
(not bound to ions/solutes) moves from higher water potential to lower water potential
47
Active & passive transport in plant cells
1. Uses ATP-dependent proton pumps to pump H+ OUT of the cell, establishing a membrane potential
2. H+/sucrose cotransporters play a key role in sugar-loading INTO the PHLOEM
3. H+/NO3 - cotransporters important for nitrate uptake BY the roots
4. Opening and closing of the guard cells in the stomata
48
What is water potential determined by?
solute potential and pressure potential
49
Solute potential
is directly proportional to its molarity
| • Also called osmotic pressure (solutes affect direction of osmosis)
50
Solutes in plants are mostly...
ions & sugars
51
Pure water has a solute potential =
0
52
As solutes are added, ions bind to water -->
less free water
| • Has a negative effect on water potential, so always written negative
53
Pressure potential
is the PHYSICAL pressure on the solution
• Can be + or -
• Water inside plant cells is usually under + pressure due to water uptake
54
The protoplast (living part of the cell)...
exerts (+) pressure on the cell wall, creating turgor pressure
55
Water inside tracheids and vessels is often under...
negative pressure (tension)
56
Flaccid cells (limp)
are from a loss of water
| - The cell has a pressure potential = 0
57
If put into a solution that has a lower water potential (hypertonic)...
water leaves the flaccid cell, resulting in plasmolysis
58
If put into a solution of pure water (hypotonic)...
water moves inside the cell since the cell has more solutes than the pure water, exerting turgor pressure and becoming turgid
59
Once the direction of water movement is determined...
aquaporins aid in the transport of water across the plasma membrane
60
Aquaporins
They affect the rate in which water moves through the membrane
61
Permeability of aquaporin channels is decreased by...
increases in cytosolic [Ca2+] or decreases in cytosolic pH
62
Short-distance transport occurs...
across plasma membranes
63
Long distance transport occurs through...
bulk flow
64
Bulk flow
Movement of a liquid in response to a pressure gradient
65
Bulk flow always occurs from...
high to low pressure
66
Bulk flow is independent of...
solute concentration
67
Where does bulk flow occur?
Occurs in tracheids and vessel elements in xylem and sieve-tube elements of the phloem
68
Mature xylem cells have no ______ & sieve-tube elements lack bulky _____
cytoplasm
organelles
69
Both kinds of transport can occur to move the same stuff around. Describe short-distance active transport & long distance transport
Short-distance active transport loads sugar into phloem cells
Long distance transport moves it from shoot to root
70
Healthy/not wiltered plant =
turgid
71
Wiltered plant =
flaccid
72
Where does most of the absorption of nutrients & water start?
at the root hairs
73
Root hairs are...
Permeable to water and its associated ions
74
Where does water pass freely through (during transpiration)?
the cell walls and extracellular spaces (apoplastic transport)
75
Pass through the cortex until it reaches the ________ surrounding the vascular stele (during transpiration)
endodermis
76
Selective transport
forces water + minerals into the symplastic route due to the Casparian strip
77
Casparian strip
highly suberized layer impervious to water
78
Water and minerals then returns to the ______ route in the tracheids and vessel elements
apoplastic
79
Once in the xylem, the xylem sap ______
move up the stem via bulk flow and into the leaf veins
80
Leaf cells get water and essential nutrients, but water is lost due to...
transpiration -> water vapour exits the leaf
81
What must the roots do continuously to counteract the loss through transpiration?
The roots must be continuously absorbing water to counteract the loss through transpiration
82
If water loss in the leaves > root absorption...
the plant wilts
83
How does xylem sap travel to the leaves?
* Root pressure pushes it up the plant
* Root cells are continuously actively pumping mineral ions in the xylem sap
* The Casparian strip prevents mineral ions for going back into the root (selectively permeable, remember?)
* Accumulation of minerals lowers water potential inside the vascular cylinder, causing water the flow from the root into the vascular stele, generating root pressure
* This pushes the xylem sap up the stem
84
Root pressure
pushes xylem sap up the plant
85
Too much pressure of xylem sap being pushed up the stem can cause what?
guttation, water droplets exude (forced out) from the leaves (NOT the same as dew)
86
Root pressure only accounts for a small fraction of what?
bulk transport in xylem
87
Cohesion-tension Hypothesis
* Transpiration provides the pull
| * Cohesion of water molecules transmits this pull from shoots to roots
88
Transpiration (Cohesion-tension Hypothesis)
provides the pull
89
Cohesion (Cohesion-tension Hypothesis)
of water molecules transmits this pull from shoots to roots
90
Xylem sap is normally under...
negative pressure (tension)
91
Transpirational pull
* Stomata on the leaves lead to internal air pockets, exposing mesophyll cells to CO2 for photosynthesis
* Air is saturated with water vapour. Air outside the leaf is drier, and therefore has lower water potential than air inside the leaf
* The negative water potential develops on the mesophyll cells, resulting in tension
92
Stomata on the leaves lead to internal air pockets...
exposing mesophyll cells to CO2 for photosynthesis
93
Air is saturated with water vapour. Air outside the leaf is drier, and
therefore has...
lower water potential than air inside the leaf
| • Causes water to leave from inside of leaf to outside
94
The negative water potential develops on the...
mesophyll cells, resulting in tension
95
Cohesion
attractive force between the same kind of molecules
• Very strong due to hydrogen bonds in water
• Can pull water molecules up without them separating
96
Adhesion
attractive force between different molecules
| • Water molecules on hydrophilic cell wall molecules
97
Upward pull on the sap creates...
tension
98
Secondary cell walls prevent the...
tracheids and vessels from collapsing
99
Air bubbles (embolisms) can disrupt the bulk flow of...
xylem sap
100
Prolonged hydraulic failure can cause...
plant death
101
What is transpiration regulated by?
stomata
102
Leaves have high ______, which maximizes ______
SA:volume ratio
photosynthesis (but also water loss!)
103
Stomata (sing. Stoma)
are flanked by 2 guard cells, which control the diameter of the stomatal pore
104
When guard cells take in water from neighbouring cells, they become...
more turgid
105
Uneven cell wall thickness causes the guard cells to...
bow (becoming bean shaped)
106
When water is lost the guard cells become...
flaccid & the pore closes
107
Change in turgor is a result of...
reversible absorption and loss of K+
108
Accumulation of K+ inside the guard cell lowers the...
water potential, forcing water inside the guard cell (H+ leaves the cell)
109
Loss of K+ ions from the guard cell raises the...
water potential of the guard cell, forcing water out of the guard cell (H+ enters the cell)
110
Accumulation/loss of K+ both facilitated by active transport of H+ ->
results in a gradient and generation of a membrane potential which drives K+ in/out of the cells
111
Opening/closing of stomata regulated by what?
circadian rhythms and plant hormones (ex. ABA produced is produced during water shortages)
112
Most large leafed plants are what?
tropical
113
Most smaller leafed plants are what?
temperate
114
Most very small leafed plants occur where?
in harsh habitats
115
What are limitations in architecture due to?
finite energy to devote to shoot growth
116
What does Active Transport allow during transpiration?
root cortex cells to absorb and store essential minerals (K+, nitrates)
