Lecture #6
-
Upload
andrae-ether-bender-genus -
Category
Documents
-
view
24 -
download
0
description
Transcript of Lecture #6
1
Discussion the two proposed mechanisms by which water is
released into the xylem? Plant physiology
Lecture #5
2/5 – 2/6
2
• Osmosis– The diffusion across a semi-permeable
membrane from a region of high to low concentration
• Exudation – Water leaks out to the xylem parenchyma
cells thru pits– Evidence for this : K+ in xylem tissue (related
to roots pressure) have been discovered via analysis of SAP that exudes form stem plant.
3
Define guttation
4
• The water at the tip of the plant leaf.– Also related to root
pressure– High in Boron (mass
flow)
5
What is the composition of xylem sap and explain how K increases
root pressure.
6
K levels Sap vol K Na Ca Mg totals
1 46.5 32.3
2 50.5 36.5
3 55.9 37.6
Three levels of sap volume are presented in the above chart. The data shows that as the K levels increases, there is a corresponding increase in the levels of sap and nutrients.
Conclusions:
1. all water movement in xylem can affect nutrient uptake.
there are 2 separate processes involved (different from adsorption-osmosis and exudation in roots).
higher water uptake does not necessarily mean high ion uptake.
2. Where water movement is unimpeded, as in transpiration stream, plant nutrients may be translocated along with water by mass flow.
7
In labeled diagram explain what happens during phloem loading.
8
• The movement of sugars in the phloem begins at the source, where (a) sugars are loaded (actively transported) into a sieve tube. Loading of the phloem sets up a water potential gradient that facilitates the movement of water into the dense phloem sap from the neighboring xylem (b). As hydrostatic pressure in the phloem sieve tube increases, pressure flow begins (c), and the sap moves through the phloem. Meanwhile, at the sink (d), incoming sugars are actively transported out of the phloem and removed as complex carbohydrates. The loss of solute produces a high water potential in the phloem, and water passes out (e), returning eventually to the xylem.
PHLOEM
PHLOEM
ChloroplastCytoplasm
Fre
e sp
ace
Amino acids
(Glycol sis)
TCA cycle
CO2
HNO2
NH3
Inorganic P
SucroseTri
phosphates
Sie
ve t
ub
e c
om
pan
ion
cel
l c
om
ple
x
9
What type of cells are in phloem and what are their functions?
10
• Sieve tube– Campion cell complex – Small holes that allow movement in phloem– Essential in phloem loading– elongated parenchyma cells in phloem tissue
– The main function of the sieve tube is transport of carbohydrates in the plant (e.g., from the leaves to the fruits and roots).
11
What are the factors affecting phloem loading?
12
• Energy supply (ATP)
• K nutritional status
• P nutritional status
• Turgor pressure– The higher the turgor pressure the more
phloem loading
13
Explain the mechanism of phloem transport
14
• Munch (1930) proposed the – “pressure flow hypothesis”– Loading is by mass flow created by pressure in sieve
tube
• Phloem loading increases pressure in sieve tubes. This pressure is responsible for mass flow action.– Can be back-up because of feed back mechanism
15
List 5 characteristics of components of phloem sap
16
• Sucrose
• Amino acid
• K and Mg
• Phytohormones– Auxin (IAA), GA, cytokinins
• High pH due to HCO3-
17
List seven the roles of auxin?
18
• Responsible for growth at the tip (snipping off apex will increase yield.)
• Rooting• Parthenocarpy• Flowering and fruit thinning• Dormancy• Control preharvest (keeping fruit longer on tree)• herbicide
19
What is parthenocarpy?
20
• the natural or artificially induced production of fruit without fertilization of ovules.
21
Transportation of nutrients thru the phloem depends on what
factor?
22
• The speed of loading in the sieve tubes.– Once loaded, moves by gradients
• K & Mg ie are very mobile because they are at high concentration.
• Movement is back and forth
23
What is the main way Ca++ and Boron get into the plant?
24
• Via mass flow through transpiration stream.
• Which means that it is not moving (immobile).
• It is retranslocated in the phloem
• Deficient in newer leaves
25
Where would you expect Ca++ and Boron deficiency in plants,
why?
26
• Ca++ and Boron deficiency would be observed in newer leaves because – they occur in lower concentrations– They are immobile
27
In what part of the plant would Ca++ and Boron be in high
concentration?
28
• In older leaves
• Because they are not mobile
• Once they get their by mass flow, they remain.
• For example cause Blossom end Rot– A whole in the leaves due to high con of Ca++
29
What is a sink?
30
• Sinks are areas in the plant where nutrients and sugars are stored:
• Fruits
• Leaves
• Stems
31
What is a source?
32
• A source is the areas of productivity or where food is manufactured
• They include:– Roots– leaves
33
What is natural thinning, what are the consequences for not
thinning?
34
• When a tree is very productive, the plant removes the fruit by a process called natural thinning.
• The tree cannot handle all of the storage
• Branches may break
• Also, if this does not occur, a lot of tiny fruits are produced.
35
Result of thinning?
36
• Small number fruits
• large size fruits
37
Describe transportation in the phloem.
38
• Bidirectional– Photosynthates are synthesized in older
leaves.– This is why
39
In terms of pn, where is most of the activities taking place?
40
• At the top (older leaves)
41
What is the sink for photosynthates of new (younger)
leaves?
42
• Younger leaves supply photosynthates to– fruits– Apex of plant
43
What is the sink for photosynthates produced by
older leaves?
44
• The roots and other lower parts of the plant.
45
List sinks and their sources in order of priority (most impo to least impo) and the direction
movement.
46
# Part of plant Source Movement or mobilization
1st Sink
Younger leaves(eventually becomes a source)
Older leaves upward
2nd sink
Developing organs
Bidirectional phloem
downward
47
What is mobilization
48
• Them movement of nutrients from storage to growing organs (or points).
49
What is the mobilization sink?
50
• Active deposition of nutrients to storage.
51
List 4 examples of mobilization sinks
52
• Tubers
• Bulbs
• Flowers
• fruits
53
What is the mobilization sink of a germinating seed?
54
• The endosperm– They store:
• fats• oil
• The nutrients are mobilized to the embryo
55
List six factors affecting mobilization
56
1. Topping (or top working)– Pruning or renewing branches
and leaves– Chop off apical dominance
• Produce lateral growth to produce new leaves
– N is mobilized
2. Effect of ovary and stamens• Removing the stamen and ovary
produce 30% increase, a sink• Starch in the peduncle• Removing the peduncle, the starch
disappears
3. Age of the fruit• Young fruits = stronger sinks• Older leaves = less effective
1. Light• Pn increases • Dark most translocation &
movement takes place in darkness
2. Temperature1. Yields a demobilization effect
• The respiration, the more plants looses the stored material
• Higher temp yields high transpiration rate
• After harvest, plants must be cooled down, or sugars will be converted to starch
3. Nutrient deficiency
57
What is GA?
58
• Gibberellins• plant hormones that regulate growth and
influence various developmental processes, including – "stem elongation, – germination, dormancy, – flowering, – sex expression, – enzyme induction – leaf and fruit senescence.
59
List some differences between Auxin and Gebberellins
60
AuX GA
Transport polar Yes No
Promote root initiation Yes No
Inhibit root growth Yes No
Delay leaf abscission Yes No
Inhibit laeral buds Yes No
Induce callus formation Yes No
Promote growth of dwarf plants
No Yes
Promote seed germination and dormancy
No Yes
Promote bolting or flowering No Yes
61
List four major physiological roles of Abscisic acid.
62
• Stomata regulation
• Bud dormancy
• Seed dormancy
• abscission
63
What is abscission? What hormone causes this ?
64
• Abscission is the shedding of a body part.
• This is caused by Abscissic acid.
65