View
223
Download
0
Category
Preview:
Citation preview
8/10/2019 2014-4-Alokasi Dan Partisi Biomassa
1/6
8/10/2019 2014-4-Alokasi Dan Partisi Biomassa
2/6
10/6/201
PATTERNS OF TRANSLOCATION: SOURCE TO SINK
1. Phloem sap is not translocated exclusively in either an upwardor downward direction and is not influenced by gravity; phloem
translocation occurs from sourcetosink.
2. Sources include any exporting organ, typically mature leaves
exporting photosynthate.
3. Storage organs (roots, tubers, seeds, etc.) can also serve assources.
4. Sinks include any non-photosynthetic organ or tissue that does
not produce sufficient photosynthate to support its own
metabolic needs: roots, underground stems, buds, immatureleaves, flowers, fruits, etc.
How do plants transport carbohydrates?
Transport in plants
Mass-flow or pressure-flow hypothesis: Carbohydrates move from source(site produced or stored) to s ink(site
used)
Carbohydrates actively transported into phloem at source
High concentration of carbohydrates causes greater osmotic
pressure in phloem; water moves in from adjacent xylem byosmosis
Water influx creates (turgor) pressure inside phloem; pushingwater and dissolved carbohydrates through phloem
At sink, carbohydrates actively removed from phloem; reducing
osmotic pressure in phloem
water leaves phloem and reenters xylem, maintaining aosmotic pressure gradient between sources and sinks
The regulation of photoassimilate distribution into
plant organs governs their productivity
Important for yield of crop plants
Maximize yield of marketable part of crop plant
e.g., wheat farmers want more carbon to go tograinthan
to roots
We can define two plant physiology terms that define how C is
allocated to plant parts
These terms are important in agronomy
They govern the destination of C in plants: allocationandpartitioning
Allocation
The regulation of the distributed of fixed carbon intovarious metabolic pathways (i.e. the fate of fixed carbon)
include storage (starch), utilization (metabolic energy,
synthesis of other compound) and synthesis of transport
sugar (sucrose).
Allocation involves storage, metabolism and transport,
process which facilitate competition for photosynthates
8/10/2019 2014-4-Alokasi Dan Partisi Biomassa
3/6
10/6/201
Synthesis of storage compounds. Starch is synthesized and
stored within chloroplasts and, in most species, is the primary
storage form that is mobil ized for translocation during the
night. Plants that store carbon primarily as starch are called
starch storers.
Metabolic utilization. Fixed carbon can be utilized within
various compartments of the photosynthesizing cell to meet
the energy needs of the cell or to provide carbon skeletons for
the synthesis of other compounds required by the cell.
Synthesis of transport compounds. Fixed carbon can be
incorporated into transport sugars for export to various sink
tissues. A portion of the transport sugar can also be stored
temporarily in the vacuole
Allocation of fixed carbon is a balancing act between
providing energy and C skeletons
The plants competing processes for C include:
Leaf metabolism
Respiration of glucose provides:
ATP Carbon skeletons for biosynthesis
Short-term storage
Plants can only photosynthesize in the light
But they need to grow at all times, therefore store carbon inleaves (form is species dependent)
Starch: dicots
Sucrose: sugarcane, sugarbeet
Sucrose polymers (fructans): grasses, monocots
Leaf carbon storage is a bufferagainst environmental factorsaffecting photosynthesis
Translokasi di dalam sel parenkimA large amount of C allocation is destined for export
from the leaf to metabolic sinks
Immediate transport (export)
About of fixed carbon
Regulation of export poorly understood
Shifts during development
Sink (young leaves)little export
Source (mature leaves)switch off/down regulatesucrose hydrolytic enzymes, increase SPS (sucrosephosphate synthase)
For most plants:
Starch (made in chloroplasts): stored
Sucrose (made in cytoplasm): transportedhigh synthesis(SPS) activity, high export rate
Export of sucrose ~constant at night
Source leaves regulate allocation
Increase in photosynthesis rate in a source leaf results in
increased translocation rate from the source
Control point for allocation
Starch syntesis
Sucrose synthesis (including distribution of sucrose
between transport and temporary storage)
Regeneration of intermediates in the reduction cycle of
the Calvin Cycle
Partitioning
The differential distribution of photosynthates within the plant ,e.g. into different sinks; efficiency of partitioning from
vegetative sinks into storage organs translates into productivity
for many crops.
The differential distribution of photosyntates within plants
- Various sinks partition sugars
- Distribution must be balanced
- Many cultivars are economically inportant because the
partition to edible plant parts (fruits, grains)
8/10/2019 2014-4-Alokasi Dan Partisi Biomassa
4/6
10/6/201
Exported carbon is partitioned between various sinks
Partitioning refers to the relative amount of exported carbon used
by metabolic sinks within the plant
Sinks compete for carbon!
Apical meristems Young leaves
Fruit
Dependent on: Vascular connections between source and sinks (best to have
direct links (vascular traces) Same side of stem
As close as possible
How close sink is to source physically
Sink strength
Kemampuan relatif dari organ untuk menarik fotosintat
tergantung pada: ukuran & stadia pertumbuhan
Kedua faktor dan jarak menentukan laju aliran
fotosintat
Jarak dan laju menentukan gradien source: sink
Sink strength depends on sink size and activity
Sink strength = sink size x activity
sink size = total biomass of the sink tissue
sink activity = rate of uptake of photosynthates per unit
biomass of sink tissue
Sink strength
Kemanpuan sinkuntuk memobilisasi fotosintat tergantung padaukuran dan aktivitas sink
Urutan kekuatan sinkuntuk hasil fotosintesis:
Biji > daging buah = pucuk daun muda > kambium > akar >
organ penyimpan lain
Source-sink pathways follow patterns
Proximity:of source to sink is a significant factor.
Upper nature leaves usually provide photosynthesis products togrowing shoot tip and young, immature leaves
Lower leaves supply predominantly the root system
Intermediate leaves export in both directions
Development:Importance of various sinks may shift during plant
development
Roots and shoots major sinks during vegetative growth
But fruits become dominant sinks during reproductive
development
8/10/2019 2014-4-Alokasi Dan Partisi Biomassa
5/6
10/6/201
Source-sink pathways follow patterns
Vascular connections:Source leaves preferentially supply sinks
with direct vascular connections
A given leaf is connected via vascular system to leaves above andbelow it on the stem
Modifi cations of translocation pathways: - Interference with a
translocation pathway by mechanical wounding (or pruning)
vascular interconnections can provide alternate pathways forphloem transport
SOURCE TO SINK PATHWAYS FOLLOW ANATOMICAL AND
DEVELOPMENTAL PATTERNS
1. Proximity is important: upper mature leaves supply photosynthate to
growing shoot tip; lower leaves supply the root; middle leaves supply both.
2. Development influences transport:
a. Young leaves begin as sinks, gradually become sources.
b. Reproductive structures become dominant sinks during flowering.
3.Vascular connections important; source leaves preferentially supply sinks
to which they have vascular connections; typically, sources leaves supplysinks along the same vertical row ororthostichy.
4. Phloem interconnections (anastomoses) can provide alternative pathways
in the event of wounding or pruning.
The sink strength of a plant organ is a measure of its
capacity to absorb photoassimilate
Sink strength= sink size(mass) Xsink activity(rate of uptake)
The sink strength of an organ definesits capacity to assimilatemacromolecules
Why sink strength changes with timeor what determines it: unknown
Good: High unloading rate
High sequestration rate into storage
Being close to source
Developing grain: very strong sink
No yield reduction even at low [CO2],carbon stolen from roots and otherless strong sinks
Factors Affecting the Translocation
Temperature
Increased temperatureincreased loading & unloading optimum 20 -30oC
Chilling Sensitive Plants (most)
Chilling Tolerant Plants (beets)
Can acclimate translocation of photosynthate to increasingly cold conditions
Factors Affecting the Translocation of Sap
Light
In the dark root translocation of photosynthate is favored
over stem translocation.
At least one study shows that the translocation of sap in
the stem was increased by BLUE and RED light.
8/10/2019 2014-4-Alokasi Dan Partisi Biomassa
6/6
10/6/201
Factors Affecting the Translocation of Sap
Hormones
Both cell division (cytokinins) and cell elongation (auxins)
creates sinks absorbs sap.
Bud break
Increased GA, decreased ABA
Partitioning control is a complex process
The steps involved in C flow to a
sink: phloem loading in a
source leaf, phloem transp ort
into the sink, unloading andshort distance transport with in
the sink and then metabol ism
and storage in the sink.
- Molecule signalling: sucrose , hormone- The status of various nutrient elements
affects the partitioning of photosynthate. n
The status of various nutrient elements affects the
partitioning of photosynthate
When plant growth is limited by a low supply of the
elements N, P, S or Fe, the ratio of root to shoot mass
rises, more organic C being delivered to the roots,
whereas limitation of the supply of Mg, Mn or K leads
to a decrease of the root : shoot mass ratio. Water
stress increases the root : shoot ratio, root growth
being stimulated while shoot growth is reduced.
Recommended