Source & Sink relationship
Source & Sink relationship
|
- The photosynthetic source cells produce the sugars, which can move symplastically to sieve tubes.
- Phloem loading increase sugar concentration to sieve tubes above apoplast
- Sink carbohydrates are utilized
- The build up of sugars in source &removal in sink establish a hydrostatic pressure which moves water &sugars
- Increase of photosynthetic rate-increase in Hydrostatic pressure & Translocation rate
- Sink have the ability to utilize more assimilate.
- If unable to increase in production of assimilate – accumulate and reduce photosynthesis
Hormonal action
- The effect of hormones on sink cell have an effect on partitioning
- IAA, Cytokinin, Ethylene, GA
- They influence –initiation, development, abortion of flowers and seeds.
- Significant effects on source sink relationship in crops.
Assimilate partitioning during vegetative phase
- Leaves, green tissues- original sources
- Some remains in green tissues-cell maintenance
- If slow –converted to starch or some storage materials
- Rest transported to vegetative sinks –roots stem leaves.
The proportion of assimilates partitioned to these 3 organs can influence plant growth & productivity depends upon the nature of crop either root, stem or leaf forms the main economic portion of the crop.
- Young leaves –matured leaves
- Self sufficient export 60-80% -to other parts &to older leaves
During reproductive phase
- Reproductive growth primary part of plant
- Fruits, seeds, flowers, tubers resultant products of larger partitioning of assimilate from vegetative (source) to sink
- In determinant species leaf &stem growth cease at flowering
- Indeterminate species – both vegetative reproductive occur simultaneously
- If much vegetative growth during reproductive phase, yield reduces
- As size of source increase photosynthesis increases
Harvest index
- Two useful terms used to describe partitioning of dry matter by the plant are
- Economic yield is used to refer to the volume or weight of those plant organs that constitute the product of economic value.
- Biological yield proposed by Niche poroviah in 1960 to represent the total dry matter accumulation of a plant’s system.
- The proportion of biological yield represented by economic yield – harvest index
HI = EY/BY*100
- Crop yield can be increased either by increasing the total dry matter produced or by increasing the proportion of economic yield or both.
- More partitioning leads to increase of HI, increase of crop yield.
Yield component
- Grain yield –product of a no of sub fractions called yield component.
Y=Nr Ng Wg
Nr-No of reproductive units Ng-No of grains/ reproductive units Wg-Avg,wt./grain
- Yield components are affected by management, genotype & environment.
Remobilization
- The movement of compounds from an area where they were once deposited to an area where they can be reutilized – Remobilization
- It occurs in organic & inorganic components
- During leaf senescence carbohydrate, nitrogenous compounds, metabolic nutrients are remobilized.
Grain filling For the development of grain photosynthate come from 3 sources:
- Current leaf photosynthesis
- From non-leaf parts
- Remobilization deposited in other plant organ.
- During drought grain yield reduces.
|
Last modified: Friday, 23 December 2011, 9:38 PM