Physiological and molecular control of sinkactivity, partitioning efficiency and harvest index
Physiological and molecular control of sink activity,
partitioning efficiency and harvest index
Dr. S.D. Upadhyaya
Jitendra Singh Painkra
M.Sc. (Ag.) Final year
Roll No - 5989
Department of Plant physiology
Jawaharlal Nehru Krishi Vishwa Vidyalaya, Jabalpur (M.P.)
A source of organic material is a region in which organic
materials are synthesised.
Example:- leaf ,root, tuber, or tuber during development.
Any non-photosynthetic organ or an organ that does not
produce enough photosynthate to meets its own needs.
Example:- root, seed, fruit, root tuber and tuber during
photoassimilate Leaf makes
Source and sink relationship
Define the terms source and sink in relation to the
transportation of organic molecules in the phloem of plants.
Source = Photosynthesis (PS)
Sink = Growth and development
Multiple sources and sinks
Beta maritime (wild beet) root
is a sink during the first
In the second season the root
becomes a source, sugars are
mobilized and used to produce
a new shoot.
In contrast, in cultivated sugar
beets roots are sinks during all
phases of development.
Translocation of sucrose
can be in any direction –
depending on source and
sink location and strength.
The flow of water in plants is
almost always from roots to
Loading and unloading in phloem
1.Phloem loading is through the sucrose–H+ symporters
Sucrose from mesophyll cell to apoplast, then to
SE/CC into sieve element.
Requirement for energy and against concentration of
This autoradiograph shows that
labeled sugar moves from the
apoplast into sieve elements and
companion cells against its
concentration gradient in sugar
beet (Beta vulgaris) . Label
accumulates in the small veins,
sieve elements, and companion
cells of the source leaf,
indicating the ability of these
cells to transport sucrose against
its concentration gradient. (From
Fondy 1975, courtesy of
(2) Phloem unloading :-
Pathways for phloem unloading. The sieve
element companion cell complex (CC/SE) is considered a
single functional unit. The presence of plasmodesmata is
assumed to provide functional symplastic continuity. An
absence of plasmodesmata between cells indicates an
apoplastic transport step
Physiological and molecular control of sink and
Besides transport of photosynthates from one part to another
phloem is also involved in transport of signal molecules.
Signal between source and sink might be physical (such as
turgor pressure) or chemical (such as hormones and
Signals indicate turgor change could be transmitted rapidly via
interconnecting systems of sieve elements.
Thus not only in sucrose in phloem, but sucrose or its
metabolites can act as signals that modify the activities of
source and sink.
useful terms used to describes portioning to dry matter by
the plant are biological yield and economical yield.
The term biological yield was proposed by Nichiporovich
(1960) the total dry matter accumulation of a plants system.
The proportion of biological yield represented by economic
yield has been called the harvest index.
The coefficient of effectiveness, or the migration coefficient
All these terms characterize the movement of dry matter to the
harvested part of the plant.
The harvest index, the most widely used term, is defined as
Harvest index = ×100
Crop yield can be increased either by increasing the total dry
matter produced in the field or by increase the proportion of
economic yield (the harvest index or both )
There is potential for increasing yields by both method
In Oat (Takeda and Frey 1976) a large genetic population
showed variability in both biological yield and harvest index.
Oat line with high biological yield and harvest index of 40-
50% showed the highest grain yield.
Grain yield is a product of a number of subfraction called yield
component and can be expressed as follow:-
Y= Nr Ng Wg
Where Y= Grain yield
Nr = The number of reproductive unit (e.g. head ears,
panicles ) per unit of ground area.
Ng = The number of grains per reproductive unit.
Wg = The average weight per Grain.
Yield components are affected by management, genotype,
and environment, which often helps explain why a reduction in
The genotype can influence emergence capability and set the
potential for tillering, flower number, number of flowers, that
develop into grain amount assimilate produced and assimilate
The environment affects the ability of the plant of express its
Water, nutrients, temperature, light, and other environmental
factor at levels other than optimum can reduced one or more
FACE studies show that the crop yields at [CO2] projected for
2050 are enhanced by an average 18% with the current
cultivars tested and ~30% with the most responsive hybrid rice
In order to achieve 50% increase in crop yield by the middle of
21st century, photosynthetic radiation use efficiency need to
be substantially improved.
Both the source activity and the sink strength will need to be
coordinately enhanced to maximize net photosynthesis and
Assimilate move to sinks, where the of sugar in the apoplast
around the causes sugar and water move the phloem.
For high yield, the should quickly produce enough leaf area
index to intercept most of the light for maximum dry matter
production, after which it should maintain high light
interception and should partitioning in the largest quantities
possible to the organs of economic value without affecting
quality of harvest ability.